towards improved collimation for the ilc

Jonathan Smith, LC-ABD, 12th April 07, RHUL1

Towards Improved Collimation for the ILC

Jonathan Smith(Lancaster University/Cockcroft Institute)


Outline

● Damage Studies● Merlin Simulations● Bench Tests● T480@ESA● EM Simulation

activity● Plans

• LC-ABD WP5.3 /EUROTeV WP2 (BDS)

• Collimation is crucial for beam delivery and detector protection/performance

http://hepunx.rl.ac.uk/swmd/talks/


People● “Spoiler Wakefield and Mechanical Design” task● Details on project web: http://hepunx.rl.ac.uk/swmd/

● Birmingham: N.Watson● CCLRC: C.Beard,G.Ellwood,J.Greenhalgh,J.O'Dell,L.Fernandez ● CERN: F.Zimmermann,G.Rumolo,D.Schulte● [DESY: I.Zagorodnov]● Lancaster: D.Burton,R.Carter,N.Shales,J.Smith,A.Sopczak,R.Tucker● Manchester: R.Barlow,A.Bungau,R.Jones● TEMF, Darmstadt: vice-M.Kärkkäinen,W.Müller,T.Weiland

● For ESA tests, working closely with– CCLRC on optics for wakefield and beam damage studies– SLAC Steve Molloy et al. for all aspects


SLAC T-480 Experiment

Vertical mover

BPMBPM

2 doublets

~40m

BPM BPM

Two triplets

~16m

• 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…


Vertical mover

BPMBPM

2 doublets

~40m

BPM BPM

Two triplets

~16m

• 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 (2006 version)

• Measure kick factor using incoming/outgoing beam trajectory, scanning collimator gap through beam

• 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– Physics runs, Mar 2007, Jul 2006, May 2006 + Jul’07?

Wakefield box

Beam


=298mrad

=168mrad

r1 =3.8mm

r2 =1.4mm

4

1=/2 rad

2 =168mrad

r1 =3.8mm

r2 =1.4mm

3

168mrad

r=1.4mm2

=/2rad

r=1.4mm1

Beam viewSide viewSlot

=298mrad

=168mrad

r1 =3.8mm

r2 =1.4mm

4

1=/2 rad

2 =168mrad

r1 =3.8mm

r2 =1.4mm

3

168mrad

r=1.4mm2

=/2rad

r=1.4mm1


h=38 mmh=38 mm

38 m

m38

mm

7 mm

208mm

28mm

159mm=/2rad

r=3.8mm4

335mrad

r=1.4mm3

335mrad

r=1.4mm2

=335mrad

r=1.9mm1


=/2rad

r=3.8mm4

335mrad

r=1.4mm3

335mrad

r=1.4mm2

=335mrad

r=1.9mm1


h=38 mm

38 m

m

h=38 mmh=38 mm

38 m

m38

mm

L=1000 mmL=1000 mmL=1000 mm

7mm

r=1/2 gate

r=2 mm

Collimator 1 is similar to collimator described in SLAC-PUB-12086

Collimator 2 is like 1 but with a narrower gap

Collimator 3 has the same taper angle and gap as 2. We hope to measure the difference due to resistive wakefield.

Collimator 2, 3 and 4 have same taper angle, but 3 and 4 just in the top. The aim is to measure the difference between each geometry, if there is any. A small taper angle is better to reduce wakefields but it also need longer (more space) collimators. Can be model it?


Slot 1

Slot 4

Slot 2

Slot 3L=1000 mm

= 324 mradr = 2 mm

= 324 mradr = 1.4 mm

= /2 r = 3.8 mm

= 324 mradr = 1.4 mm

(r = ½ gap)


Collimator Measured4

Kick Factor V/pc/mm (2/dof)

Linear fit

Measured4

Kick Factor V/pc/mm (2/dof)

Linear + Cubic Fit

Analytic Prediction1

Kick Factor V/pc/mm

3-D Modelling

Prediction2

Kick Factor

V/pc/mm

1 1.4 ± 0.1 (1.0)3 1.2 ± 0.3 (1.0) 1.1 1.7

2 1.4 ± 0.1 (1.3) 1.2 ± 0.3 (1.4) 2.3 3.1

3 4.4 ± 0.1 (1.5) 3.7 ± 0.3 (0.8) 6.6 7.1

4 0.9 ± 0.2 (0.8) 0.5 ± 0.4 (0.8) 0.3 0.8

5 1.7 ± 0.3 (2.0) 1.7 ± 0.3 (2.2) 2.3 2.4

6 1.7 ± 0.1 (0.7) 2.2 ± 0.3 (0.5) 2.4 2.7

7 0.9 ± 0.1 (0.9) 0.9 ± 0.3 (1.0) 2.3 2.4

8 3.7 ± 0.1 (7.9) 4.9 ± 0.2 (2.6) 2.3 6.8

1Assumes 500-micron bunch length2Assumes 500-micron bunch length, includes analytic resistive wake; modelling in progress3Kick Factor measured for similar collimator described in SLAC-PUB-12086 was (1.3 ± 0.1) V/pc/mm4Still discussing use of linear and linear+cubic fits to extract kick factors and error bars

→ Goal is to measure kick factors to 10%

Preliminary results:

L=1000 mm

208mm

28mm

159mm


GdfidL EM simulations…

beam


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

beam


Collim.# Side view (“SLAC sandwich”) Beam view Revised

08-Nov-2006

13

1=/2 rad

2=168mrad

r1=4.0mm

r2=1.4mm

14

1=/2 rad

2=168mrad

r1=4.0mm

r2=1.4mm

15

1=/2 rad

2=50mrad

r1=4.0mm

r2=1.4mm

16=exp., sin

r=1.4mm

h=38 mm

38

mm

21 mm

21 mm

52 mm

Ti6Al4V

OFE Cu

21 mm

125 mm

21 mm

= 0.6Ti6Al4V


Data analysis from this run…

● Is ongoing, but here is a preview...


Longitudinally Asymmetric?


Damage Studies

● EGS/Geant4/FLUKA in agreement● ANSYS modelling of temperature flow done.● Shockwave studies underway● Focus now on manufacturability – e.g. wire erosion● Search for a site to conduct damage tests (CERN?

Discussions at EPAC… )

Last time:

Now:● Wire erosion method tested in manufacture on non-linear

profile collimator.● Proposal for damage tests at ATF in preparation,

awaiting discussion at next ATF users meeting.


Including EM simulations into Merlin

Fourier DeconvolutionWbunch(s,m)=Wdelta(s,m)Gaussian

Take FT of ECHO result (here mode=1) and FT of Gaussian

(red and blue are sine and cosine parts)

Divide to obtain FT of delta wake

Back-transform.Horrible! (Look at y axis scale)

But mathematically correct: combined with Gaussian reproduces original

Due to noise in spectra at high frequency. Well known problem


Delta wakes: Consistency check

Give the same delta wakes

Use FT to extract delta wakes from the different bunch wakes

Agreement reasonable: method validated

Green oscillation artefact of ECHO2D, not of Fourier extraction


Merlin studies: emittance dilution due to wakefield

Looked at emittance dilution due to higher order mode wakefields -> get an increase in the beam size and consequently a decrease in luminosity

Beam excursions due to small offsets are under study.

A.Bungau - Manchester University


Cylindrical jobs...

● W modal decomposition

● Jobs still running● w(s,r,r',θ,θ')→w(s,r,θ,m)● Useful for rectangular

geometry?


Bench “wire method” setup

● Calculate impedence of structure

● Simulate mode structure

● Use where wire is not interfering with the mode, or use simulation results to subtract wire induced effects

Plot from S.F.Hill and M.J.Pugh, paper at EPAC'94


Summary● Run 3 at ESA successful, data analysis well

advanced● Collimator damage simulations in 2006…

– ATF proposal in preparation, submission 2 May 2007

● EM simulations – Being used to design optimal spoiler geometries

● Wire tests– devices in production, test utility of method at DL

● Merlin/Placet simulations with wakefields– Quantify effect of higher order modes

towards improved collimation for the ilc

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