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Operation with ADT increased bandwidth. W. Höfle , G. Kotzian , D. Valuch Special thanks to: G. Cipolla , F. Dubouchet , D. Jacquet , F. Killing, E. Montesinos. The transverse damper in general. - PowerPoint PPT Presentation
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Operation with ADT increased bandwidth
W. Höfle, G. Kotzian, D. Valuch
Special thanks to:G. Cipolla, F. Dubouchet, D. Jacquet, F. Killing, E. Montesinos
The transverse damper in general The transverse damper is a feedback system: it
measures the bunch oscillations and damps them by fast electrostatic kickers
BPM
BPM Signal Processing
andCorrection calculation
Kicker
Power Amplifier
Ideal equilibrium orbitBeam trajectory
BPM Beam position monitor
Tbeam
Tsignal
Key elements: Beam position
monitor(s) Signal processing
system Power amplifiers Electrostatic kickers Key parameters: Feedback loop gain,
phase and delay Kick strength Bandwidth
Tbeam
Tsignal
LHC transverse damper (ADT)
IP4
beam 2
beam 1
Q7LQ9L Q9RQ7RH.M2.B2H.M1.B2V.M1.B2V.M2.B2
V.M2.B1V.M1.B1H.M1.B1H.M2.B1
beam 2
beam 1
SR4
[V]
[H]
[V]
[H]
[H]
[V]
[H]
[V]
Point 5Point 3 UX451
BPos Q9
BPos Q7
DSPU M1
DSPU M2
BPos Q9
BPos Q7
DSPU M1
DSPU M2
BPos Q9
BPos Q7
DSPU M1
DSPU M2
BPos Q9
BPos Q7
DSPU M1
DSPU M2
SR4
Bpos – Beam Position ModuleDSPU – Digital Signal Processing Unit
ADT Frequency response Power amplifiers, 1st order low pass, -3 dB @ 1
MHz Power amplifier phase response compensated by
digital filter
kick @ 10 MHz,10% strength left
Frequency domain measurements February 2012 B. Lojko.
Step response measurements 19.9.2012 D.Valuch, G.Kotzian
Impulse response Phase compensation makes the impulse response
symmetric and removes the exponential tail
Frequency response/damping time Consequence: “crosstalk” and different damping
time for different bunches within the train
12b already
circulating
New injection 144b
Dam
ping
tim
e fo
r ind
ivid
ual
bunc
hes w
ithin
the
144b
trai
n.
Inje
ctio
n os
cilla
tion
fill 2
676,
2nd
in
ject
ion
Frequency response/damping time Damping of individual bunches in case they
become unstable still follows the system frequency response: -3 dB point at 1 MHz i.e. 10% strength available at 10MHz if two adjacent
bunches oscillate in anti-phase (50ns beam)
Damping of single bunch instabilities Impulse response of damper spreads oscillation to
adjacent bunches
Simulation with simplified damper model (no delays, ideal system) A train of 48 bunches, 25ns bunch spacing Random initial conditions in amplitude and phase for
all bunches 1 bunch is unstable (rise time of 300 turns)
Stan
dard
ban
dwid
thHi
gh b
andw
idth
A train of 48 bunches, 25ns, random initial conditions for all bunches, 1 bunch is unstable
Enhancement of the frequency response The full power is needed only for efficient injection
oscillation damping, damper uses <1% of its strength otherwise
Small signal response could be enhanced by drive signal pre-distortion
Once commissioned, enhanced bandwidth should provide faster damping of high frequency modes “Ideal damper” – could treat each bunch individually Potential drawback – increase of noise injected
through the damper System more sensitive to precise setting up and
drifts
Enhancement of the frequency response Drive signal pre-distortion enhances the frequency
response up to 25 MHz (with symmetric roll off)
15
25
Enhancement of the frequency response Symmetric roll off in frequency domain will
eliminate the bunch by bunch crosstalk
Enhancement of the frequency response Measured enhanced frequency response reaches
beyond 20 MHz Bunch by bunch damper!
12dB needs to be compen-sated for same damping time
Enhancement of the frequency response Measured enhanced frequency response reaches
beyond 20 MHz Bunch by bunch damper!
Commissioning and operation The high bandwidth operation was commissioned
for 25ns operation, including proper setting up with beam
Settings for 50ns operation were not yet optimized need 1-2 hours at injection to fine adjust the one-
turn delay measure the damping time quantify the noise behaviour w.r.t. standard
operation
Preliminary results are very encouraging Demonstrated increase of bandwidth while
maintaining the high gain
Operational experience with 50ns beam High BW operation was already tested through the
cycle
Since fill 3212: High BW during the squeeze up to collision than back to “standard” bandwidth
Normal ADT High BW ADT (ramp till physics)
High BW ADT (ramp till collision process)
High BW ADT (squeeze till collision process
3203, 3207 3200, 3201, 3204 3208, 3209 Since 3210
3110 3130 3150 3170 3190 3210 32300.002.004.006.008.00
10.0012.00
Chart Title
High BW ADT during stable beams
Plot
and
tabl
e G.
Ard
uini
Operational experience with 50ns beam High BW operation was already tested through the
cycle
Since fill 3212: High BW during the squeeze up to collision than back to “standard” bandwidth
Normal ADT High BW ADT (ramp till physics)
High BW ADT (ramp till collision process)
High BW ADT (squeeze till collision process
3203, 3207 3200, 3201, 3204 3208, 3209 Since 3210
3110 3130 3150 3170 3190 3210 32300.002.004.006.008.00
10.0012.00
Chart Title
High BW ADT during stable beams
Plot
and
tabl
e G.
Ard
uini
More benchmarking
required to understand
and optimize the
performance
Summary For operational modes where the full kick strength is
not needed the ADT frequency response could be enhanced to provide “bunch-by-bunch” damper while keeping the gain high
Method proved to be valid, already part of the LHC cycle (High BW during the squeeze up to collision). Implemented as a sequencer task
Enhanced response could have a potential drawback – increase of noise injected through the damper needs to be studied
Wide bandwidth system is less tolerant to imperfections in settings (such as the 1-turn delay)
Input for our LS1 upgrade activities: Noise reduction is important for high BW operation Precise control of frequency response up to 25 MHz