beam diagnostics at diamond light source

01/04/2009 1st DITANET school on Diagnostics 1

Beam DiagnosticsBeam Diagnosticsat Diamond Light Sourceat Diamond Light Source

Guenther RehmGuenther RehmHead of Diagnostics GroupHead of Diagnostics Group

11stst DITANET school on Diagnostics DITANET school on Diagnostics1 April 20091 April 2009

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Outline

• What is a Light Source?

• Diagnostics Requirements for a Light Source

• Diagnostics in the Injector

• Diagnostics in the Storage Ring

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A Light Source?

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How Is Synchrotron Light Produced?

Synchrotron Light (or Radiation) is electromagnetic radiation emitted when a high energy beam of charged particles (electrons) is deflected by a magnetic field

a single bending magnet produces a wide fan of

radiation

multiple bends in an "undulator" or "wiggler"

magnet give higher intensity and more directed radiation

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A Brief History of Synchrotron Light Sources :

• Discovery: 1947, General Electric 70 MeV synchrotron

• First use for experiments: 1956, Cornell 300 MeV synchrotron

• 1st generation: machines built for other purposes, mainly High Energy Physics

• 2nd generation: purpose-built storage rings for production of synchrotron light

• 3rd generation: higher brightness synchrotron light sources, using mainly ‘insertion devices’ (undulators and wigglers) as the X-ray sources

• 4th generation: LINAC followed by ‘Free Electron Laser’, i.e. a series of undulators producing coherent synchrotron light of even higher peak brightness and shorter duration

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SR and the Electromagnetic Spectrum

Electromagneticwaves

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Layout of a 3G Light Source A beam of electrons is accelerated in

a LINAC, further accelerated in a booster synchrotron, then

accumulated in a storage ring.

The circulating electrons emit intense beams of synchrotron light that are

sent along beamlines to the experimental stations.

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235 m

100 MeV Linac

3 GeV BoosterC = 158.4 m

3 GeV Storage RingC = 562.6 m

Experimental Hall and Beamlines

235 m

office building

peripheral labs. and

offices

future long beamlines

technical plant

Layout of Diamond

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Key Parameters of Diamond

Electron Beam Energy 3 GeV

Storage ring circumference 561.6 m

Available space for Insertion Devices 4x8m, 18x5m

Beam current 300 mA

Emittance (hor., vert.) (nm rad) 2.7, 0.03

Minimum ID gap 5 mm

Electron beam sizes (hor., vert) (m) 123, 6

Electron beam divergences (hor., vert) 24, 4 rad

Peak brightness* 2*1020

Peak brightness* (1Å) 1019

* photons/s/mrad2/mm2/0.1%bw

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Diagnostics Requirements• Track charge trough Injector

– Integrating Current Transformers, Faraday Cups and Wall Current Monitors

– Stripline BPMs in transfer paths, buttons in booster– Screens / Cameras / Synchrotron Light Monitors

• Keep stored beam stable– Fast Global Orbit Feedback: Monitor beam position and correct

orbit 10000 per second to sub-um– Transverse Bunch by Bunch Feedback: Monitor bunch motion

and correct after each turn to damp coupled bunch instabilities– Measure betatron tunes without visibly disturbing beam– Monitor beam size, calculate emittance, coupling and energy

spread– Measure stored current and bunch by bunch charge

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230 BLM

5 Faraday-C

7 ICT

2 DCCT

5 SLM

2 Tune Excite

204 BPMs

2 Pinholes

17 Screens

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Faraday Cups, WCMs, ICTs

LTB FC

LINACFC

WCM for LINAC,LTB,BTS

ICT and electronics

ICT shield

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The first bunches on WCM and ICT

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Bunch Charge and Train Structure

from LINAC from booster

WCMs intransferpaths

Buttonin SR

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Booster Current on DCCT

First measurement

Later with extraction after 100ms

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Strip Line BPM Pickups in Transfer Paths

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Screens and Optics

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IEEE1394 Cameras

Camera Repeater

PP

C I

OC

1

Diagnostics VME crate

PP

C I

OC

2

IEE

E1

39

4 P

MC

Eve

nt

Rx

24 V PSU

Repeater

Controls NetworkEvent Network

CameraTrigger

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EDM Camera Display

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Precisely Triggered Acquisition

edge of screen

beam in booster during ramp

kicked beam before main septum

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Image Analysis

1D fits2Dfit

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Orbit Stability Requirements in 3rd Generation Light Sources

mmx 3.121231.0 radradx 4.2241.0' mmy 6.04.61.0

xx 1.0 '1.0' xx

yy 1.0 '1.0' yy

Beam stability should be better than 10% of the beam size

For Diamond nominal optics (at short straight sections)

radrady 4.041.0'

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Motivation and Challenges

• Sources of beam motion:– Insertion devices not fully compensated, ID motion

leads to orbit displacement– Ground vibrations amplified through girders– Magnet power supply drift– Vibrations from water cooling

• Sources of errors in EBPM measurement:– Mechanical / electrical offsets– Noise– Beam current dependence– Pickup thermal motion

Correct as Correct as fast as possiblefast as possible

Minimise or removeMinimise or removefrom correctionfrom correction

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7 BPMs each in 24 cells

Standard BPM

Primary BPM

-50 -40 -30 -20 -10 0 10 20 30 40

-20

-10

0

10

20

-40 -30 -20 -10 0 10 20 30 40

-10

-5

0

5

10

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Button Pickup

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Primary BPM with reference pillar

carbon fibrepillar with lowtemperatureexpansioncoefficient

bellows for mechanical isolation

length gauges senseH/V position with 0.5um resolution

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Standard BPM near Quad

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Some BPMs move after beam loss

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Multiplexing in BPM Electronics

• Crossbar switch routes all four inputs through all processing channels in parallel, but permutes routing

• After digitisation, but before further filtering, the permutation is reversed• By averaging over 4 permutations, any differences/drifts between the

channels will be removed (each input will have been routed through each channel during the averaging period)

• By examining the changes in the outputs during permutation, the gains of the individual channels can be retrieved and then digitally equalised to reduce artefacts of switching

A/D

A/D

A/D

A/DCro

ssba

r S

witc

hFPGA

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Pro

cess

or

Controls Network

PS VME crate

eBPM eBPM eBPM eBPM eBPM eBPM eBPM

Cell -m

Cell -n Cell +n

Cell +m

Fast Orbit Feedback

14 Corrector PSUs

PSU 1 PSU 14

PS

U I

F

…

Event Network

FB

Pro

cess

or

PM

C R

ock

et

IO

Pro

cess

or

Diagnostics VME crate

Eve

nt

Rx

PS

U I

F

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FOFB Installation (one of 24 cells)

Power supplyVME crate

Corrector power supplies

Diagnostics rack

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FOFB Performance60mA

Suppressionof beam motion

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Transverse Bunch-by-Bunch Feedback

RFFrontend

Modulatorand

Amplifier

4 AD converters

(slicing)

Digital Signal Processing

DAConverter

History buffer

FPGA based Feedback Processor

Control

System

StriplineKicker

Button

Pickup

4-waySplitter

500 MHz RF clock

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Beam artificially made unstable in both planes:

1) no feedback → horizontally

unstable

2) feedback in horiz. plane only

→ vertically unstable

3) feedback in both planes

→ stable in both planes

Bunch-by-Bunch Feedback in Action

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Tune Measurement:Kick and Fourier Transform

0 500 1000 1500 2000-400

-200

0

200

400horizontal

turns

posi

tion

[um

]

0 20 40 60 80 100-400

-200

0

200

400

turns

posi

tion

[um

]

0 0.1 0.2 0.3 0.4 0.50

10

20

30

40

50

tune

ampl

itude

[um

]0 500 1000 1500 2000

-150

-100

-50

0

50

100

150vertical

turns

posi

tion

[um

]

0 20 40 60 80 100-150

-100

-50

0

50

100

150

turns

posi

tion

[um

]

0 0.1 0.2 0.3 0.4 0.50

2

4

6

8

10

tuneam

plitu

de [

um]

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More Elegant Tune Measurement: Harmonic Excitation and Detection

cos

sin

Exitation

Beam Position Pickup

In phase

Out of phase

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Amplitude and Phase of Beam Response to Swept Sine Excitation

0.2 0.205 0.21 0.215 0.22 0.225 0.23-400

-200

0

200

400

600

800

tune

in phase signal

out of phase signal

0.2 0.205 0.21 0.215 0.22 0.225 0.230

200

400

600

800

tune

mag

nitu

de

0.2 0.205 0.21 0.215 0.22 0.225 0.23-200

-100

0

100

200

phas

e

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Tune Measurement of Individual Bunches

• Only one bunch is excited with swept sine wave

• Tune depends on charge per bunch

• Head-Tail mode leads to asymmetry of Synchrotron sidebands for larger charges

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X-ray Pinhole Cameras

Pinholes

9.6m 3.85m

Sourcepoints

ScreensOptics

Cameras

12.7m

4.5m

d2 d1

Magnification

1

2

d

dm

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Modified Beam Port Absorbers and Pinholes

X/Z translationand rotation

2 stacks of 4 slabs5mm*1mm*30mm

with shims as spacers

Aluminium/Steelexplosion bondedflange as window

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Pinhole Screens and Optics

CdWO4 screen

mirror

50mm macro lensmagnification 1:1

focus and irisremote control

1024x768 camera4.65um pixel

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Pinhole Image Analysis

Skew quads offSkew quads on

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Storage Ring DCCT

First accumulation of stored current at Diamond

Stored current and life time

Decaying beamMachine

development Top-Up mode

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Fill Pattern Measurement by Time Correlated Single Photon Counting

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Acknowledgements

• Diagnostics: Alun Morgan, Cyrille Thomas, Chris Bloomer, Graham Cook

• Controls: Michael Abbott, Isa Uzun,James Rowland, Mark Heron

• Accelerator Physics: Ian Martin, Riccardo Bartolini

• Engineering: Nigel Hammond, Ron Godwin, Darren Simmons

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Thank you for your attention!