E-XFEL Intra-bunch train feedback

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Transcript E-XFEL Intra-bunch train feedback

Paul Scherrer Institut

The European XFEL Intra Bunch Train Feedback

Boris Keil For the PSI E-XFEL Team Paul Scherrer Institut Boris Keil, PSI DEELS Workshop 2014 DEELS Workshop 2014

E-XFEL IBFB Overview


Daisy-Chain 2 of BPM Units


IBFB Upstream BPM Pickups IBFB Kicker Magnets (Horizont. & Vertical)

H1 V1 H2 V2

IBFB Downstream BPM Pickups e-beam - - - - - - - - - - - Analog Signals (Coax Cables) - - - - - - - - - Daisy-Chain 1 of BPM Units

SASE 1 IBFB Electronics

Digital Signals (Duplex Fiber Optic Cables)

• Low-latency (~1μs) beam position correction upstream of beam distribution.

• Can kick each bunch individually, using feedback + feed-forward algorithm.

• Uses undulator BPM data (latency 5-10μs) for fine-tuning of undulator orbit (to correct kicks between IBFB and undulators: Vibrations, distribution kicker, ...).

Boris Keil, PSI DEELS Workshop 2014 13.5.14


Transverse Perturbations

• IBFB kickers should provide enough kick to correct perturbations, plus reserve.

• IBFB removes perturbations, but also adds noise to the beam (dominated by BPMs): Noise should not have negative impact on FEL performance → Low-noise BPMs (goal: <1μm RMS). Pickups: 3.3GHz cavity, same as TL.

• Feedback loop latency <1.5μs expected to be sufficient.

Spurious dispersion and 3% chirp Nonlinear dispersion and 3% chirp Spurious dispersion and 1e -4 energy jitter Nonlinear dispersion and 1e -4 energy jitter Wake fields Kicker Drift Kicker Jitter Quad Motion Power Supply Jitter Dispersion jitter Total kick x eff [μm] 15 15 0.5 0.15 25 0 1 28 12.6 2.5 Max. Freq. 1 kHz 1 kHz 1 kHz 1 kHz 5 MHz 1 kHz 5 MHz 10 Hz 10 Hz 10 Hz Plane x/y x x/y x x/y x x x/y x/y x/y Pertur bation Type repetitive repetitive random random repetitive repetitive random random random random X Kick [μrad] ±0.5 ±0.5 ± 0.01 ± 0.003 ±0.8 ±0 ± 0 ± 1.0 ± 0.4 ± 0.1 ±3.3 Y Kick [μrad] ±0.5 ±0 ± 0.01 ± 0 ±0.8 ±0 ± 0.03 ± 1.0 ± 0.4 ± 0.1 ±2.8

*Worst-case estimate (DESY), 30m beta function at kicker & BPM, adding of peak values.

Boris Keil, PSI DEELS Workshop 2014 13.5.14


IBFB Kicker Magnet

• 50 Ohms stripline kicker (picture shows cut / only half).

• Kicker design by PSI (based on CTF3/Daphne design by F. Marcellini et al., INFN Frascati), supported by DESY (wakefield simulations, M. Dohlus).

• Tapered 2m long strips.

• Wakefield simulations: Kicker vessel needs no taper.

• Prototype built by company COMEB, RF test successful.

• DESY uses modified version (aperture, ...) for dump kickers.

Flexible RF feedthrough Ceramic spacers & RF feedthroughs allow thermal expansion of strip relative to vessel (bakeout, tolerances, ...) 3 DESY standard steel flanges Boris Keil, PSI Aluminum vessel and strips (low weight, easy to fabricate) DEELS Workshop 2014 13.5.14

IBFB Kicker: S-Parameters

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IBFB Kicker: Diff. Impedance

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Kicker Positions & Beam Optics

Baseline: 4 Kickers of 2m length for IBFB.

Reserved space for upgrade: Double number of kickers and max. kick 6 Dump kickers Boris Keil, PSI DEELS Workshop 2014 13.5.14

IBFB Kickers: RF Power Amps

• Commercial amplifiers from Company TOMCO (class AB solid state).

• Improved at request of PSI: Redundant power supply & amp modules to maximize MTBF.

• Two amplifiers purchased & tested extensively: Meet PSI specifications.

• Kick: > ±4μrad baseline (4 kickers), > ±8μrad upgrade (8 kickers).

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IBFB Kickers: RF Power Amps

TOMCO guarantees 3kW pulse power, but amp reached 6kW!

Prototype test at PSI: IBFB will most likely use 18MHz amplitude-modulated sine or square wave.

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IBFB Kickers: RF Power Amps

9 Droop of kick voltage over bunch train (thermal effects in MOSFETs, ...): IBFB digital electronics will compensate droop 13.5.14

Boris Keil, PSI DEELS Workshop 2014

IBFB: Electronics Topology

downstream BPMs undulator BPMs upstream BPMs RFFE1 6xADC 16-bit FPGA1 RFFE2 6xADC 16-bit P0 FPGA2 GPAC1 RFFE3 6xADC 16-bit FPGA3 RFFE4 6xADC 16-bit P0 FPGA4 GPAC2 RFFE5 6xADC 16-bit FPGA5 RFFE6 6xADC 16-bit P0 FPGA6 GPAC3 Feedback/Feed forward algorithm: Same FPGA board as BPMs, but with 0.5-1GSPS DAC mezzanine to generate kicker waveforms FPGA7 P0 32GFLOPS DSP PDC FPGA8 6xADC 16-bit 4xDAC 14-bit to kicker amplifiers Boris Keil, PSI DEELS Workshop 2014 13.5.14


IBFB: Algorithm

K1x Pfor K2x Pfor ADC, position, angle, control ...

Data Acquisition kicker signal from y plane kicker signal from x plane Timing Control Kicker Linearization x-y Plane Decoupling Control & Status Registers + kicker signal Position & Angle Calculation x 1 x ’ 2 x 2 Position & Angle Calculation Feedback Kicker Control x 3 x ’ 4 x 4 Position & Angle Calculation DDR2 SDRAM QDR2 SRAM from/to control system RIO Link Processor Local Bus (PLB) Adaptive Feed Forward Table Ebeam Lattice Transfer Matrices Adaptive Feed Forward Algorithm x 5 x ’ 5 x 6 • Ultra-fast feedback removes random perturbations, e.g. beam offset of whole bunch train due to mechanical vibrations etc.

• Adaptive feed-forward corrects reproducible perturbations that are the same for each bunch train (or change very slowly).

• IBFB can use same FPGA carrier board as BPMs. Present version (Xilinx Virtex-5 FPGA, PowerPC) sufficient, new version (Artix-7/Kintex-7 FPGAs + DSP) under development, will simplify development of more complex algorithms for future operating modes.

Boris Keil, PSI DEELS Workshop 2014 13.5.14


IBFB: Cavity BPM Pickups

Transfer Line Cavity BPM

• 3.3GHz, 40.5mm aperture.

• Used for: Transverse intra-train feedback, energy measurements, launch jitter control & correction (energy, BAM, linac entry, …), optics measurements, …

Prototype at SwissFEL Injector Test Facility 255mm Similar to undulator type, slightly less resolution (~20%). Main differences: ~16x more angle signal (→ align 16x better), cavity spacing ( → crosstalk).

Frequency (both resonators) Loaded Q (both resonators, desired mode) Q (uncoupled modes) Sensitivity Thermal noise (lossless cables & electronics, …) Angle signal (90 ° to position signal. Cause: Misalignment) 3.3GHz

~70 typ. 200-300 2.5V/(nC*mm) 65nm @ 20pC ~16mm * dx/dz

D. Lipka DESY

Boris Keil, PSI DEELS Workshop 2014 13.5.14


IBFB: Cavity BPM Electronics

New: 63dB range, 0.5dB steps RFFE MBU Crate: Removable fan tray, redundant main power supply, ...

13 Differential coax cabling from RFFE to ADCs • I/Q downconversion to baseband.

• Active temperature stabilization (several sensors + heaters).

• Works with or without external trigger & ref. clock.

DOOCS & Timing Interface (SFP/Optical, PCIe/Ethernet /..., up to 6.5Gbps) Boris Keil, PSI DEELS Workshop 2014 13.5.14

ADC Sample Clock Phase Feedback


Digital ADC sampling clock phase alignment loop

• Eliminates phase drift effects • Retains maximal S/N ratio • Monitors possible reference signal malfunctions & beam arrival time changes

Present algorithm: Uses just one ADC sample at top to calculate beam position.

Boris Keil, PSI DEELS Workshop 2014 13.5.14

RFFE: Nominal vs. Measured Gain

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Gain Dependence of Phase Delay

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Cavity BPM ElectronicsTemp. Drift


Temperature drift scales with beam offset. Active temperature stabilization active: <100nm/ °C drift at 1mm offset (0.01%/ °C)


Boris Keil, PSI DEELS Workshop 2014

GUI For Automated Lab Calibration

18 • Presently using commercial RF generator (pulsed) for automated lab calibration (gain & phase delay for each attenuator setting; IQ imbalance, ...).

• Developing low-cost test/calibration system (external "customers", ...).

Boris Keil, PSI DEELS Workshop 2014 13.5.14

Position Calculation in BPM FPGA

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SwissFEL BPM Test Area

Correlation of 3 E-XFEL Undulator Cavity BPMs


Sampled RFFE IQ Signals

Boris Keil, PSI

See IBIC’12, TUPA27, M. Stadler et al.

DEELS Workshop 2014

Only top sample used (so far ...), plus baseline subtraction Histogram (X1+X3)/2 – X2


IBFB: Cavity BPM Performance

Position Noise (RMS, 1 Bunch) • Undulator cavity (Ø=10mm): ~11 μm @ 2pC ( ±5mm range) <0.5μm @ 100-1000pC ~1μm @ 100-1000pC ( ( ±1mm range) • Transfer line cavity (Ø=40.5mm): ±1mm range) 2x improvement feasible by digital removal of angle signal (15x bigger than for undulator BPMs) – work in progress ...

20mm offset at 1nC: 50V signal! RFFE may need input protection via attenuator (4x worse low-charge resolution), or extra protection circuit (to be developed for IBFB) Charge Measurement RMS Noise (1 Bunch) • Undulator cavity (Ø=10mm): <0.06% @ 100-1000pC <60fC @ 100pC <10fC @ 2pC Boris Keil, PSI DEELS Workshop 2014 13.5.14


IBFB Status

IBFB BPMs (Will Dominate IBFB Performance ...) • Using standard E-XFEL cavity BPM electronics (maybe with external RFFE input protection circuit (1nC & big beam offsets ...), necessity being investigated).

IBFB (Non-BPM) Electronics Hardware • Can use BPM FPGA carrier board also for IBFB signal processing.

• DAC mezzanine to driver kicker amps under development.

IBFB Firmware/Software • Feedback/Feed-forward algorithm & feedback network via multi-gigabit fiber optic links to be implemented (re-using building blocks from BPM firmware/software).

Boris Keil, PSI DEELS Workshop 2014 13.5.14


Team & Acknowledgements


• M. Stadler

(Cavity BPM RF front-end)

• M. Roggli, M. Gloor

(ADC/DAC Mezzanine)

• R. Baldinger, D. Engeler

(FPGA carrier board HW)

• G. Marinkovic, W. Koprek

(Firmware & software)

• C. Beard, F. Marcellini, M. Rohrer, D. Treyer,

(IBFB kicker magnet & RF power amps)


• S. Vilcins, D. Lipka, D. Nölle

(Cavity BPM pickup)

• M. Dohlus

(Kicker wakefield simulations)

• N. Golubeva, W. Balandin, W. Decking

(Magnet lattice & beam optics) ... and all other supporters at PSI & DESY/E-XFEL

Boris Keil, PSI DEELS Workshop 2014 13.5.14


Paul Scherrer Institut

Boris Keil, PSI

Thank you for your attention!

DEELS Workshop 2014 13.5.14