Implementation of the feed forward correction for the FLASH photo injector laser and future plans for a feedback system

Implementation of the feed forward correction for the FLASH photo injector laser and future plans for a feedback system Sebastian Schulz 1,2, Vladimir Arsov 2, Patrick Gessler 2, Olaf Hensler 2, Karsten Klose 2, Kay Rehlich 2, Holger Schlarb 2, Siegfried Schreiber 2 1 Institut für Experimentalphysik Universität Hamburg 2 Deutsches Elektronen-Synchrotron, Hamburg FLASH Seminar, 2008/12/02 S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 1 / 18

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 S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 2 / 18

Motivation and Introduction 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. S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 3 / 18

Motivation and Introduction 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 S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 3 / 18

Motivation and Introduction 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) Photo Injector Feed Forward and Feedback FLASH Seminar 3 / 18

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) Photo Injector Feed Forward and Feedback FLASH Seminar 4 / 18

Hardware Installation and Commissioning Commissioning of the Hardware Step 1: Investigation of the DAC output DAC values should be constant, but: not machine-synchronous writing observed, 5% error rate modification of DOOCS server necessary DAC output TD [0:2047]us 1 0.8 0.6 0.4 0.2 0 0.2 2008 07 24T084915 test dac8 inj laser I failed DAC writing errors resolved 0.4 0.6 0.8 0 500 1000 1500 2000 2500 time [us] 2008 07 24T084915 test dac8 inj laser 0.35 I Buff+1 Q Buff+1 0.3 I Buff+2 Q Buff+2 noise DAC output std(adc) [V] 0.25 0.2 0.15 0.1 0.05 0 0 50 100 150 200 250 300 350 400 Phase variation [deg] S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 5 / 18

Hardware Installation and Commissioning Commissioning of the Hardware Step 2: Power calibration cable extended approx. by 75 cm 7 dbm at RF input of the VM VM set to 12 dbm output level, 5 db attenuator after coupler Output power (dbm) 20 15 10 5 0 5 10 Injector Laser 1: Vector Modulator amplitude calibration original power levels restored 15 20 25 0 0.5 1 1.5 2 2.5 3 DAC8 amplitude setpoint S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 5 / 18

Hardware Installation and Commissioning 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) Photo Injector Feed Forward and Feedback FLASH Seminar 6 / 18

Hardware Installation and Commissioning 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: 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 Simple control of the feed forward system suited for operators! S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 6 / 18

Hardware Installation and Commissioning 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: 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 Simple control of the feed forward system suited for operators! S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 6 / 18

First Measurements First Measurements with installed Vector Modulator Measurement Principle gun detuning precise charge measured with toroid translates to phase S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 7 / 18

First Measurements First Measurements with installed Vector Modulator Charge 3GUN toroid [nc] 0.7 0.6 0.5 0.4 0.3 Cal. harge verus RF gun phase: 2008 07 26T194444 phase scan data cal = 0.0542nC/deg center = 104.75deg Measurement Principle gun detuning precise charge measured with toroid translates to phase Calibration constant 0.0524 nc/deg 0.2 0.1 0 98 100 102 104 106 108 110 Gun Phase [deg] S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 7 / 18

First Measurements First Measurements with installed Vector Modulator phase gun [deg] 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 0.2 0.1 0 0.1 0.2 0.3 Measurement Principle gun detuning precise charge measured with toroid translates to phase Calibration constant 0.0524 nc/deg Phase Stability over 6 Minutes after removing slow drifts 0.105 deg (rms) 0.4 0 1 2 3 4 5 6 time [min] S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 7 / 18

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 6.3 Shot to shot intra train rms= 0.099deg Measurement Principle gun detuning precise charge measured with toroid translates to phase Phase gun versus laser [deg] 6.4 6.5 6.6 6.7 6.8 6.9 7 0 5 10 15 20 25 30 35 time [us] Calibration constant 0.0524 nc/deg Phase Stability over 6 Minutes after removing slow drifts 0.105 deg (rms) Phase Stability across Macro Pulse bunch-to-bunch 0.156 deg (rms) S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 7 / 18

First Measurements Laser Response to EOM Phase Jumps Applying Phase Steps to EOM φ { 2, 1, 0, 1, 2} deg S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 8 / 18

First Measurements Laser Response to EOM Phase Jumps 0.8 0.7 0.6 Cal. harge verus RF gun phase: 2008 10 07T184118 phase scan data cal = 0.0746nC/deg center = 37.75deg Applying Phase Steps to EOM φ { 2, 1, 0, 1, 2} deg Calibration constant -0.0746 nc/deg Charge 3GUN toroid [nc] 0.5 0.4 0.3 0.2 0.1 0 32 34 36 38 40 42 44 Gun Phase [deg] S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 8 / 18

First Measurements Laser Response to EOM Phase Jumps Normalized amplitude response laser [%] Laser response to EOM phase step;2008 10 07T184114 step resp inj laser 106 104 102 100 98 96 94 92 2.0 deg 1.0 deg 0.0 deg 1.0 deg 2.0 deg Applying Phase Steps to EOM φ { 2, 1, 0, 1, 2} deg Calibration constant -0.0746 nc/deg Charge Measurement normalized to first 3 bunches phase jump may induce amplitude modulation 90 0 10 20 30 40 50 60 70 time [us] S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 8 / 18

First Measurements Laser Response to EOM Phase Jumps Step response laser [deg] Laser response to EOM phase step;2008 10 07T184114 step resp inj laser 2 1.5 1 0.5 0 0.5 1 1.5 2 0 10 20 30 40 50 60 70 time [us] 2.0 deg 1.0 deg 0.0 deg 1.0 deg 2.0 deg Applying Phase Steps to EOM φ { 2, 1, 0, 1, 2} deg Calibration constant -0.0746 nc/deg Charge Measurement normalized to first 3 bunches phase jump may induce amplitude modulation Response to Phase Jumps corrected with charge measurement nominal value not reached systematic error? S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 8 / 18

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) Photo Injector Feed Forward and Feedback FLASH Seminar 9 / 18

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) Photo Injector Feed Forward and Feedback FLASH Seminar 10 / 18

Future Plans for a Feedback System 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) Photo Injector Feed Forward and Feedback FLASH Seminar 11 / 18

Future Plans for a Feedback System Balanced Optical Cross-Correlation Balanced Optical Cross-Correlation II Beta barium borate (BBO) large birefringence (n o > n e, n 0.13) low temperature sensitivity large phase-matching bandwidth Some considerations collinear type-i phase matching walk-off of sum frequency component focussing pulse lengths GVD effective length... optimal crystal length 5 mm conversion efficiency > 1.5% Control Signal ADC voltage (V) 1 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 SFG intensities I (t) I + (t) slope near zero crossing highly sensitive to timing jitter measured data Gaussian fitted data slope = 8.723 mv/fs 1 1.5 1 0.5 0 0.5 1 1.5 relative time t (ps) (SFG-Control signal measured with center wavelength of 800 nm and 1550 nm in another X-Correlator setup) S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 12 / 18

Future Plans for a Feedback System 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. S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 13 / 18

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) Photo Injector Feed Forward and Feedback FLASH Seminar 14 / 18

Summary and Outlook Acknowledgements Thank you for your attention! S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 15 / 18

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 Überlagerung zweier Laserpulszüge 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) Photo Injector Feed Forward and Feedback FLASH Seminar 16 / 18

Further Ideas and Plans Further Idea: Amplitude Stabilization S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 17 / 18

Further Ideas and Plans Further Idea: LO Generation S. Schulz (Uni Hamburg, DESY) Photo Injector Feed Forward and Feedback FLASH Seminar 18 / 18