jonathan smith, 1 st march, colsim, cern 1 recent developments with ilc collimator wakefield...

Jonathan Smith, 1st March, COLSIM, CERN1

Recent Developments with ILC Collimator Wakefield

Calculations

Jonathan Smith(Lancaster University/Cockcroft Institute)


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


Wakefield box

ESA z ~ 300m – ILC nominaly ~ 100m (Frank/Deepa design)

Magnet mover, y range = mm, precision = 1m

1500mm

Ebeam=28.5GeV

Slide reproduced from talk by Nigel Watson


=/2rad

r=4.0mm4, 4

324mrad

r=1.4mm3, 3

324mrad

r=1.4mm2, 2

=324mrad

r=2.0mm1, 1

Revised

4-May-2006Beam viewSide view (“DESY sandwich”)Collim. #,

slot

h=38 mm

38

mm

L=1000 mm

7mm

r=1/2 gap

As per last set in Sector 2, commissioningAs per last set in Sector 2, commissioning

Extend last set, smaller r, resistive WF in CuExtend last set, smaller r, resistive WF in Cu

cf. same r, taperedcf. same r, tapered Slide reproduced from talk by Nigel Watson


=/2rad

r=1.4mm5, 4

166mrad

r=1.4mm6, 3

1=/2 rad

2=166mrad

r1=4.0mm

r2=1.4mm

7, 2

r1 =4.0mm

r2 =1.4mm =289mrad

=166mrad

8, 1

Revised

4-May-2006Beam viewSide view (“SLAC sandwich”)Collim.#, slot

h=38 mm

38

mm

7 mmcf. collim. 4 smaller rcf. collim. 4 smaller r

211mmcf. collim. 2, same rcf. collim. 2, same r

31mm

cf. collims. 4 and 6cf. collims. 4 and 6

133mm

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

Slide reproduced from talk by Nigel Watson


Small improvement on the

Chisq/n

Run 1206 (ref. 1207)

Multiplying each bunch by its ebpm_x ADC value


Analytical estimate

● Stupakov says:●Stupakov says:●Stupakov says:●Stupakov says:

●Stupakov asserts that the h»b is met, but is this really valid?


For SLAC collimators...


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)


EM Simulations with GdfidL

11 22

33

55

66

7744

88


Wakefields @300µm

(6 cells/sigma)


Wakefields @500µm

(12 cells/sigma)


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.


What do we do about it? (1)


What do we do about it?(2)


Effect of mesh filtering…


Misallignment


Further collimator designs

semi-circle, with[9]/without[10] flat, opposing demi-circles[10], 8 with flat[11].


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)


166mrad

r=1.4mm12

=166mrad

r =1.4mm11

=166mrad

r =1.4mm10

166mrad

r=1.4mm

(1/2 gap)6

Revised

27-Nov-2006Beam viewSide viewCollim.#

h=38 mm

38

mm

Roughened surface, compare with 12Roughened surface, compare with 12

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

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

Runs 3, 2007

Exists, from 2006 runs. For reproducibilityExists, from 2006 runs. For reproducibility

~211mm

1.4mm

=21mm

=21mm

=21mm


non-linear taper

r=1.4mm16?

1=/2 rad

2=50mrad

r1=4.0mm

r2=1.4mm

15

1=/2 rad

2=166mrad

r1=4.0mm

r2=1.4mm

14

1=/2 rad

2=166mrad

r1=4.0mm

r2=1.4mm

13

Revised

27-Nov-2006Beam viewSide viewCollim.#

h=38 mm

38

mm

cf. ?cf. ?

Polished, cf. collim. 13Polished, cf. collim. 13

Polished, cf. collims. 7, 11, 13Polished, cf. collims. 7, 11, 13

Polished, cf. collim. 7, 12, 13Polished, cf. collim. 7, 12, 13

Ti6Al4V

OFE Cu

OFE Cu=21 mm

Form t.b.d.

= 0.6Ti6Al4V

Runs 3, 2007

~52 mm

=21 mm

~52 mm

=21 mm

~125 mm

=21 mm


Variation of collimator kick with bunch length


WB's suggestion:

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


Two possibilities:s_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

xs_ma

x

s_max

“colimator 23”

“colimator 22”


Longitudinally Asymmetric?


Results...


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● TEMF working on ECHO/PBCI – 3D,

moving mesh, conformal, non-dispersive solver

s/σ

σ/Δz=6

W║(s

)/(V

/pC

)

GdfidLPBCI

With thanks to Mikko Kärkkäinen

jonathan smith, 1 st march, colsim, cern 1 recent developments with ilc collimator wakefield...

Documents

mrad r

cellssigma slide

smaller r

gev slide

tapered slide

misallignment slide

nigel watson slide

bunch length slide