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
13.5.14
E-XFEL IBFB Overview
1
IBFB
Daisy-Chain 2 of BPM Units
IBFB Upstream
BPM Pickups
LINAC
IBFB Kicker Magnets
(Horizont. & Vertical)
H1
V1
H2
V2
IBFB Downstream
BPM Pickups
SASE 2
e-beam
Daisy-Chain 1 of BPM Units
- - - - - - - - - - - Analog Signals (Coax Cables) - - - - - - - - - -
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
2
• 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
xeff
[μm]
Max.
Freq.
Plane
15
15
0.5
0.15
25
0
1
28
12.6
2.5
1 kHz
1 kHz
1 kHz
1 kHz
5 MHz
1 kHz
5 MHz
10 Hz
10 Hz
10 Hz
x/y
x
x/y
x
x/y
x
x
x/y
x/y
x/y
Perturbation
Type
repetitive
repetitive
random
random
repetitive
repetitive
random
random
random
random
X Kick
[μrad]
Y Kick
[μrad]
±0.5
±0.5
±0.01
±0.003
±0.8
±0
±0
±1.0
±0.4
±0.1
±3.3
±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
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.
Flexible RF
• Wakefield simulations: Kicker vessel needs no taper.
feedthrough
• Prototype built by company COMEB, RF test successful.
• DESY uses modified version (aperture, ...) for dump kickers.
Ceramic spacers & RF feedthroughs allow
thermal expansion of strip relative to vessel
(bakeout, tolerances, ...)
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
Boris Keil, PSI
DEELS Workshop 2014
4
13.5.14
IBFB Kicker: Diff. Impedance
Boris Keil, PSI
DEELS Workshop 2014
5
13.5.14
Kicker Positions & Beam Optics
Baseline: 4 Kickers of
2m length for IBFB.
6
Reserved space for upgrade:
Double number of kickers and
max. kick
Dump kickers
Boris Keil, PSI
DEELS Workshop 2014
13.5.14
IBFB Kickers: RF Power Amps
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
Boris Keil, PSI
DEELS Workshop 2014
13.5.14
IBFB Kickers: RF Power Amps
8
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.
Boris Keil, PSI
DEELS Workshop 2014
13.5.14
IBFB Kickers: RF Power Amps
9
Droop of kick voltage over
bunch train (thermal effects
in MOSFETs, ...):
IBFB digital electronics will
compensate droop
Boris Keil, PSI
DEELS Workshop 2014
13.5.14
IBFB: Electronics Topology
BPM6r
BPM6y
BPM6x
BPM5r
BPM5y
BPM5x
undulator BPMs
BPM4r
BPM4y
BPM3r
BPM3y
BPM3x
BPM2r
BPM2y
BPM2x
BPM1r
BPM1y
BPM1x
BPM4x
downstream BPMs
upstream BPMs
10
RFFE1
RFFE2
RFFE3
RFFE4
RFFE5
RFFE6
6xADC 16-bit
6xADC 16-bit
6xADC 16-bit
6xADC 16-bit
6xADC 16-bit
6xADC 16-bit
FPGA1
FPGA2
FPGA3
FPGA4
FPGA5
FPGA6
P0
Boris Keil, PSI
PDC
32GFLOPS
DSP
6xADC 16-bit
4xDAC 14-bit
K1x
K2x
K2y
K2y
FPGA8
K1x Pfor
K1y Pfor
K2x Pfor
K2y Pfor
FPGA7
Ebeam
GPAC3
P0
P0
Feedback/Feedforward algorithm:
Same FPGA board
as BPMs, but with
0.5-1GSPS DAC
mezzanine to
generate kicker
waveforms
RIO
P0
GPAC2
RIO
RIO
RIO
RIO
RIO
GPAC1
to kicker amplifiers
DEELS Workshop 2014
13.5.14
kicker signal
from y plane
kicker signal
from x plane
...
Data Acquisition
from/to
control system
RIO Link
Timing
Control
x1
x’2
Position & Angle
Calculation
BPM4r
BPM4x
BPM3r
BPM3x
BPM4r
BPM4x
BPM3r
BPM3x
BPM2r
BPM2x
Position & Angle
Calculation
x-y Plane
Decoupling
Position & Angle
Calculation
x2
x3
kicker
signal
+
DDR2 SDRAM
BPM1r
Kicker
Linearization
ADC, position,
angle, control
signals, etc.
QDR2 SRAM
BPM1x
K1x Pfor
K2x Pfor
11
K2x
K1x
IBFB: Algorithm
Control &
Status
Registers
Processor Local Bus (PLB)
Adaptive
Feed
Forward
Table
Ebeam
Feedback Kicker
Control
x’4
x4
Lattice
Transfer Matrices
Adaptive Feed
Forward
Algorithm
x5
x’5
x6
• 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
Prototype at SwissFEL
Injector Test Facility
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, …
12
255mm
Similar to undulator type, slightly less
resolution (~20%). Main differences:
~16x more angle signal (→ align 16x
better), cavity spacing (→ crosstalk).
Frequency (both resonators)
3.3GHz
Loaded Q (both resonators, desired mode)
~70
Q (uncoupled modes)
typ. 200-300
Sensitivity
2.5V/(nC*mm)
Thermal noise (lossless cables & electronics, …)
65nm @ 20pC
Angle signal (90° to position signal. Cause: Misalignment)
~16mm * dx/dz
Boris Keil, PSI
DEELS Workshop 2014
D. Lipka
DESY
13.5.14
IBFB: Cavity BPM Electronics
New: 63dB range,
0.5dB steps
RFFE
MBU Crate: Removable
fan tray, redundant main
power supply, ...
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.
Boris Keil, PSI
DEELS Workshop 2014
13
DOOCS &
Timing
Interface
(SFP/Optical,
PCIe/Ethernet
/..., up to
6.5Gbps)
13.5.14
ADC Sample Clock Phase Feedback
14
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
Boris Keil, PSI
DEELS Workshop 2014
15
13.5.14
Gain Dependence of Phase Delay
Boris Keil, PSI
DEELS Workshop 2014
16
13.5.14
Cavity BPM ElectronicsTemp. Drift
17
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
13.5.14
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
Boris Keil, PSI
DEELS Workshop 2014
19
13.5.14
SwissFEL BPM Test Area
20
Correlation of 3 E-XFEL Undulator Cavity BPMs
Sampled RFFE
IQ Signals
Only top sample
used (so far ...),
plus baseline
subtraction
Histogram
(X1+X3)/2 – X2
See IBIC’12, TUPA27, M.
Stadler et al.
Boris Keil, PSI
DEELS Workshop 2014
13.5.14
IBFB: Cavity BPM Performance
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)
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
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).
Boris Keil, PSI
DEELS Workshop 2014
13.5.14
Team & Acknowledgements
23
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
Paul Scherrer Institut
Thank you for your
attention!
Boris Keil, PSI
DEELS Workshop 2014
13.5.14