[en] Electron field emission (FE) from broad-area metal surfaces is known to occur at a much lower electric field than predicted by the Fowler-Nordheim law. This enhanced field emission (EFE) presents a major impediment to high electric field operation in a variety of applications, e.g., in superconducting niobium radio-frequency cavities for particle accelerators, klystrons, and a wide range of high voltage vacuum devices. Therefore EFE has been the subject of wide fundamental research for years. Although micron or submicron particles are often observed at such EFE sites, the strength and number of emitting sites and the causes of EFE strongly depend on surface preparation and handling, and the physical mechanism of EFE remains unknown. To systematically investigate the sources of this emission and to evaluate the best available surface preparation techniques with respect to resulting field emission, a DC scanning field emission microscope (SFEM) has been built at Thomas Jefferson National Accelerator Facility (Jefferson Lab). Broad-area samples can be moved laterally in a raster pattern (2.5 mu-m step resolution) under a high voltage micro-tip for EFE detection and localization in the SFEM. The emitting sites can then be characterized by SEM and EDX without breaking ultra high vacuum. EFE sources from planar Nb have been studied after preparation by chemical etching and electropolishing combined with ultrasonic deionized water rinse (UWR). Emitters have been identified and analyzed, and the preparation process has been refined and improved based on scan results. With the improved preparation process, field-emission-free or near field-emission-free surfaces at -140 MV/m have been achieved consistently on a number of samples

[en] An ECR-plasma reactor has been built to do energetic ion deposition of refractory metals in vacuum. The system uses an E-beam gun to create refractory metal flux. The neutral metal flux feeds into a microwave resonator and forms pure metal plasma created by Electron Cyclotron Resonance (ECR). The metal ions are extracted to a biased substrate for direct deposition. A retarding field energy analyzer is developed and used to measure the kinetic energy of metal ions at the substrate location. A high quality niobium thin film is obtained through this deposition system. The niobium film exhibits an excellent superconducting transition. The niobium ion energy distribution has been measured. The niobium ion at the substrate location has a median kinetic energy of 64-eV with an energy spread of 20-eV under certain plasma conditions

[en] The Spallation Neutron Source project includes a superconducting linac section in the energy range from 192 MeV to 1000 MeV. For this energy range two types of cavities are needed with geometrical beta - values of beta 0.61 and beta = 0.81. An aggressive cavity prototyping program is being pursued at Jlab, which calls for fabricating and testing of four beta = 0.61 cavities and two beta = 0.81 cavities. Both types consist of six cells made from high purity niobium and feature one HOM coupler of the TESLA type on each beam pipe and a port for a high power coaxial input coupler. Three of the four beta = 0.61 cavities will be used for a cryomodule test at the end of the year 2001. At this time two cavities of each type have been fabricated and the first tests on the beta = 0.61 cavity exceeded the design values for gradient and Q - value: Eacc = 10.3 MV/m and Q = 6.5 x 10⁹ at 2.1K. This paper will describe the cavity design with respect to electrical and mechanical features, the fabrication efforts and the results obtained with the different cavities existing at the time of the conference