Design and testing of the Beam Delivery System collimators for the International Linear Collider

Design and testing of the Beam Delivery System collimators for the International Linear Collider

J. L. Fernandez-Hernando

STFC/ASTeC Daresbury Lab

The International Linear Collider (ILC) will accelerate 2E10 electrons on one side, and 2E10 positrons on the other up to a center of mass energy of 1 TeV (500 GeV in the first period of operation) in their collision.

The ILC will be complementary to the LHC and will allow to study “in detail” the new particles discovered at the LHC.

The ILC collimation system is composed of a spoiler and an absorber.

The collimator mission is to clean the beam halo from e- or e+ off orbit which could damage the equipment, but mainly to clean the beam from photons generated during the bending of the beam towards the Interaction Point. These photons, if not removed, would generate a noise background that would not allow the detectors to work properly.

• Long, shallow tapers (~20mrad?), reduce short range transverse wakes

• High conductivity surface coatings• Robust material for actual beam spoiling• Long path length for errant beams striking spoilers

– Large materials (beryllium…, graphite, ...)

• Require spoilers survive at least 2 (1) bunches at 250 (500) GeV

• Design external geometry for optimal wakefield performance, reduce longitudinal extent of spoiler if possible

• Use material of suitable resistivity for coating• Design internal structure using in initial damage survey seems most

appropriate.

0.6

Starting pointStarting point

Spoilers considered include…Spoilers considered include…

0.3 Xo of Ti alloy upstream and downstream tapers

0.6 Xo of metal taper (upstream), 1 mm thick layer of Ti alloy

Option 1: Ti/C, Ti/Be

2mm

2.1010 e-, Ebeam=250 GeV,

xy=1119m2

also, Ebeam=500 GeV

2.1010 e-, Ebeam=250 GeV,

xy=1119m2

also, Ebeam=500 GeV10mm

Ti, Cu, Al

Option 3: Ti/COption 2: Ti/C, Cu/C, Al/C

Graphite regions

0.6

335mrad

[Details, see Eurotev Reports 2006-015, -021, -034]

As per T480

2 mm deep from top

Full Ti alloy spoiler

∆Tmax = 870 K per a bunch of 2E10 e- at 500 GeV

σx = 79.5 µm, σy= 6.36 µm

135 K

270 K

405 K

810 K

Ti / Graphite SpoilerTi / Graphite Spoiler

∆Tmax = 575 K per a bunch of 2E10 e- at 500 GeV

σx = 79.5 µm, σy= 6.36 µm

270 K

405 K

540 K

2 mm deep from top

Ti alloy and graphite spoiler

400 K

Temperature data in the left only valid the Ti-alloy material. Top increase of temp. in the graphite ~400 K. Dash box: graphite region.

beamTi

C

Summary of simulationsSummary of simulations

2mm depth 10mm depth

250 GeV e-

1119 µm2

500 GeV e-

79.56.4 µm2

250 GeV e-

1119 µm2

500 GeV e-

79.56.4 µm2

Solid Ti alloy 420 K 870 K 850 K 2000 K

Solid Al 200 K 210 K 265 K 595 K

Solid Cu 1300 K 2700 K 2800 K 7000 K

Graphite+Ti option 1

325 K 640 K 380 K 760 K

Beryllium+Ti option 1

- - - 675 K

Graphite+Ti option 2

290 K 575 K 295 K 580 K

Graphite+Al option 2

170 K 350 K 175 K 370 K

Graphite+Cu option 2

465 K 860 K 440 K 870 K

Graphite+Ti option 3

300 K 580 K 370 K 760 K

Temperature increase from 1 bunch impactExceeds fracture temp.

Exceeds melting temp.

• Wakefields deteriorate the beam quality.

• A final collimator design should minimise this effect.

• Studies on wakefields generated by different collimator geometries.

• Comparison to analytic predictions and simulations in order to improve both methods.

Beam Parameters at SLAC ESA and ILCParameter SLAC ESA ILC-500Repetition Rate 10 Hz 5 Hz

Energy 28.5 GeV 250 GeV

Bunch Charge 2.0 x 1010 2.0 x 1010

Bunch Length 300 m 300 m

Energy Spread 0.2% 0.1%

Bunches per train 1 (2*) 2820

Microbunch spacing - (20-400ns*) 337 ns

*possible, using undamped beam

BPMBPMBPM BPM

Vertical mover

~15 m2 triplets

~40 m2 doublets

• Wakefield measurement:

– Move collimators around beam (in steps of 0.2 mm, from -1.2 mm to +1.2 mm, being 0 mm the centre of the collimator).

– Measure deflection from wakefields vs. beam-collimator separation

BPMBPMBPM BPM

Vertical mover

~15 m2 triplets

~40 m2 doublets

• Wakefield measurement:

– Move collimators around beam (in steps of 0.2 mm, from -1.2 mm to +1.2 mm, being 0 mm the centre of the collimator).

– Measure deflection from wakefields vs. beam-collimator separation

Col. 1

Col. 3L=1000 mm

= 324 mradr = 2 mm

= 324 mradr = 1.4 mm

Col. 12 = 166 mradr = 1.4 mm

Col. 6 = r = 1.4 mm

(r = ½ gap)

Coll. 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 1.2 ± 0.3 (1.0) 2.27 1.7 ± 0.37

2 1.2 ± 0.3 (1.4)/

1.3± 0.6 (1.0)

4.63 3.1 ± 0.84

3 3.7 ± 0.3 (0.8) 5.25 7.1 ± 0.94

4 0.5 ± 0.4 (0.8) 0.56 0.8

5 4.9 ± 0.2 (2.6) 4.59 6.8

6 0.9 ± 0.3 (1.0) /

0.7 ± 0.2 (0.9)

4.65 2.4 ± 1.14

7 2.2 ± 0.3 (0.5) 4.59 2.7 ± 0.53

8 1.7 ± 0.3 (2.2) 4.59 2.4 ± 0.89

10 1.1± 0.2 (2.2)

11 2.5± 0.3 (0.9)

12 1.5± 0.2 (1.1)

14 2.6 ± 0.4 (1.0) )/

2.3± 0.3 (1.0)

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

L=1000 mm

Bunch xy

(m2), material

Estimated damage region, x

Estimated damage region, y

Estimated damage region, z

1.90.5, Ti alloy

11 (14) m 4 (5.6) m 5 (8) mm

202, Ti alloy

45 (90) m 5 (9) m 2 (7) mm

202, Cu 65 (100) m 7 (10) m 3 (7) mm

sample holder

x

y

referencepin hole

guide channels

pin hole

low mass mounting

Cu Ti

target area

10mm

The purpose of the first test run at ATF is to:

1. Make simple measurements of the size of the damage region after individual beam impacts on the collimator test piece. This will permit a direct validation of FLUKA/ANSYS simulations of properties of the materials under test.

2. Allow us to commission the proposed test system of vacuum vessel, multi-axis mover, beam position and size monitoring.

3. Validate the mode of operation required for ATF in these tests.

4. Ensure that the radiation protection requirements can be satisfied before proceeding with a second phase proposal.

Assuming a successful first phase test, the test would be to measure the shock waves within the sample by studying the surface motion with a laser-based system, such as VISAR (or LDV), for single bunch and multiple bunches at approximate ILC bunch spacing.

Material damage test beam at ATFMaterial damage test beam at ATF

0

100

200

300

400

500

600

700

0.5 1 1.5 2 2.5 3

Incident e-/um^2 (+/- 2 sigma)x10^7

Melte

d ar

ea (u

m^2

)

[Measurements c/o Marc Ross et al., Linac’00]

A similar test done in SLAC FFTB gave the results that can be seen in the bottom left plot of this section.

Results of a FLUKA simulation using same beam and target specification can be seen in the bottom right plot of this section.

There is a systematic divergence of ~100 µm2 but both plots agree in the slope.

Summary & Future PlansSummary & Future Plans

• Resulting mechanical stresses examined with ANSYS3D• Continue study into beam damage/materials

– Experimental beam test to reduce largest uncertainties in material properties• Study geometries which can reduce overall length of spoilers while

maintaining performance• Means of damage detection, start engineering design of critical

components

• Combine information on geometry, material, construction, to find acceptable baseline design for– Wakefield optimisation– Collimation efficiency – Damage mitigation