1. Design and testing of the Beam Delivery System collimators for the International Linear Collider
J. L. Fernandez-Hernando
STFC/ASTeC Daresbury Lab

2. 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.

3. a
0.6c0
Starting point
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 c0 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.

4. [Details, see Eurotev Reports 2006-015, -021, -034]
Spoilers considered include…
0.6c0
e-, Ebeam=250 GeV, sxsy=1119mm2
also, Ebeam=500 GeV
2mm
335mrad
10mm
Option 1: Ti/C, Ti/Be
As per T480
Ti, Cu, Al
Graphite regions
Option 3: Ti/C
Option 2: Ti/C, Cu/C, Al/C
0.3 Xo of Ti alloy upstream and downstream tapers
0.6 Xo of metal taper (upstream), 1 mm thick layer of Ti alloy
[Details, see Eurotev Reports , -021, -034]

5. ∆Tmax = 870 K per a bunch of 2E10 e- at 500 GeV
2 mm deep from top
Full Ti alloy spoiler
810 K
405 K
270 K
135 K
∆Tmax = 870 K per a bunch of 2E10 e- at 500 GeV
σx = 79.5 µm, σy= 6.36 µm

6. Ti / Graphite Spoiler Ti C beam
Temperature data in the left only valid the Ti-alloy material. Top increase of temp. in the graphite ~400 K. Dash box: graphite region.
540 K
405 K
400 K
270 K
∆Tmax = 575 K per a bunch of 2E10 e- at 500 GeV
σx = 79.5 µm, σy= 6.36 µm
2 mm deep from top
Ti alloy and graphite spoiler

7. Temperature increase from 1 bunch impact
Summary of simulations
Temperature increase from 1 bunch impact
Exceeds fracture temp.
2mm depth
10mm depth
250 GeV e-
1119 µm2
500 GeV e-
79.56.4 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
Graphite+Ti option 3
300 K
Exceeds melting temp.

8. A final collimator design should minimise this effect.
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.

9. Beam Parameters at SLAC ESA and ILC
Repetition Rate
10 Hz
5 Hz
Energy
28.5 GeV
250 GeV
Bunch Charge
2.0 x 1010
Bunch Length
300 mm
Energy Spread
0.2%
0.1%
Bunches per train
1 (2*)
2820
Microbunch spacing
- (20-400ns*)
337 ns
*possible, using undamped beam

10. ~40 m 2 doublets ~15 m 2 triplets BPM BPM BPM BPM Vertical mover
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

11. ~40 m 2 doublets ~15 m 2 triplets BPM BPM BPM BPM Vertical mover
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

13. Col. 1 Col. 6 Col. 3 L=1000 mm Col. 12 a = 324 mrad r = 2 mm
(r = ½ gap)
a = 166
r = 1.4 mm
Col. 6
Col. 12
a = 166 mrad
r = 1.4 mm
L=1000 mm
Col. 3
a = 324 mrad
r = 1.4 mm

14. 1Assumes 500-micron bunch length
Coll.
Measured4
Kick Factor
V/pC/mm (c2/dof)
Linear + Cubic Fit
Analytic Prediction1
V/pC/mm
3-D Modelling
Prediction2 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)
2.7 ± 0.53 8
1.7 ± 0.3 (2.2)
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 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

15. Material damage test beam at ATFx y
reference
pin hole
guide channels
low mass mounting Cu Ti
target area
10mm
The purpose of the first test run at ATF is to:
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.
Allow us to commission the proposed test system of vacuum vessel, multi-axis mover, beam position and size monitoring.
Validate the mode of operation required for ATF in these tests.
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.
sample holder
Bunch sxsy (mm2), material
Estimated damage region, x
Estimated damage region, y
Estimated damage region, z
1.90.5, Ti alloy
11 (14) mm
4 (5.6) mm
5 (8) mm
202, Ti alloy
45 (90) mm
5 (9) mm
2 (7) mm
202, Cu
65 (100) mm
7 (10) mm
3 (7) mm

16. 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.
[Measurements c/o Marc Ross et al., Linac’00]

17. Resulting mechanical stresses examined with ANSYS3D
Summary & 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