1. Transverse Feedback System (LHC Damper)
W. Hofle CERN AB/RF
Transverse Feedback System (LHC Damper)
presented by
Wolfgang Hofle CERN AB/RF/FB
Acknowledgements:
P. Baudrenghien, A. Blas, T. Bohl, A. Findlay, G. Kotzian,
R. Louwerse, T. Linnecar, E. Montesinos, V. Rossi, D. Valuch
& JINR, Dubna, Russia, V. Zhabitskiy
20 October 2006
LHC-LUMI-06 Workshop - Valencia

2. Transverse Feedback System (LHC Damper)
W. Hofle CERN AB/RF
Transverse Feedback System (LHC Damper)
Outline
Overview: Transverse feedback systems (dampers) at CERN’s synchrotrons (PS Booster, AD, LEIR, PS, SPS and LHC); example: SPS damper; RF group is responsible for all these systems
Functional Specification and overview of LHC Damper System
Expected noise performance for LHC transverse feedback
Possible upgrades of LHC damper system
Upgrades and consolidation of injector transverse feedbacks, including new PS2
Conclusions
20 October 2006
LHC-LUMI-06 Workshop - Valencia

3. Transverse multi bunch feedback
W. Hofle CERN AB/RF
LHC Transverse Feedback (“LHC Damper”)
Transverse multi bunch feedback
Kicker
Need real-time digital
signal processing
Match delays:
t signal = t beam + MT 0
T0 : beam revolution time
M=1: very common ->
“One -Turn-Delay” feedback
But M>1 also possible
phase and delay adjustments
t signal
Signal
processing
gain g
t beam D
Pick-up 1
Pick-up 2
damping: of transverse injection oscillations
feedback: curing transverse coupled bunch instabilities
excitation: of transverse oscillations for beam measurements & other applications
20 October 2006
LHC-LUMI-06 Workshop - Valencia

4. Transverse Feedback Systems in Synchrotrons at CERN
W. Hofle CERN AB/RF
LHC Transverse Damper
Transverse Feedback Systems in Synchrotrons at CERN
Currently installed transverse feedback systems in CERN Synchrotrons
Accelerator
Digital / analogue processing
Power / kicker / bandwidth
Usage in operation
PS Booster (protons)
50 MeV – 1.4 GeV kin. E.
multi turn injection from Linac 2
analogue beam offset signal suppression, analogue delay (cables & switches)
100 W, 50 W stripline
Limited to 13 MHz in operation
But built for 100 MHz bandwidth, baseband
H-plane: used and required
V-plane: beam stable w/o FB
AD (anti-proton decelerator)
3.57 GeV – 0.1 GeV
Copy of booster system
100 MHz bandwidth baseband
used only for excitation purposes
SPS (protons, ions)
(14 – 450) GeV/c protons FT
(26 – 450) GeV/c LHC beam
digital notch filter and 1T-delay (Altera FPGA, 80 MHz clock)
commissioned in 2000/2001
tetrode amplifiers with two
30 kW tetrodes in push-pull directly coupled to a kicker (base band); feedback bandwidth
~10 kHz to 20 MHz
H-plane: used in operation
V-plane: used in operation
used and required for operation
above 5x1012 protons
(max ~5.5x1013 ppp accelerated)
20 October 2006
LHC-LUMI-06 Workshop - Valencia

5. Transverse Feedback Systems in Synchrotrons at CERN
W. Hofle CERN AB/RF
LHC Transverse Damper
Transverse Feedback Systems in Synchrotrons at CERN
Current transverse feedback system projects at CERN
Accelerator
Digital / analogue processing
Power / kicker / bandwidth
Planned commissioning
and usage
LEIR ( ions: Pb54+ )
4.2 MeV/u – 72 MeV/u
copy of PS Booster System
New: remote control of pick-up vector sum
100 W, 50 W stripline
2005
damping during e-cooling may be necessary
PS (protons, ions)
1.4 GeV – 25 GeV (kinetic E)
synergy with LHC Damper
3 kW pulsed, 200 W CW, upgrade towards more CW power possible (loads); 112 W stripline (0.9 m length), planned with ~30 MHz bandwidth in baseband, lower cut-off ~50 kHz
upgrade possible with magnetic kicker (0.9 m length, 12.5 W, but bandwidth considered too limited); H-plane magnetic kicker built already, but BW limited
2006
injection damping and feedback
will be beneficial in particular for high intensity CNGS beams and LHC beams. Currently horizontal instabilities are cured by introducing coupling to the vertical plane which constrains the tunes
LHC (protons, ions)
protons: 450 GeV/c – 7 TeV/c
digital notch filter and 1T-delay,
built-in diagnostics
14 bit ADC/DAC
Altera FPGA, 40 MHz clock
new development in progress
tetrode amplifiers with two
30 kW tetrodes in push-pull directly coupled to kicker (base band) similar to SPS system
3 kHz -> 20 MHz
2007
injection damping
feedback loop closed during ramp
switch off during physics?
20 October 2006
LHC-LUMI-06 Workshop - Valencia

6. LHC-LUMI-06 Workshop - Valencia
W. Hofle CERN AB/RF
LHC Transverse Feedback (“LHC Damper”)
Example SPS (CNGS type beam, 1 batch, 1013 protons):
3 ms growth rate
0.5 ms damping time
injection with damper off
damper being switched on 7 ms (300 turns) after injection
20 October 2006
LHC-LUMI-06 Workshop - Valencia

7. LHC-LUMI-06 Workshop - Valencia
W. Hofle CERN AB/RF
LHC Transverse Feedback (“LHC Damper”)
Example SPS (LHC beam, 48 / 72 bunches spaced 25 ns)
injection with damper off (~4x1012 p total in 48 bunches)
injection with damper on (~6x1012 p total in 72 bunches)
20 October 2006
LHC-LUMI-06 Workshop - Valencia

8. LHC-LUMI-06 Workshop - Valencia
W. Hofle CERN AB/RF
LHC Transverse Feedback (“LHC Damper”)
LHC Damper is being installed in point 4 of LHC along with the accelerating 400 MHz RF system
20 October 2006
LHC-LUMI-06 Workshop - Valencia

9. Nominal LHC filling pattern: 2808 bunches
W. Hofle CERN AB/RF
Transverse Feedback (“LHC Damper”)
Nominal LHC filling pattern: 2808 bunches
Basic bunch spacing is 25 ns (every 10th bucket of 400 MHz RF)
Running-in with 75 ns bunch spacing possible
Trains of 72 bunches created in PS accelerator
Up to 4x72 bunches accelerated in SPS and injected into LHC
1 ms gap between batches injected into LHC
20 October 2006
LHC-LUMI-06 Workshop - Valencia

10. Performance specification (1) (LHC Design Report)
W. Hofle CERN AB/RF
LHC Transverse Feedback (“LHC Damper”)
Performance specification (1) (LHC Design Report)
Beam parameters and requirements for nominal intensity:
Injection beam momentum 450 GeV/c
Static injection errors mm (at bmax=183 m)
ripple (up to 1 MHz) mm (at bmax=183 m)
resistive wall growth time ms
assumed de-coherence time 68 ms
tolerable emittance growth 2.5 %
Overall damping time ms (46 turns)
bunch spacing 25 ns
minimum gap between batches 995 ns
lowest betatron frequency > 2 kHz
highest frequency to damp 20 MHz
20 October 2006
LHC-LUMI-06 Workshop - Valencia

11. LHC-LUMI-06 Workshop - Valencia
W. Hofle CERN AB/RF
LHC Transverse Feedback (“LHC Damper”)
Performance specification (2)
Equipment performance specification:
choice: “electrostatic kickers” (“base-band”)
aperture mm
kickers per beam and plane 4
length per kicker m
nominal voltage up to 1 MHz at b=100m +/- 7.5 kV
kick per turn at 450 GeV/c 2 mrad
rise-time 10-90%, DV= +/- 7.5 kV 350 ns
rise-time 1-99%, DV= +/- 7.5 kV 720 ns
must provide sufficient gain from 1 kHz to 20 MHz
noise must be less than quantization noise due to 10 bit / 2s
rise time fast enough for gap of 38 missing bunches
20 October 2006
LHC-LUMI-06 Workshop - Valencia

12. The LHC Transverse Damping System (high power part)
W. Hofle CERN AB/RF
Transverse Feedback (“LHC Damper”)
The LHC Transverse Damping System (high power part)
Damper system
IP4 H V
Beam 1
Beam 2 R1
Engagements of collaboration V H
“Electrostatic”
kicker
Wideband
amplifier
Unit
20 electrostatic kickers
40 wideband amplifiers,
i.e. 40 tetrodes
(RS2048 CJC, 30 kW)
20 amplifier cases + H V
Spare units
Module
20 October 2006
LHC-LUMI-06 Workshop - Valencia

13. LHC optics at injection in IR4 (beams do not cross!)
W. Hofle CERN AB/RF
LHC Transverse Damper
LHC optics at injection in IR4 (beams do not cross!)
Beam 1
high horizontal beta left of IP4
high vertical beta right of IP4
Beam 2
high horizontal beta right of IP4
high vertical beta left of IP4
Optics 6.4, sorry, 6.5 not very different for ADT)
20 October 2006
LHC-LUMI-06 Workshop - Valencia

14. Achievable performance (“baseline”) without upgrade
W. Hofle CERN AB/RF
LHC Transverse Damper
Achievable performance (“baseline”) without upgrade
LHCADT performance in LHC optics version compared to original assumptions (at 450 GeV/c),
assuming 7.5 kV maximum kick voltage
b=100 m performance
Optics performance
Kick per turn in s
Kick per turn in b in m
ADTH beam 1
0.2 s
0.271 s at b=183 m
ADTH beam 2
0.274 s at b=189 m
ADTV beam 1
0.301 s at b=227 m
ADTV beam 2
0.331 s at b=275 m
Estimate of maximum capabilities (usage as beam exciter, abort gap cleaning etc.), assumes optics 6.5
as in table above, 450 GeV/c and 7 TeV and running with up to ~15 kV DC for tetrode anode voltage (at 1 MHz 1.4x nominal)
100 kHz
1 MHz
10 MHz
20 MHz
ADTH
0.42 s / 0.11 s
0.38 s / 0.10 s
0.12 s / 0.03 s
0.044 s / s
ADTV
0.46 s / 0.12 s
0.42 s / 0.12 s
0.14 s / 0.04 s
0.049 s / s
20 October 2006
LHC-LUMI-06 Workshop - Valencia

15. Physical layout in point 4 underground LHC
W. Hofle CERN AB/RF
LHC Transverse Damper
Physical layout in point 4 underground LHC
ADT racks
(driver amplifiers,
PLC controls, fast interlocks)
ADT (4 modules)
left of IP4
+ space for 2 more modules (upgrade)
ADT (4 modules)
right of IP4
+ space for 2 more modules (upgrade)
Beam 2
Beam 1
20 October 2006
LHC-LUMI-06 Workshop - Valencia

16. Overview of one Damper system
W. Hofle CERN AB/RF
LHC Transverse Damper
Overview of one Damper system
Most of electronics on surface -> easy access !
20 October 2006
LHC-LUMI-06 Workshop - Valencia

17. LHC ADT Low level electronics
W. Hofle CERN AB/RF
Transverse Feedback (“LHC Damper”)
LHC ADT Low level electronics
System will be based on experience gained with SPS Damper
Two coupler type pick-ups with betatron phase advance of ~90 degrees will be used (BPMC/BPMCA, provided by the BDI group and integrated in quad)
Spectrum repeats every 40 MHz (25 ns bunch spacing) -> analogue down conversion with a multiple of 40 MHz to baseband , LO of 400 MHz chosen
One of the horizontal pick-ups is installed at ~zero dispersion and it will be possible to use this pick-up and a Hilbert transformer (FIR filter) for the phase adjustment if wanted; Hilbert filter tested in SPS but not used in operation (reduced phase stability margin at very high gain)
FPGA technology for implementing most of the functions digitally (notch filter, fine delay adjustment, betatron phase adjustment by two pick-ups or Hilbert filter and single pick-up use)
20 October 2006
LHC-LUMI-06 Workshop - Valencia

18. LHC-LUMI-06 Workshop - Valencia
W. Hofle CERN AB/RF
Transverse Feedback (“LHC Damper”)
Coupler type pick-ups
Length of electrodes 150 mm
Frequency domain: maximum of transfer impedance MHz
Peak voltage for ultimate collision: ~140 V -> very large
Sensitivity: mW/mm => 9.6 V/mm peak in time domain after ideal hybrid
install hybrid on surface (12 dB cable attenuation will avoid saturation) -> peak voltage reduced to ~25 V, OK for wideband hybrid H9
Hybrid: 2 dB (+3 dB -1 dB), estimate: cable and bandpass filter generating) 8 periods of 400 MHz
after filtering: ultimate beam: ~ MHz; nominal 0.26 V/mm (duty cycle 0.8)
20 October 2006
LHC-LUMI-06 Workshop - Valencia

19. Signal Levels from pick-ups
W. Hofle CERN AB/RF
LHC Transverse Damper
Signal Levels from pick-ups
LHC Beam Parameters
Injection
Collision
Beam Energy
450 GeV
7000 GeV g
479.6
7461
RMS bunch length in cm
11.24
7.55
FREV in kHz
11.245
FRF in MHz (h=35640) ^
Range of intensities for LHC beam and expected pick-up signal levels (ZT = 3.23 W; ZT (w) = 6.46 W)
Pilot
Nominal beam
Ultimate beam
Particles per bunch
5x109
1.15x1011
1.7x1011
Number of bunches 1
2808
Circulating current (DC) in A
9 x 10-6
0.582
0.860
Bunch peak injection in A
0.9
19.6
29.0
Bunch peak collision in A
1.3
29.2
43.1
Peak Voltage from inj. in V
2.8
63.4
93.6
Peak Voltage from coll. in V
4.1
94.3
139.4
20 October 2006
LHC-LUMI-06 Workshop - Valencia

20. LHC-LUMI-06 Workshop - Valencia
W. Hofle CERN AB/RF
Transverse Feedback (“LHC Damper”)
Performance with respect to noise: aim at a better than 1 mm resolution
Assume bunches oscillate with 1 mm rms (bunch-to-bunch)
Power available from MHz (+/- 20 MHz): 433 pW (nominal beam)
Thermal noise at 290 K: kBT = 4x10-21 W/Hz; in 40 MHz BW: 0.16 pW
Digitization with 14 bit: discrete levels, assume 1 mm -> 4 steps then 14 bit are sufficient to cover +/- 2 mm
Margin with respect to thermal noise: To use this margin we need to limit orbit variations at the pick-ups to less than +/- 2 mm.
20 October 2006
LHC-LUMI-06 Workshop - Valencia

21. LHC ADT upgrade possibilities (1)
W. Hofle CERN AB/RF
Transverse Feedback (“LHC Damper”)
LHC ADT upgrade possibilities (1)
In case of lack of kick strength
Push system to its limits +40% feasible (pulsed mode, reliability?)
Increase of beta functions at kickers (to be checked), scales with b1/2
Additional kickers (expensive) but space is reserved (4 MCHF for +50%)
In case of large instability growth limit of bandwidth (20 MHz)
New power amplifiers with increased bandwidth, possibly dedicated damping of modes which are unstable
New kickers (matched strip-line) and power amplifiers -> expensive; signal processing electronics can be re-used
20 October 2006
LHC-LUMI-06 Workshop - Valencia

22. LHC ADT Upgrade possibilities (2)
W. Hofle CERN AB/RF
Transverse Feedback (“LHC Damper”)
LHC ADT Upgrade possibilities (2)
In case of insufficient Signal-to-Noise ratio (S/N)
Digitization of pick-up signals underground -> save 600 m of cable -> gain 12 dB (factor 4), but need to develop hybrids, filters and electronics to process large amplitude signals; alternatively use 1 5/8” cable: gain ~6 dB (factor 2)
If limited by interference & noise on link from surface to tunnel (3 kHz- 20 MHz) -> built digital link and have Digital-to-Analogue conversion as close as possible to amplifiers (possibly find new space for driver amplifiers that are now in UX45)
Increase beta functions at pick-ups (not very likely but worth a thought since otherwise no additional cost); in particular vertical beta function at BPMC.7L4.B2 for beam 2 somewhat low in optics version 6.5 (=87 m)
Average in the signal processing over several turns, i.e. 9 turns, gain of a factor 3 in S/N if noise turn-by-turn uncorrelated - more turns not feasible due to limited signal processing power and sensitivity to tune.
Use additional pick-ups; strip-line pick-ups at Q8 and Q10 may be available; gain in S/N 50%, additional cables and electronics must be installed; further improvement by installing additional pick-ups, spread around the ring?
20 October 2006
LHC-LUMI-06 Workshop - Valencia

23. Strategy for transverse feedback projects and upgrades in injectors
W. Hofle CERN AB/RF
Transverse Feedback (“LHC Damper”)
Strategy for transverse feedback projects and upgrades in injectors
Goal: Move towards common hardware for signal processing for all dampers
Currently strong push to commission PS transverse feedback system -> in work
Concentrate resources on LHC transverse feedback commissioning in
Consolidate Booster/AD/LEIR Systems from 2008 onwards; use of LHC signal processing hardware to be checked (bandwidth required, large frequency swing!)
Retrofit LHC hardware to SPS in 2009; possibly install third horizontal system to cure ongoing e-cloud problem (horizontal systems are at limit); SPS damper needs upgrade to go to ultimate
Use as much as possible the experience with the new PS transverse feedback system (to be gained during next years) when defining system needed for the PS2
Keep experience in operation and electronics development close together (same team) to be able to have short development cycles
20 October 2006
LHC-LUMI-06 Workshop - Valencia

24. Potential benefits of injector transverse feedbacks upgrades for LHC
W. Hofle CERN AB/RF
Transverse Feedback (“LHC Damper”)
Potential benefits of injector transverse feedbacks upgrades for LHC
Upgrade a must for SPS [unless one changes vacuum chamber]: resistive wall and electron cloud instability; upgrade required to go to the ultimate beam intensity; damper control upgrade to LHC standards
It is likely that we need in the PS the transverse feedback working for ultimate beam
Booster requires in the horizontal plane a transverse feedback system for stabilization, future upgrade required due to obsolete hardware -> assure future reliability
20 October 2006
LHC-LUMI-06 Workshop - Valencia

25. LHC-LUMI-06 Workshop - Valencia
W. Hofle CERN AB/RF
Transverse Feedback (“LHC Damper”)
Conclusions
Before considering to implement upgrades in injectors, finish LHC transverse feedback first
Better than 1 mm resolution seems achievable for LHC transverse feedback
Upgrade possibilities for LHC transverse feedback exist (kick strength, bandwidth, noise performance
Upgrade and consolidation needs in injectors for ultimate beam need attention
Build PS2 with transverse feedback from start
20 October 2006
LHC-LUMI-06 Workshop - Valencia