Post on 15-Mar-2020
1 Henrik Loosloos@slac.stanford.edu
1Feedback Requirements for SASE FELsIPAC 2010
Feedback Requirements for SASE FELS
Henrik Loos, SLACIPAC 2010, Kyoto, Japan
2 Henrik Loosloos@slac.stanford.edu
2Feedback Requirements for SASE FELsIPAC 2010
Outline
Stability requirements for SASE FELsDiagnostics for beam parameters
Transverse: Beam position monitorsLongitudinal: Bunch length/compression/arrival monitors, synchrotron radiation monitors
Feedback implementationsLCLS transverse feedbackXFEL orbit IBFBLCLS longitudinal feedbackFLASH longitudinal IBFBs
Summary
3 Henrik Loosloos@slac.stanford.edu
3Feedback Requirements for SASE FELsIPAC 2010
Ensure electron beam quality for lasingProvide stable photon beam for users
SASE FEL Feedback
InjectorInjector AccAcc UsersUsersUndulatorUndulatorBCBCBCBC AccAcc AccAcc
λ, Δt, ΔxE, φ E, φ E, φ100 MeV ~ GeV
Energy (GeV)
Wave length
Und. length
Bunch Charge
Peak Current
Gain length
Beam size
Rate (Hz)
13.6 1.5 Å 100m 0.25-1nC 3kA 3.5 m 30 μm 120
8 1 Å 100m 0.3nC 2.5kA ~10 m 35 μm 60
17.5 1 Å 130m 0.1-1nC 5kA 3.7 m 45 μm
10/ 5E6
4 Henrik Loosloos@slac.stanford.edu
4Feedback Requirements for SASE FELsIPAC 2010
Transverse requirementsUndulator orbit for efficient SASELG ~ 3 – 10 m, λ ~ 1 Å→ x’ < 5 μrad over several LG
Beam position x < σ/10 for stable photon beamβ ~ 30 m, εn ~ 1 μm→ x < 5 μm
SASE FEL Feedback Requirements
-60 -40 -20 0 20 40 60 80 1000
1
2
3
4
Undulator Beam Position X (μm)
FEL
Pul
se E
nerg
y (m
J)
LCLS example:Transverse jitter in undulator from leaked dispersion
Lasing rms widthat 6.7 GeVσ = 90 μm
G' Lx λ<
5 Henrik Loosloos@slac.stanford.edu
5Feedback Requirements for SASE FELsIPAC 2010
Longitudinal requirementsSASE process: ρ parameter ~ 10-4
Photon BW ~ ρ → energy stability 10-4
Bunch compressor R56 ~ 4 cm→ timing jitter Δt ~ R56 ρ/c ~ 10s of fsEnergy measurement R16 ~ 10 cm → R16 ρ ~ 10 μmEnergy in BC from position measurement in BC or from TOF measurement with beam arrival monitors
Bandwidth requirementsNC accelerator ~100 Hz rate → Feedback stabilizes slow driftsSC accelerator bunch train MHz rate → Intra Bunch FB required
Feedback Requirements cont’d
6 Henrik Loosloos@slac.stanford.edu
6Feedback Requirements for SASE FELsIPAC 2010
LCLS Strip Line BPM Performance
Strip line BPMsContinuous calibration with test pulse between beam triggersBeam synchronous data acquisition system at 120 Hz
Noise level measurementMeasure beam orbits at ~150 BPMs for 500 shots in main linac through undulatorAverage value for strip-line 3.5 μm, for RF cavity 250 nm at 250 pC 0
2
4
6
Noi
se rm
s ( μ
m)
250 pC
Stripline BPMRF BPM
0 500 1000 15000
10
20
30
Position (m)
Noi
se rm
s ( μ
m)
20 pC
RF BPMσ = 300 nm
Strip Line BPMσ = 3 μm
RF BPMσ = 2 μm
Strip Line BPMσ = 25 μm
E. Medvedko et al., BIW 2008, TUPTPF037
7 Henrik Loosloos@slac.stanford.edu
7Feedback Requirements for SASE FELsIPAC 2010
LCLS Undulator RF Cavity BPMs
Few micron beam orbit straightness in undulator required for FEL operationSub-micron resolution met with RF cavity BPM design11.4 GHz dipole cavityReference cavity for normalizationCalibration with beam signals
Move supporting girder of undulatorInduce known orbit oscillation upstream of undulator
8 Henrik Loosloos@slac.stanford.edu
8Feedback Requirements for SASE FELsIPAC 2010
RF BPMs at XFEL/Spring-8
Dipole mode cavity at 4.76 GHz + monopole cavityShifted from main RF frequency to avoid dark currentMeasurements at SCSS test acceleratorPosition resolution < 200 nmTiming resolution from TM010 cavity < 25 fs
Timing resolutionPosition resolution
H. Maesaka et al., DIPAC09, MOPD07 See also H. Maesaka et al., MOPE003S. Matsubara et al., MOPE004
9 Henrik Loosloos@slac.stanford.edu
9Feedback Requirements for SASE FELsIPAC 2010
RF BPMs for X-FEL
Based on Spring-8 designFrequency 3.3 GHzLow Q to resolve bunch train at 5 MHz10 mm high precision version for undulator40 mm version for IBFBDesigned for 1 μm resolution
Test stand at FLASH 40 mm RF BPM for IBFBD. Noelle, BIW10, WECNB01
See also B. Keil et al., MOPE064
10 Henrik Loosloos@slac.stanford.edu
10Feedback Requirements for SASE FELsIPAC 2010
LCLS Transverse Feedback
Launch FB for each linac sectionLoops for transport line and undulatorFB are independent of each otherDecoupling by use of different time scalesFB response matrix from online model
L0L0
GUNGUN
L3L3L2L2XX
DL1 BC1 DL2L1L1
σσzz11
δδ11ϕϕ11 VV11
σσzz22
δδ22ϕϕ22 VV22
δδ33
VV33
δδ00VV00
BC2
BPMsBPMsCER detectorsCER detectors
Steering LoopSteering LoopLaserLaser
J. Wu et al., PAC 2009, WE5RFP046
11 Henrik Loosloos@slac.stanford.edu
11Feedback Requirements for SASE FELsIPAC 2010
Undulator Feedback Performance
Upstream LTU FB runs at 10 HzUndulator FB slower with 1 HzHorizontal jitter 13 μm / 2 μrad30 – 40% largerthan vertical due to dispersion leakageResidual jitter ~ 25%of beam size -80
-40
0
40
Pos
ition
(μm
)
σx = 13 μm
0 50 100 150 200
-5
0
5
10
Time (s)
Ang
le (μr
ad)
σx' = 2 μrad
ActualCorrection
Beam at Undulator Entrance, 6 GeV
12 Henrik Loosloos@slac.stanford.edu
12Feedback Requirements for SASE FELsIPAC 2010
XFEL/PSI Intra-Bunch Orbit Feedback
Use downstream BPMs for feedback loopLatency ~ 1 μs bunch spacingFPGA for feedback calculationFast strip-line kicker for orbit correctionUse upstream BPMs for calibrationBPMs in undulator for slow feedback
B. Keil et al., EPAC08, THPC123
13 Henrik Loosloos@slac.stanford.edu
13Feedback Requirements for SASE FELsIPAC 2010
LCLS Bunch Length Monitor
Edge radiation from last dipole of each BCIntegrated measurement sensitive from mm to 20 μmBlock NIR radiation from bunching instability with filters3% rms noise from correlation with bunch length dependent wake field energy loss in undulator
Edge Radiation
Beam
Paraboloid
Beam Splitter
Mesh Filter
Pyro Detector
Edge Radiation
Beam
Paraboloid
Beam Splitter
Mesh Filter
Pyro Detector
0 5 10 15 20 25 30
1300
1400
1500
1600
1700
Wake Energy Loss (MeV)
BC
2 P
eak
Cur
rent
(A
)
<I> = 1507 A
σI = 50 A
14 Henrik Loosloos@slac.stanford.edu
14Feedback Requirements for SASE FELsIPAC 2010
LCLS BLM Calibration
Empirical fit of signal to (σz)-4/3
Use fit to calculate peak current
10 20 30 40 500
2
4
6
8
Bunch Length (μm)D
etec
tor S
igna
l (1
0 5 c
ts)
ee−−
σσzz
2.44 m2.44 m
ββdd ββss
ΔΔψψ ≈≈ 9090°°
VV((tt)) σσyy
RFRF‘‘streakstreak’’
SS--bandband
BPM provides only signal related to bunch lengthCalibration with absolute measurement from transverse deflecting cavity
15 Henrik Loosloos@slac.stanford.edu
15Feedback Requirements for SASE FELsIPAC 2010
LCLS Longitudinal Feedback
Cascaded FB at 5 Hz (Matlab implementation)Fixed energy gain in L2 & L3 klystronsChange global L2 phaseAdjust L2 & L3 energy with several klystrons at opposite phasesFeedback uses orthogonal actuators to separate energy gain and chirp of L2
L0L0
GUNGUN
L3L3L2L2XX
DL1 BC1 DL2L1L1
σσzz11
δδ11ϕϕ11 VV11
σσzz22
δδ22ϕϕ22 VV22
δδ33
VV33
δδ00VV00
BC2
BPMsBPMsCER detectorsCER detectors
Steering LoopSteering LoopLaserLaser
16 Henrik Loosloos@slac.stanford.edu
16Feedback Requirements for SASE FELsIPAC 2010
Longitudinal Feedback Performance
7% peak current jitter6% X-ray pulse energy jitter (best 3%)Stability achieved over hrsFeedback controls enable bunch length & energy changes (few %) in 10s of seconds
Operation soon at 120 HzFast orbit and energy/phase feedback in developmentTime-slot aware control for different 60 Hz phases
-40
0
40
δE/E
(10
-4)
σδ = 11 x10-4
1250
1500
1750
I Pea
k (A
)
σI = 98 A
0 10 20 30 400
2
4
Time (s)
EΦ
(m
J)
σE = 0.25 mJ
Beam energy/peak current, 6 GeV
See also F.-J. Decker et al., TUPE071
17 Henrik Loosloos@slac.stanford.edu
17Feedback Requirements for SASE FELsIPAC 2010
LCLS Phase Cavities
PhaseCavity
AdjustableAttenuator
Mixer
¼ Divider
16 BitDigitizer
X6Multiplier
PhaseMeasurement
Software
2805 MHz
51 MHz
2856 MHz
476 MHzReference
119 MHz
Trigger
Jitter between two cavities 15 fsNot used for e-beam FBSignal used for offline analysis
J. Frisch et al., TUPE066
Synchronize laser of user experiment to electron beamJ. Byrd et al., MOOCRA03
See also J. Byrd et al., TUPEA033T. Ohshima et al., TUPEA030
18 Henrik Loosloos@slac.stanford.edu
18Feedback Requirements for SASE FELsIPAC 2010
FLASH Bunch Compression Monitor
Coherent diffraction radiation detectorRadiator is metal screen with slitOptical radiation transport with GHz to THz bandwidthSignal from pyroelectric detectorFast detection resolves bunch trainC. Behrens et al., MOPD090
19 Henrik Loosloos@slac.stanford.edu
19Feedback Requirements for SASE FELsIPAC 2010
FLASH Beam Arrival Monitor
Laser clock via length stabilized fiber with 6 fs stabilityBeam signal from 4 button pick-upsElectro-optic modulator encodes beam signal on laser amplitudeFast sampling with 108 MHz ADC
F. Loehl, TESLA-FEL2009-08
M. Bock et al., FEL09, WEPC66
Operate at zero-crossing of amplitude modulationDelivers arrival time of each bunch in bunch train with < 10 fs resolution
See also M. Bock et al., WEOCMH02
20 Henrik Loosloos@slac.stanford.edu
20Feedback Requirements for SASE FELsIPAC 2010
Longitudinal Intra-bunch Feedback
FPGA based controller boardPID controller for amplitude correction from BAM signalPhase control from BCM signalRapid change at head of bunch train from beam loadingLatency of 30 μs due to SC RF
F. Loehl et al., EPAC08, THPC158
F. Loehl et al., FEL08, THBAU02
Phase feedback
Amplitude feedback
21 Henrik Loosloos@slac.stanford.edu
21Feedback Requirements for SASE FELsIPAC 2010
FLASH Synchrotron Radiation Monitor
Energy measurement with < 10-4 resolutionICCD for energy spread of single bunchesFast centroid readout with multi-anode PMT14-bit ADC at 1 MHz for bunch train resolution
A. Wilhelm et al., DIPAC09, TUPD43
C. Gerth et al., DIPAC09, TUPD22
SRM signal resolution
22 Henrik Loosloos@slac.stanford.edu
22Feedback Requirements for SASE FELsIPAC 2010
Effect of beam loading at head of bunch train minimized after a few iterations of the FF algorithm
FLASH Energy Feedback using SRM
Correct stochastic and deterministic disturbances with a learning FF algorithm
C. Gerth et al., DIPAC09, TUPD22
23 Henrik Loosloos@slac.stanford.edu
23Feedback Requirements for SASE FELsIPAC 2010
Summary
Diagnostics available to meet resolution requirements for SASE FELsSASE FEL feedback systems achieve beam stability to do user experiments over many hoursOptical synchronization schemes enable < 10 fs timing measurements and synchronization of user experimentsEnergy stability of ~ 10-3 still exceeds photon beam bandwidth
24 Henrik Loosloos@slac.stanford.edu
24Feedback Requirements for SASE FELsIPAC 2010
Acknowledgements
Thanks to all the people working on X-ray laser facilities worldwide and to my colleagues from the LCLS commissioning team to make stable X-ray beams a reality