1. SRF Cavity Designs for the International Linear Collider*
L. Xiao, A. Candel, A. Kabel, Z. Li, C.Ng, K. Ko, V. Akcelik, L. Ge, R. Lee, E. Prudencio, G. Schussman, R.Uplenchwar, S. Chen, SLAC;
J. Sekutowicz, DESY; T. Higo, K. Saito, KEK
SLAC is contributing to the design of SRF cavities for the International Linear Collider (ILC) by performing highly accurate, high fidelity electromagnetic modeling using the advanced tools developed under the US DOE SciDAC program. The parallel finite element codes include the eigensolver Omega3P for calculating mode damping, S3P for finding S-parameters, the time-domain solver T3P for computing wakefields and the particle tracking code Track3P for simulating multipacting and dark current. We present the results from their applications to the ILC main linac cavity including the baseline TDR design and the alternate Low-Loss and Ichiro designs, and also to the 3.9 GHz deflecting cavity for the interaction region.
Baseline TDR Cavity – Cavity Imperfections
ICHIRO Cavity
Multipacting Barriers
Notch gap
Antenna tip
HOM Notch Filter 1
Cell elliptical distortion
Cell length distortion
Ideal cavity
split
scatter
shift
Gap Tuning
dr=0.25mm
Notch gap (mm)
@30MV/m
Notch gap field (MV/m)
Antenna tip Field
Qext of HOM
Up-stream
Down-stream
1.63
16.9
5.0
0.8
0.2
6.1e+9
1e+12
1.73
16.5
4.9
1.4
0.4
5.2e+8
9.e+9
2.73
13.3
3.9
6.1
3.0
1.4e+7
1.7e+8
Track3P
Cell deformation:
elliptical shape increases frequency split
cell length error causes frequency shift.
Comparing measurements (color) with Omega3P (black) eigenmode solutions
shows data scatter around ideal cavity results due to shape deformations
ICHIRO single cell reached ~ 50 KEK
9-cell cavities can’t process above 30 MV/m
Low-Loss Cavity - End Group Optimization
3.9 GHz Deflecting Cavity Damping
1st monopole
band
1st dipole band
400
450
2nd dipole band
HOM
Coupler
SOM
Coupler
Operating Mode
5.0
By adjusting the end-pipe radius, the HOM coupler azimuthal location, and the loop shape and configuration, the Qe of the dangerous 3rd band mode was reduced to below stability threshold (Qe<105). Similar improvements carried out for the ICHIRO cavity which is based on the LL design.
Input
Coupler
LOM
Coupler
Solid – FNAL design
Hollow – w/ SLAC modifications
* Work supported by DOE contract DE-AC02-76SF00515