W. Hofle / March 5, 2008 Extended LTC meeting 1/22
Acknowledgements:P. Baudrenghien, A. Butterworth, E. Ciapala,
B. Goddard, A. Koschik,F. Killing, G. Kotzian, R. Louwerse,
E. Metral E. Montesinos, V. Rossi, D. Valuch,
V. Zhabitsky (for JINR / Dubna collaboration)
Wolfgang Hofle
CERN AB/RF/FB
LHC Transverse Damper Beam Commissioning
W. Hofle / March 5, 2008 Extended LTC meeting 2/22
Outline
LHC Transverse Damper Beam Commissioning
Overview of System, do we need the damper on day ONE ?
Readiness for beam commissioning stages of the commissioning with beam
Summary
W. Hofle / March 5, 2008 Extended LTC meeting 3/22
Pick-up 1
Kicker
Signal processing
beam
signal
Pick-up 2
gain g
Need real-time digitalsignal processing
Match delays: t signal = t beam + MT 0
T0 : beam revolution time
M=1: very common -> “One -Turn-Delay” feedbackBut M>1 also possible
phase and delay adjustments
• feedback: curing transverse coupled bunch instabilities
• excitation: of transverse oscillations for beam measurements & other applications
• damping: of transverse injection oscillations
Transverse multi bunch feedback principle
W. Hofle / March 5, 2008 Extended LTC meeting 4/22
feedback: curing transverse coupled bunch instabilities, necessary at start of phase B
-> will become important as intensity is raised, scrubbing in regime with e-cloud present etc.
present estimate (E. Metral, PAC2007, WEOAC03):7 TeV half nominal intensity @ nominal scheme (2808 bunches) requires feedback450 GeV ~ 1/10 of nominal stable, i.e. factor ~2 margin for 156x156 schemephase A -> damper on only for injection dampingphase B -> beam unstable w/o damper !
excitation: damper can be easily used to do a transverse excitation of the beam
-> requested for the continuous tune measurement -> can be used to kick out unwanted beam (“abort gap cleaning”) etc.
AB-RF-FB provides an input for the BI tune measurement, ready today
damping: transverse injection oscillations
-> filamentation of injection error will lead to larger transverse emittance w/o dampereven for perfect steering there are errors from the injection kicker ripple (see next slides)
Why do we need Transverse damper on day ONE ?
W. Hofle / March 5, 2008 Extended LTC meeting 5/22
where dec de-coherence time in absence of instability and active dampinginst instability rise-timead active damping time as it would follow from damper gain without having any instability and without de-coherence phenomena
and assuming dec >> nst > ad the emittance increase becomes
without damper a steering / kick error of x in position and x’ in angle will lead to a relative emittance increase of
Introducing the effective (overall) damping rate
Reminder: Emittance increase by filamentation
222
2
00
)('
)(
2
1 xx
x
instaddec
1111
2
inst
dec
ad
dec22
22
00
1)(
')(
2
1
x
xx
typically dec > 10 x ad hence emittance increase reduced by factor >100 !-> justifies having damper from start
blow-upreduction factor
W. Hofle / March 5, 2008 Extended LTC meeting 6/23
Injection kicker pulse with ripple (prototype)
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-0.2
0
0.2
0.4
0.6
0.8
1
1.2Normalized measured kicker pulse
Time in revolutions
Inje
ctio
n K
icke
r st
reng
th in
%
kicker ripplefinite rise time
Scanning with single bunch suggested in phase A4
to verify effective kick seen by beam
(see talk by V. Kain)
Bunch positions for 43 bunch filling pattern
243/3564=0.0682 or 6075 ns
W. Hofle / March 5, 2008 Extended LTC meeting 7/23
Results of a simulation (kicker prototype waveform)
550 600 650 700 750 800 850 900 950 10003
3.5
4
4.5
5
5.5
6
bunch number
beam
em
ittan
ce
Beam emittance after 2000 turns, instabilities OFF, Feedback OFF/ON
Feedback OFF
Feedback ON
emittance blowup in previous SPS batch
beam blowup due to injection kicker imperfections and TFB OFF (red)
beam emittance with TFB ON (black)within design parameters (3.75um)
G. Kotzian, simulations ongoing, new kicker waveforms from AB-BT for actual kickers need to be included
[nor
mal
ised
rm
s in
m
]
bunch positions for 43 bunch filling pattern (4 bunches injected)
batch length 243x25 ns, e.g. pos. 650->893
batch length for 156 bunch scheme is 315 bunch positions (16 bunches), longer than nominal batch of 25 ns operation
(311 positions)
W. Hofle / March 5, 2008 Extended LTC meeting 8/22
LHC Commissioning phase A: 1 to 156 bunches
1) Single bunch transferred from SPS to LHC:bunch can be placed on flat part of injection kickerno issue with ripple, just question of reproducibility shot-to-shot
2) 43 bunch scheme: batch transferred from SPS to LHC: 4x(b+80e) -> length is (4x81-80-1) x 25 ns = 243 x 25 ns = 6075 nsstill some margin to place batch, 3 of the 4 bunches look OK, 1 bunch requires damper
3) 156 bunch scheme: batch transferred from SPS to LHC: 4x(4x(b+20e)) -> length is (4x4x21-20-1) x 25 ns = 315 x 25 ns = 7875 nsoccupies full length of kicker pulse -> damper required to preserve emittancesome margin due to adjustable kicker pulse length, but fall- (and rise- ?) time issue
Reminder: filling patterns, kicker ripple and transverse feedback
compare with nominal scheme
2808 bunch scheme: batch transferred from SPS to LHC: 4x(72b+8e) -> length is (4x80-8-1) x 25 ns = 311 x 25 ns = 7775 ns
W. Hofle / March 5, 2008 Extended LTC meeting 9/22
Outline
LHC Transverse Damper Beam Commissioning
Overview of System, why do we need the damper on day ONE ?
Readiness for beam commissioning stages of the commissioning with beam
Summary
W. Hofle / March 5, 2008 Extended LTC meeting 10/22
The LHC Transverse Damping System (high power part)
20 kickers 40 wideband amplifiers, i.e. 40 tetrodes
(RS2048 CJC, 30 kW) 20 amplifier cases
Damper system
Beam 1
IP4
damperkicker
Beam 2
WidebandamplifierUnit
H H V V
H H H HV VV V
H H H H V V V V
Module
Installed, hardware commissioning under way
calibrations and phasing still need to be completed,
quite some work for AB/RF group
Status of installation and hardware commissioning: see talk by Olivier Brunner on Tuesday
W. Hofle / March 5, 2008 Extended LTC meeting 11/22
Overview of one damper system (there are four, one per beam and plane)
pick-ups (tunnel)
kickers and power amplifiers (tunnel)
low levelelectronics(surface)
controls amplification and interlocking (UX45, underground)
phase A2: put excitationon beam to verify kick strength
phase A
1, A2
does not re
quire ca
pture
signal le
vels,
phasing (d
elay)
feedback loop start commissioning in phase A3close loop in phase A4:requires RF capture
W. Hofle / March 5, 2008 Extended LTC meeting 12/22
Beam Commissioning Phase A1 and A2First turn and circulating beam(can start before RF capture)
Observation of beam at damper pick-ups Q7, Q9 and delay equalization:
Verification of signal levels (sum signals)Verification of signal levels versus transverse bunch position (calibrate using orbit system)Delay equalization of damper pick-up signals from Q7 and Q9 (local adjustment in SR4)
Excite transverse oscillations (phase A2) in order to check available damper kick strength[calibration of kick]
Most activities do not require dedicated beam time, they can be done in the shadow of other users / MDs, except for excitation experiments -> suggest 2x4 hours dedicated time for this
As beam instrumentation becomes available (position & intensity, fast BCT), compare damper signals with standard BPM readings, do calibrations
work will be done by RF group, some help required from OP & BI for instruments (standard BPMs, bunch-to-bunch intensity)
Q9
ADC
FPGA
S
...
S
...
SERDES
S
...
S
...
Q7
ADC
SERDES
SERDES
SERDES
SERDES
FPGA
Xilinx Altera
Q
I
fc = 40 MHz
fc = 40 MHz
ADC
ADCQ
I
fc = 40 MHz
fc = 40 MHz
DAC
ADC
FPGA
SERDES
ADC
SERDES
SERDES
SERDES
SERDES
FPGA
Xilinx Altera
Q
I
fc = 40 MHz
fc = 40 MHz
ADC
ADCQ
I
fc = 40 MHz
fc = 40 MHz
DAC
ΔxQ7
ΔxQ7
ΔxQ9
ΔxQ9
Δx
Δx
400.8 MHz
180º
180º
Coaxial Transmission LinesAndrew HELIAX
7/8" Dielectric Foam
length ~ 650mlength ~ 450m
Macom H-92-2000 MHz
Comb Filter400.8 MHz
W. Hofle / March 5, 2008 Extended LTC meeting 13/22
beam position VME module signal processing VME moduleDSPU (“Damper Loop”)based on 1T-FB module
Overview of signal processing
prototypes exist, firmware (FPGA) being developednot static, i.e. evolution of firmware to incorporate additional functionalities, upgrades, optimizations
commission in A3 commission in A4
intensity nomalised bunch positiondigitised and synchronised (two pick-ups)
W. Hofle / March 5, 2008 Extended LTC meeting 14/22
Beam Commissioning Phase A3(after RF capture)
Commissioning RF front-end (beam position module) of damper and check optics:
Verify RF signals from RFLLCommission analog front-endCommission digitization and frev tagging of bunch
Check phase advance Q7->Q9->damper (both beams and planes)Verify beta functions at Q7, Q9, dampers
Setting-up requires stable RF conditions, so no parallel RF MDsassume 4 hours per beam and plane dedicated beam time
work to be done by RF group, some help from OP and ABP required for optics checkadditionally 1 shift for optics checks in IR4 per beam ?
W. Hofle / March 5, 2008 Extended LTC meeting 15/22
LHC ADT Loop – Digital Processing Module
Serdes Chip
Sync ScalingNotchFilter
PhaseShifter
Delay (à 1 Turn)incl. Fine Delay
Serdes Chip
Sync ScalingNotchFilter
PhaseShifter
Observation Perturbation
Interpolation80 MHz
DAC
(Δ/Σ)PU 1
Gigabit Serial Link
(Δ/Σ)PU 2
fREV(PU1)
FIR Phase Comp.
ON/OFF
VME, Timing
a1 ON/OFF
ON/OFF
Delay
Switch/Changea2
b2
Factor 0.5÷1
Factor 0.5÷1
VME, Timing
Gain Function via reference voltage
~ 20 dB
ON/OFF
if board works with 80 MHz !
Switch/Change b1
ON/OFF
Gigabit Serial Link
Function Delay
Function Phase
φ
b2 = sin(φ)
b1 = cos(φ)not exact,
calculation in VME
fREV
fREV(PU1)
+1/-1
Gain Equalizationdynamically changing FIR Low Pass
~20 MHz
signal processing VME module (DSPU, “damper loop”) based on 1T-FB module
Input:nomalised bunch positionsynchronised (two pick-ups)
commission in A4
scaling: -functionsPhase shifter optionalnot needed on day 1
FGC control “phase”, two functions
FGC control “delay”
FGC control “gain”
Built in NWA for setting-upor use of external NWAFor open loop transfer function measurement
Functionality on built into VME module Damper DSPU (based on 1T-FB module)
W. Hofle / March 5, 2008 Extended LTC meeting 16/22
We need to adjust the phase in the feedback by combining the signal from the two pick-ups in the correct way with coefficients b1 and b2, coefficient C can be chosen C=1, rendering gain independent of phase setting-up
Adjustment of Phase
mkfQkm 3 Q
)2/sin(
)sin(
)2/cos(
)cos(
2
1 QkmQkm1
C
b
Pick-up 1 Pick-up 2 Kicker module
m=2-1
k
beam
)2/sin(
)sin(
)2/cos(
)cos(
2
1 QkmQkm2
C
b
kicker
pick-up 1 (1)
pick-up 2 (2)
target phase (kicker + 1.5 x Qf)
m
coefficients for pick-up mixing b1, b2 can be calculated from opticsin practice adjustment through open loop transfer function measurement SPS damper: open loop
transfer function measurement
W. Hofle / March 5, 2008 Extended LTC meeting 17/22
Beam Commissioning Phase A4[450 GeV]
Commissioning Damper Loop (450 GeV):
Measure de-coherence time with damper off, non-linearities corrected
Measure open loop transfer function (mainly at ~low frequency)
Make necessary adjustments (gain, phase, delay)Close damper loopScan gain, phase, delay and measure damping time and stability limits
for initial setting-up with one bunch assume 4 hours per beam and plane; steps to be repeated for multi-bunch operation and when intensity is increased
Commission beam blow-up facility (tailoring of transverse emittance)[to produce nominal emittance at lower intensity, could also be done in SPS]
Measure beam lifetime as function of damper gain
scan injection kicker pulse by moving bunch
initial setting-up done by RF group, some help from OP and ABP … welcome for the specialized MDs listed above, add some MD time for the specialized MDs
W. Hofle / March 5, 2008 Extended LTC meeting 18/22
Beam Commissioning Phase A6[first 2 minutes of ramp]
Abort gap cleaning and machine protection (start in A5, B. Goddard dixit):
Check machine protection, are we protected if damper wrongly set-up, meaning:one should check with a low intensity bunch and the damper in anti-damping, if the BLMs register losses correctly and in time in order to prevent damage in case this happens with a high intensity beam
dedicated MD time 2x4 hours, in collaboration with OP, BI, machine protection team
Try out abort gap cleaning techniques (this requires the collimators)
Optimize abort gap cleaning programs
to start with assume a dedicated MD time of 2x4 hours to set-up initial abort gap cleaning in collaboration with OP, ABP, BT, collimator team
W. Hofle / March 5, 2008 Extended LTC meeting 19/22
Beam Commissioning Phase A7[ramp]
Commissioning Damper Loop (7 TeV):
Measure open loop transfer function (low frequency)Make necessary adjustments (gain, phase, delay)Close damper loopMeasure open and closed loop transfer functions
Check abort gap cleaning at higher energies (this requires collimators)
Would be useful to have the orbit feedback in order to optimize damper gain before digitization
Count MD time in number of successful ramps ? Plan on 3 ramps for above program per beam ?
Collaboration with BI, BT, ABP, collimator team …
Principal of abort gap cleaning using the transverse damper
cleaning pulse (gate) centered in abort gapmodulation of pulse with betatron frequencyfull amplitude up to ~ 1 MHz possible
LHC nominal bunch pattern 2808 bunches
1st injected batch abort gap (119 missing bunches)
amplitude can be modulated with any frequency between 1 kHz and 20 MHz; gate feedback action off during gap
resonant excitation of transverse oscillationscapture of beam by aperture limit(LHC: by collimators)
Extended LTC meetingW. Hofle / March 5, 2008 20/22
0 0.5 1 1.5 2 2.5
x 104
0
10
20
30
40
50
60
70
80
90
100
Position s [m]
NLo
st [
%]
Loss Pattern
Simulation results for the LHC Beam 1 (450 GeV/c)LHC Modelnominalwith multi-poles+ correction
resonant excitation with damper
primary collimatorsbetatron cleaningTCP.D6L7.B1TCP.C6L7.B1TCP.B6L7.B1
primary collimatorsmomentum cleaningTCP.6L3.B1
Simulations (MAD) A. Koschik
abort gap cleaning in LHC using transverse damper
Extended LTC meetingW. Hofle / March 5, 2008 21/22
compare with MDsas early as possible
W. Hofle / March 5, 2008 Extended LTC meeting 22/22
Damper essential to avoid increase of transverse emittance already in phase A (1-156 bunches)(shot-to-shot reproducibility with single bunch, kicker ripple effect with 43 to 156 bunches
Damper commissioning can start from phase A1 with observation of signals
Between now and first beam a lot of hardware commissioning, delay adjustments, calibrationsin order to minimize time needed to get damper operational with beam
Dedicated MD time required from phase A3 onwards (after RF capture) to set-up the system
Injection damping available from phase A4 onwards
Commissioning of abort gap cleaning from phase A5-A6 onwards (first 2 minutes of ramp)
Commissioning damper during ramp in A7 to prepare for higher intensity of phase BInstability threshold expected to be hit in phase B
Summary