Implementation of the feed forward correction for the ... - DESY - FLASH

Implementation of the feed forward correction for the FLASH photo injector laser and future plans for a feedback system Sebastian Schulz1,2 , Vladimir Arsov2 , Patrick Gessler2 , Olaf Hensler2 , Karsten Klose2 , Kay Rehlich2 , Holger Schlarb2 , Siegfried Schreiber2 1

2

Institut f¨ ur Experimentalphysik Universit¨ at Hamburg

Deutsches Elektronen-Synchrotron, Hamburg

FLASH Seminar, 2008/12/02

S. Schulz (Uni Hamburg, DESY)

Photo Injector Feed Forward and Feedback

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Outline 1

Motivation and Introduction

2

The Photo Injector Laser Feed Forward System Hardware Installation and Commissioning First Measurements

3

Future Plans for a Feedback System Implementation Balanced Optical Cross-Correlation Detectors and the uTCA-System

4

Summary and Outlook



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Motivation and Introduction During FEL operation of FLASH SASE intensity highly sensitive to changes of the gun RF gradient (0.2%) and the phase (0.2 deg). Understanding of all subsystems beginning with the gun is crucial.



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Motivation and Introduction During FEL operation of FLASH SASE intensity highly sensitive to changes of the gun RF gradient (0.2%) and the phase (0.2 deg). Understanding of all subsystems beginning with the gun is crucial. Observations slope in gun RF phase: ≈ 4 deg over 800 µs can be corrected for with RF gun feedback system remaining phase unstability traced back to the EOM of the injector laser



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Motivation and Introduction During FEL operation of FLASH SASE intensity highly sensitive to changes of the gun RF gradient (0.2%) and the phase (0.2 deg). Understanding of all subsystems beginning with the gun is crucial. Observations slope in gun RF phase: ≈ 4 deg over 800 µs can be corrected for with RF gun feedback system remaining phase unstability traced back to the EOM of the injector laser The laser itself should be stabilized (especially the arrival time). Step 1: feed forward system to correct for the phase slope Step 2: feedback to stabilize the arrival time Synchronization to the optical timing reference and monitoring is desirable to correlate arrival time jitter of the injector laser with other diagnostic systems. S. Schulz (Uni Hamburg, DESY)


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The Photo Injector Laser Feed Forward System

Hardware Installation and Commissioning

Feed Forward: Hardware Installation

Vector Modulator incorporated into the 1.3 GHz branch driving the electro-optic modulator (EOM) inside the pulse train oscillator (PTO) of injector laser 1 I and Q set-points delivered by a DAC installed in VMESYNCH0, simultaneously monitored by an ADC DAC is controlled by a new DOOCS server to set the feed forward tables S. Schulz (Uni Hamburg, DESY)


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Commissioning of the Hardware Step 1: Investigation of the DAC output

2008−07−24T084915−test−dac8−inj−laser 1 I failed 0.8

DAC values should be constant, but:

modification of DOOCS server necessary

DAC output TD [0:2047]us

0.6

not machine-synchronous writing observed, 5% error rate

0.4 0.2 0 −0.2 −0.4

⇒ DAC writing errors resolved

−0.6 −0.8 0

500

1000 1500 2000 time [us] 2008−07−24T084915−test−dac8−inj−laser

2500

0.35 I Buff+1 Q Buff+1 I Buff+2 Q Buff+2

noise DAC output std(ADC) [V]

0.3

0.25

0.2

0.15

0.1

0.05

0 0



50

100

150 200 250 Phase variation [deg]

300

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400

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Commissioning of the Hardware Injector Laser 1: Vector Modulator amplitude calibration 20

Step 2: Power calibration

15

cable extended approx. by 75 cm Output power (dBm)

7 dBm at RF input of the VM VM set to 12 dBm output level, 5 dB attenuator after coupler

10 5 0 −5 −10 −15

⇒ original power levels restored

−20 −25 0



0.5

1 1.5 2 DAC8 amplitude setpoint

2.5

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DOOCS Server & Panel for the Feed Forward Tables Principle of operation: linear interpolation between six nodes: t, (A, φ) memory writing process triggered by VME interrupt and finished before machine trigger

a) DOOCS > Crates > Synch Crates > VMESYNCH0 > Laser Phase Control b) Injector > Laser > PhaseCtrl

Simple control of the feed forward system suited for operators! S. Schulz (Uni Hamburg, DESY)


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DOOCS Server & Panel for the Feed Forward Tables Principle of operation: linear interpolation between six nodes: t, (A, φ) memory writing process triggered by VME interrupt and finished before machine trigger timing structure: I

I

chosen with respect to known DAC bug additional node allows more complex pattern

a) DOOCS > Crates > Synch Crates > VMESYNCH0 > Laser Phase Control b) Injector > Laser > PhaseCtrl



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DOOCS Server & Panel for the Feed Forward Tables Principle of operation: linear interpolation between six nodes: t, (A, φ) memory writing process triggered by VME interrupt and finished before machine trigger timing structure: I

I

chosen with respect to known DAC bug additional node allows more complex pattern

features: e.g. SR (auto) a) DOOCS > Crates > Synch Crates > VMESYNCH0 > Laser Phase Control b) Injector > Laser > PhaseCtrl



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First Measurements

First Measurements with installed Vector Modulator Measurement Principle “gun detuning” precise charge measured with toroid translates to phase



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First Measurements

First Measurements with installed Vector Modulator Cal. harge verus RF gun phase: 2008−07−26T194444−phase−scan 0.7 data cal = −0.0542nC/deg center = 104.75deg 0.6

Calibration

0.5 Charge 3GUN toroid [nC]

Measurement Principle “gun detuning” precise charge measured with toroid translates to phase

constant 0.0524 nC/deg 0.4

0.3

0.2

0.1

0 98

100

102

104 Gun Phase [deg]


106

108

110


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First Measurements

First Measurements with installed Vector Modulator Gun − laser rf stability; cal= −0.054nC/deg;2008−07−26T194441−detuning−gun 0.5 rms = 0.138deg fit = 0.089deg 0.4 rms w/o drift = 0.105deg 0.3

Measurement Principle “gun detuning” precise charge measured with toroid translates to phase Calibration

phase gun [deg]

0.2

constant 0.0524 nC/deg

0.1

Phase Stability over 6 Minutes

0

after removing slow drifts 0.105 deg (rms)

−0.1 −0.2 −0.3 −0.4 0

1

2


3 time [min]

4

5

6


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First Measurements

First Measurements with installed Vector Modulator Gun − laser rf stability; cal= −0.054nC/deg;2008−07−26T194441−detuning−gun −6.2 Bunch to bunch rms = 0.156deg Repetetive intra−train rms = 0.067deg Shot−to−shot intra−train rms= 0.099deg

Phase gun versus laser [deg]

−6.3

Measurement Principle “gun detuning” precise charge measured with toroid translates to phase Calibration

−6.4

constant 0.0524 nC/deg

−6.5 −6.6

Phase Stability over 6 Minutes

−6.7

after removing slow drifts 0.105 deg (rms)

−6.8 −6.9 −7 0

5

10

15 20 time [us]


25

30

35

Phase Stability across Macro Pulse bunch-to-bunch 0.156 deg (rms)


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First Measurements

Laser Response to EOM Phase Jumps Applying Phase Steps to EOM ∆φ ∈ {−2, −1, 0, 1, 2} deg



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First Measurements

Laser Response to EOM Phase Jumps Applying Phase Steps to EOM Cal. harge verus RF gun phase: 2008−10−07T184118−phase−scan 0.8

∆φ ∈ {−2, −1, 0, 1, 2} deg

data cal = −0.0746nC/deg center = 37.75deg

0.7

Calibration

Charge 3GUN toroid [nC]

0.6

constant -0.0746 nC/deg

0.5

0.4

0.3

0.2

0.1

0 32

34

36

38 Gun Phase [deg]


40

42

44


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First Measurements

Laser Response to EOM Phase Jumps Applying Phase Steps to EOM

Normalized amplitude response laser [%]

Laser response to EOM phase step;2008−10−07T184114−step−resp−inj−laser 106 −2.0 deg −1.0 deg 0.0 deg 1.0 deg 2.0 deg

104 102

∆φ ∈ {−2, −1, 0, 1, 2} deg Calibration constant -0.0746 nC/deg

100

Charge Measurement 98

normalized to first 3 bunches

96

phase jump may induce amplitude modulation

94 92 90 0

10

20

30 40 time [us]


50

60

70


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First Measurements

Laser Response to EOM Phase Jumps Applying Phase Steps to EOM Laser response to EOM phase step;2008−10−07T184114−step−resp−inj−laser 2 −2.0 deg −1.0 deg 0.0 deg 1.0 deg 2.0 deg

1.5

Step response laser [deg]

1

∆φ ∈ {−2, −1, 0, 1, 2} deg Calibration constant -0.0746 nC/deg

0.5

Charge Measurement

0

normalized to first 3 bunches −0.5

phase jump may induce amplitude modulation

−1 −1.5 −2 0

Response to Phase Jumps 10

20

30 40 time [us]

50

60

70

corrected with charge measurement nominal value not reached systematic error?



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First Measurements

Notes on the Measurements recently a very good charge stability had been observed operation with EOM phase shifted by 180 deg possible, but then PTO slow feedback does not work results are somehow academic (only slope expected) phase steps advantageous to optimize feedback

Future investigations must include long pulse trains amplitude modulation of the laser oscillator phase relation of the AOMs and the EOM ... and taking these into account in the measurement routine S. Schulz (Uni Hamburg, DESY)


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Future Plans for a Feedback System

Implementation

Feedback: Planned Implementation

master laser oscillator (MLO) delivers precise timing information over a “Short FiberLink” gating to repetition rate of PTO with an EOM and amplification by an EDFA measuring timing jitter between PTO and reference on O(10 fs) level with the optical cross-correlator stabilize 1.3 GHz phase of the PTO’s EOM by closing a control loop implemented in a uTCA system driving the VM S. Schulz (Uni Hamburg, DESY)


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Balanced Optical Cross-Correlation

Balanced Optical Cross-Correlation I

collinear overlap of incoming pulses (⇒ collinear phase matching) sum-frequency generation I+ and detection “1” after dichroic mirror seperation of the pulses and generation of a “temporal swap” sum-frequency generation I− of backward travelling pulses and detection “2” ⇒ difference signal I− − I+ (“S-curve”) is control signal for feedback loop S. Schulz (Uni Hamburg, DESY)


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Balanced Optical Cross-Correlation

Balanced Optical Cross-Correlation II Control Signal

Beta barium borate (BBO) large birefringence (no > ne , ∆n ≈ 0.13)

SFG intensities I− (t) − I+ (t)

low temperature sensitivity large phase-matching bandwidth

slope near zero crossing highly sensitive to timing jitter

Some considerations

1

−

focussing pulse lengths GVD

0.4 0.2 0 −0.2 −0.4 −0.6 −0.8

effective length ...

−1 −1.5

⇒ optimal crystal length 5 mm ⇒ conversion efficiency > 1.5% S. Schulz (Uni Hamburg, DESY)

measured data Gaussian fitted data slope = 8.723 mV/fs

0.6

ADC voltage (V)

collinear type-I phase matching ⇒ walk-off of sum frequency component

0.8

−1

−0.5 0 0.5 relative time ∆t (ps)

1

1.5

(SFG-Control signal measured with center wavelength of 800 nm and 1550 nm in another X-Correlator setup)


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Detectors and the uTCA-System

Detectors and the uTCA-System Planned feedback control loop detection of SFG intensities with fast photo diodes or photo multipliers 2 ADC input channels · minimum sampling rate is 27 MHz FPGA-based algorithm · clock speed up to 500 MHz possible · signal filtering easy and cheap · implementation not started yet DAC output for Vector Modulator control latency and signal propagation delay might be a problem ⇒ investigations necessary fall-back is proven but very slow VME system First non-prototype uTCA-system running at FLASH.



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Summary and Outlook

Tentative Schedule and Summary Jul 2008: Hardware installation and commissioning for the feed forward system (done) Jul & Oct 2008: First measurements and investigations with the feed forward system (done) Oct 2008: Installation of optical fibers from synch hutch to both lasers (done) Sep – Nov 2008: Ordering of optics and opto-mechanics (mostly done) Nov – Dec 2008: Installation and commissioning of the optical synchronization system (infrastructure ready, systems to be installed) Dec 2008 – Feb 2009: Setup and commissioning of the optical cross-correlator (using unstabilized fibers) Mar 2009: Installation and Commissioning of the uTCA system Apr 2009: First measurements and results May 2009: Completion and Installation of the Short-FiberLink S. Schulz (Uni Hamburg, DESY)


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Summary and Outlook

Acknowledgements

Thank you for your attention!



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References

References I. Will, G. Koss, I. Templin The upgraded photocathode laser of the TESLA Test Facility Nucl. Instr. Meth. A, 541:467–477, 2005 H. Schlarb et al. Precision RF Gun Phase monitor System for FLASH Proc. EPAC 2006, Edinburgh, Scotland, TUPCH025, 2006 A. Winter et al. Layout of the Optical Synchronization System for FLASH Proc EPAC 2006, Edinburgh, Scotland, TUPCH026, 2006 J. Zemella ¨ Driftfreier Detektor zur Messung des Zeitversatzes durch Uberlagerung zweier Laserpulsz¨ uge auf einer Photodiode DESY-THESIS-2008-xxx, Diploma Thesis, University of Hamburg, 2008 V. G. Dmitriev, G. G. Gurzadyan, D. N. Nikogosyan Handbook of Nonlinear Optical Crystals Springer Verlag - Berlin Heidelberg New York, 3rd Edition, 1999 S. Schulz (Uni Hamburg, DESY)


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Further Ideas and Plans

Further Idea: Amplitude Stabilization



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Further Ideas and Plans

Further Idea: LO Generation



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