design report of the phase-i tps...

Design Reportof the

Phase-I TPS Beamlines

Project Leader: Di-Jing HuangProject Co-Leader: Shih-Chun Chung

PIs of the beamline construction:Yuch-Cheng Jean, Hok-Sum Fung,

Hong-Ji Lin, Yu-Shan Huang,Hsin-Yi Lee, Mau-Tsu Tang,

and Chia-Hung Hsu

Editorial team:Kaidee Lee (editor-in-chief),

Kuan-Yeu Pan, and Hui-Rung Su

National Synchrotron Radiation Research Center

Version 2.1

December 31, 2013

Contents

1 Temporally Coherent XRD 11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Scientific Opportunities . . . . . . . . . . . . . . . . . . . . . . 21.3 Photon Source . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.4 Beamline Optical Design . . . . . . . . . . . . . . . . . . . . . 10

1.4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 101.4.2 High Heat Load Optics . . . . . . . . . . . . . . . . . . 171.4.3 Monochromatic Optics . . . . . . . . . . . . . . . . . . 291.4.4 Beamline Control and Data Management . . . . . . . . 401.4.5 Performance Evaluation . . . . . . . . . . . . . . . . . 41

1.5 End Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . 521.5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 521.5.2 Preliminary Design of the End Station 1 . . . . . . . . 521.5.3 Preliminary Design of the End Station 2 . . . . . . . . 65

1.6 Radiation Safety . . . . . . . . . . . . . . . . . . . . . . . . . 681.6.1 Bremsstrahlung Ray Tracing . . . . . . . . . . . . . . . 681.6.2 Hutches . . . . . . . . . . . . . . . . . . . . . . . . . . 71

1.7 Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 741.8 Commissioning Plan . . . . . . . . . . . . . . . . . . . . . . . 751.9 Construction Team . . . . . . . . . . . . . . . . . . . . . . . . 77

i

Chapter 1

Temporally Coherent X-rayDiffraction

1.1 Introduction

Information about the static and dynamic structures of matters, in eithercrystalline or non-crystalline form, is most desirable in condensed matterphysics, chemistry, biology, and materials science. In terms of space, atomicarrangements in materials can be understood, and in terms of time, the in-teractions, reactions, and functions of materials can be delineated. X-rayscattering is well known as a powerful and direct method to probe the struc-ture of materials with atomic resolution. The temporally coherent diffrac-tion beamline has been approved as one of the TPS phase-I beamlines forstatic and dynamic structure investigation with hard X-ray scattering asthe core experimental technique. It is designed to perform temporally co-herent X-ray diffraction, ultrafast time-resolved X-ray scattering, and mag-netic X-ray scattering measurements. This beamline is aimed to provide ameans of extracting such spatial and temporal information from coherentdiffraction/scattering with ultrahigh temporally and spatially coherent X-ray sources, which will facilitate the understanding of material structures,functionalities, syntheses, and designs under various physical, chemical, andbiological conditions. In addition, the development of an experimental facil-ity for time-resolved X-ray diffraction/scattering with an ultrahigh temporalresolution is another target of this beamline. The studies of the ultrafaststructural dynamics of materials upon external stimulation will be pursued.Magnetic X-ray scattering/diffraction with polarization analysis capabilityto investigate the magnetic structure of novel materials will also be carriedout here.

1

2 CHAPTER 1. TEMPORALLY COHERENT XRD

1.2 Scientific Opportunities

The scientific programs planned for the beamline are diverse and covervarious disciplines. The scientific opportunities offered by the three majortechniques implemented in this beamline are described in the following:

Probing static and dynamic atomic structures with ultrahigh spa-tially and temporally coherent X-rays

The development of X-ray optics with ultrahigh spatial and temporal co-herences and the application of such coherent sources to probe the static anddynamic atomic structures of materials are the major focuses of this beam-line. X-rays with ultrahigh spatial and temporal coherences can be achievedby cavity resonance resulting from coherent interaction between X-ray wavefields generated by two or multiple plates with a gap or gaps smaller than theX-ray coherence length. Recent experiments in realizing X-ray cavity reso-nance indicated that two-plate X-ray cavity of silicon[1, 2, 3] could providea transmitted beam of temporal coherence length of about 700 micrometers,corresponding to 1.6 ps in time resolution. Based on this idea, developmentof two-plate or multi-plate cavities with improved finesse will be pursued.The transmitted beams through these cavities are expected to possess a hightemporal coherence. In addition, the low emittance (1.6 nm·rad) of the 3GeV ring planned could also provide excellent spatial coherence. New exper-iments taking advantage of the highly coherent feature of the X-rays out ofthe cavity could be designed for scattering, diffraction, imaging, as well asspectroscopy. Two types of time-resolved pump-probe experiments are pro-posed. Type I experiments are pump and probe experiments to investigatepicosecond motion in laser-excited solids using the transmitted beam fromthe X-ray cavity as the probing beam. The purpose is to explore interactionsbetween electronic, magnetic and atomic subsystems under non-equilibriumconditions generated by ultrafast optical pulses[4, 5, 6, 7, 8]. In the case oflaser-induced lattice motion of semiconductors, wide-angle and grazing-anglereflections for the quasi coherent X-rays coming from a cavity will be used toprobe the lattice motion. Type II experiments concern excitation of materialsin an X-ray cavity. The molecules and crystalline materials investigated willbe placed inside the X-ray cavity. The formation of standing-waves insidethe cavity will excite in-cavity material, provided that a proper X-ray photon

1.2. SCIENTIFIC OPPORTUNITIES 3

energy is applied. Time-resolved avalanche photo-diode (APD), micro-stripedetector, or the like, will be used to measure the response of the material asfunctions of energy and time. Possible candidates for this investigation areMössbauer effects, or having transitions in the vicinity of the photon energyused.

Probing structural dynamics by X-rays of an ultrahigh temporalresolution

The X-ray pulses with 9.5 picoseconds natural bunch length (σ) out of theTPS are an ideal light source for picosecond scale time-resolved X-ray studies.The temporal evolution of structural responses to the non-equilibrium con-dition in this time scale can be captured by time-resolved X-ray scattering.The picosecond time scale is an excellent match for fundamental time scaleof structural dynamics of nanometer-scale systems and thermal transport re-lated phenomena. Femtosecond-laser-based time-resolved X-ray studies willbe the heart of this part of research. The investigations will be carried out inthe laser-pump and X-ray-probe fashion and the structure changes inducedby optical excitation by ultrafast laser pulses will be explored. By synchroniz-ing X-ray pulses with ultrashort laser pulses, time-resolved crystallographywith tens of picosecond time resolution will be conducted with the existingdiffraction/scattering techniques. The phase transitions of crystals inducedby ultrafast lasers, such as laser-induced surface melting, surface roughness,and magnetic phase transition will be explored. The temporal evolutionof atomic and molecular motion of laser-strained crystals to unravel coher-ent acoustic phonon dynamics, especially for the nanometer-materials whichexhibit different properties from those of their bulk counterparts, and thelattice expansion upon laser heating which reflects the thermal transportproperties of crystals will be investigated. These studies will provide insightsinto phonon-phonon interactions in materials.

Probing magnetic structures by X-ray magnetic scattering

X-ray magnetic scattering is a unique tool to study the magnetic prop-erties of solids, especially magnetic, charge, and orbital orderings. Eventhough the cross section of X-ray magnetic scattering is about six ordersof magnitude smaller than that of charge scattering, the magnetic Braggsatellites beside the intense lattice reflections bear the important structuralinformation on the spin and orbital modulations. Moreover, large resonant


enhancement of the scattering cross section occurs when the incident photonenergy is tuned close to an atomic absorption edge, which not only dramat-ically increases the sensitivity of X-ray scattering to magnetic structure butalso adds the site and shell selectivities to the technique. Combining thepolarization manipulation and analysis capability, further information aboutthe magnetic moment direction and the relative contributions from orbitaland spin to the magnetic moments become feasible. With all these features,X-ray (resonant) magnetic scattering is particularly suitable for the stud-ies of the mechanism of magnetoelectric coupling in multiferroics, where theinterplay between structural and magnetic properties is of interest. The in-vestigation of interfacial magnetic structure of thin films and multilayers isanother field which will benefit from the X-ray magnetic scattering facility.Correlation between superconductivity and the charge density wave (CDW),and that between superconductivity and the spin density wave (SDW) areother topics to pursue.

Beside what have been mentioned above, general X-ray scattering tostudy the structures of thin films, multilayers, and materials under extremeconditions will also be performed here. Integration of various techniques, inparticular the non-synchrotron-based ones, to perform measurements underidentical sample conditions for different techniques and/or simultaneouslywill be implemented. Pushing the sample environment to more extreme con-ditions will be the target for the next stage development.

Moreover, to relieve the pressure of oversubscribed beam time on diffrac-tion and to bridge smoothly the research momentum during the transitionfrom the TLS to the TPS, a medium-resolution powder diffraction stationwill be implemented in this beamline for the first few years of operation.Chemical dynamics in solid state probed by time-resolved powder diffractionwith sub-millisecond resolution will be the focus of this station. Subjectssuch as the growth of crystals, structural phase transition of electrode mate-rials of the Li-ion battery during charging and discharging, the phenomenaof transient states of light-induced excited spin-state trapping, the structuremodification of cathode material due to oxygen transport in solid oxide fuelcell are a few examples.

1.3 Photon Source

A set of two 3 m long in-vacuum undulators with a period of 22 mm(IU22) is chosen as the light source, and will be installed in the straight

1.3. PHOTON SOURCE 5

section at port 9, which has a double minimum-βy lattice design and canaccommodate two IDs up to 4.9 m each in length. The basic parameters ofthe IU22 undulator are summarized in Table 1.1. Please note a total mag-net length of 6 m is adopted to simulate two 3 m long IU22s in series. Themaximal magnetic field is set to 0.72 tesla at a minimal magnet gap of 7mm, which yields a deflection parameter (Kymax) of 1.48. The total powerradiated from the 6 m long undulators is 8.86 kW for a stored ring current of500 mA. As requested by the users, the target spectral range of the beamlinefalls in between 5 and 25 keV, which covers the K -edges of most transitionmetals and the L-edges of rare earths and actinides. The energy spectrumof the 6 m long IU22 is illustrated in Figure 1.1. There exists a large gapbelow 5.6 keV between the first and the third harmonics. The lowest energyof the beamline is thus limited to 5.6 keV, delivered by the third harmonic.In the future, it is considered to raise the magnetic field to 1.05 tesla and/orreduce the magnet gap down to 5 mm to gain more flux and brightness. Theminimum of the spectral range could thus be further extended down to 3.5keV. In the initial stage, one 2 m and one 3 m long IU22 will be installedinstead of two 3 m IU22s. Nevertheless, the results of all the calculationspresented in this report are based on the 6 m long IU22s with parameterslisted in Table 1.1.

Table 1.1: Basic parameters of a set of two 3 m IU22 undulators in tandem

In-vacuum undulator IU22

Photon energy (keV) 5.6 - 25 (3.52 - 25)

Current (mA) 500

Period length, λu (mm) 22

Number of periods, Nperiod 140 × 2Total magnetic length, L (m) 3.08 × 2Peak field (T) 0.72 (1.05)

Deflection parameter, Kymax 1.48 (2.16)

Minimum magnet gap (mm) 7 (5)

Peak power density (kW/mrad2) 86.1 (127)

Total power (kW) 9.1 (19.21)

Note: The numbers in parentheses are obtained by adoptinga minimum undulator magnet gap of 5 mm.


0 5000 10000 15000 20000 25000 300001E17

1E18

1E19

1E20

1E21

Bri

llian

ce (

ph/s

/mr^

2/m

m^2

/0.1

%)

n=1

n=3

n=5

n=7

n=9

n=11

n=13

Energy (eV)

14.4 keV

Figure 1.1: Brilliance as a function of energy from a set of two 3 m IU22undulators in tandem at the TPS. The brilliance at 14.4 keV using the 7thharmonic is 4.8 × 1019 photons·s−1 ·mrad−2 ·mm−2 ·(0.1%BW)−1.

The spectral brilliance and flux of a set of two 3 m IU22 undulators in tan-dem at the TPS filled with 500 mA current are shown in Figures 1.1 and 1.2,respectively. Owing to the low 1.6 nm·rad emittance of the TPS, the theoret-ical photon brilliance and flux integrated over the central cone of the undula-tors are greater than 3.44 ×1018 photons ·s−1 ·mrad−2 ·mm−2 ·(0.1%BW )−1and 1.56 ×1013 photons ·s−1 · (0.1%BW )−1, respectively, as determined at24 keV using the 11th harmonic. The theoretical spatial coherence flux fromthe IU22s as a function of photon energy is shown in Figure 1.3. The spatialcoherence flux is greater than 2.2 ×109 photons·s−1 · (0.1%BW )−1 at 24 keVphoton energy.

The horizontal and vertical source sizes of the IU22 are shown in Fig-ure 1.4 and Figure 1.5 as a function of the photon energy. The horizontalsource size varies insignificantly in the energy range of 5.6−25 keV with anRMS value of 163.1 µm (full width at half maximum, FWHM, of 383 µm).The vertical source size over the same energy range has an RMS value vary-ing from 6.69 to 5.64 µm (FWHM of 15.7 to 13.3 µm).

The horizontal and vertical photon source divergences of the IU22 source


0 5000 10000 15000 20000 25000 300001E12

1E13

1E14

1E15

1E16

Flu

x (

ph

/s/0

.1%

)

Energy (eV)

n=1

n=3

n=5

n=7

n=9

n=11

n=13

14.4 keV

Figure 1.2: Spectral flux as a function of energy from a set of two 3 mIU22 undulators in tandem at the TPS. The flux at 14.4 keV using the 7thharmonic is 2.4 × 1014 photons·s−1 ·(0.1%BW)−1.

each as a function of the photon energy are shown in Figure 1.6 and Fig-ure 1.7, respectively. The RMS horizontal source divergence varies between16.09 and 15.56 µrad, (FWHM of 37.81 and 36.57 µrad) over the energy rangeof 5.6−25 keV. The change in vertical divergence over this energy range ismore than that of the horizontal divergence with an RMS value of 9.07 to8.09 µrad (FWHM of 21.31 to 19.01 µrad). In an absolute scale, the verti-cal divergence is relatively small, indicating the excellent collimation of thephoton beam.


0 5000 10000 15000 20000 25000 300001E8

1E9

1E10

1E11

1E12

1E13

1E14

Coh

ere

nt flu

x (

ph

/s/0

.1%

)

Energy (eV)

n=1

n=3

n=5

n=7

n=9

n=11

n=13

14.4 keV

Figure 1.3: Spatial coherence flux as a function of energy from a set of two 3m IU22 undulators in tandem. The spatial coherence flux at 14.4 keV usingthe 7th harmonic is 8.8 × 1010 photons·s−1 ·(0.1%BW )−1.

5000 10000 15000 20000 25000 30000156

158

160

162

164

166

168

170

Ho

rizo

nta

l S

ize

(m

)

Energy (eV)

Figure 1.4: Horizontal photon source size of a set of two 3 m IU22 undulatorsin tandem.


5000 10000 15000 20000 25000 30000

5.50

5.75

6.00

6.25

6.50

6.75

7.00

Ve

rtic

al S

ize

(m

)

Energy (eV)

Figure 1.5: Vertical photon source size of a set of two 3 m IU22 undulatorsin tandem.

0 5000 10000 15000 20000 25000 3000014.5

15.0

15.5

16.0

16.5

17.0

Ho

rizo

nta

l d

ive

rge

nce

(ra

d)

Energy (eV)

Figure 1.6: Horizontal source divergence of a set of two 3 m IU22 undulatorsin tandem.


0 5000 10000 15000 20000 25000 30000

7

8

9

10

Ve

rtic

al d

ive

rge

nce

(ra

d)

Energy (eV)

Figure 1.7: Vertical source divergence of a set of two 3 m IU22 undulators intandem.

1.4 Beamline Optical Design

1.4.1 Overview

The three major experimental methods implemented in this beamlineplace different requirements on the X-ray beams. For temporally coherentX-ray diffraction, X-rays with an ultrahigh energy resolution (∆E/E ∼ 10−8)is an essential condition and a sub-millimeter spot size is desirable (mode1). For time-resolved and general X-ray scattering, as well as powder diffrac-tion, the energy resolution can be relaxed to 10−4 and a sub-millimeter spotsize matches the experimental needs (mode 2). For magnetic scattering, areasonably good energy resolution (∆E/E ∼ 10−4) and a beam size of a fewtens of micrometers are required (mode 3). The beamline has been designedto have two end stations operated in a time-sharing mode to satisfy differentexperimental requirements. Figure 1.8 presents the beamline layout.

Outside the front end and the radiation-shielding wall is Hutch 1, on theleft-hand side of Figure 1.8, which is the first optical enclosure. It houses awater-cooled aperture, a 200 µm thick diamond filter to remove low energyphotons and reduce radiation power, a Bremsstrahlung baffle, two Be win-

1.4. BEAMLINE OPTICAL DESIGN 11

Figure

1.8:

Top

view

andsideview

ofthebeamlinelayout.


dows, and a double crystal monochromator (DCM). The DCM, with liquidnitrogen-cooled Si(111) crystals, is located at 28 m from the source. To in-crease the photon flux at the sample positions, a horizontal focusing mirrorHFM1 with an ellipse-plane shape is implemented after the DCM at 30.5 mfrom the source to provide a nearly 2:1 focused beam.

The end station 1 (ES1) is located inside the second hutch, which housesa high resolution four-bounce monochromator (HRM), a compact 4-circlediffractometer, a large 6-circle diffractometer, and a 3-circle diffractometer.The HRM provides the ultrahigh energy resolution required for the tempo-rally coherent diffraction experiments. The compact 4-circle diffractometerlocated immediately after the HRM serves as a goniometer to position a cav-ity or a diamond phase retarder. A 7.9 m stretch of an area between thesecond and the third hutches, free of beamline optical components, accom-modates a femtosecond laser system for pump-probe studies and beamlinecontrol modules. One Kirkpatrick-Baez (K-B) focusing mirror system andthe end station 2 (ES2) are located in the third hutch, which has a relativelylarge space to house various instruments. ES2 consists of an 8-circle diffrac-tometer, designed for (resonant) magnetic scattering and scattering undernon-ambient sample conditions.

The optical layout of the ES1 is displayed in Figure 1.9 when the beamlineis operated at mode 1 for temporally coherent diffraction studies. The beam-line is operated at mode 2 for time-resolved and general scattering as HRM ismoved out of the beam path to relax the energy resolution. Sufficient spaceis reserved in hutch 2 to install an additional K-B focusing system to reducethe beam size at the center of the diffractometer, located at 36.7 m, downto a few micrometers. With the HRM out of the way, X-rays will pass theES1 and be focused by the K-B system onto the center of the diffractometerat the ES2, as illustrated in Figure 1.10, when the beamline is operated inmode 3.

The major components of the beamline are listed in Table 1.2 and thedesigns of the major components are described in more details in sections1.4.2−1.4.4.


Mo

de

1

Mo

de

2

Figure

1.9:

Opticallayoutformodes

1an

d2.

14 CHAPTER 1. TEMPORALLY COHERENT XRDU

nd

ula

tor

Fix

ed

P

rim

ary

a

pe

rtu

re

Slits

1

DC

M2

8m

HFM

3

mra

d4

0c

m(L

)x1

0c

m(W

)3

0.5

m

Slits

2

VFM

2

3 m

ra

d4

0c

m(L

)x1

0c

m(W

)5

2m

HFM

2

3 m

ra

d4

0c

m(L

)x1

0c

m(W

)5

5.2

5m

Sa

mp

le

57

.25

m

Ph

ase

pla

te

33

m

Figure

1.10:Opticallayoutformode3.


Table 1.2: List of beamline components and the utilitiesrequired

Beamline componentsDistancefrom

source [m]

Comp.Air

D.I.Water

Description

Front End

Primary slits Y

Optical Hutch

Gate valve 24 Y GV1

Diamond filter 24.875 Y

White beam slits 25.4 Y slit

Bremsstrahlungbaffle-I-system

25.98 Y W, ID 10 mm

Be window 26.3 Y

Cooled fluorescentscreen-I-system

26.95 Y Y screen

Gate valve 27.3 Y GV2

DCM 28DCM and 480

L/s TP


Bremsstrahlungstopper-II-system

28.97 Y W

Shutter 29.7 Yshutter and

300T (modelnumber) IP

Gate valve 30 Y GV4

HFM 30.5

Be window 30.94

ES1 Hutch

High resolutionmonochromator

32.3 air

Continued on next page


Table 1.2 – Continued from previous page

Beamline componentsDistancefrom

source [m]

Comp.Air

D.I.Water

Description

Compact 4-cdiffractometer forcavity and phaseretarder

34.95

1st station (large 8-cdiffractometer)

36.7 1st station

Be window 38.7

Cross 38.93Cross and 300T

IP


IP



IP

ES2 Hutch

Fluorescent screen 51.25 Y screen


VFM system 52 VFM2


Fluorescent screen 54.42 Y screen


HFM system 55.25 HFM2

Be window 55.7

2nd station (8-cantimagneticdiffractometer)

57.2 2nd station


1.4.2 High Heat Load Optics

All the optical elements before X-rays being rendered monochromatichave to sustain and/or reduce the high heat load deposited by radiationout of the insertion device. They include aperture, filter, window, slits, andDCM. The designs/specifications of these components are depicted below.

Fixed Aperture

A water-cooled fixed aperture is the first beamline optical element, whichdefines the opening of the photon exit of the front end and reduces the heatload of downstream components. It is installed after the first vacuum valveand mounted on a 2-axis electrically motorized stage. The maximum travel-ing ranges of this motorized stage are ±2 mm in both X and Y axes with a1 µm resolution to compensate for the installation error.

White Beam Filter and Windows

Heat load evaluation shown below is carried out by assuming the highestpossible heat load as the undulator magnet gap is reduced down to 5 mmand the magnetic field is raised to 1.05 tesla. Total power, integrated over allthe harmonics, is then 120.75 Watt at 3.52 keV (the lowest energy availableout of the third harmonic of the IU22), provided an angular acceptance of40 µrad × 25 µrad (H × V) is adopted. A white beam filter is used to filterout the X-rays with low energies to reduce the unnecessary heat load to thedownstream components. The results of transmission simulation for diamondfilters with different thickness are shown in Figure 1.11. After considering theheat load of the DCM and the optimized transmission, we decide to adopt a200 µm thick CVD diamond with water flow-cooling. It will remove about40% of the total heating power of 48.43 W at 3.52 keV. When 48.43 W poweris applied to the diamond filter, the maximal Von Mises stress is 60.6 Mpawhich is within the safety region (< tensile stress of 1,200 Mpa). After thewhite beam filter, a 200 µm thick Be window which will remove further 2.5W heat load at 3.52 keV, is installed to separate the storage ring from thebeamline. Because most of the heat power at low energies is absorbed bythe white beam filter, the window only needs to sustain the local thermalstrain induced by the residual heat. When 2.5 W power is applied to the Bewindow, the maximal Von Mises stress is 1.2 Mpa which is within the safetyregion (< yield stress of 240 Mpa). The stress simulations of the diamondfilter and the Be window are shown in Figure 1.12 (a) and (b), respectively.


Besides, the simulations for a 500 µm Be filter and a 500 µm Be window(after a 500 µm Be filter) are also illustrated in Figure 1.12 (c) and (d) asa reference. After the white beam filter and window, the residual power is69.8 W which is mainly absorbed by the first crystal of the DCM.

0 5000 10000 15000 20000 25000

0.0

0.2

0.4

0.6

0.8

1.0

Tra

nsm

issi

on

Photon Energy (eV)

200 um Be100 um Diamond200 um Diamond400 um Diamond

Figure 1.11: Simulation transmission for diamond filters with different thick-ness.

White Beam Slits

The white beam slits consist of two orthogonal sets of slit blades. The slitsare stepper motor driven and fitted with limit switches and datum switches.Encoders can be fitted, as an option, for continuous position feedback. Slitblades are made of tungsten or tungsten carbide and are each chamfered toa knife edge. The slit mechanisms are mounted on a flange with the slitblades precisely aligned to the face of the flange and tested for parallelismand precision of motion. The detailed specifications of the white beam slitsare listed in Table 1.3.


( )a

( )b

( )c

( )d

200 um diamond filter

3.52 keVAbsorbed power: 48.43 WMax temp.: 108.4 CMax stress: 60.6 Mpa

(


Table 1.3: Specifications of the white beam slits

Item Specification

Vacuum 5 1 × 10−9 TorrMaximum available aperture 8 mm (H) × 8 mm (V)Slit motion resolution 5 0.1 µmSlit motion repeatability (uni-directional) 5 0.5 µmSlit motion accuracy 1 µm

Blade straightness 1 µm over 10 mm

Parallelism of each set of the slit blades < 20 µm

Cooling Indirect cooling

Maximum total power 100 W

Slit material tungsten

Device flange to flange length 300 mm

Entrance and exit flange size 4.5 inch CF flange

DCM

The primary function of the DCM is to provide a stable beam with areasonably good energy resolution in modes 2 and 3 and to act as the sourcefor the high-resolution monochromator further downstream in mode 1. TheDCM covering a spectral range of 5.57−25 keV will be located at 28 m awayfrom the photon source. A pair of Si(111) crystals are adopted. Because the1st crystal of the DCM needs to sustain most of the heat power from thebeam, cryo-cooling is necessary for the 1st crystal to ensure sufficient heatdissipation and a stable optical performance. Proper radiation shields shouldbe installed to protect the DCM motion mechanism against the scattered X-rays to minimize the thermally induced drift. The system operates in a fixedoffset mode with an entrance-exit beam offset of 25 mm. For this beamline,the entrance height of the beam is 1,350 mm, and the exit height is 1,375mm. Table 1.4 describes the basic specifications of the DCM.

The heart of a monochromator is a precise rotation mechanism. It shouldbe strong enough to maintain high accuracy and repeatability of crystal rota-tion over the required energy range. The definition of the coordinate system


Table 1.4: The basic specifications of the DCM

Parameter Specification

Bragg angle range 4 − 25◦

Height of the incident beam 1,350 ± 25 mmExit beam offset 25mm upwards

Maximum beam size 30 (width) x 50 (height) mm2

Crystal type Si (111) for 1st & 2nd crystal

Crystal size1st: 50 (L) x 40 (W) x 40 (H) mm3

2nd: 160 (L) x 40 (W) x 30 (H) mm3

Crystal cooling indirect LN2-cooling

1st crystal adjustment mechanism θ1, Z1 - motorized

2nd crystal adjustment mechanism χ2 - motorized

Supporting structure mechanismZT - manual jacks

XTB, YTB, χTB - horizontal bolts

Ultimate pressure 3 × 10−7 Torr

of the DCM is the following. X-axis is along the crystal surface perpendicularto the diffraction plane, Z-axis is along the normal to the crystal surface, andY-axis along the crystal surface within the diffraction plane. Pitch θ meansrotation around the X-axis, yaw ϕ and roll χ are rotations around the Z- andY-axes, respectively.

Because the beam offset is upwards, the 1st crystal is below the 2ndone. Surface of the 1st crystal is faced up. The surface of 2nd crystal isset in the center of the main axis goniometer as shown in Figure 1.13. Ad-justment mechanism for the 1st crystal consists of the motorized verticaltranslation stage Z1 and the motorized θ1 rotation with piezo actuator forfine pitch adjustment. The 2nd crystal surface is faced down and the ad-justment mechanism for the 2nd crystal is motorized χ2 roll adjustment. Inorder to keep the offset constant and beam footprint at the crystal center,the crystal has to be translated along Z and Y axes, respectively. Amount


of travel is expressed by formulas:

Y2 = h/(2 sin θM) Z1 = h/(2 cos θM)

where h and θM denote the offset and the Bragg angle. Rotation center (0,0)coincides with the center of the main axis goniometer.

The adjustment mechanism of the 2nd crystal consists of a roll χ2 tiltingmechanism, which provides fixed offset for various Bragg angles, and allowadjustment of the outgoing beam direction. In this design, the long lengthof the 2nd crystal is adopted instead of Y2 translation.

YZ

X

Fixed h = 25 mm

Figure 1.13: Coordinate system of the DCM.

All motorized in-vacuum translations of the crystals will be achieved viastepper motors which are compatible with high vacuum conditions. Possi-ble collisions between the first and the second crystals must be preventedby means of properly set limit switches and hard stops. All in-vacuum mo-tions must be fitted with suitable high vacuum-compatible encoders. Allmaterials used in the crystal cage must be high vacuum-compatible. All in-vacuum wiring must be Kapton-insulated and the connectors are suggestedto be gold-plated. Supporting structure of the monochromator consists ofone big granite table. The manual adjustment of the monochromator heightZT by vertical jacks are assembled between the granite block and a base plateon a floor. This can be also used for adjusting the tilting. Position of themonochromator in the beamline can be adjusted manually with horizontalbolts at the bottom of the granite. Table 1.5 summarizes the mechanical


Table 1.5: Specifications for the DCM Motions

Motion Parameter* Specification

Bragg angle θM

Range-1◦ to 30◦ (Feasible range)

4◦ to 25◦ (Operational)

Resolution 0.1′′/half step

Repeatability 1′′

Speed 0.1◦/sec

Drive In-vacuum stepping motor

Pitch θ1 of the 1stcrystal

Range ±2◦ (coarse)/ 16.5′′ (fine)

Resolution0.05′′ (coarse)/ 0.0007′′

(fine)

Repeatability coarse 1′′

DriveIn-vacuum stepping motor/In-vacuum piezo

translation Z1 of the 1stcrystal

Range +3 to -10 mm

Resolution 0.1 µm

Repeatability ± 1 µm

Driveground screw 1mm, 1:10gear reduction

Roll χ2 of the 2ndcrystal

Range ± 2◦

Resolution 0.4′′

Repeatability 1′′

Drive

Vertical translation ZT

Range -5 to +13 mm

Tilting range ± 0.3◦

Actuator Manual

Drive 4 precision jacks

Bolt positioningmechanism

Horizontal bolt adjustments XTB, YTB, χTB

Tilt range ± 1◦

Translation range ± 10 mm∗The definitions of the terms in the parameter column are described inthe text


specifications of the DCM.

There are LN2-cooling pipes for both crystals and water-cooling pipes forCompton shield. These cooling tubes are led through the vacuum feedthroughon the airside of the main axis shaft, and through central hole of this hollowshaft to the common rotation table. A white beam stop is mounted insidethe exit port of the DCM chamber. It consists of a water-cooled copperblock, which protects the downstream components from exposure to the di-rect beam.

The following are the definitions of the optical and mechanical character-istics of the system:

Resolution: amount of motion corresponding to one step of the actuator (fullstep mode, unless specified otherwise).

Increment: the smallest amount of motion which can be executed by themechanism with a 10% accuracy.

Accuracy: maximum difference between the amount of motion demanded ofthe actuator and that actually executed by the mechanism for any motionwithin the specified range. Absolute accuracy means accuracy within thewhole range of motion.

Repeatability: the largest difference between the primary position and theposition to which the mechanism returns after any loop of travel within themotion range, while approaching the target position from the same directionas that for the primary position.

Lost Motion (backlash): the largest difference between the primary positionand the position to which the mechanism returns after any loop of travelwithin the motion range, while approaching the target position from the op-posite direction as that for the primary position.

Stability : the largest deviation from the specified position during the speci-fied time.

The 1st crystal of the DCM absorbs almost all the deposited heat. Ther-mal induced lattice deformation may significantly deteriorate its optical per-formance. Thermal induced slope error was thus estimated at 3 photonenergies of 5.6, 8, and 25 keV under several absorbed power between 60 −97 Watt as shown in Table 1.6. The value of applied heat transfer coefficientis 1,156 W/m2/K determined by assuming fair thermal contact between the


copper cooling blocks and the Si crystal in a side cooling configuration andoptimal LN2 cryogenic unit operation parameters with acceptable mechan-ical vibration. Figure 1.14 illustrates the scheme of crystal temperature,surface displacement, and slope error data for absorbed power of 96.6, 72.5,and 60.4 W at 8 keV, where the slope error in the 1st case is almost 5 timeslarger than the 3rd case. At 5.6 keV with absorbed power of 96.6 W, crystalsurface exhibits an large slope error 47.63 µrad which leads to a reductionof transmission intensity down to 71%. For the absorbed power lower than72.5 Watt (in the case of 200 µm diamond + 250 µm Be), the transmissionis expected to be better than 95% for the entire operation energy range. Forthe absorbed power lower than 84.5 Watt (in the case of 1,000 µm Be), thetransmission is expected to be better than 87% for the entire operation en-ergy range. In order to mitigate the thermal load effect, at phase 1 we willuse a 200 µm thick diamond filter and a 250 µm thick Be window.

Table 1.7 and 1.8, respectively, represent the estimated absorbed poweron the first crystal of the DCM after a 200 µm thick diamond filter and a250 µm thick Be window and after two 500 µm thick Be windows. The cal-culation was based on an X-ray beam with a solid angle of 40 µrad (H) x25 µrad (V) and a fixed horizontal footprint of 1.12 mm. The highest powerdensity in both cases occurs at 5 keV, due to the largest Bragg angle. In thechosen case of 200 µm diamond and 250 µm Be, the power deposited on the1st crystal of the DCM is lower than 70 W for the entire operation energyrange.

Table 1.6: The thermal induced slope error analysis for the DCM.

EnergyAbsorbed

Power (W)Beam size

Max Temp

(K)

Min Temp

(K)

Slope error

(μrad)

Si (111)

Darwin

width (μrad)

Mono.

Transmission

96.6 156.3 100.6 47.63 52 0.71

84.5 140.8 98.04 22.2 52 0.87

72.5 128.7 95.47 8.41 52 0.95

66.6 123.3 94.2 4.79 52 0.97

60.4 118.3 92.9 2.05 52 0.99

96.6 140.9 100.6 21.54 34.8 0.82

84.5 130.3 98.04 9.512 34.8 0.92

72.5 121.1 95.47 3.65 34.8 0.97

66.6 116.9 94.9 1.48 34.8 0.99

60.4 112.8 92.91 1.17 34.8 ~1.00

96.6 116.5 100.6 2.32 10.55 0.95

72.5 106.3 95.47 1.57 10.55 0.97

66.6 103.8 94.19 2.41 10.55 0.96

60.4 101.4 92.91 2.43 10.55 0.96

5.6 keVV :1.982

H:1.12

8 keVV :2.832

H:1.12

25 keVV:8.843

H: 1.12


8 keVAbsorbed Power: 96.6 WPeak temp.: 140.9 K

8 keV/96.6 W


( )a ( )b

( )c ( )d

-30 -20 -10 0 10 20 30

0.000

0.005

0.010

0.015DisplacementSlope Error

Along the BeamDirection (mm)

Dis

pla

cem

ent(m

icro

ns)

-15

-10

-5

0

5

10

15

Slo

pe

Erro

r(m

icro

-rad)

8 keV/72.5 W

-30 -20 -10 0 10 20 30

-0.010

-0.008

-0.006

-0.004

-0.002

0.000


Dis

pla

cem

ent(m

icro

ns)

-2

-1

0

1

2

Slo

pe

Erro

r(m

icro

-rad)

-30 -20 -10 0 10 20 30

-0.012

-0.010

-0.008

-0.006

-0.004

-0.002

0.000


Dis

pla

cem

ent(m

icro

ns)

-2

-1

0

1

2

Slo

pe

Erro

r(m

icro

-rad)

( )f

8 keV/60.4 W

( )e


Figure 1.14: (a) Temperature on the 1st crystal due to an X-ray beam withphoton energy 8 keV with a total power of 96.6 W. (b) The thermal induceddisplacement and slope error for (a). (c) Temperature on the 1st crystal dueto an X-ray beam with with photon energy 8 keV with a total power of 72.5W. (d) The thermal induced displacement and slope error for (c). (e) Tem-perature on the 1st crystal due to an X-ray beam with with photon energy8 keV with a total power of 60.4 W. (f) The thermal induced displacementand slope error for (e).


Table 1.7: Energy dependent power loading on the DCM after a 200 µmthick diamond filter and a 250 µm thick Be window.

Energy

(keV)

Deflecting

parameter (K)

Bragg

angle(°)

Vertical

footprint (mm)

Power out of

ID22 (W)

Transmitted pwr. after 200

μm Diamond + 250 μm Be

(W)

Absorbed pwr. Density

(W/mm^2)

5 1.63 23.293 1.77 85.84 46.62 23.51

6 1.36 19.24 2.124 77.95 33.82 14.21

6.22 2.06 18.534 2.202 120.75 69.82 28.31

7 1.89 16.407 2.478 114.8 60.78 21.9

8 1.7 14.309 2.832 89.01 49.77 15.69

9 2 12.69 3.186 119.58 68.11 19.09

10 1.86 11.403 3.54 102.67 59.08 14.9

11 1.73 10.355 3.894 97.78 51.95 11.91

12 1.95 9.483 4.249 111.78 65.57 13.78

13 1.84 8.748 4.603 103.09 58.4 11.33

14 2.03 8.119 4.957 105.6 66.62 12

15 1.92 7.574 5.311 105.22 62.62 10.53

16 1.83 7.098 5.665 113.34 57.08 9

17 1.98 6.679 6.019 123.52 65.48 9.71

18 1.89 6.306 6.373 114.8 60.78 8.52

19 2.03 5.973 6.727 105.6 66.62 8.84

20 1.95 5.673 7.081 111.78 65.57 8.27

21 1.89 5.402 7.435 114.8 60.78 7.3

22 2 5.156 7.789 119.58 68.11 7.81

23 1.93 4.931 8.143 108.23 62.41 6.84

24 2.03 4.725 8.497 105.6 66.62 7

25 1.98 4.536 8.851 123.52 65.48 6.61


Table 1.8: Energy dependent power loading on the DCM after two 500 µmthick Be windows.

Energy

(keV)

Deflecting

parameter (K)

Bragg

angle(°)

Vertical

footprint (mm)

Power out of

ID22 (W)

Transmitted pwr. after

2x500μm Be (W)

Absorbed pwr. Density

(W/mm^2)

5 1.63 23.293 1.77 85.84 54.05 27.26

6 1.36 19.24 2.124 77.95 39.99 16.81

7 1.89 16.407 2.478 114.8 69.07 24.88

8 1.7 14.309 2.832 89.01 57.15 18.02

9 2 12.69 3.186 119.58 76.47 21.43

10 1.86 11.403 3.54 102.67 66.9 16.87

11 1.73 10.355 3.894 96.83 60.93 13.97

12 1.95 9.483 4.249 111.78 74.4 15.64

13 1.84 8.748 4.603 103.09 66.25 12.85

14 2.03 8.119 4.957 105.6 73.83 13.3

15 1.92 7.574 5.311 105.22 70.99 11.94

16 1.83 7.098 5.665 113.34 65.34 10.3

17 1.98 6.679 6.019 123.52 73.88 10.96

18 1.89 6.306 6.373 114.8 69.07 9.68

19 2.03 5.973 6.727 105.6 73.83 9.8

20 1.95 5.673 7.081 111.78 74.41 9.38

21 1.89 5.402 7.435 114.8 69.07 8.29

22 2 5.156 7.789 119.58 76.47 8.77

23 1.93 4.931 8.143 108.23 70.61 7.74

24 2.03 4.725 8.497 105.6 73.83 7.76

25 1.98 4.536 8.851 123.52 73.88 7.45


1.4.3 Monochromatic Optics

After the DCM, there are three focusing mirrors in the beamline opticaldesign. The first one is a horizontal focusing mirror used for both end sta-tions. The second and the third ones will be implemented in the Kirkpatrick-Baez (K-B) configuration. Because the residual heat on these mirrors is low(less than 1 Watt), no cooling mechanism is needed. All the mirrors will beoperated in an ultrahigh vacuum environment.

Horizontal and Vertical Focusing Mirrors

The first horizontal focusing mirror (HFM1) with an ellipse-plane shapeis located at 30.5 m away from the photon source. With a 3.0 mrad glancingincident angle, the 40 cm long mirror collects a 0.04 mrad radiation fan inthe horizontal direction. It has a 2:1 focusing ratio and yields a beam sizeof 612 µm (H) × 733 µm (V) at the sample position of the ES1 (36.7 m).Considering that the X-ray cavity only accepts a beam of 500 µm (H) × 100µm (V) in size, the installation of the HFM1 will result in an increase of in-cident photon flux by a factor of 1.5 to a cavity sitting at the sample position.

The K-B focusing mirror system is implemented for the ES2. A 40 cmlong vertical focusing mirror (VFM2) with an ellipse-plane shape is locatedat 52 m from the source to provide a nearly 10:1 vertically-focused beam atthe sample position of the ES2 (57.25 m). A 40 cm long horizontal focusingmirror (HFM2), also with an ellipse-plane shape, is located at 54.75 m fromthe source to provide a nearly 5:1 horizontally-focused beam at the sampleposition of the ES2. The glancing incident angle for the two mirrors is 3mrad. The overall horizontal focusing ratio at the sample position of theES2 is near 10:1 with the focusing ratio of mirror HFM1 (2:1) taken intoaccount.

To cover the specified energy range, 5.6−25 keV, three coating materialsare adopted for all mirrors. Si, Rh, and Pt will cover the energy ranges of5.6−9, 9−20, and 15−25 keV, respectively. Energy range switching can beaccomplished readily by selecting one of the three parallelly arranged stripesby a lateral translation. With a 3.0 mrad glancing angle, the reflectivities ofboth Si in 5.6−9 keV and Rh in 9−20 keV energy ranges are approximately90%. In the range of 15−25 keV the reflectivity of Pt is about 80% shownin Figure 1.15. An advantage of choosing Si is that it helps to eliminate thesecond order contamination in the low energy 5.6−9 keV range. A surface


roughness of5 3 Å and a slope error of5 0.5 µrad are set for all three mirrors.

The specifications of the mirrors are summarized in Table 1.9, and the de-tailed specifications of the three mirrors are summarized in Tables 1.10−1.12.

5000 10000 15000 20000 25000 30000-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Refle

ctivity

Photon Energy (eV)

Si(3mrad)

Rh(3mrad)

Pt(3mrad)

Figure 1.15: Reflectivity curves of Si, Rh, and Pt mirror coatings with a 3.0mrad glancing incident angle.

Each mirror will be mounted on a holder and installed in a high vacuummirror chamber. In order to properly position the mirror at the right positionand orientation, mechanical mechanisms for fine rotational and translationaladjustments are required. The definitions of the mirror coordinate systemsare illustrated in Figure 1.16. The mechanical specifications for the mir-ror adjustment apparatus are summarized in Table 1.13. Special attentionis required in the chamber design to avoid thermally-, pressure-, or othermechanically-induced distortions of the chamber wall, which will affect themirror performance. An independent granite support (on the floor) of themirror holder and mechanical mechanism is preferred, as illustrated in Fig-ure 1.17.


Table 1.9: Performance parameters of three mirrors. The sizes of the mirrorsare all 40 cm × 10 cm (L × W). The surface roughness is 3 Å, and the slopeerror is 0.5 µrad for all the mirrors.

End station ES1 ES2

Optics HFM1 VFM2 HFM2

GeometryTangential-elliptical

Tangential-elliptical

Tangential-elliptical

Objective focus r1(cm)

3,050 5,200 950

Image focus r2 (cm) 1,525 525 200

Glancing incidentangle (π

2− θ ) (mrad) 3.0 3.0 3.0

Semi-major axis a(cm)

2,287.500 2,862.500 595.000

Semi-minor axis b(cm)

6.4700 4.957 1.308

Semi-focal length d(cm)

2,287.491 2,862.496 574.999

High Resolution Monochromator

To achieve the desired ultrahigh energy resolution, an antiparallel (+,+)crystal arrangement is essential to narrow down the spectral bandwidth.Therefore, the (+,−,−,+) arrangement is employed with a dispersive set bytwo non-dispersive crystal arrangements, as illustrated in Figure 1.18. A pic-ture of a similar HRM used at BL12XU of SPring-8 is shown in Figure 1.19.Furthermore, four asymmetric Bragg reflections were used for changing therocking width (Darwin width) of each reflection by a factor of

√bn to ac-

quire a narrower bandwidth, where bn is the asymmetry factor of the nthreflection, bn = γ0/γn, where γ0 (γn) denotes cosine of the angle betweenthe incident (exit) beam and the crystal surface normal. The energy resolu-tion (∆E

E) of the four-bounce crystal monochromator is closely related to the

Darwin width and asymmetry factors of the two pairs of Bragg reflections.Atomic planes with high Miller indices, e.g., Si(11 5 3), and configurationwith an excessive b-value, e.g., ∼ 1/20, are usually chosen to achieve the


Table 1.10: Technical specifications of HFM1


Shape Tangential-elliptical

Bender mechanism Fixed radius

Clear aperture (mm,longitudinal × sagittal)

400 × 30 (L × W, eachstrip)

Mirror size (cm) TBD with the vendor

Focus (away from thesource, cm)

4,575

Demag. Ratio 2.0

Acceptance angle (µrad) 40

Grazing angle (mrad) 3

Slope error (µrad) 0.5

Roughness (Å) 3

Coatings

Three strips

• Bare Si• Rh• Pt


Table 1.11: Technical summary specifications of VFM2.








5,725

Demag. Ratio 9.9




Roughness (Å) 3

Coatings

Three strips



Table 1.12: Technical summary specifications of HFM2.








5,725

Demag. Ratio 4.75




Roughness (Å) 3

Coatings

Three strips



Figure 1.16: Coordinate systems of the focusing mirrors. (a) horizontal fo-cusing geometry (b) vertical focusing geometry.


Figure 1.17: A typical focusing mirror chamber with an ion pump. Themechanical adjustment mechanism is stabilized by a piece of granite.


Table 1.13: Mechanical specifications of the focusing mirror chamber. Theoperating conditions of the vacuum chamber are a vacuum pressure of < 10−9

Torr (ultrahigh vacuum), a temperature at 25 ◦C under normal operation,and 200 ◦C maximum during system bake-out (without mirror installed).

Motion Parameter Specification

Pitch (z-axis rotation)

Range ±2◦

Resolution < 0.5 µrad

Repeatability < 1 µrad

2 hr stability < 0.5 µrad

DriveIn-vacuum stepping motor,

0.1 µm encoded

Roll (y-axis rotation)

Range ±2◦

Resolution < 2 µrad


Yaw (x-axis rotation)

Range ±2◦

Resolution < 2 µrad


Vertical translation(normal to the mirrorsurface)

Range ±50 mmResolution < 0.5 µm

Repeatability < 1 µm

DriveMotorized; Encoder & limit

switches to be fitted

Horizontal translation(for coating exchange)

Range ±50 mmResolution < 5 µm

Repeatability < 20 µm

DriveMotorized; Encoder & limit

switches to be fitted


high resolution. The requirement of performing accurate and precise angulartuning over a narrow angular width and at a tiny glancing angle places strictdemands on the motion mechanisms of the crystals.

Figure 1.18: A four-bounce monochromator design for a 10−8 energy resolu-tion using Si(4 2 2) and Si(11 5 3) reflections.

The monochromator is composed of three parts: a swivel stage, a high-precision coaxial (θ-2θ) goniometer, and a heavy duty stage. Each crystal ismounted on a swivel stage which has a degree of freedom for either roll oryaw adjustment. Two high-precision coaxial goniometers with a (+,−) con-figuration house the two pairs of crystals; independent pitch adjustment foreach pair is available. Each high-precision goniometer will stand on a heavyduty translation stage for horizontal and vertical positionings. The detailedspecifications of the HRM are summarized in Table 1.14.

The spectral range of the HRM is much smaller than that of the DCMdue to the former’s complicated mechanism. A set of crystals in the HRMcan only serve no more than ±100 eV, out of which either the energy band-width broadens or the transmitted X-ray intensity is significantly attenuated.This implies that a long range scan cannot be performed with this design.Therefore several sets of HRM crystals are needed to cover different energyranges. Table 1.15 summaries several sets of crystal configurations with theirperformances calculated by dynamical X-ray theory.


Table 1.14: Specifications of the HRM mechanical mechanism.

Item Specification

Swivel angular range(crystal roll/yaw)

±10 degrees

Resolution 3 arcseconds

Repeatability 5 ±0.001 degrees

Goniometer rotation range(crystal pitch)

±2 degrees (fine)360 degrees (coarse, manual)

Resolution 0.005 arcseconds

Wobble ±1 arcsecond/ 360 degrees

Translation range ±50 mm (horizontal and vertical)

Resolution 1 µm

Accuracy 15 µm

Repeatability 3 µm

Table 1.15: Crystal parameters of the HRM and the resulting performances.

Energy(h,k,l)

Width thB Miscut Peak b1 b2∆E/E

Band-

(keV) (µrad) (deg.) (deg.) reflectivity—— —— passb3 b4 (µeV)

15.816(2,2,-4) 5.2 20.7 13.8/18.8 0.9744/0.9439 1/4.71 1/19.13 3.94E-08 624

(12,-4,4) 1.07 73.23 70.8 0.7382 13.88 13.88

14.438(4,2,2) 5.7 22.79 15.79/20.85 0.9674/0.9299 1/5.12 1/20.4 2.82E-08 406

(11,5,3) 1.7 79.82 77.83 0.6372 10.9 10.9

14.412(4,2,2) 5.8 22.83 15.79/20.85 0.9675/0.9305 1/5.1 1/20. 3.36E-08 485

(11,5,3) 2 80.42 77.83 0.6811 8.21 8.21

14.315(4,2,2) 6.3 22.99 15.79/20.85 0.9674/0.9323 1/5.0 1/18.5 6.54E-08 936

(11,5,3) 2.8 83.09 77.83 0.7647 3.57 3.57

12(4,2,2) 7.8 27.77 15.7/25.7 0.9648/0.8971 1/3.29 1/22.2 6.69E-08 804

(8,6,2) 4.5 75.94 73.5 0.781 11.94 11.94

10(4,2,2) 10 34 20/26.2 0.9492/0.8435 1/3.34 1/26.2 8.47E-08 847

(8,2,2) 9.4 75.59 73.5 0.772 14.06 14.06


swivel stage

heavy duty stage

high precision

coaxial goniometer

Beam

Figure 1.19: The four-bounce crystal monochromator at BL12XU, SPring-8,which adopts asymmetric Si(422), Si(422), Si(11 5 3), and Si(11 5 3) crystalswith the following b factors: b1 = 1/5.1, b2 = 1/20, b3 = b4 = 8.21. Energyresolution can reach up to 3.36 × 10−8 at 14.412 keV (∆E = 485 µeV).

1.4.4 Beamline Control and Data Management

Experimental Physics and Industrial Control System, EPICS, is adoptedfor beamline component control. To comply with the protocol of EPICS con-trol at the NSRRC, we have chosen Galil DMC-4080 motor controller as thestandard type. This type of controller has the capability of controlling up to8 motors via the communication interface of either Ethernet port or RS-232serial port. Furthermore, it can drive 4 motors simultaneously. Either digitalinput or analog input is available and only digital output is supplied. In ad-dition to the standard type, other controllers for special applications can alsobe integrated into the control software if the controller is compatible withthe EPICS protocol. The software for controlling beamline components isSPEC and other LabVIEW-like GUI. Table 1.16 summarizes all the steppingmotors for beamline component control. We need at least 20 Galil motorcontrollers. Considering a standard 35u rack, we need 4 racks at least, plus


1 for the front end and vacuum gauge controllers.

In addition to the stepping motors, pneumatic cylinder is another motioncontrol mechanism, which is used to drive components such as photon screenand photon shutter. It is mainly for quick beam intersection for safety con-sideration in particular. We adopt the programmable logic controller (PLC)as the core device for the beamline interlock system, which controls the inter-lock of hutch doors, vacuum environment, and the cooling system. The datalog of the beamline conditions will be available. Moreover, the status sig-nals sent from the front end are integrated into the beamline interlock system.

1.4.5 Performance Evaluation

The optical performances of the beamline are evaluated for the three op-eration modes using the shadow ray-tracing program. In mode 1, incomingX-rays pass the DCM, HFM1, and HRM. The characteristics of the beamare calculated at the sample position of the ES1 (at 36.7 m). In mode 2, theHRM is moved out of the beam, the performance is also calculated at thesample position of the ES1. In mode 3, with the HRM out of the beam, thetransmitted X-rays out of the ES1 will be focused by a pair of K-B mirrors.The performance of the beam is evaluated at the sample position of the ES2(at 57.25 m). The overall optical performances, including photon flux, en-ergy resolution, beam size, and high order harmonic suppression, of the threeoperation modes are presented in the following. Considering the sequence ofthe optical components used, the results are presented in the sequence ofmode 2, mode 1, and mode 3.

Mode 2

The energy resolution (∆EE) of the double crystal monochromator (DCM)

with a pair of Si(111) crystals is 1.33 × 10−4. The total energy resolutionvaries from 1.5 × 10−4 to 4.0 × 10−4 as the energy changes from 5.6 to 25keV, as shown in Figure 1.20. The contribution from various sources, includ-ing the vertical source size, the Darwin width of Si(111), and the acceptedangular divergence which is defined by the slit 1 at 24 m with a full openingcorresponding to 40 µrad (H) × 25 µrad (V) to match the focusing mirrorsize are also displayed. The calculated photon flux is depicted by the redcurve in Figure 1.21; the source flux is also displayed as the black curve as acomparison. With a 500 mA storage ring current, the flux is maximal at 4.8


Table 1.16: Summary of the stepping motors used for beamline componentcontrol.

Device name Motor name Number Type

Optical hutch

White beam slits x1, x2, z1, z2, 4

DCM th, pitch1, roll2, Z1 4

HFM1 Pitch, roll, yaw, Z-stage, X-stage 7

ES1 hutch

8-C diffractometerth/tth, phi, chi, ath/atth, beta,alpha

8

Diffractometer table X1, X2, Z1, Z2, Z3, beta rotation 6

Slits X, Y, ∆X1, ∆X2, ∆Y1, ∆Y2 24 (× 4 sets)

HRM th/tth, Z, swivel 8 (× 2 sets)

Goniometer head X, Y, arc X, arc Y 8 (× 2 sets)

Sample rod Z 2 (× 2 sets)

Cryostat carrier X, Y, Z 3

Optical table X1, X2, Z1, Z2, Z3 5

Phase retarder/cavity th/tth, phi, chi, Z, X 6

ES2 hutch

Slits X, Y, ∆X1, ∆X2, ∆Y1, ∆Y2 24 (× 4 sets)

VFM2 Pitch, roll, yaw, Z-stage, X-stage 7

HFM2 Pitch, roll, yaw, Z-stage, X-stage 7

Diffractometer table X1, X2, Z1, Z2, Z3, beta rotation 6

Diffractometer th/tth, phi, chi, ath/atth, beta 7

Goniometer head X, Y, arc X, arc Y 4

Sample rod Z 1

Reserved controllers 15

Total 156


× 1013 photons/s at 5.6 keV and drops to a minimum at 2.8 × 1012 photons/sat 25 keV.

5 10 15 20 25 300.0

1.0x10-4

2.0x10-4

3.0x10-4

4.0x10-4

En

erg

y r

eso

lutio

n (

E/E

)

Energy (keV)

Overall

Slit defined divergence

Si(111) Darwin width

Source size effect

Figure 1.20: Energy resolution (∆E/E ) of mode 2.

With the slit 1 defining an acceptance angle of 40 µrad (H) × 25 µrad(V), the focused beam size at the sample position of the ES1 is smaller than612 µm × 733 µm (FWHM, H × V), and the beam divergence is smallerthan 68.4 µrad × 20 µrad (FWHM, H × V) as shown in Figure 1.22, the sizeand divergence of the source used is also displayed.

Mode 1

The energy resolution (∆EE) of the four-bounce crystal monochromator

operated in the Si(422), Si(422), Si(11 5 3) and Si(11 5 3) configuration(shown in section 1.4.3) can reach up to 3.36 × 10−8 at 14.41 keV. We as-sume that the energy resolution remains at 10−8 throughout the availablespectral range from 5.6 to 25 keV for the performance calculations of mode1 . With the reflectivities of the two Si(422) crystals (0.9 each) and the twoSi(11 5 3) crystals (0.78 each) taken into account, the calculated photon fluxis shown as the blue curve in Figure 1.21. The photon flux is in the order of1010 photons/s (1 × 10−6 %BW)−1 at energies below 10 keV and drops to


5000 10000 15000 20000 25000 300001E7

1E8

1E9

1E10

1E11

1E12

1E13

1E14

1E15

Flu

x(P

hoto

ns/

sec)

Photon Energy (eV)

Source FluxES1 Calculated FluxES1 Calculated Flux passed HRM

14.4 keVn=4.8x109

Figure 1.21: Expected photon fluxes at the ES1 in modes 1 and 2.


Size Divergence

Source

Hori. : 385 m (FWHM)

Vert. : 15 m (FWHM)

Hori. : 37.5 rad (FWHM)

Vert. : 20 rad (FWHM)

Sample

Position

at ES1

(36.7m) Hori. : 612 m (FWHM)

Vert. : 733 m (FWHM) Hori. : 68.4 rad (FWHM)

Vert. : 20.1 rad (FWHM)

Figure 1.22: The simulated beam size and divergence in mode 2.


109 photons/s between 10 and 20 keV. The temporal coherence length (ℓtc),which varies from 2.2 × 104 to 5.0 × 103 µm as the energy changes from5.6 to 25 keV, is shown in Figure 1.23. The horizontal and vertical spatialcoherence lengths (ℓsc), varying from 3.4 to 0.8 µm and from 86.2 to 19.3µm, respectively, as the energy is tuned from 5.6 to 25 keV, are illustratedin Figure 1.24.

6 8 10 12 14 16 18 20 22 24

5.0x103

1.0x104

1.5x104

2.0x104

2.5x104

Te

mp

ora

l co

here

nce le

ngth

(m

)

Photon Energy (keV)

Figure 1.23: Temporal coherence length (ℓtc) of mode 1.

Mode 3

In mode 3, the DCM only is used to render the beam monochromatic andthe sample is placed at the ES2 at 57.25 m. The energy resolution (∆E

E) of

mode 3 is similar to that of mode 2, shown in Figure 1.20. The temporal co-herence length (ℓtc) at the ES2 is shown in Figure 1.25, which monotonicallychanges from 1.62 to 0.14 µm as the beam energy increases from 5.6 to 25 keV.

The photon flux at the ES2 is shown in Figure 1.26, which is 3.3 × 1013photons/s at 5.6 keV and drops to 1.7 × 1012 photons/s at 25 keV. Severalfactors, such as (1) a 200 µm thick diamond filter and four Be windows witha total thickness of 1,000 µm, (2) two Si(111) crystals with a 1.33 × 10−4 en-ergy resolution and a reflectivity of 0.85 each, convoluted with the accepted


6 8 10 12 14 16 18 20 22 240.1

1

10

100

1000

Sp

atia

l coh

ere

nce

le

nth

(m

)

Photon Energy (keV)

Vertical spatial coherence length

Horizontal spatial coherence length

Figure 1.24: Spatial coherence lengths (ℓsc) of mode 1.

6 8 10 12 14 16 18 20 22 240.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Tem

pora

l cohere

nce len

gth

(m

)

Photon Energy (keV)

Figure 1.25: Temporal coherence length (ℓtc) at the ES2 in mode 3.


angular divergence, (3) two horizontal focusing mirrors with a 40 cm lengthand 3.0 mrad glancing incident angle, and (4) one 40 cm long vertical focus-ing mirror with 3.0 mrad glancing incident angle, all affect the photon flux.The abrupt drop of the photon flux at 21 keV is caused by switching themirror coating from Rh stripe to Pt. The focused beam size at the ES2 issmaller than 34 µm × 17.2 µm (FWHM, H × V), and the beam divergenceis less than 300 µrad × 187 µrad (FWHM, H × V) as shown in Figure 1.27.

5000 10000 15000 20000 25000 300001E9

1E10

1E11

1E12

1E13

1E14

1E15

1E16

Photon Energy (eV)

Source FluxES2 Calculated Flux

The flux drop comes from thereflectivity changed from Rh to Ptcoating mirror

Figure 1.26: Photon flux at the ES2 in mode 3 with a 500 mA storage ringcurrent.

High-order Contamination

Because the upper limit of the covered spectral range is more than twicethat of the lower limit, high-order harmonic contamination will be a problemfor experiments with very weak signals; magnetic scattering conducted at thelow energy region is an example. High-order harmonic contamination can beeffectively suppressed by installing a high-order rejection mirror located be-fore the sample. The HFM1 will not only de-magnify beam size but also serveas a high harmonic rejection mirror. The spectral flux of the IU22 sourcewith the contribution of even harmonics included is shown in Figure 1.28.Because λ/3 can be easily rejected with pulse-amplitude discrimination in


Size Divergence

ES2

Sample

Position

57.25m

Hori. : 34 m (FWHM)

Vert. : 17.2 m (FWHM)

Hori. : 300 rad (FWHM)

Vert. : 187 rad (FWHM)

Figure 1.27: Simulated beam size and divergence at the sample position ofthe ES2 by ray-tracing program Shadow.


the detecting system, we will concentrate on the contribution of the secondharmonic. I. R. Entin, et al.[9] reported that double-crystal rocking curve ofthe forbidden Si(222) reflection was 0.14 arcsecond (FWHM) and its struc-ture factor F was 1.456 for 20 keV photons. At 10 keV, the structure factor ofSi(111) is about 60. The ratio of F(111)/F(222) is about 41. The diffractionintensity ratio of I111/I222 is proportional to the ratio of |F(111)/F(222)|2,which is larger than 103. The overall second order contamination ratio withthe contributions from (1) the source flux, (2) the structure factors of Si(222)and Si(111), (3) the windows transmission, and (4) the reflectivities of Si, Rh,Pt at a 3.0 mrad grazing incident angle all included, is shown in Table 1.17.The ratio is on the order of 10−6 or less.

5 10 15 20 25 301E11

1E12

1E13

1E14

1E15

1E16

n=15

n=14

n=13

n=12

n=11n=10

n=9

n=8n=6

n=7

n=5

n=4

n=3

Ph

oto

n F

lux (

Ph

oto

ns/s

ec/0

.1W

)

Photon Energy (keV)

n=16

Figure 1.28: Photon flux with the even harmonics from the IU22 included.


Tab

le1.17:Con

taminationbythesecondop

ticalorder

attheES1in

mode2.

n∗

E(eV)

Peak

inten-

sity

(photon

s·s−1

·(0.1%BW

)−1)

Percentage

ofthe2n

dop

tical

order

†

Ratio

ofcontamination

by

thesecondop

ticalorder

§

Si

Rh

Pt

(3mrad)

(3mrad)

(3mrad)

35,555

3.30

x10

15

7.9%

(n=6/n=3)

<10

−6

<10

−5

<10

−5

59,268

1.44

x10

15

5.9%

(n=10/n

=5)

<10

−9

<10

−5

<10

−5

712,937

6.05

x10

14

3.4%

(n=14/n

=7)

<10

−7

<10

−5

916,678

2.45

x10

14

1.7%

(n=18/n

=9)

<10

−9

<10

−7

1120,390

1.07

x10

14

0.7%

(n=22/n

=11)

<10

−9

<10

−9

∗ndenotes

theorder

oftheundulatorharmon

ics.

†Opticalorder

refers

totheharmon

icorder

ofthemon

ochromator.

§In

additionto

theintrinsicsourceflux,thisratiotakesinto

accountof

the

attenuationeff

ects

ofthestructure

factor,window

s’tran

smission

s,an

dmirrorreflectivitieson

ligh

tsof

differentorders.


1.5 End Stations

1.5.1 Overview

X-ray diffraction and scattering are the main experimental techniques ofthis beamline. The applicable experimental methods include single crystalscattering, grazing incident X-ray diffraction (GIXD), and X-ray reflectivity.X-ray absorption measurements can also be conducted. Two end stations,operated in a time sharing mode, are designed to accommodate 3 opera-tion modes. Mode 1 for temporally coherent diffraction will be conductedin the ES1, located in hutch 2. Mode 2 for time-resolved X-ray diffraction(TR-XRD) will also be performed in the ES1. Mode 3 for static and dy-namic magnetic scattering will be carried out in the ES2, located in hutch3. A femtosecond laser system required for the pump-probe studies will beinstalled between the two end stations to provide ultrafast optical pulses forboth end stations. The designs of the two end stations to match the technicalrequirements are described as follows.

1.5.2 Preliminary Design of the End Station 1

The ES1 is designed for temporally coherent diffraction and time-resolvedX-ray scattering. The setup of the ES1 is shown in Figure 1.29. The HRM, acritical component to provide the ultrahigh energy resolution, is installed onan optical table located in the upstream of hutch 2. A compact 4-c diffrac-tometer is also mounted on this optical table. The compact diffractometerprovides the necessary degrees of freedom for X-ray cavity studies. The trans-mitted beam with high temporal and spatial coherences will be employed asthe light source of temporally coherent diffraction studies in mode 1, wherethe sample is mounted on a large 6-c diffractometer downstream of hutch 2.For pump-probe type of time-resolved scattering experiments, laser pulseswill pass the rear wall of hutch 2 and be directed using a series of opticalreflecting mirrors to the center of the large 6-c diffractometer. The opticaldesign for the pump-probe measurement in mode 2 will be described in moredetails later. The highly coherent X-rays out of the cavity can be used asa probe for the laser-excited sample system. If the intrinsic time structureof the ring current need be used, the HRM will be moved out of the beampath and the beamline will be operated in mode 2. Under the absence ofthe HRM, medium-resolution powder diffraction experiment can also be pro-ceeded by 3-c powder diffractometer. At the end of the ES1, a beam stopperis installed to block the transmitted X-rays.

1.5. END STATIONS 53

The major components in the ES1 are described below.

Be Window

A beryllium window on the last flange of the beamline at 30.94 m pro-vides an X-ray exit out of the vacuum beam pipe. The Be window thicknessis 250 µm. To reduce the wavefront distortion, a well-polished Be foil will beused to maintain the spatial coherence.

Optical Table

An optical table in hutch 2 will provide a stable base for several beamlineoptic components, including slits, a beam monitor, HRM, and a goniometerfor cavities or phase retarders. To accommodate these components, the tablesize will be approximately 2.4 m long by ∼ 1 m wide with translation and ro-tation mechanisms. The table surface material will be steel for the magneticbases.

Slits

Several sets of standard motorized in-air slits will be installed to definethe X-ray beam passage and adjust the beam size/divergence. Each set ofslits has four blades driven by stepping motors. Each slit system has its owntranslation stages (both horizontal and vertical) for positioning the slits nearthe center of the beam. The specifications of the slits are summarized inTable 1.18.

High Resolution Monochromator

The HRM is mounted on the optical table. The details of the HRM canbe found in section 1.4.3. When the beamline is operated in mode 2, thecrystals will be translated out of the beam path.


HR

M

Co

mp

ac

t 4

-C

dif

fra

cto

me

ter

6-C

dif

fra

cto

me

ter

ES

1 s

am

ple

po

s. 3

-C P

ow

de

r

dif

fra

cto

me

ter

Figure

1.29:Setupof

theES1.


Table 1.18: Mechanical specifications of the slits.

Aperture sizeMax. 20 × 20 mm (standard)

Max. 8 × 8 mm (high precision)Blades Tungsten carbide with knife-edge

Resolution (aperture)1 µm (standard)

0.5 µm (high precision)

Resolution (translation) 1 µm

Precision20 µm (standard)

6 µm (high precision)

Asymmetric adjustment Yes

Diffractometers

There are three diffractometers in the ES1. The first one is a compact 4-circles placed on the optical table for alignments of X-ray cavities[1] or phaseretarders. To meet the requirement of a fine cavity orientation adjustment,high resolutions of the rotation axes are required, as listed in Table 1.19.A piezoelectric motion mechanism may be necessary to realize the required10−4 degrees resolution for the azimuthal rotation (phi) stage.

The second diffractometer is located at the rear part of hutch 2 (at 36.7m) for X-ray scattering experiments. A diffractometer with 6+2-circle geom-etry, where 6 degrees of freedom are for sample and detector motions, andthe additional 2 degrees of freedom are for analyzer stages. The base table ofthe diffractometer supplies transverse translations along the vertical (z-) andthe horizontal (x-) directions with at least < 5 µm resolutions. A scheme ofthe diffractometer configuration is shown in Figure 1.30.

The third one is two-circle diffractometer located at 39.3 m for medium-resolution powder diffraction experiment. The detailed specifications of thediffractometer is described in the following subsection ‘Preliminary Designfor Powder X-ray Diffraction Station’.

Depending on the experimental requirements, different sample conditionswill be available in the ES1. A cryomagnet and a commercial cryostat sys-


Table 1.19: Specifications of the motion mechanisms of the compact 4-cdiffractometer

Motor Range Resolution

Th -10 - 60◦ (1 × 10−4)◦

Phi 360◦ (1 × 10−4)◦

Chi 0 - 180◦ (3 × 10−3)◦

Table translation in Z ±30 mm 50 µmTable translation in X ±30 mm 50 µmGoniometer translation in X-Y ±20 mm 10 µmGoniometer translation in Z ±10 mm 10 µm

tem with a motorized carrier will be the basic equipment to provide themagnetic field and low temperature (down to 1.7 K) sample environments.Other equipments will be built up gradually to match the experimental needs.Femtosecond laser pulses will be directed to the diffractometer center for thepump-probe type time-resolved measurements in mode 2.

Detectors

Several detector systems will be available to users. An ionization cham-ber has the advantages of being an X-ray beam monitor without blockingthe beam and simple maintenance. An NaI:Ti scintillation counter providesa standard method to scattered photon counting. A 1-D strip detector or 2-Darea detector will also be implemented to increase the acceptance angle andreduce the counting time. An avalanche photodiode detector (APD) systemwith a rise time < 2 ns, a FWHM < 4 ns, and a 100 MHz count rate is indis-pensable for time-resolved experiments. An ultrafast X-ray streak camera isanother option for the TR-XRD detector. The measurement range is aboutseveral tens of picoseconds to several nanoseconds for a single sweep with a1 ps temporal resolution or less.


Figure 1.30: 6-circle diffractometer with a translation base table and anoptional goniometer head.

Preliminary Design for Powder X-ray Diffraction Station

A powder diffraction station with a medium angular resolution will beinstalled downstream of the ES1. Figure 1.31 is the scheme of the pow-der station which consists of a large 3-circle diffractometer equipped with aMYTHEN 18K microstrip detector (18 modules assembled, cover 90◦ in 2θshown in Figure 1.32(c) and (d)). The preliminary specifications of the 3-circle diffractometer and MYTHEN 18K detector system are shown in Table1.20 and 1.21. The detector is located at an arc with a radius of 761.5 mmfrom the sample position and provides intrinsic angular resolution of 0.004◦.The massively parallel X-ray detection and fast readout of modern micro-strip detectors render time-resolved powder diffraction measurements with asub-millisecond time resolution. The sample environment could be cooled orheated by a cryostat or a heating gun. An optical table is placed next to thesample which could accommodate a robotic arm for a quick sample changeto increase the operation efficiency.


Figure 1.31: Schematic of the 3-circle powder diffractometer with MYTHEN18K detector system.

Figure 1.32: (a) MYTHEN 1K detector module without housing, (b) De-tector Control System (DCS24), (c) and (d) front view and back view ofMYTHEN 18K detector system.


Table 1.20: Preliminary specifications for the 3-circle diffractometer

2-circle Diffractometer Sample Circle Detector Circle Notes

Axis height (mm) 1,375

Motor type Stepper or DC

Sphere of confusion (mm) ≤0.01Angle resolution (◦) ≤0.0001Angle accuracy (◦) ≤0.001Angle repeatability (◦) ≤0.0001Encoder Yes

Alignment base Range

Vertical translation Tz (mm) ± 50Horizontal translation Tx (mm) ± 50Rotation Ry (◦) ± 1Rotation Rz (◦) ± 1

XYZ-Sample Stage Range

Y&Z travel range (mm) ± 5X travel range (mm) ± 14


Table 1.21: Specifications of MYTHEN18 detector system

MYTHEN 18K

Detector Control System DCS24

Number of detector modules 18

Radius sensitive area (mm) 761.5

Angular coverage of one detector modulewith 1280 channels (◦)(sensitive area (◦))

5(4.81)

Gap between modules (mm) 2

Radius entrance window (mm) 221

Frame rate (Hz) Up to 100

Weight (kg) 107 (with DCS24)

Sensor material Silicon

Sensor Reverse biased pn-junction array

Detection principle Single photon counting

Sensor thickness (µm) 320

Sensitivity area(module x width x length)(mm2)

18 x 64 x 8

Dimensions of channel(module x width x length)(µm2)

18 x 50 x 8,000

Read out time (ms) 0.3

Maximum count rate per channel (Xrays/s) 1× 106

Dynamic range (bit) 4, 8, 16, 24 (1:16,777,216)

Energy range (keV) 5-30

Cooling Air cooled


Preliminary Design of the Optical System for Pump-and-ProbeExperiments

The pump-probe time-resolved X-ray diffraction setup integrates high-power femtosecond lasers and an X-ray scattering setup. The laser systemprovides suitable ultra-short excitation pulses over a large spectral range foroptical excitation to stimulate the dynamic process being studied. The tech-nical requirements for the laser system are:

1. 3−4 mJ pulse energy output for high-field experiments2. 35 fs pulse duration, 1 kHz repetition rate

The laser system consists of a Ti:Sapphire oscillator (Micra) and an am-plified laser system (Legend). It will provide ∼ 800 nm wavelength laserpulses with a 4 mJ power at a 1 kHz repetition rate and a 35 fs pulse width.The specifications of the femtosecond laser system are listed in Table 1.22.The laser system will be housed in a laser hutch with light-gage partitionwalls located between ES1 hutch and ES2 hutch. The room will providethe optical shielding required by laser safety regulations and an environmentwith good temperature (25 ± 1 ◦C ), and humidity (5 RH 40%) control.Because dusts can absorb photons and create hot spots that can burn thecoating and dramatically degrade the performance of laser, special attentionto the environment cleanness is needed to prevent the laser optical devicesfrom damage and to improve the femtosecond laser stability.

Table 1.22: Specifications of the laser oscillator and the laser amplifier.

Parameter of laser Micra (laser oscillator) Legend (laser amplifier)

Pulse width 35 fs 35 fs

Central wavelength 790 nm 790 nm

Bandwidth 90 nm 30 nm

Energy per pulse 5.3 nJ 4 mJ

Repetition rate (tunable) 84.75 MHz 1 kHz

Average power 450 mW 4 W

Peak power 1.5 x 105 W 1.15 x 1011 W


The power supplies for laser modules and related water chiller will be in-stalled outside the laser hutch. The electrical power, inclusive of laser, waterchiller and uninterrupted power supply, is estimated to be larger than 9,580Watt. An evaluation of the electrical power load for the optical system islisted in Table 1.23. An electrical power capacity of 12,000 Watt is suggestedto provide the room for future expansion. The laser signals should be inter-locked with the laser hutch door by a shutter.

The laser beam is guided to outside of the laser hutch by optical tubesto conform to laser safety regulations. After guided to ES1 and ES2 by aseries of ultrafast reflection mirrors, the laser pulses hit the sample surfaceand used as pump sources. There are two geometries where the pulsed laserbeam excites sample surface. One is the ‘holey mirror’ geometry, as shownin Figure 1.33. It can couple X-rays and laser pump light collinearly onthe sample to reduce non-collinear temporal smear and aid in spatial over-lap. The other is the ‘Normal incidence’ geometry, as shown in Figure 1.34,where the pump beam incidents normally to sample surface to increase theabsorption volume of laser light in material.

To synchronize the laser pulses and the pulsed X-ray beam, three signallines for the RF frequency, one-sixth of the RF frequency, and the revolu-tion signal of the electron bunch filling pattern of the storage ring, will beintegrated with the laser system. Ethernet communication will be utilized toremotely control the laser system. Since the repetition rate of X-ray pulsesis substantially greater than the laser repetition rate (1 kHz), the high-speedavalanche photodiodes (APD) will be gated electronically in a time scale of afew nanoseconds to pick up the signals of interest. An ultrafast X-ray streakcamera is another option to be the TR-XRD detector. It can probe shortertime scale than X-ray pulse for recording ultrafast physical event.


Table 1.23: An evaluation of the electrical power load of the laser system

Voltage Max. CurrentPower

Real Power

(V) (A) (UPS loss included)

Oscillatorpump laser

220 7 1,540 W 2,200 W

Oscillatorchiller

220 3 660 W 940 W

Amplifierpump laser

220 3 660 W 940 W

Amplifierchiller

220 8 1,760 W 2,500 W

Oscilloscope 100 15 1,500 W 1,500 W

Accessories 100 15 1,500 W 1,500 W

Toatl power 7,620 W 9,580 W

Iris

Iris

Diffractometer

X-ray

Laser beam

Figure 1.33: The ‘holey-mirror’ configuration that allows nearly collinearpropagations of the laser and the X-ray beams.


Figure 1.34: The ‘Normal incidence’ configuration increases the absorptionvolume of laser light in material.


1.5.3 Preliminary Design of the End Station 2

In mode 3, scattering measurements will be conducted in the ES2, whichis located in hutch 3 and is designed for magnetic X-ray scattering. With theHRM and the beam stopper in hutch 2 moved out of the beam path, X-raysbypassing the ES1 will be focused both horizontally and vertically by a pairof K-B mirrors to the sample position (at 57.25 m). The specifications of theK-B mirrors are described in section 1.4.3. To probe the magnetic domainstructure, a beam spot of a micrometer size is desirable. The beam size atthe sample position will be about 30 µm × 20 µm (H × V, FWHM) and thebeam divergence is less than 300 µrad × 200 µrad (H × V, FWHM). Themagnetic scattering end station is composed of a phase retarder assembly, adiffractometer which can accommodate a sizable magnet, and a polarizationanalyzer. A magnet and a low temperature cryostat will also be part of theES2 to provide different sample conditions. The diffractometer configura-tion and the instruments to provide various sample conditions are shown inFigure 1.35. The instruments proposed in this experimental hutch are listedbelow.

Phase retarder

The compact 4-c diffractometer on the optical table in the ES1 will alsoserve as the goniometer for the phase retarder to achieve polarization con-trol. Depending on the experimental requirement, a phase retarder can be aquarter-wave plate, which converts the linearly polarized incoming beam toa circularly polarized one, or a half-wave plate, which generates a beam ofvertically linear polarization. A single crystal of diamond will be utilized asthe phase retarder. When the crystal is slightly detuned from the Bragg po-sition, the transmitted σ and π waves are phase shifted with respect to eachother. Polarization of the transmitted beam can be selected by adjusting thephase difference and the orientation of the phase plates scattering plane withrespect to the incident polarization (horizontal).

Circular polarization is obtained when the phase shift is set to (±λ/4)(quarter-wave plate) and the scattering plane is inclined by 45 ◦. Circularpolarization is particularly useful for the study of ferromagnetic and helicalmagnetic structures. Linear polarization is obtained when the phase shift isset to (±λ/2) (half-wave plate). The plane of polarization is then rotated bytwice the angle by which the scattering plane is inclined. Linear polarizationwith variable orientation will offer an alternative way to probe azimuthal


Figure 1.35: The configuration of the diffractometer in the ES2 and instru-ments for various sample conditions.

dependence, especially in experimental configurations that prohibit an az-imuthal rotation of the sample. The cases where a sample is mounted onto acryomagnet or grazing incidence diffraction is performed are a few examples.

Magnet

A ma

design report of the phase-i tps...

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