#### 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**

IBFB

**Daisy-Chain 2 of BPM Units**

SASE 2 LINAC

**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

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**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

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**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

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**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

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**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

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**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**

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### 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**

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

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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

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**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 **

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**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

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**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

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**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*

Boris Keil, PSI DEELS Workshop 2014 13.5.14

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**Paul Scherrer Institut**

Boris Keil, PSI

### Thank you for your attention!

DEELS Workshop 2014 13.5.14