• J. Norem, A. Hassanein, Z. Insepov, I. Konkashbaev
  ANL, Argonne, Illinois

We present a simple model of breakdown in rf cavities. For most events this involves tensile stress and tensile strength, however other effects can also contribute. We discuss the effects of different materials, fatigue, high pressure gas, primary and secondary emission sites, local field enhancements, dark currents, secondary emission, work functions, magnetic fields, macro and microscopic fracture mechanisms high current densities, surface and subsurface defects, and astronomical power densities. While primarily devoted to normal conductors, this work also has consequences for superconducting rf surfaces.

• J. Norem
  ANL, Argonne, Illinois
• A. Bross, A. Moretti, Z. Qian
  Fermilab, Batavia, Illinois
• R.P. Johnson
  Muons, Inc, Batavia
• D. Li, M.S. Zisman
  LBNL, Berkeley, California
• R.A. Rimmer
  Jefferson Lab, Newport News, Virginia
• R. Sandstrom
  CUI, Geneva
• Y. Torun
  IIT, Chicago, Illinois

The rf R&D program for high gradient, low frequency cavities to be used in muon cooling systems is underway in the Fermilab Muon Test Area. Cavities at 805 and 201 MHz are used for tests of conditioning techniques, surface modification and breakdown studies. This work has the Muon Ionization Cooling Experiment (MICE) as its immediate goal and efficient muon cooling systems for neutrino sources and muon colliders as the long term goal. We study breakdown, and dark current productions under a variety of conditions.

• J. Norem
  ANL, Argonne, Illinois
• P. Bauer
  Fermilab, Batavia, Illinois
• J. Sebastian, D.N. Seidman
  NU, Evanston

We are constructing a facility which combines an atom probe field ion microscope with a multi-element, in-situ deposition and surface modification capability. This system is dedicated to rf studies and the initial goal will be to understand the properties of evaporative coatings: field emission, bonding interdiffusion etc, to suppress breakdown and dark currents in normal cavities. We also hope to use this system to look more generally at interactions of surface structure and high rf fields. We will present preliminary data on structures relevant to normal and superconducting rf systems.

• X. Yang, C.M. Ankenbrandt, J.R. Lackey, R.D. Padilla, W. Pellico
  Fermilab, Batavia, Illinois
• J. Norem
  ANL, Argonne, Illinois

Since a wider aperture has been obtained along the Fermilab Booster beam line, this opens the opportunity for Booster running a higher intensity proton beam than ever before. Sooner or later, the available RF accelerating voltage will become a new limit for the beam intensity. Either by increasing the RF accelerating voltage or by reducing the accelerating rate can achieve the similar goal. The motivation for the 6-GeV study is to gain the relative accelerating voltage via a slower acceleration.