acknowledgements: p. baudrenghien, a. butterworth (ab/rf/cs), g. kotzian, r. louwerse,

W. Hofle / December 4, 2007 LHC Commissioning Working Group 1/30

Acknowledgements:P. Baudrenghien, A. Butterworth (AB/RF/CS), G. Kotzian, R. Louwerse,

E. Montesinos (AB/RF/SR), 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, why do we need the damper on day ONE ?

Status of damper system – ongoing hardware commissioning

The different stages of initial 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

-> will become important as intensity is raised, scrubbing in regime with e-cloud present

excitation: damper can be easily used to do multiple excitations per cycle

-> required for continuous tune measurement -> can be used to kick out unwanted beam (“abort gap cleaning”) -> making this mode operational requires software effort

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 ?


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

injection kicker starts firing ~100 bunches in advance


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

]


Performance specification (1)(LHC Design Report)

Beam parameters and requirements for nominal intensity:

Injection beam momentum 450 GeV/cStatic injection errors 2 mm (at max=183 m)ripple (up to 1 MHz) 2 mm (at max=183 m)resistive wall growth time 18.5 msassumed de-coherence time 68 mstolerable emittance growth 2.5 %Overall damping time 4.1 ms (46 turns)

bunch spacing 25 nsminimum gap between batches 995 nslowest betatron frequency > 2 kHzhighest frequency to damp 20 MHz


Performance specification (2)

Equipment performance specification:

choice: “electrostatic kickers” (“base-band”)aperture 52 mm

kickers per beam and plane 4length per kicker 1.5 mnominal voltage up to 1 MHz at b=100m +/- 7.5 kVkick per turn at 450 GeV/c 2 rad

rise-time 10-90%, V= +/- 7.5 kV 350 nsrise-time 1-99%, V= +/- 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 / 2 rise time fast enough for gap of 38 missing bunches


The LHC Transverse Damping System (high power part)

20 electrostatic kickers 40 wideband amplifiers, i.e. 40 tetrodes

(RS2048 CJC, 30 kW) 20 amplifier cases

Damper system

Beam 1

IP4

“Electrostatic”kicker

Beam 2

WidebandamplifierUnit

H H V VSpare units+

H H H HV VV V

H H H H V V V V

Module


LHC optics at injection in IR4(beams do not cross!)

Beam 1high horizontal beta left of IP4high vertical beta right of IP4

Beam 2high horizontal beta right of IP4high vertical beta left of IP4

Plots are Optics 6.4, sorry, 6.5 not very different for ADT)


Performance

LHCADT performance in LHC optics version 6.500 compared to original assumptions (at 450 GeV/c), assuming 7.5 kV maximum kick voltage

=100 m performance Optics 6.500 performance

Kick per turn in Kick per turn in @ in m

ADTH beam 1 0.2 0.271 at =183 m

ADTH beam 2 0.2 0.274 at =189 m

ADTV beam 1 0.2 0.301 at =227 m

ADTV beam 2 0.2 0.331 at =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 kHz1 MHz 10 MHz 20 MHz

ADTH 0.42 0.11 0.38 0.10 0.12 0.03 0.044 0.011

ADTV 0.46 0.12 0.42 0.12 0.14 0.04 0.049 0.012


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 1

Beam 2

SR4 (surface):Signal Processing electronics (VME crates)HV Power ConvertersPLC controls


Overview of one damper system

pick-ups (tunnel)

kickers and power amplifiers (tunnel)

low levelElectronic(surface)

controls amplification and interlocking (UX45, underground)


Q7

ADC

FPGA

S

...

S

...

SERDES

S

...

S

...

Q9

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 module

Overview of signal processing hardware


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 (intelligence)


Coupler Type Beam Position Monitor

Peak voltage (beam centered) for ultimate beam @ collision: ~140 V -> very large

Peak sensitivity: 0.264 / mm => 8.1 V/mm peak in time domain after ideal hybrid

Frequency domain: maximum of transfer impedance ZT = 6.46 @ 500 MHz^


8 Dedicated Pick-ups BPMC @ Q7L, Q7R, Q9L, Q9R 50 couplers of 150 mm length on one end short circuited


Simulation model enables to study imperfections of hardware and also propagate noise or interferences throughsystem and evaluate their impactBunch synchronous sampling with a 40 MHz clock rate

Detection of bunch by bunch oscillations


Outline




The different stages of the commissioning with beam

Summary


Status of Transverse Damper (1)

Underground installation and Hardware Commissioning

RB 44/46 (tunnel):

Kickers installed, vacuum bake out OKPower amplifiers installed, tested, water cooling OK, final characteristics to be measured in situPick-ups @ Q7, Q9: installed, external cabling partially OK, loads to be installed for unused portsEqualization of cable lengths: Non-conformities to be followed-up

UX45:

200 W driver amplifiers installedHOM loads from kickers installedPLC controls installed and testedInterlock crates installed and tested; calibration of power interlock to be doneSignal observation crates: Not yet installed, cables to be pulled between racks


Assembly and Installation of kickers


Measured Characteristics of 16 installed amplifiers

-4.0E+01

-3.0E+01

-2.0E+01

-1.0E+01

0.0E+00

1.0E+01

2.0E+01

3.0E+01

4.0E+01

5.0E+01

1.0E+05 1.0E+06 1.0E+07 1.0E+08

n1-norm

n2-norm

n3-norm

n4-norm

n6-norm

n7-norm

n8-norm

n9-norm

n10-norm

n11-norm

n13-norm

n14-norm

n15-norm

n16-norm

n17-norm

n19-norm

E. Montesinos (AB/RF/SR) for CERN-JINR collaboration

Actual performance between 10-20 MHz will be better than shown on graph -> calibrated measurements necessary to show real voltage on kickers(hardware commissioning)

frequency

gain


Status of Transverse Damper (2)

Surface installation and Hardware Commissioning (SR4)

Power equipment:

8 power converters installed and commissioned (anode voltage for tetrode amplifiers)Full loading of 2x2 MW 18kV/400V transformers feeding damper power converters to be checked48 smaller auxiliary power converters installed and commissioned (Ug1, Ug2 for tetrode amplifiers)PLC controls commissioned

Lowlevel electronics for damper in SR4:

Main cables pulled, crates installedPrototypes of beam position and signal processing modules hardware wise OKmodifications to be implemented for series productionFPGA code to be developed and tested for final boardsControls software to be defined and implemented


Outline




The different stages of the commissioning with beam

Summary


Beam Commissioning Phase A1 and A2First turn and circulating beam

(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


Beam Commissioning Phase A3(after RF capture)

Commissioning RF front-end 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, dampersScan injection kicker pulse by moving bunch


Beam Commissioning Phase A4[450 GeV]

Commissioning Damper Loop (450 GeV):

Measure de-coherence time with damper off, non-linearities correctedMeasure open loop transfer function (low frequency)Make necessary adjustments (gain, phase, delay)Close damper loopScan gain, phase, delay and measure damping time and stability limits

Commission beam blow-up facility

Measure beam lifetime as function of damper gain


Beam Commissioning Phase A6[first 2 minutes of ramp]

Abort gap cleaning and machine Protection:

Check machine protection interlocks, OK when damper goes crazy ?

Try out abort gap cleaning techniques (this requires the collimators)

Optimize abort gap cleaning programs


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


Hardware commissioning of power system well advanced

Lowlevel electronics prototypes OK

Focus now shifting to final FPGA programming, testing and software

Damper commissioning can start from phase A1 with observation of signals

Damper essential to avoid increase of transverse emittance (kicker ripple effect when full batch)

Summary

acknowledgements: p. baudrenghien, a. butterworth (ab/rf/cs), g. kotzian, r. louwerse,

Documents

transverse oscillations

beam measurements

beamsummarylhc commissioning

mmlhc commissioning

advancelhc commissioning

injection kicker ripple

injection kicker imperfections

beam revolution timem