• M. Popovic, C.M. Ankenbrandt, A. Moretti, S. Nagaitsev, T.J. Peterson, G.V. Romanov, N. Solyak, V.P. Yakovlev, K. Yonehara
  Fermilab, Batavia
• R.A. Baartman
  TRIUMF, Vancouver
• I.B. Enchevich, R.P. Johnson, M.L. Neubauer
  Muons, Inc, Batavia
• R.A. Rimmer
  JLAB, Newport News, Virginia

Modern technology allows us to consider operating an 8 GeV Linac in a cw mode to accelerate a high-current H^- beam. By using appropriate accumulation rings, the linac could provide simultaneous beams for direct neutrino production, neutrino factories, fixed target experiments, and muon colliders. Several other unique accelerator applications could also be served and improved by the same continuous beam, including studies of energy production and nuclear waste reduction by transmutation, rare muon decay searches, and muon catalyzed fusion. The trade-offs between cw operation compared to pulsed operation that are considered include the maximum rf gradient and corresponding linac length or energy, the rf frequency, rf peak power and coupler requirements, and refrigeration. Methods for accumulating the beam from a cw linac to serve the special needs of the potential future Fermilab programs mentioned above are considered. In this paper we also examine the use of a cyclotron as a source of high current beams to reduce the cost and complexity of the linac front end.

• R. Sah, M. Alsharo'a, R.P. Johnson, M.L. Neubauer
  Muons, Inc, Batavia
• M. BastaniNejad, A.A. Elmustafa
  Old Dominion University, Norfolk, Virginia
• J.M. Byrd, D. Li
  LBNL, Berkeley, California
• D. Rose, C.H. Thoma, D.R. Welch
  Voss Scientific, Albuquerque, New Mexico
• G.M. Wang
  ODU, Norfolk, Virginia

The performance of many particle accelerators is limited by the maximum electric gradient that can be realized in rf cavities. Recent studies have shown that high gradients can be achieved quickly in 805 MHz cavities pressurized with dense hydrogen gas, because the gas can suppress, or essentially eliminate, dark currents and multipacting. In this project, two new test cells operating at 500 MHz and 1.3 GHz will be built and tested, and the high pressure technique will be used to suppress the vacuum effects of evacuated rf cavities, so that the role of metallic surfaces in rf cavity breakdown can be isolated and studied as a function of external magnetic field, frequency, and surface preparation. Previous studies have indicated that the breakdown probability is proportional to a high power of the surface electromagnetic field, in accordance with the Fowler-Nordheim description of electron emission from a cold cathode. The experiments will be compared with computer simulations of the rf breakdown process.