1. Boris Keil, PSIDEELS Workshop 201413.5.14 The European XFEL Intra Bunch Train Feedback Boris Keil For the PSI E-XFEL Team Paul Scherrer Institut Paul Scherrer Institut 13.5.14DEELS Workshop 2014

2. Boris Keil, PSIDEELS Workshop 201413.5.14 1 E-XFEL IBFB Overview IBFB 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,...).

3. Boris Keil, PSIDEELS Workshop 201413.5.14 2 *Worst-case estimate (DESY), 30m beta function at kicker & BPM, adding of peak values. 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. Transverse Perturbations

4. Boris Keil, PSIDEELS Workshop 201413.5.14 3 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. Aluminum vessel and strips (low weight, easy to fabricate) DESY standard steel flanges Ceramic spacers & RF feedthroughs allow thermal expansion of strip relative to vessel (bakeout, tolerances,...) IBFB Kicker Magnet Flexible RF feedthrough

5. Boris Keil, PSIDEELS Workshop 201413.5.14 4 IBFB Kicker: S-Parameters

6. Boris Keil, PSIDEELS Workshop 201413.5.14 5 IBFB Kicker: Diff. Impedance

7. Boris Keil, PSIDEELS Workshop 201413.5.14 6 Dump kickers Baseline: 4 Kickers of 2m length for IBFB. Reserved space for upgrade: Double number of kickers and max. kick Kicker Positions & Beam Optics

8. Boris Keil, PSIDEELS Workshop 201413.5.14 7 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). Two Amplifiers IBFB Kickers: RF Power Amps

9. Boris Keil, PSIDEELS Workshop 201413.5.14 8 Prototype test at PSI: IBFB will most likely use 18MHz amplitude-modulated sine or square wave. TOMCO guarantees 3kW pulse power, but amp reached 6kW! IBFB Kickers: RF Power Amps

10. Boris Keil, PSIDEELS Workshop 201413.5.14 9 Droop of kick voltage over bunch train (thermal effects in MOSFETs,...): IBFB digital electronics will compensate droop IBFB Kickers: RF Power Amps

11. Boris Keil, PSIDEELS Workshop 201413.5.14 10 Feedback/Feed- forward algorithm: Same FPGA board as BPMs, but with 0.5-1GSPS DAC mezzanine to generate kicker waveforms IBFB: Electronics Topology

12. Boris Keil, PSIDEELS Workshop 201413.5.14 11 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. IBFB: Algorithm

13. Boris Keil, PSIDEELS Workshop 201413.5.14 12 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, … Frequency (both resonators)3.3GHz Loaded Q (both resonators, desired mode)~70 Q (uncoupled modes)typ. 200-300 Sensitivity2.5V/(nC*mm) Thermal noise (lossless cables & electronics, …)65nm @ 20pC Angle signal (90° to position signal. Cause: Misalignment)~16mm * dx/dz Similar to undulator type, slightly less resolution (~20%). Main differences: ~16x more angle signal (→ align 16x better), cavity spacing ( → crosstalk). 255mm D. Lipka DESY Prototype at SwissFEL Injector Test Facility

14. Boris Keil, PSIDEELS Workshop 201413.5.14 13 New: 63dB range, 0.5dB steps I/Q downconversion to baseband. Active temperature stabilization (several sensors + heaters). Works with or without external trigger & ref. clock. Differential coax cabling from RFFE to ADCs DOOCS & Timing Interface (SFP/Optical, PCIe/Ethernet /..., up to 6.5Gbps) RFFE MBU Crate: Removable fan tray, redundant main power supply,... IBFB: Cavity BPM Electronics

15. Boris Keil, PSIDEELS Workshop 201413.5.14 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.

16. Boris Keil, PSIDEELS Workshop 201413.5.14 15 RFFE: Nominal vs. Measured Gain

17. Boris Keil, PSIDEELS Workshop 201413.5.14 16 Gain Dependence of Phase Delay

18. Boris Keil, PSIDEELS Workshop 201413.5.14 17 Cavity BPM ElectronicsTemp. Drift Temperature drift scales with beam offset. Active temperature stabilization active: <100nm/°C drift at 1mm offset (0.01%/°C)

19. Boris Keil, PSIDEELS Workshop 201413.5.14 18 GUI For Automated Lab Calibration 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",...).

20. Boris Keil, PSIDEELS Workshop 201413.5.14 19 Position Calculation in BPM FPGA

21. Boris Keil, PSIDEELS Workshop 201413.5.14 20 SwissFEL BPM Test Area Correlation of 3 E-XFEL Undulator Cavity BPMs See IBIC’12, TUPA27, M. Stadler et al. Only top sample used (so far...), plus baseline subtraction Histogram (X1+X3)/2 – X2 Sampled RFFE IQ Signals

22. Boris Keil, PSIDEELS Workshop 201413.5.14 21 Position Noise (RMS, 1 Bunch) Undulator cavity (Ø=10mm): ~11μm @ 2pC (±5mm range) <0.5μm @ 100-1000pC (±1mm range) Transfer line cavity (Ø=40.5mm): ~1μm @ 100-1000pC (±1mm range) Charge Measurement RMS Noise (1 Bunch) Undulator cavity (Ø=10mm): <0.06% @ 100-1000pC <60fC @ 100pC <10fC @ 2pC 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) IBFB: Cavity BPM Performance

23. Boris Keil, PSIDEELS Workshop 201413.5.14 22 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). IBFB Status

24. Boris Keil, PSIDEELS Workshop 201413.5.14 23 Team & Acknowledgements PSI: 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) DESY: 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

25. Boris Keil, PSIDEELS Workshop 201413.5.14 Paul Scherrer Institut Thank you for your attention!