1. 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

2. 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)

3. 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

4. Electric field RF Electric and Magnetic Fields for 1MW Input Power TM01 modeTE01 mode Magnetic field A.. D. Yeremian, V. A. Dolgashev, S. G. Tantawi 2011 Electric field Magnetic field RF in

5. S-parameters vs. Frequency A.. D. Yeremian, V. A. Dolgashev, S. G. Tantawi 2011

6. Surface Magnetic and Electric fields normalized to 1 MW of Input Power A.. D. Yeremian, V. A. Dolgashev, S. G. Tantawi 2011 to choke TM Electric field TM Magnetic field TE Magnetic field

7. 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.