• F. Wang, C. Adolphsen, J.W. Wang
  SLAC, Menlo Park, California

Funding: Work supported by Department of Energy contract DE-AC03-76SF00515.
A 5-cell, normal-conducting, 1.3 GHz, standing-wave cavity was built as a prototype capture accelerator for the ILC positron source. Although the ILC uses predominately super-conducting cavities, the capture cavity location in both a high radiation environment and in a solenoidal magnetic field requires it to be normal conducting. With the ILC requirements of relatively long beam pulse on-time (1 msec at 5 Hz) and high gradient for efficient positron capture (15 MV/m), achieving adequate cavity cooling to prevent detuning was challenging. This paper presents the operational performance of this cavity including its breakdown characteristics as a function of gradient, pulse length and solenoidal magnetic field strength. In addition, these results are compared with those from other normal-conducting cavities at various frequencies

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

Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.
We report on the L-band rf power distribution system (PDS) developed at SLAC for Fermilab's NML superconducting test accelerator facility. The makeup of the system, which allows tailoring of the power distribution to cavities by pairs, is briefly described. Cold test measurements of the system and the results of high power processing are presented. We also investigate the feasibility of eliminating the expensive, lossy circulators from the PDS in the ILC linacs by taking advantage of our scheme of pair-feeding through 3-dB hybrids. A computational model is used to simulate the impact on field stability of inter-cavity coupling due to reduced isolation. Measurements of typically achievable hybrid port isolations provide the likely magnitude for such coupling.

• S. Döbert, A. Grudiev, G. Riddone, M. Taborelli, W. Wuensch, R. Zennaro
  CERN, Geneva
• C. Adolphsen, V.A. Dolgashev, L. Laurent, J.R. Lewandowski, S.G. Tantawi, F. Wang, J.W. Wang
  SLAC, Menlo Park, California
• S. Fukuda, Y. Higashi, T. Higo, S. Matsumoto, K. Ueno, K. Yokoyama
  KEK, Ibaraki

In recent years evidence has been found that the maximum sustainable gradient in an accelerating structure depends on the rf power flow through the structure. The CLIC study group consequently designed a new prototype structure for CLIC with a very low group velocity, input power and average aperture (a/λ = 0.12). The 18 cell structure has a group velocity of 2.4% at the entrance and 1% at the last cell. Several of these structures have been made in collaboration between KEK, SLAC and CERN. A total of five brazed-disk structures and two quadrant structures have been made. The high power results of some of these structures are presented. The first KEK/SLAC built structure reached an unloaded gradient in excess of 100 MV/m at a pulse length of 230 ns with a breakdown rate below 10-6. The high-power testing was done using the NLCTA facility at SLAC.