• J. R. Lackey, F. G. Garcia, M. Popovic, E. Prebys
  Fermilab, Batavia, Illinois

The operation and performance of the new, 15 Hz, H^- charge exchange injection system for the FNAL Booster is described. The new system installed in 2006 was necessary to allow injection into the Booster at up to 15 Hz. It was built using radiation hardened materials which will allow the Booster to reliably meet the high intensity and repetition rate requirements of the Fermilab's HEP program. The new design uses three orbit bump magnets (Orbmps) rather than the usual four and permits injection into the Booster without a septum magnet. Injection beam line modification and compensation for the quadrupole gradients of the Orbmp magnets is discussed.

• R. P. Johnson
  Muons, Inc, Batavia
• C. M. Ankenbrandt, C. M. Bhat, M. Popovic
  Fermilab, Batavia, Illinois
• S. A. Bogacz, Y. S. Derbenev
  Jefferson Lab, Newport News, Virginia

The idea of coalescing multiple muon bunches at high energy to enhance the luminosity of a muon collider provides many advantages. It circumvents space-charge, beam loading, and wakefield problems of intense low-energy bunches while restoring the synergy between muon colliders and neutrino factories based on muon storage rings. A sampling of initial conceptual design work for a coalescing ring is presented here.

• M. BastaniNejad, A. A. Elmustafa
  Old Dominion University, Norfolk, Virginia
• M. Alsharo'a, P. M. Hanlet, R. P. Johnson, M. Kuchnir, D. J. Newsham
  Muons, Inc, Batavia
• C. M. Ankenbrandt, A. Moretti, M. Popovic, K. Yonehara
  Fermilab, Batavia, Illinois
• D. M. Kaplan
  Illinois Institute of Technology, Chicago, Illinois

Microscopic images of the surfaces of metallic electrodes used in high-pressure gas-filled 800 MHz RF cavity experiments are used to investigate the mechanism of RF breakdown. The images show evidence for melting and boiling in small regions of ~10 micron diameter on tungsten, molybdenum, and beryllium electrode surfaces. In these experiments, the dense hydrogen gas in the cavity prevents electrons or ions from being accelerated to high enough energy to participate in the breakdown process so that the only important variables are the fields and the metallic surfaces. The distributions of breakdown remnants on the electrode surfaces are compared to the maximum surface gradient E predicted by an ANSYS model of the cavity. The surface local density of spark remnants, presumably the probability of breakdown, shows a power law dependence on the maximum gradient, with E¹⁰ for tungsten and molybdenum and E⁷ for beryllium. This is reminiscent of Fowler-Nordheim behavior of electron emission from a cold cathode, which is explained by the quantum-mechanical penetration of a barrier that is characterized by the work function of the metal.