08/01/2007juan luis fernandez-hernando end station a measurements on collimator wakefields 4th...
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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
08/01/2007 Juan Luis Fernandez-Hernando
Content:
• ESA
• Set up and collimators
• Analysis of T480
• Results
• Conclusion
08/01/2007 Juan Luis Fernandez-Hernando
• 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.
08/01/2007 Juan Luis Fernandez-Hernando
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
08/01/2007 Juan Luis Fernandez-Hernando
Magnet mover, y range = mm, precision = 1m
Ebeam=28.5GeV
08/01/2007 Juan Luis Fernandez-Hernando
1500mm
08/01/2007 Juan Luis Fernandez-Hernando
T480“wakefield box”
ESA beamline
ESA beamline
08/01/2007 Juan Luis Fernandez-Hernando
08/01/2007 Juan Luis Fernandez-Hernando
1000mm OFE Cu, ½ gap 1.4mm
08/01/2007 Juan Luis Fernandez-Hernando
08/01/2007 Juan Luis Fernandez-Hernando
Designed Collimators
08/01/2007 Juan Luis Fernandez-Hernando
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.
08/01/2007 Juan Luis Fernandez-Hernando
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
08/01/2007 Juan Luis Fernandez-Hernando
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
08/01/2007 Juan Luis Fernandez-Hernando
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
08/01/2007 Juan Luis Fernandez-Hernando
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
08/01/2007 Juan Luis Fernandez-Hernando
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)
08/01/2007 Juan Luis Fernandez-Hernando
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
08/01/2007 Juan Luis Fernandez-Hernando
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.
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