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Jonathan Smith (Lancaster University/Cockcroft Institute). Recent Developments with ILC Collimator Wakefield Calculations. Introduction/Project Objectives. LC-ABD WP5.3 (Nigel Watson)/EUROTeV WP2 (BDS)

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jonathan smith lancaster university cockcroft institute
Jonathan Smith

(Lancaster University/Cockcroft Institute)

Recent Developments with ILC Collimator Wakefield Calculations
introduction project objectives
Introduction/Project Objectives
  • LC-ABD WP5.3 (Nigel Watson)/EUROTeV WP2 (BDS)
  • Collimation is crucial for beam delivery and detector protection/performance of a particle accelerator
  • Quantification of longitudinal and transverse wakefield effects of collimators on the beam
  • Optimization of collimator design
  • Use and understanding of simulation tools, potential improvements and support of other projects
  • Verification by test beam measurement
slac t 480 experiment

2 doublets

Two triplets

BPM

BPM

BPM

BPM

~40m

~16m

SLAC T-480 Experiment

Vertical mover

  • Wakefields measured in running machines: move beam towards fixed collimators
  • Problem
    • Beam movement  oscillations
    • Hard to separate wakefield effect
  • Solution
    • Beam fixed, move collimators around beam
    • Measure deflection from wakefields vs. beam-collimator separation
    • Many ideas for collimator design to test…
slide4

2 doublets

Two triplets

BPM

BPM

BPM

BPM

~40m

~16m

Vertical mover

  • Wakefields measured in running machines: move beam towards fixed collimators
  • Problem
    • Beam movement  oscillations
    • Hard to separate wakefield effect
  • Solution
    • Beam fixed, move collimators around beam
    • Measure deflection from wakefields vs. beam-collimator separation
    • Many ideas for collimator design to test…
esa beamline layout plan
ESA beamline layout (plan)

Wakefield box

Beam

  • Measure kick factor using incoming/outgoing beam trajectory, scanning collimator gap through beam
  • Stage 1, 5 rf cavity BPMs, 1 stripline BPM, 2 wire scanners
    • Downstream BPMs themselves R&D project …layout has changed over course of runs.
  • Wakefield box, proposal for 2 sets of four pairs of spoiler jaws
  • Each set mounted in separate “sandwich” to swap into WF box
    • (Relatively) rapid change over, in situ – ½ shift for access
    • Commissioning run, Jan 4-9, 2006
    • Physics run, May06, July06, Mar07, July07
wakefield box

1500mm

Wakefield box

Slide reproduced from talk by Nigel Watson

Ebeam=28.5GeV

ESA z ~ 300m – ILC nominal

y ~ 100m (Frank/Deepa design)

Magnet mover, y range = mm, precision = 1m

slide7

Collim. #, slot

Side view (“DESY sandwich”)

Beam view

Revised

4-May-2006

1, 1

=324mrad

r=2.0mm

38 mm

h=38 mm

2, 2

324mrad

r=1.4mm

3, 3

324mrad

r=1.4mm

L=1000 mm

4, 4

=/2rad

r=4.0mm

r=1/2 gap

As per last set in Sector 2, commissioning

Extend last set, smaller r, resistive WF in Cu

7mm

cf. same r, tapered

Slide reproduced from talk by Nigel Watson

slide8

Collim.#, slot

Side view (“SLAC sandwich”)

Beam view

Revised

4-May-2006

8, 1

r1 =4.0mm

r2 =1.4mm =289mrad

=166mrad

133mm

38 mm

cf. collim. 7, and same step in/out earlier data

h=38 mm

7, 2

1=/2 rad

2=166mrad

r1=4.0mm

r2=1.4mm

31mm

cf. collims. 4 and 6

6, 3

166mrad

r=1.4mm

cf. collim. 2, same r

211mm

5, 4

=/2rad

r=1.4mm

7 mm

cf. collim. 4 smaller r

Slide reproduced from talk by Nigel Watson

slide9

a = 324 mrad

r = 1.4 mm

Slot 2

a = 324 mrad

r = 2 mm

Slot 1

(r = ½ gap)

Slot 3

L=1000 mm

a = 324 mrad

r = 1.4 mm

a = p/2

r = 3.8 mm

Slot 4

slide10

Run 1206 (ref. 1207)

Multiplying each bunch by its ebpm_x ADC value

Small improvement on the

Chisq/n

slide11

208mm

L=1000 mm

28mm

159mm

Preliminary results:

1Assumes 500-micron bunch length

2Assumes 500-micron bunch length, includes analytic resistive wake; modelling in progress

3Kick Factor measured for similar collimator described in SLAC-PUB-12086 was (1.3 ± 0.1) V/pc/mm

4Still discussing use of linear and linear+cubic fits to extract kick factors and error bars

→ Goal is to measure kick factors to 10%

analytical estimate
Analytical estimate
  • Stupakov says:
  • Stupakov says:
  • Stupakov says:
  • Stupakov says:
  • Stupakov asserts that the h»b is met, but is this really valid?
assessment familiarization of simulation tools
Assessment/Familiarization of Simulation Tools
  • MAGIC (easy to use tool for first comparison with new calculations)
  • ECHO/ECHO3D
    • Thomas Weiland, Mikko Karkkainen(TEMF, Darmstadt) Igor Zagorodnov (DESY). Code development as part of EUROTeV project
  • MAFIA
    • CDB and JS working on comparison with Cho Ng’s results (PAC 2001)
  • GdfidL
    • Overlapping interest with David Miller and Alexei Liapine (UCL) as part of EUROTeV WP5 (Spectrometry)
  • Additional software for research if required:
    • BCI/TBCI/ABCI (old CERN tools), XWAKE, XOOPIC
    • Tau3P, Omega, T3P (next generation SLAC codes)
    • Boundary Element (BEM) codes (Sapporo, Japan)
mesh stability collimators 1 2
Mesh stability: Collimators 1&2
  • Only 3 decent points at 300µm for most collimators
  • More at 500µm
  • 1mm ~ OK – can use spline fit on data to get an estimate – not done so far – further analysis to see if this takes us closer to ECHO/PBCI.
further collimator designs
Further collimator designs

semi-circle, with[9]/without[10] flat,

opposing demi-circles[10], 8 with flat[11].

more possible collimators
More possible collimators

7 with flat [13], half exponential[14], 13 with shallower angle[15]

exponential profile[16],

13 with ellipse connecting 4mm and 1.4mm aperture[17]

13 with ellipse connecting beam pipe radius and 1.4mm aperture (also see 9)[18]

half cosine taper [19], raised cosine taper [20], tanh tapers [21]

(set typically to the length of collimator 6)

wakefields @300 m
Wakefields @300µm

(6 cells/sigma)

wakefields @500 m
Wakefields @500µm

(12 cells/sigma)

slide25

Collim.#

Side view

Beam view

Revised

27-Nov-2006

6

166mrad

r=1.4mm

(1/2 gap)

~211mm

38 mm

1.4mm

h=38 mm

10

=166mrad

r =1.4mm

=21mm

11

=166mrad

r =1.4mm

=21mm

12

166mrad

r=1.4mm

=21mm

Exists, from 2006 runs. For reproducibility

Runs 3, 2007

Roughened surface, compare with 12

As 10, in Ti-6Al-4V, polished, cf. 12

As 10, in OFE Cu, polished, cf. collim. 6, 13

slide26

Collim.#

Side view

Beam view

Revised

27-Nov-2006

13

1=/2 rad

2=166mrad

r1=4.0mm

r2=1.4mm

=21 mm



38 mm

~52 mm

h=38 mm

14

1=/2 rad

2=166mrad

r1=4.0mm

r2=1.4mm

=21 mm



~52 mm

15

1=/2 rad

2=50mrad

r1=4.0mm

r2=1.4mm



=21 mm

~125 mm

16?

non-linear taper

r=1.4mm

=21 mm

OFE Cu

Polished, cf. collim. 7, 12, 13

Ti6Al4V

= 0.6

Ti6Al4V

Runs 3, 2007

Polished, cf. collims. 7, 11, 13

Polished, cf. collim. 13

OFE Cu

Form t.b.d.

cf. ?

wb s suggestion
WB's suggestion:

Chop this bit off as beam will never see wake that has travelled this far from the bunch

two possibilities

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

s_max

Two possibilities:

“colimator 22”

“colimator 23”

cylindrical jobs
Cylindrical jobs...
  • W modal decomposition
  • See Adriana's talk...
  • Jobs still running
  • w(s,r,r',θ,θ')→w(s,r,θ,m)
  • Useful for rectangular geometry?
gdfidl pbci
GdfidL & PBCI
  • TEMF working on ECHO/PBCI – 3D, moving mesh, conformal, non-dispersive solver

GdfidL

σ/Δz=6

PBCI

W║(s)/(V/pC)

With thanks to Mikko Kärkkäinen

s/σ

summary
Summary
  • Experimental programme to measure collimator wakefields at SLAC-ESA.
  • Numerical simulations to provide direction to the collimator design programme.
  • Alternative numerical/analytical techniques under development, which will provide useful comparison.