1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E+10

2.7E+09 3.0E+09 3.3E+09 3.6E+09 3.9E+09 4.2E+09 4.5E+09 4.8E+09 5.1E+09

F (Hz)

Qex

t

1st dipole band

1st monopole band

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

Low-Loss Cavity - End Group Optimization

* Work supported by DOE contract DE-AC02-76SF00515

2.451 , 3.2282E+05

1.929 , 1.6681E+051.719 , 7.5188E+04

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.600 1.700 1.800 1.900 2.000 2.100 2.200 2.300 2.400 2.500 2.600F (GHz)

R/Q

(ohm

/m^2

/cav

ity)

1.719 , 6.22E+04 2.451 , 3.58E+04

1.929 , 1.45E+04

2.451 , 3.939E+05

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.600 1.700 1.800 1.900 2.000 2.100 2.200 2.300 2.400 2.500 2.600F (GHz)

Qex

t

LL-new-designLL-original-design

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

Comparing measurements (color) with Omega3P (black) eigenmode solutions shows data scatter around ideal cavity results due to shape deformations

1

ICHIRO Cavity

ICHIRO single cell reached ~ 50 MV/m @ KEK 9-cell cavities can’t process above 30 MV/m

3.9 GHz Deflecting Cavity Damping

Operating Mode

Solid – FNAL design Hollow – w/ SLAC modifications

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.

Multipacting Barriers HOM Notch Filter

Notch gap (mm)

Notch gap field (MV/m)

@30MV/m

Antenna tip Field (MV/m) @30MV/m

Qext of HOM port @1.3GHz

Up-stream

Down-stream

Up-stream

Down-stream

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

power flow at HOM coax ports @30MV/m

0.001

0.01

0.1

1

10

100

1.4 1.5 1.6 1.7 1.8 1.9 2

notch gap (mm)

Po

we

r (w

)

upstream

dow nstream

Notch gap

Antenna tip

Track3P

1.E+04

1.E+05

1.E+06

1879 1880 1881 1882F (MHz)

Qe

xt

tdr-ori-cavitytune two end cupstune cell 1 (increasing L 0.1mm)tune cell 1 (decreasing L 0.1mm)

Cell deformation: elliptical shape increases frequency split cell length error causes frequency shift.

400

450

5.0

Gap Tuning

HOMCoupler

2nd dipole band

SOMCoupler

InputCoupler

LOMCoupler

Ideal cavity

split

scatter

shift

dr=0.25mm1.E+04

1.E+05

1.E+06

1879 1880 1881 1882F (MHz)

Qex

t

defor cell1 along xdefor cell4 along xdefor cell6 along xdefor cell9 along xidea cavity

Cell elliptical distortion Cell length distortion