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 (MV/m) @30MV/m Qext of HOM port @1.3GHz 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 MV/m @ 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