FFeedbackeedback O Onn N Nano-secondano-second T Timescales:imescales:An IP Feedback System for the FutureAn IP Feedback System for the Future

Linear ColliderLinear Collider

•Requirement for a fast IP beam-based feedback system

•Simulation results of analogue feedback design

•BPM processor hardware tests

•Impact of system in LC interaction region

University of Oxford:

Phil Burrows, Glen White, Simon Jolly, Colin Perry

SLAC:

Steve Smith, Thomas MarkiewiczOctober 2001

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

From Ground Motion studies by A.Seryi et al. (SLAC)

• ‘Fast’ motion (> few Hz) dominated by cultural noise

• Concern for structures with tolerances at nm level (Final Quads)

Ground Motion

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Luminosity Loss at IP

• Relative offsets in final Quads due to fast ground motion leads to beam offsets of several y (2.7 nm for NLC-H 500 GeV).

•Correct using beam-based feedback system near IP or by active mechanical stabilization of Quads or both.

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

LC Bunch Structure

NLC-H 500 NLC-H 500 GeVGeV

TESLA 500 TESLA 500 GeVGeV

CLIC CLIC

500 GeV500 GeVParticles/Bunch x Particles/Bunch x

10101010 0.750.75 2.02.0 0.40.4

Bunches/trainBunches/train 190190 28202820 154154

Bunch Sep (ns)Bunch Sep (ns) 1.41.4 337337 0.70.7xx//y y (nm)(nm) 245 / 2.7245 / 2.7 553 / 5553 / 5 202 / 2.5202 / 2.5

•Feedback system demonstrated for NLC-H 500 GeV

•Can be modified for use at TESLA and CLIC

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Beam-Beam Interaction

•Beam-beam EM interactions at IP provide detectable signal

•Beam-beam interactions modelled with GUINEA-PIG

•Shown is the kick angle and percentage luminosity loss for different vertical beam offsets

0 10 20 30 400

20

40

60

80

100

Vertical Beam Offset ( sy )

% L

um

ino

sity

Lo

ss

0 10 20 30 400

50

100

150

200

250

300

Vertical Beam Offset ( sy )

Be

am-B

eam

Kic

k (

mra

d )

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Fast Feedback Operation

Kicker Gain

Bunch Charge

•Measure deflected bunches with BPM and kick other beam to eliminate vertical offsets at IP

•Feedback loop assesses intra-bunch performance and maintains correction signal to the kicker

•Minimise distance of components from IP to reduce latency

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

NLC Feedback Components

Stripline BPMStripline BPM

Distance to IPDistance to IP

Stripline radiusStripline radius

Stripline WidthStripline Width

Stripline lengthStripline length

Stripline ImpedanceStripline Impedance

Roundtrip timeRoundtrip time

4.3 m4.3 m

1 cm1 cm

4.4 mm4.4 mm

10 cm10 cm

50 50 0.7 ns0.7 ns

Stripline KickerStripline Kicker

Distance to IPDistance to IP

Stripline radiusStripline radius

Stripline lengthStripline length

Stripline ImpedanceStripline Impedance

Roundtrip timeRoundtrip time

Azimuthal coverageAzimuthal coverage

Drive voltage requiredDrive voltage required

Drive Power 100nm correctionDrive Power 100nm correction

4.3 m4.3 m

6 mm6 mm

75 cm75 cm

50 50 5 ns5 ns

120 degrees120 degrees

250 mV/nm250 mV/nm

12.5 W12.5 W

•BPM response peak near 714 MHz bunch spacing frequency

•Kicker rise-time represents slowest component

•System Design by Steve Smith (SLAC)

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Feedback Simulation

•Simulations performed using Simulink in Matlab

[[0 SIGMA_Y]; [267e-9 0]]

Y Posi tionBeam 2

[[0 Y_OFFSET ]; [267e-9 0]]

Y Posi tionBeam 1

T erm inator

In1

In2

Store Beam Info

Round-tripDelay

In1

Kicker Angle

Kicker Monitor

Kicker

IP angle Def lection at BPM

IP-to-BPMDynamics

IP scope

Beam 1

Beam 2Out1

IPDynamics

1

Gain1

1Gain

[[0 bunch_charge]; [250e-9 0]]

Bunch ChargeBeam 2

[[0 bunch_charge]; [ 250e-9 0]]

Bunch ChargeBeam 1

Q

Y Out1

Beam2

Q

Y Out1

Beam1In1 Out1

Beam Ji tter

BeamQ

Y

BeamParameters

BPMCableDelay

Kick angleKick at IP

BPM-to-IPDynamics

BPMScope

Beam In Position Out

BPM

[[0 SIGMA_Y]; [267e-9 0]]

Y Posi tionBeam 2

[[0 Y_OFFSET ]; [267e-9 0]]

Y Posi tionBeam 1

T erm inator

In1

In2

Store Beam Info

Round-tripDelay

In1

Kicker Angle

Kicker Monitor

Kicker

IP angle Def lection at BPM

IP-to-BPMDynamics

IP scope

Beam 1

Beam 2Out1

IPDynamics

1

Gain1

1Gain

[[0 bunch_charge]; [250e-9 0]]

Bunch ChargeBeam 2

[[0 bunch_charge]; [ 250e-9 0]]

Bunch ChargeBeam 1

Q

Y Out1

Beam2

Q

Y Out1

Beam1In1 Out1

Beam Ji tter

BeamQ

Y

BeamParameters

BPMCableDelay

Kick angleKick at IP

BPM-to-IPDynamics

BPMScope

Beam In Position Out

BPM

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

BPM Processor3 ns rise- time

[[0 SIGMA_Y]; [267e-9 0]]

Y Posi tionBeam 2

[[0 Y_OFFSET ]; [267e-9 0]]

Y Posi tionBeam 1

T erm inator

In1

In2

Store Beam Info

Round-tripDelay

In1

Kicker Angle

Kicker Monitor

Kicker

IP angle Def lection at BPM

IP-to-BPMDynamics

IP scope

Beam 1

Beam 2Out1

IPDynamics

1

Gain1

1Gain

[[0 bunch_charge]; [250e-9 0]]

Bunch ChargeBeam 2

[[0 bunch_charge]; [ 250e-9 0]]

Bunch ChargeBeam 1

Q

Y Out1

Beam2

Q

Y Out1

Beam1In1 Out1

Beam Ji tter

BeamQ

Y

BeamParameters

BPMCableDelay

Kick angleKick at IP

BPM-to-IPDynamics

BPMScope

Beam In Position Out

BPM

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Feedback Performance

Latency = 37.3 nsLatency = 37.3 ns

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Feedback Performance

[[0 SIGMA_Y]; [267e-9 0]]

Y Posi tionBeam 2

[[0 Y_OFFSET ]; [267e-9 0]]

Y Posi tionBeam 1

Terminator

In1

In2

Store Beam Info

Round-tripDelay

In1

Kicker Angle

Kicker Monitor

Kicker

IP angle Def lection at BPM

IP-to-BPMDynamics

IP scope

Beam 1

Beam 2Out1

IPDynamics

1

Gain1

1Gain

[[0 bunch_charge]; [250e-9 0]]

Bunch ChargeBeam 2

[[0 bunch_charge]; [ 250e-9 0]]

Bunch ChargeBeam 1

Q

Y Out1

Beam2

Q

Y Out1

Beam1In1 Out1

Beam Ji tter

BeamQ

Y

BeamParameters

BPMCableDelay

Kick angleKick at IP

BPM-to-IPDynamics

BPMScope

Beam In Position Out

BPM

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Kicker Gain Optimisation

[[0 SIGMA_Y]; [267e-9 0]]

Y Posi tionBeam 2

[[0 Y_OFFSET ]; [267e-9 0]]

Y Posi tionBeam 1

Terminator

In1

In2

Store Beam Info

Round-tripDelay

In1

Kicker Angle

Kicker Monitor

Kicker

IP angle Def lection at BPM

IP-to-BPMDynamics

IP scope

Beam 1

Beam 2Out1

IPDynamics

1

Gain1

1Gain

[[0 bunch_charge]; [250e-9 0]]

Bunch ChargeBeam 2

[[0 bunch_charge]; [ 250e-9 0]]

Bunch ChargeBeam 1

Q

Y Out1

Beam2

Q

Y Out1

Beam1In1 Out1

Beam Ji tter

BeamQ

Y

BeamParameters

BPMCableDelay

Kick angleKick at IP

BPM-to-IPDynamics

BPMScope

Beam In Position Out

BPM

Luminosity loss as function of Luminosity loss as function of gain input and beam offsetgain input and beam offset

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Luminosity Performance

•Lower gains gives better performance at smaller offsets, higher gains give better performance at higher offsets

•Vary gain dependent on observed beam conditions

0 5 10 15 20 25 30 35 400

10

20

30

40

50

60

70

80

90

100

Vertical Beam Offset ( sy )

% L

um

ino

sit

y L

os

s Feedback OffGain = 4.0 ́10 -6

Gain = 5.0 ́10 -6

Gain = 6.4 ́10 -6

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Feedback Enhancements

Original FB

FB with Signal Averaging

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Feedback Enhancements

Original Feedback model

Feedback with signal averaging

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Feedback Enhancements

•Feedback performance with and without signal averaging

•Left: Optimum gain for different offsets

•Right: Luminosity loss with different offsets

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Bunch Jitter Effects

•Introduction of random bunch-bunch jitter causes feedback system to exacerbate luminosity loss at larger gains

•Shown is the effect of randomly offsetting the bunches in a train about a zero offset, assuming a gaussian noise distribution

1e-7 4e-6 8e-6 1.2e-5 1.6e-5 2.0e-50

10

20

30

40

50

60

70

Kicker Gain

Pe

rce

nta

ge

Lu

min

os

ity

Lo

ss

No Beam Offset

Beam Jitter RMS = 0.1 sy

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Effect of Angle Offset

0 1 2 3 40

10

20

30

40

50

60

70

Vertical Beam Angle Offset ( sy'

)

Pe

rcen

tag

e L

um

ino

sity

Lo

ss

0 0.5 1 1.5 2 2.5 3 3.5 40

0.5

1

1.5

2

2.5

3

3.5

4

Vertical Beam Offset ( sy'

)

Be

am-B

eam

Kic

k ( m

ra

d )

•Beams get small additional kick if incoming with non-compensated crossing angle, also additional lumi loss

•Effect not addressed with this feedback system- if significant angle offset present, additional feedback system further up-stream of IP required

y’y’= 27 = 27 radrad y’y’= 27 = 27 radrad

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

BPM Processor Tests

•Hardware tests carried out at SLAC by Simon Jolly and Steve Smith

•Left: Simulated output of band-pass filter at 714MHz using sine-wave generator

•Middle: 3ns rise time of processor: mixer + 200MHz low-pass filter

•Right: Rise of processor and BPM signal showing approx 2ns delay due to passage of signal through mixer and filter

3ns Rise

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

IR Layout With FB System

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

IR Pair Backgrounds

•e+e- Pairs and ’s produced in Beam-Beam field at IP

•Interactions with material in the IR produces secondary e+e- ,, and neutron radiation

•Study background encountered in Vertex and tracking detectors with and without FB system and background in FB system itself

•Use GEANT3 for EM radiation and Fluka99 for neutrons

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

EM Backgrounds at BPM

•Absorption of secondary emission in BPM striplines source of noise in Feedback system

•System sensitive at level of about 3 pm per electron knocked off striplines

•Hence, significant noise introduced if imbalanced intercepted spray at the level of 105

particles per bunch exists

•GEANT simulations suggest this level of imbalance does not exist at the BPM location z=4.3m for secondary spray originating from pair background

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Detector EM Backgrounds

•Insertion of feedback system at z=4.3 m has no impact on secondary detector backgrounds arising from pair background

•Past studies suggest backgrounds adversely effected only when feedback system installed forward of z=3 m

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Detector n Backgrounds

Default IR: 5.5 Default IR: 5.5 ± 0.8 × 10± 0.8 × 1099

IR with FB: 6.6 ± 1.3 × 10IR with FB: 6.6 ± 1.3 × 1099

(neutrons/cm(neutrons/cm22/1 MeV n equiv./yr)/1 MeV n equiv./yr)

•No significant increase in neutron flux in vertex detector area seen arising from pair background

•More statistics being generated

VTD Layer

Hit

s/cm

2 /1

MeV

n e

qu

iv./y

r

Sum Over all Layers:

G.R.White: G.R.White: 20/04/2320/04/23

F.O.N.F.O.N.T.T.

Summary

•Ground motion moving final Quads major source of luminosity loss at a future linear collider.

•Fast IP feedback system simulations show considerable luminosity recovery even beyond linear kick region.

•Backgrounds do not seem to be an issue for detector components or the FB system itself in simulated BPM and kicker installation positions.

•Hardware tests ongoing at SLAC.

•Working towards full beam-line tests in NLCTA.

•Studies ongoing into improvements to feedback response and effect of mis-shaped bunches due to wakefield effects.