1

DR -> IP Beam Transport DR -> IP Beam Transport Simulations with Intra-Train Simulations with Intra-Train

Feedback Feedback

Glen White, SLAC

Jan 19th 2006

2

Multi-Bunch ILC Simulations•Generate a representation of the ILC bunch train at a ‘snapshot’ in time to study the ILC machine Luminosity performance with ground motion and other error sources for different machine parameters.

•Track 600 bunches through Linac, BDS and IP to observe dynamics of fast feedback correction (IP position and angle) + Lumi feedback and determine estimate of train luminosity.

•Use PLACET for Linac simulation and MatMerlin for BDS (GUINEA-PIG used for IP collision).

•Model case of tuned lattice + 1 pulse of GM (Linac + BDS).

•TESLA TDR & ILC IR-1 (20mrad IP x-ing) BDS currently implemented.

•Typical simulation times 60 hours+ depending on simulation parameters (per seed).

•To gauge performance for a variety of parameters/simulation environments/machines need many CPU hours.

3

Parallel Computing Infrastructure

QMUL HTC

MDCE – 256 nodes

GRID Interface

…...GRIDGRID

MySQLDatabase

PHP-Web Interface

http://hepwww.qmul.ac.uk/lcdata

……

4

Linac SimulationPLACET:

•Train enters linac with 20nm vertical emittance.

•Structure Misalignment: 0.5mm RMS y, 0.3mrad y’ error.

•Long- and short-range transverse and longitudinal wakefield functions included.

•BPM misalignment: 25um (y).

•Apply 1-1 steering algorithm.

•Pick random seed which gives 50% emittance growth .

•Apply y, y’ RMS Injection error.

•Apply Inter-Train Ground Motion (K-Model).

•Generate 600 bunches (multiple random seeds).

•Long-range wakes have strong effect on bunch train.

•Need to perform steering on plateau not first bunch.

5

BDS/IP SimulationMATMERLIN:

•Inter-Train Ground motion applied (K-model).

•Add 1.4ppm energy jitter on e- bunches (simulates passage of e-’s through undulator).

•Track 80,000 macro-particles per bunch.

•Feedback (Simulink model in Matlab):

•BPM Resolution: 2m (ANG FB) 5m (IP FB)

•Kicker errors: 0.1% RMS bunch-bunch.

•IP (Guinea-Pig):

•Input macro-beam from MatMerlin BDS (non-gaussian).

•Calculates Lumi & Beam-Beam kick.

•Produces e+e- pairs -> track through solenoid field and count number hitting LCAL first layer for Lumi FB signal.

6

IP Fast Feedback System

•Detect beam-beam kick with BPM(s) either side of IP.

•Feed signal through digital feedback controller to fast strip-line kickers either side of IP.

•Digital PI control algorithm is used for feedback algorithm.

7

IP Fast Feedback System

0 5 10 15 20 25 30 35 40 45-50

0

50

100

150

200

250

300

350

400

450

y* / y

Ver

tical

bea

m-b

eam

kic

k /

urad

data1data2

data3

data4

data5

data6data7

8

IP-Angle Feedback System

•Place kicker at point with relatively high function and at IP phase.

•BPM at phase 900 downstream from kicker.

•To cancel angular offset at IP to 0.1y’ level :

•BPM required resolution ~ 2um

•FB latency = 4 bunches.

•Other FB locations possible:

•Start of BDS to act as a pulse-flattener to reduce orbit error

•Requires ~100nm BPM resolution with these optics.

0 500 1000 1500 2000 25000

50

100

150

200

250

ANG KickerIPBPMSqrt(

/ m

S /m

9

Banana Bunches

•Short-range wakefields in accelerating cavities acting back on bunches cause systematic shape distortions:

•Z-Y plane of a sample bunch:

•Only small increase in vertical emittance, but large loss in luminosity performance with head-on collisions due to strong, non-linear beam-beam interaction.

•Change in beam-beam dynamics from Gaussian bunches.

10

Banana-Bunch DynamicsBanana-Bunch Dynamics

•Luminosity of a sample bunch over range of position and angle offsets.

•Feedback strategy: wait for IP and ANG FB systems to ‘zero’ (coloured ellipse in figure)– then fine tune by stepping in y then y’ using LUMI monitor (count e+e- hits in first layer of BeamCal) to find optimum collision conditions.

11

Banana-Bunch DynamicsBanana-Bunch Dynamics

•Luminosity of a sample bunch over range of position and angle offsets.

•Feedback strategy: wait for IP and ANG FB systems to ‘zero’ (coloured ellipse in figure)– then fine tune by stepping in y then y’ using LUMI monitor (count e+e- hits in first layer of BeamCal) to find optimum collision conditions.

•Recent simulation results suggest better results possible with 2-D scan.

y (rad)

y' (

nm

)

-27 -21 -15 -9 -3 3 9 15 21 27

-4.5

-3.5

-2.5

-1.5

-0.5

0.5

1.5

2.5

3.5

4.5 0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

12

IP Feedback

•Single example seed shown.

•Corrects < 10 bunches.

•Corrects to finite y due to banana bunch effect.

•Vertical Beam-Beam scan @ bunch 150.

5 Bunch e+e- Int. Signal

13

Angle Feedback

•Single example seed shown.

•Angle scan after 250 bunches when position scan complete.

•Noisy for first ~100 bunches (HOM’s).

•FB corrects to <0.1 y’

14

Luminosity

•Luminosity through example seed bunch train showing effects of position/angle scans.

•Total luminosity estimate: L(1-600) + L(550-600)*(2820-600)/50

0 100 200 300 400 500 6000

1

2

3x 10

34

Bunch #

Lu

min

os

ity

/ c

m-2

s-1

15

Luminosity – 100 Seeds

1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.850

5

10

15

20

25

Luminosity / cm-2 s-1 1034

= 1.6747 0.067286

2.7 2.75 2.8 2.85 2.9 2.95 3 3.050

2

4

6

8

10

12

14

16

18

Luminosity / cm-2 s-1 1034

= 2.8788 0.075445

•ILC-IR1 350 GeV (left) 500 GeV (right) CME.

•No improvement seen with addition of upstream FFB system.

16

Luminosity vs. IP Beam Size

8 8.5 9 9.5 10 10.5 11

x 10-3

1.5

1.55

1.6

1.65

1.7

1.75

1.8

1.85

( 2y(e-)

+ 2y(e+)

)1/2 / nm

6.4 6.6 6.8 7 7.2 7.4 7.6 7.8 8

x 10-3

2.7

2.75

2.8

2.85

2.9

2.95

3

3.05

( 2y(e-)

+ 2y(e+)

)1/2 / nm

350 GeV CME 500 GeV CME

•Lumi not directly proportional to IP beam spot size due to banana-beam effect.

17

Effect of Lumi-Scan (500 GeV)

•Effect of Pos & Ang Lumi scans compared with start of pulse with FB only.

•Angle feedback gives only small improvement.

•After position scan

•After position and angle scan

0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.220

5

10

15

Fractional Lumi Change After IP FB

= 0.12124 0.031719

0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.220

5

10

15

Fractional Lumi Change After ANG FB

= 0.12149 0.03356

18

Simulink Model

us1e

us1p

us2e

us2p

B(us1e)

B(us1p)

B(us2e)

B(us2p)

Upstream Feedback

z

1

FB_ANG

FB_IP

B(ey )

B(ey ')

B(py )

B(py ')

lumiopt

B(us1e)

B(us1p)

B(us2e)

B(us2p)

ey

ey '

py

py '

the

thp

lcal_hits

us1e

us1p

us2e

us2p

MATMERLIN+GUINEA-PIG

B(in)

Lumi ScanB(out)

Lumi Scan

-2Z

-1Z

-1Z

-1Z

-1Z

-1Z

ey

py

the

thp

set point

PI enable

B(ey )

B(py )

BPM

IP feedback

Demux

Demux

US_on

1

ey '<Lo>

py '<Lo>

set point<Lo>

PI enable<Lo>

B(ey ')

B(py ')

BPM

Angle Feedback

B(in)

Lumi

BPM

B(out)

PI enable

B(out) (IP)

BPM SetPoint

2-D Lumi Search

19

2-D Lumi Feedback

4

BPMSetPoint

3

B(out) (IP)

2

PI enable

1

B(out)

Int Lumi

Write to MaxLumi

In_pos

In_ang

prev

Continue

Write New LookupValues

z

1z

1

z

1

z

1

posmoves

Switch on point

STOP

Set MaxLumi_last

In1

In2

Out1

Out2

Sample & Hold

>

x

xdat

ydat

y

x

xdat

ydat

y

-1Z

-1Z

-1Z

-1Z

-1Z

-1Z

-1Z

-1Z

Counter Enable

Counter Trigger

EnablingSequences

In1 Out1In1 Out1

In1 Out1

EnabledCounter

Demux

MovesXDAT

MovesYANGDAT

MovesYPOSDAT

MaxLumi

LastMove_ang

LastMove_pos

MaxLumi_last

MovesYANGDAT

MovesYPOSDAT

MovesXDAT

BPM_set

MaxLumi

1

lscan_dy

1

1

lscan_dyp

1

sig_in

trigger_inTriggered Mean

sig_in

trigger_inTriggered Mean

3

BPM

2

Lumi

1

B(in)

20

2-D Lumi Feedback

21

ILC Simulation Web Page

•Store all beam data from simulation runs online

•http://hepwww.ph.qmul.ac.uk/lcdata

22

Summary and Plans

•Facility for parallel processing of accelerator codes set-up.

•Shown here to test ILC performance with Fast-Feedback.

•Final luminosity performance appears to be limited by banana-bunch shape.

•Add full Linac + BDS alignment and inter-pulse feedback to provide full time-evolved simulation.

•Add Crab Cavities to study crossing angle stability (requires addition of x-feedback)

•Other lattices + Beam Parameters (@350, 500 & 1000 GeV).

•Add Collimator Wakes.