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