Acknowledgements: P. Baudrenghien, A. Butterworth, E. Ciapala, B. Goddard, A. Koschik,

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


Outline


Overview of System, do we need the damper on day ONE ?

Readiness for beam commissioning stages of the commissioning with beam

Summary


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


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 ?


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


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


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)


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


Outline


Overview of System, why do we need the damper on day ONE ?

Readiness for beam commissioning stages of the commissioning with beam

Summary


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


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


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


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)


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 ?


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)


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


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


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


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


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

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Acknowledgements: P. Baudrenghien, A. Butterworth, E. Ciapala, B. Goddard, A. Koschik,

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