• C.D. Nantista, C. Adolphsen, F. Wang
  SLAC, Menlo Park, California

The phenomenon of rf breakdown presents a technological limitation in the application of high-gradient particle acceleration in normal conducting rf structures. Attempts to understand the onset of this phenomenon and to study its limits with different materials, cell shapes, and pulse widths has been driven in recent years by linear collider development. One question of interest is the role magnetic field plays relative to electric field. A design is presented for a single, non-accelerating, rf cavity resonant in two modes, which, driven independently, allow the rf magnetic field to be increased on the region of highest electric field without affecting the latter. The design allows for the reuse of the cavity with different samples in the high-field region. Available high-power data will also be presented.

• K.M. Schirm, S. Curt, S. Döbert, G. McMonagle, G. Rossat, I. Syratchev, L. Timeo
  CERN, Geneva
• A.A. Haase, A. Jensen, E.N. Jongewaard, C.D. Nantista, D.W. Sprehn, A.E. Vlieks
  SLAC, Menlo Park, California
• A. Hamdi, F. Peauger
  CEA, Gif-sur-Yvette
• S.V. Kuzikov, A.A. Vikharev
  IAP/RAS, Nizhny Novgorod

The CLIC RF frequency has been changed in 2008 from the initial 30 GHz to the European X-band 11.9942 GHz permitting beam independent power production using klystrons for CLIC accelerating structure testing. A design and fabrication contract for five klystrons at that frequency has been signed by different parties with SLAC. France (CEA Saclay) is contributing a solid state modulator purchased in industry to the CLIC study. RF pulses over 120 MW peak at 230 ns length will be obtained by using a novel SLED I type pulse compression scheme designed and fabricated in Nizhny Novgorod, Russia. The X-band power test stand has been installed in the CLIC Test Facility CTF3 for independent structure and component testing in a bunker, but allowing, in a later stage, for powering RF components in the CTF3 beam lines. The design of the facility, results from commissioning of the RF power source and the performance of the Test Facility are reported.

• D.W. Sprehn, A.A. Haase, A. Jensen, E.N. Jongewaard, C.D. Nantista, A.E. Vlieks
  SLAC, Menlo Park, California

A 12 GHz 50MW X-band klystron is under development at the SLAC National Accelerator Laboratory Klystron Department. The klystron will be fabricated to support programs currently underway at three European Labs; CERN, PSI, and INFN Trieste. The choice of frequency selection was due to the CLIC RF frequency changing from 30 GHz to the European X-band frequency of 11.9942 GHz in 2008. Since the Klystron Department currently builds 50MW klystrons at 11.424 GHz known collectively as the XL4 klystrons, it was deemed cost-effective to utilize many XL4 components by leaving the gun, electron beam transport, solenoid magnet and collector unchanged. To realize the rf parameters required, the rf cavities and rf output hardware were necessarily altered. Some improvements to the rf design have been made to reduce operating gradients and increase reliability. Changes in the multi-cell output structure, waveguide components, and the window will be discussed along with testing of the devices. Five klystrons known as XL5 klystrons are scheduled for production over the next two years.