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Feedback Simulations with Amplifier Saturation, Transient and Realistic Filtering. Mauro Pivi, Claudio Rivetta, Kevin Li Webex CERN/SLAC/LBNL 13 September 2012. Simulation Code Development. - PowerPoint PPT Presentation
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Feedback Simulations with Amplifier Saturation, Transient and Realistic
Filtering
Mauro Pivi, Claudio Rivetta, Kevin Li
Webex CERN/SLAC/LBNL13 September 2012
Simulation Code Development
• Realistic single-bunch feedback system have been implemented in 3 simulation codes: Head-Tail, C-MAD, WARP.
• At SLAC (by Rivetta, Pivi, Li):– Feedback implemented firstly in C-MAD– Developed and tested then translated in
HeadTail
Plans for codes utilization
The feedback system is simulated with:• HeadTail which comes with different options for the
SPS: electron cloud, TMCI and advanced impedances model for the SPS.
• For benchmarking, C-MAD parallel code: electron cloud instability, Intra-Beam Scattering IBS. Allows uploading the full SPS lattice from MAD for increased realistic simulations.
HeadTail-CMAD codes comparison
• Initial beam offset of 2 mm, no electron cloud• Feedback Bandwidth 200MHz
turns
Verti
cal b
eam
pos
ition
(m) HeadTail
CMAD
Following simulation results
• For our feedback simulations, here:– To reduce the statistical noise, used bunch slices
with same constant charge (rather than slices with constant distance).
– Kicker bandwidth 500MHz, cloud density of 6e11 e/m3, gain = 15 (equivalent to Kevin’s 0.5)
– Bunch extent: ±4 sz (as feedback input matrices)
Feedback system design
Saturation in the Receiver: ± 250mV
Saturation in the Amplifier: defined by DAC ± 200mV
Corresponds to kicker signal: ± 4e-5 eV-sec/m
Feedback system and electron cloud: reference simulation run
*equivalent to 0.5 for Kevin
parameter valueKicker bandwidth 500 MHzCloud density 6×1011 e/m3
Feedback gain 15*
Emittance evolution Vertical displacement - each slice
Rivetta, Pivi
turns
• Set high electron cloud density
Momentum signal delivered by kicker is within saturation limits ± 4e-5 ev-sec/m
Central bunch slice # 32: DAC Voltage is within the saturation values ± 200mV
Central bunch slice # 32: kicker signal
Rivetta, Pivi
Feedback system and electron cloud: reference simulation run
Rivetta, Pivi
(above) Vertical slice positions(central) ADC Voltage at Receiver, well within saturation ± 250mV(below) Yout=fir(Yin) in Volts
Each of 64 bunch slices is shown
Feedback system and electron cloud: reference simulation run
Next• Set Amplifier saturation (or DAC saturation)• Introduce a transient in the bunch
Set Amplifier saturation and beam with initial offset
parameter valueKicker bandwidth 500 MHzCloud density no cloud
Set:• No electron cloud • Amplifier saturation corresponds to
saturation limits for DAC ± 200 mV• “Transient” or initial beam offset 500 um
Rivetta, Pivi
• Without electron cloud, the feedback damps the oscillation• The question was: with an electron cloud, will it still dump?
Vertical displacement Kicker signal constrained
See also Claudio presentation:
Set Amplifier Saturation and beam with initial offset
*equivalent to 0.5 for Kevin
parameter valueKicker bandwidth 500 MHzCloud density 6×1011 e/m3
Feedback gain 15*
Emittance Vertical displacement - each slice
Set:• Turn electron cloud ON • Saturation limits for DAC ± 200 mV• “Transient” or initial beam offset of
500 um (representing position jitter)
Rivetta, Pivi
turns
Set Amplifier saturation (DAC 200 mV), and a beam with initial offset 500um
Rivetta, Pivi
Constrained kicker saturation limits ± 4e-5 eV-sec/m
DAC Control Voltage when saturation is set to ± 200mV
Bunch slice # 32: kicker signal
• Effective Damping of emittance and vertical motion with DAC saturation limits
Rivetta, Pivi
(above) Vertical slice positions(central) ADC Voltage at Receiver, well within saturation ± 250mV
Each of 64 bunch slices is shown
Set Amplifier saturation (DAC 200 mV), and a beam with initial offset 500um
Shift of beam signal due to realistic Filter
Even more shift at kickershift at filter processing
measured
See also Claudio presentation:
• Note: All previous simulations (also Kevin’s) did not include a realistic Filter yet, but an ideal one.
turns
• We included a realistic filter in the feedback system• Not compensating the signal shift internally in the feedback
results in an unstable beam.
Shift of beam signal due to realistic Filter
Beam unstable!
EmittanceVertical displacement - each slice
kicker signal exceeds saturation limits
• Including a realistic filter results in a shift (+ distortion) of the beam signal by ~ +7 slices
• Beam unstable• We compensated by shifting back the beam
signal at kicker by shifting -7 slices• Transparent process for beam: all internal
processing inside feedback system
Compensation of shifted beam signal due to Filter
compensate shift at kickershift at filter processing
measured
See also Claudio presentation:
Compensation of shifted beam signal due to Filter
Rivetta, Pivi
Compensation of shifted beam signal due to Filter
*equivalent to 0.5 for Kevin
parameter valueKicker bandwidth 500 MHzCloud density 6×1011 e/m3
Feedback gain 15*
Emittance growth Vertical displacement - each slice
turns
Rivetta, Pivi
Compensation of shifted beam signal due to Filter
Momentum signal delivered by kicker is within saturation limits of ± 4e-5 ev-sec/m
Rivetta, Pivi
• Effective damping of emittance and beam motion
Simulation plan
M. Pivi, C. Rivetta, K. Li, SLAC/CERN
Support for proof of principle
prototype design
final design
LHC Long Shutdown
What we didn’t include, in these simulations
• Although the codes have full features capabilities
• In these results we are not showing issues:– Noise: both in the receiver and amplifier– Limitations in the bunch sampling– Other processing algorithms– Realistic SPS lattice
• Step by step adding more physics and more reality into simulations
Summary• Successful implementation of a realistic single-
bunch feedback system into codes and very promising initial results
• Preliminary studies to include: -Amplifier Saturation (DAC)-Beam transient -Compensation of shift due to realistic Filtering
• Simulation plan to support the feedback prototype, the final design and construction
Code comparison
(M. Pivi et al. SLAC) (G. Rumolo et al. CERN) (J-L Vay et al. LBNL)