Dual Mode Cavity for Testing
Effects of RF Magnetic field on Breakdown
Properties
A. Dian Yeremian, Valery Dolgashev, Sami Tantawi
SLAC National Accelerator Laboratory
Many thanks to Sami Tantawi for inspiring the work.
US High Gradient Research Collaboration Workshop 2011
February 9-10, 2011
SLAC National Accelerator Laboratory
History
1. Dedicated experiments to determine effects of RF magnetic fields on RF
breakdown in waveguides showed that when magnetic fields is increased in
place of peak electric fields, this decreased the breakdown limit.
V. A. Dolgashev and S. G. Tantawi, "RF Breakdown in X-band Waveguides",
Poc. of EPAC 2002, Paris, France, 2002, 2139-2141.
2. During NLC program we discovered that moderate electric field at same
location as high magnetic fields (at sharp edges of accelerating structure
couplers) leads to “magnetic breakdowns”.
V. A. Dolgashev, "High Magnetic Fields in Couplers of X-band
Accelerating Structures,” Proc. of IEEE PAC 2003, Portland, Oregon,
2003, pp. 1267-1269, SLAC-PUB-10123.
3. We discovered that breakdown rate is highly correlated with peak pulse heating
in single-cell-SW structures of disc-loaded waveguide type, made of soft copper.
V. Dolgashev, S. Tantawi, Y. Higashi, B. Spataro, “Geometric dependence of
radio-frequency breakdown in normal conducting accelerating structures”,
Appl. Phys. Lett. 97, 171501 (2010); doi:10.1063/1.3505339 (3 pages)
Motivation
We propose to study effect of rf magnetic field on accelerating
gradient in geometry as close as practical to a standing wave
accelerator cell.
S. Tantawi, "Experimental Evaluation of Magnetic Field Effects
on Breakdown Rates", CERN Breakdown Physics Workshop,
May 2010
RF Electric and Magnetic Fields for 1MW Input Power
TM01 mode
TE01 mode
Electric field
Electric field
RF in
RF in
Magnetic field
Magnetic field
RF in
RF in
A.. D. Yeremian, V. A. Dolgashev, S. G. Tantawi 2011
S-parameters vs. Frequency
A.. D. Yeremian, V. A. Dolgashev, S. G. Tantawi 2011
Surface Magnetic and Electric fields
normalized to 1 MW of Input Power
TE Magnetic field
90
80
TM Magnetic field
E [MV/m], H*Zo[MV/m]
70
60
TM Electric field
50
40
30
to choke
20
10
0
-10
0
20
40
60
80
100
Distance Along Surface [mm]
A.. D. Yeremian, V. A. Dolgashev, S. G. Tantawi 2011
Summary
We designed a dual mode cavity with geometry as
close as practical to a Standing Wave accelerator
cell in order to study effects of rf magnetic fields on
rf breakdown rate.
We plan to build it and test at ASTA.