Diagnostics & Lasers R&D at Daresbury
S.P. Jamison Accelerator Science and Technology Centre,
STFC Daresbury Laboratory
Preparing for the needs of an ultrafast FEL facility
Diagnostics & Lasers • Fast beam position monitors
• Timing distribution & beam arrival monitors
• Electro-optic longitudinal profile diagnostics
• THz driven modulation of electron beam
• Ultrafast Photon diagnostics
Daresbury accelerator projects • ALICE - Accelerators and Lasers in Combined Experiments
• EMMA - non-scaling FFAG demonstrator
• VELA -
• CLARA - planned FEL test facility
ALICE Accelerator and Lasers in Combined Experiments
30MeV Energy recovery linac
• Initial motivation as testbed for planned 100mA ERL
• Principally for accelerator and light source R&D • Some light-source user experiments
60pC, 81MHz, 100us train @10Hz (8000bunches, 5mA peak)
CSR THz source
60pC, 16MHz, 100us train @10Hz IR FEL
10-40pC, single bunch @ 5Hz
EMMA injector
• Mid-IR FEL • THz for cell irradiation
• “DICC” high current cryo-module currently being installed for with-beam testing
• Synchronised lasers available – including 20 TW TiS (Compton scattering expt)
Typical operating
modes
EMMA Electron Model for Many Applications
First demonstration of non-scaling FFAG acceleration
Single bunch injection from ALICE Acceleration from 10MeV – 20MeV in Serpentine acceleration mode
• 42 cells in 16m circumference • One cell for each of injection, extraction • 50+ BPMs, single bunch, multiple-turn readout
Very compact & dense accelerator:
VELA formally Electron Beam Test Facility
• High brightness RF Photoinjector • Available for industry to develop new accelerator-based
technologies • Healthcare • Security scanners • Water treatment • ….
• Two independent beam areas available
• Funded August 2011 • Commissioning has started
Parameter Value Units
Frequency 2998.5 MHz
Bandwidth < 5 MHz
Accelerating Voltage < 6 MeV
Accelerating Gradient <100 MV/m
Peak RF Input Power up to 10 MW
Beam charge 250 pC
VELA Beam Transport Layout
Beam Enclosure 1
Beam Enclosure 2
Beam Injector
Photoinjector laser • 11 mJ @ 800nm • 2 mJ @266nm • Up to 400Hz
Photoinjector laser transport
• l = 266 nm • ~8.5 mm FWHM • M2 ≈ 3.5 • ZR ~ 175 m • 180 fs FWHM • 1 mJ (2 mJ) • 400 Hz
• ~1 mm FWHM • ZR ~ 2.5 m
~14
m
source
cathode
Laser Transport Design • The beam focusing done in stages
– Minimum 3 optics to achieve required demagnification – Mirror Box 2 compresses beam (two optics) – Mirror Box 3 makes final demagnification (single optic)
• “off-the-shelf” spherical mirrors – not a true image at the cathode – Build-up of astigmatism from successive spheres even – Main aim is for an illuminated spot of about the correct size
• custom toroids required for true image relay
FM1 = 750 mm FL
FM2 = 100 mm FL
FM3 = 2500 mm FL
Wavefront propagation
using FOCUS code
Ideal Source, Spherical Mirrors
To develop a normal conducting test accelerator able to generate longitudinally and transversely bright electron bunches and to use these bunches in the
experimental production of stable, synchronised, ultra short photon pulses of coherent light from a single pass FEL with techniques directly applicable to the
future generation of light source facilities.
• Stable in terms of transverse position, angle, and intensity from shot to shot. • A target synchronisation level for the photon pulse ‘arrival time’ of better than 10 fs
rms is proposed. • In this context “ultra short” means less than the FEL cooperation length, which is
typically ~100 wavelengths long (i.e. this equates to a pulse length of 400 as at 1keV, or 40 as at 10 keV). A SASE FEL normally generates pulses that are dictated by the electron bunch length, which can be orders of magnitude larger than the cooperation length.
CLARA Compact Linear Accelerator for Research and Applications
Major upgrade of VELA
Other Aims and Prerequisites To deliver the ultimate objectives of CLARA will encompass development across many areas:
NC RF photoinjectors and
seed laser systems
Generation and control of bright electron
bunches – manipulation by externally injected
radiation fields – mitigation against unwanted short
electron bunch effects High temporal coherence and wavelength stability through seeding or other
methods Generation of coherent higher harmonics of a
seed source
Photon pulse diagnostics for single shot
characterisation and arrival time monitoring
Low charge single bunch
diagnostics
Synchronisation systems
Advanced low level RF systems Novel short period
undulators
CLARA Flexible FEL Layout
Chicane (1m long)
Diagnostic/Matching Section
Modulator Undulator (1.5m long)
Radiator Undulator (2.5m long)
e-beam
Laser seed
0m 3m 6m 9m 12m 15m 18m 21m
• By implementing a flexible FEL layout, especially in the modulator region, it will be possible to test several of the most promising schemes.
• We are carefully comparing the various schemes and their detailed requirements – we do not anticipate testing them all!
• We aim to design in this flexibility from the start.
Current principle seed/modulation wavelengths • 30um-50um. Difference frequency generation & OPA • 800nm & harmonics
EXAMPLES OF FEL SCHEMES ON CLARA
SINGLE SPIKE SASE 100pC tracked bunch compressed via velocity bunching
SLICING + CHIRP/TAPER Short pulse generation using an energy chirped electron bunch and a tapered undulator E. L. Saldin et al, Phys. Rev. STAB 9, 050702, 2006
MODE-LOCKING Mode-locked amplifier FEL using the standard CLARA lattice with electron beam delays between undulators N. R. Thompson and B. W. J. McNeil, Phys. Rev. Lett. 100, 203901, 2008
MATCHED MODE-LOCKING Electron beam delays matched to the rms electron bunch length to distinguish a single spike from the pulse train
Plots courtesy of Ian Martin and Neil Thompson
Parameters
The parameters have now been broken down to cover 5 different operating modes. This helps us understand which parameters we need simultaneously.
FEL output wavelengths from 400nm to 100nm • Can make use of 800nm laser for harmonic generation experiments • Can use well established laser diagnostics for single shot pulse length measurements • No need for long photon beamlines, can deflect by 90 degrees
Operating Mode Seeded (long pulse) Unseeded (SASE) Ultra Short Pulse Multibunch High Rep Rate
Motivation Flat top for seeded FEL experiments
SASE FEL Single Spike SASE FEL Oscillator FEL (RAFEL)
Technology demonstration & commercial applications
Max Beam Energy (MeV)
250 250 250 250 100
Max Macropule Rep Rate (Hz)
100 100 100 100 400
Bunch Charge (pC) 250 250 20 to 100 25 250
Number of Bunches per macropulse
1 + pilot 1 + pilot 1 + pilot 20 1
Peak Current at FEL Entrance (A)
400/125 400 1500 25 N/A
Nominal Bunch Length (fs)
250/800 (flat region) 250 (rms) <30 250 (rms)
CLARA Layout
Gun
2m linac
VELA exploitation
area
4m linac
Bunch Compressor
Laser Heater 4m linacs
4th Harmonic
Cavity
TDC1
TDC2
FEL modulators
Further exploitation
line
FEL radiators
FEL afterburner
Dump
Photon Diagnostics
70MeV 250MeV
Total Length ~ 90m
CLARA - Next Steps
CDR now being drafted
TDR will follow
CLARA funding still to be secured
If procurement starts April 2014 then could install in first half of 2016
CLARA first commissioning – mid 2016
Diagnostics & Lasers • Fast beam position monitors
• Timing distribution & beam arrival monitors
• Electro-optic longitudinal profile diagnostics
• THz driven modulation of electron beam
• Ultrafast Photon diagnostics
Daresbury accelerator projects • ALICE - Accelerators and Lasers in Combined Experiments
• EMMA - non-scaling FFAG demonstrator
• VELA -
• CLARA - planned FEL test facility
rapid serpentine acceleration with large tune variation.
EMMA was constructed for study of non-scaling FFAG acceleration
During accelerating the bunch executes up to ten turns
• Expanding trajectory sweeps about a half of the pickup aperture. • For machine tuning, the bunch can be kept circulating >1000turns. • Revolution period is T=55.2ns, • bunch charge is up to 30pC, the bunch length is about 10ps.
The rapid dynamics needs advanced diagnostics.
EMMA Diagnostics
The trajectory should be measured on each turn, in each of 42 F-D cells.
EMMA Beam Position Monitor System
world-fastest-rate BPM system, ASTeC designed, built and commissioned
The system is applicable to ERL machines for bunch-by-bunch-in-train measurements, in particular, to ALICE.
faced a problem of a BPM noise caused by a RF power leakage from the EMMA RF system waveguide. Noise suppression required improvement to Front-End module shielding.
Meeting requirements of EMMA beam diagnostics.
Commissioning issues
hor. and vert. time-multiplexed converter outputs (4ns/div)
• developed concept of BPM self-synchronisation with beam, when the BPM detector reference signals and the ADC clock are being manufactured from the BPM input signal, which makes them automatically synchronous with the beam signal.
• We devised a way of use of a fast and precise pipe-line-type ADC chip for single bunch/train measurements which opened a possibility to use such ADCs in fast-rate BPMs.
pickup signal (0.5ns/div)
• The system comprises total 53 of BPMs that is about 400 boards & cards.
• Functional architecture, solutions and design of electronics was done by ASTeC.
• In-house EPICS implementation
• In collaboration, a VME interface and its firmware was designed by WareWorks Ltd (UK).
Poincare map.
Board/card fabrication was done by UK Electronics Ltd. Components & fabrication cost is about 150kGBP.
* Leakage in vertical plane due to pick-up geometry and spurious vertical dispersion
Combined BPM/BAM/FEL Diagnostics at ALICE
"20121213"" ""22:30:57.522037"
0 500 1000 15001.5
2.0
2.5
3.0
3.5
4.0
4.5
Horizontal BPM
0 500 1000 15000.4
0.3
0.2
0.1
0.0
Vertical BPM
0
0
0
0
0
Horizontal BPM
Charge
Bunch Number Bunch Number
Bunch Number
Posit
ion
(mm
)
0 500 1000 150045
50
55
60
65Charge
Vertical BPM* FEL Output
Bunch Number
* Leakage in vertical plane due to pick-up geometry and spurious vertical dispersion
Charge
22
Optical Clock Distribution & beam arrival monitors
Single Mode Distribution Fibre (100m)
Dispersion Comp. Fibre
Faraday Rotating Mirror (50:50)
RF pickup
Beamline
BEAM ARRIVAL MONITOR
MZM
Scope
PLL
Fibre Stretcher
STABILIZED FIBRE LINK
Mode-locked fibre ring laser
(81.25MHz)
~
RF crystal oscillator
(81.25MHz)
Pol. Contr. λ/2
A pulsed timing system, similar to DESY, is being used to deliver short pulses for accelerator diagnostics. Currently linked to ALICE, will migrate to VELA/CLARA The delivered clock stability is aimed at the few femtosecond level.
Delay
detector
The laser master oscillator is a mode-locked fibre ring laser at 81.25 MHz (81.08MHz for CLARA)
Mode-locked Eribum laser from Toptica Photonics
65fs output pulses
An actively stabilized fibre delivers the short pulses to diagnostic locations
Beam arrival monitors have
been implemented using the delivered short pulses
Fast BPM electronics will be modified for use in BAM
Laser Master Oscillator
Dt
RF pickup
Beamline
Mod. Scope
From stabilized link
The Optical Link Link stabilization is currently achieved using a
balanced optical cross-correlator to measure the group delay between the reference and reflected beams
10.2fs jitter in link (some issues with the RF master oscillator at time of experiment)
The links on ALICE are ~100m long and run though the basement (no environmental control)
Beam Arrival Monitors Beam arrival monitors convert the timing jitter
information into amplitude jitter
Some issues with sensitivity at low bunch charges since we are using existing stripline BPM.
Optical Clock Distribution System
phase noise.
103 104 105 106 102 101 100
Carrier-phase studies – towards 1fs links
Monitoring effect of fibre stretching on changes in carrier phase offset
Deliberate stretching of fibre enable studies of fibre response at different frequencies
Feasibility study on locking both group and phase velocity in distribution link.
Pulsed interferometric system can potentially give higher locking resolution while maintaining short pulse delivery.
ALICE
Study of beam dynamics with combined diagnostics
As well as clock delivery, the distributed femtosecond pulses are used to implement beam arrival monitoring. A combined experiment using multiple diagnostics was performed to study instabilities in the FEL and ALICE
as a whole.
Developing bunch-by-bunch understanding of how beam affects FEL and how FEL affects beam
Changes in timing, charge and position along a train were measured with optical BAMs and BPMs. Simultaneous recordings of these signals were correlated with FEL output power to measure effects due to beam jitter.
26
Study of FEL with combined diagnostics
Combine with fast FEL detector and BAM measurements, similar instabilities observed
Correlations of diagnostics give information about Arc 2
Tracing of trends though pre-lasing and lasing parts of pulse train.
position charge
Frequency (MHz)
FEL pulse energy
Frequency (MHz)
Several instabilities observed in beam by fast BPM system 100 kHz bunch position oscillation 300 kHz charge oscillation. Confirmed
in faraday cup and PI laser power On-going investigation into laser position
stability courtesy F. Jackson
Beam arrival time
Electro-Optic temporal profile monitors
Spectral Decoding
Spatial Encoding
Temporal Decoding
Spectral upconversion**
o Chirped optical input o Spectral readout o Use time-wavelength relationship o >1ps limited
o Ultrashort optical input o Spatial readout (EO crystal) o Use time-space relationship
o Long pulse + ultrashort pulse gate o Spatial readout (cross-correlator crystal) o Use time-space relationship
o monochomatic optical input (long pulse) o Spectral readout o **Implicit time domain information only
• Deconvolution for ~100fs resolution
• In beamline BAMs
• Robust EO systems (no fs lasers required!)
• Extension to time domain readout (FROG)
(?)
χ (2)(ω;ωthz,ωopt)
ωopt + ωthz
convolution over all combinations of optical
and Coulomb frequencies
Electro-optic detection bandwidth
ωthz
ωopt
ωopt - ωthz
ωopt
description of EO detection as sum- and difference-frequency mixing
THz spectrum (complex)
propagation & nonlinear efficiency
geometry dependent
(repeat for each principle axis)
optical probe spectrum (complex)
EO c
ryst
al
This is “Small signal” solution. High field effects c.f. Jamison Appl Phys B 91 241 (2008)
DC “THz” field.... phase shift (pockels cell)
temporal sampling
of THz field
Monochromatic THz & optical
Chirped optical Parameter dependent results
optical sidebands
Delta-Fnc ultrafast pulse...
Spectral decoding as optical Fourier transform Why does it work, when does it fail?
Consider (positive) optical frequencies from mixing Positive and negative Coulomb (THz) frequencies; sum and diff mixing
Linear chirped pulse:
Assume broad input probe spectrum Fourier transform form
Convolution function limits time resolution…
… but will aid in identifying the arrival time
ALICE Electro-optic experiments o Energy recovery test-accelerator intratrain diagnostics must be non-invasive
o low charge, high repetition rate operation typically 40pC, 81MHz trains for 100us
Spectral decoding results for 40pC bunch
o confirming compression for FEL commissioning o examine compression and arrival timing along train o demonstrated significant reduction in charge requirements
Deconvolution possible.
“Balanced detection” χ(2) optical pulse interferes with input probe (phase information retained)
“Crossed polariser detection” input probe extinguished...phase information lost
Deconvolution not possible [ Kramers-Kronig(?)]
Oscillations from interference with probe bandwidth ⇒ resolution limited to probe duration
Spectral decoding deconvolution
Spectral decoding Kramer-Kronig deconvolution
Phase inferred from measured amplitude spectrum
Widely used in CSR/CTR temporal diagnostic… …can it work for spectral decoding?
“measured” spectral amplitude
KKphase actual phase (chirp removed)
Surprisingly close retrieval of phase information
- Does not recover chirp - Some turning points missing
“known” & retrieved temporal profiles
Linear chirp phase reintroduced - independently
measurable quantity
Spectral upconversion diagnostic measure the bunch Fourier spectrum...
... accepting loss of phase information & explicit temporal information
... gaining potential for determining information on even shorter structure
... gaining measurement simplicity
Long pulse, narrow bandwidth, probe laser
→ δ-function
NOTE: the long probe is still converted to optical replica
same physics as “standard” EO
different observational outcome
Spectral upconversion
difference frequency mixing
sum frequency mixing Spectral sidebands contain the
temporal (phase) information
ALICE single shot CTR expt
• Femtosecond diagnostic without femtosecond laser • Capability for <20fs resolution
FE
LIX
FE
L ex
pt
Ap
p P
hys
Let
t (2
01
0)
Sidebands generated by 2.0THz FEL output
• Measure octave spanning THz spectrum in single optical spectrometer
• Add temporal readout as extension. (FROG, SPIDER)
0-10 THz ( λ= mm – 30um) → 800nm �20nm
Wavelength [um]
Observe non-propagating spectral components which are
not accessible to radiative techniques (CSR/CTR/SP)
Expected Upconversion
spectra for short bunches
& narrow bandwidth probe
Ti:S probe, ~5ps duration, transform limited.
Spectral upconversion
Δν <50GHz (Δ t >9ps)
Laser based test-bed at Daresbury
Femtosecond laser pulse spectrally filtered to produce narrow bandwidth probe
• Photoconductive antenna THz source mimics Coulomb field. • Field strengths up to 1 MV/cm.
1.5mm 150μm Asymmetry in sum and difference spectra - not explainable by (co-linear) phase matching
Due angular separation of sum & difference waves - general implications for THz-TDS and EO diagnostics
ZnTe Probe
Sum Freq.
THz Diff Freq. Detection
Followed to by NC-CPOPA & FROG
fs time domain diagnostic without fs laser
Problem: Up-conversion is relatively weak – our calculations suggest energies of a few nJ. Signal needs amplifying without loss of information. Solution: Non-collinear Chirped Pulse Amplification (NCPA)
~800nm femtosecond signal
Stretcher Compressor
Stretching factor 103 or more to prevent saturation, damage, NL effects
Amplified pulse then recompressed BBO
Routinely used to produce “single-cycle” optical pulses Amplification with robust nanosecond pulse lasers High gains of 107 or more Gain bandwidths >100nm (50THz) Preservation of phase of pulse is possible
Beams ~1.5mm diameter
Gain >1000x (~300MW/cm2)
Spectral upconversion & FROG extension
Laser-lab development system
(2) Amplification
Stretcher Compressor Single Shot FROG
NL crystal
(3) Measure: 𝐸� 𝜔 = 𝑆 𝜔 𝑒−𝑖𝜑 𝜔
(4) Calculate properties at NL crystal (to remove remaining spectral amplitude and any residual phase distortion)
50ps 60mJ 1064nm Nd:YAG (doubled)
Spectrally filtered Ti:Sapphire
THz Source (Spectral intensity and phase distortions can be both modelled and measured)
(2) Amplification
Stretcher Compressor Single Shot FROG
NL crystal
(3) Measure: 𝐸� 𝜔 = 𝑆 𝜔 𝑒−𝑖𝜑 𝜔
(4) Calculate properties at NL crystal (to remove remaining spectral amplitude and any residual phase distortion)
(1) up-convert Coulomb field
(Spectral intensity and phase distortions can be both modelled and measured)
In beam pipe
Commercial nanosecond Nd Laser Integrated frequency conversion
(OPO)
Envisaged integrated system
Picosecond periods match time scale of compressed bunches lengths in conventional accelerators.
• No oscillatory smearing as in optical bunch slicing
• Controllable field profile on sub-ps time scale.
• Octave spanning spectrum possible
Terahertz carrier-phase is synchronised to laser pulse envelope
• Potential for the whole bunch to be “resynchronised” or compressed (in contrast to the selection/tagging from within the bunch)
Laser driven synchronisation ?
Laser driven THz sources for electron-beam manipulation
Energy gain for 20 MeV beam
AEMITR ALICE Energy Modulation by Interaction with THz Radiation
Vacuum acceleration of bunch with TEM10-like single-cycle THz pulses
100 MV/m fields achievable long slippage period ~1 m for 20 MeV (β = 1 - 10-3 )
Ey
Radial bias (120kV pulse)
Longitudinal polarised THz pulses from Photoconductive antenna
Ex
Simple & efficient but Lacks temporal shaping capability
Transverse field from current surge
generates charge separation
origin of longitudinal
field
Longitudinal field implicit from
now working on nonlinear generation of longitudinal beams temporal shaping capability
AEMITR layout
Energy spread diagnostic
• Two-bunch train, separation
• 790ns (reference & modulated)
• YAG:Ce screen (t~100ns)
• Double shutter gated camera, measuring both reference & modulated bunches
• 20MeV, 20pC
• Minimising projected energy spread “on-crest” acceleration. <50keV spread
Electron beam parameters
• THz generation adjacent to accelerator f~1.5 m
• <2 mJ, 50 fs TiS & photoconductive antenna
THz generation
Two experimental periods completed, no acceleration observed yet • Many issues resolved, improvement made • Synchronisation significant remaining issue
CLARA FEL Photon diagnostics
Expected FEL output from CLARA: 100nm-250 nm, <10 fs pulse duration.
Schematic of SDFG setup: DF output is generated by bringing test and probe pulses to focus on metal mirror.
ΘΘ θ
ω1
ω2
ω3
Metal mirror
Potential solution: surface sum/difference frequency generation
Test system currently under development:
– Use SDFG to characterise EBTF photo-injector laser: 266 nm, ~180 fs
Photon temporal characterisation ? - characterisation of the FEL schemes
Challenges in bandwidth, phase-matching, absorption
• Removes practical phase-matching requirement.
• Amplitude and phase possible using SPIDER or similar
3rd order autocorrelation from Au, from Dia et al. (2005)
Thank you