08/01/2007Juan Luis Fernandez-Hernando End Station A Measurements on Collimator Wakefields 4th...

08/01/2007 Juan Luis Fernandez-Hernando

End Station A Measurements on Collimator Wakefields

4th Wakefield Interest Group - CI 05/03/2008

Luis Fernandez-Hernando, CCLRC DL, ASTeC

Adriana Bungau, Manchester University

Jonathan Smith, Lancaster University


Content:

• ESA

• Set up and collimators

• Analysis of T480

• Results

• Conclusion


• 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


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

Ebeam=28.5GeV


1500mm


T480“wakefield box”

ESA beamline

ESA beamline


1000mm OFE Cu, ½ gap 1.4mm


Designed Collimators


BPMBPMBPM BPM

A run with the beam going through the middle of the collimator (or without the collimator) is used as reference for the next run where the collimator will be moved vertically. This run also serves to calculate the resolution of each BPM.

BPMBPMBPM BPM

The analysis will do a linear fit to the upstream and downstream BPM data separately, per each pulse (bunch) . For this fit the data is weighted using the resolution measured for each BPM.


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


The slopes of each linear fit are subtracted obtaining a deflection angle. This angle is transformed into V/pC units using the charge reading and the energy of the beam.

All the reconstructed kicks are averaged per each of the different collimator positions and a cubic fit of the form:

y’ = A3·y3 + A1·y + A0

is done to the result. The error in the kick reconstruction at each collimator position weights the different points for the fit.

The kick factor is defined as the linear term of the cubic fit (A1).

BPMBPMBPM BPM


Col. 12 = 166 mradr = 1.4 mm

Ang

ular

kic

k (

V/p

C)

Collimator y (mm)

T480 (prelim.)2007 data

T480 (prelim.)2007 data

Luis Fernandez - Daresbury

Data analysis


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)


Collim No

Experimental measurements

(V/pC/mm)

Analytic predictions (V/pC/mm)

3-D Modeling prediction kick (V/pC/mm)

1 1.2 0.3 2.27 1.63 0.37

2 1.9 0.2 4.63 2.88 0.84

3 4.4 0.3 5.25 5.81 0.94

4 0.6 0.4 0.56 9.09 0.06

5 4.9 0.3 4.59 6.880.58

6 1.0 0.1 4.65 2.12 1.14

7 1.4 0.3 4.59 2.87 0.53

8 1.0 0.2 4.59 2.39 0.89

10 1.4 0.2

11 1.7 0.1

12 1.7 0.1

13 1.9 0.2 3.57 0.98

14 2.6 0.1 3.57 0.98

15 1.6 0.1 2.51 1.16

16 1.6 0.2 2.35 1.50

Measured and calculated kick factor

Note: quoted errors are estimates

Assuming 500 um bunch lenght

Colimators 4-5 and 13-16 do not include

the resistive component of the kick


SWMD: Deliverable Summary

“Engineering design for ILC mechanical spoiler, including prototype evaluations of wakefield and beam-damage performance.”

Wakefields: T480 at SLAC to evaluate wakefield performance of candidate spoiler designs, benchmarking calculations/modelling

16 jaw designs studied

Outcome of ongoing wakefield optimisation likely to require further iteration on candidate designs

First conceptual design for mechanical spoiler design available, to report at EPAC’08.

08/01/2007Juan Luis Fernandez-Hernando End Station A Measurements on Collimator Wakefields 4th...

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