No abstract

Superconducting radio frequency niobium cavities are the building blocks of modern accelerators for scientific applications. Lower surface resistance, higher fields, and high operating temperatures advance the reach of the future accelerators for scientific discovery as well as potentially enabling cost-effective industrial solutions. We describe the design and performance of an Nb3Sn coating system that converts the inner surface of niobium cavities to an Nb3Sn film. The niobium surface, heated by radiation from the niobium retort, is exposed to Sn and SnCl2 vapor during the heat cycle, which results in about 2 μm Nb3Sn film on the niobium surface. Film composition and structure as well as radio frequency properties with 1-cell R&D cavities and 5-cell practical accelerator cavities are presented.

The Spallation Neutron Source project includes a superconducting linac section in the energy range from 186 MeV to 1000 MeV. For this energy range two types of cavities are needed with geometrical β values of β=0.61 and β=0.81. An aggressive cavity prototyping program is being pursued at Jefferson Lab, which calls for fabricating and testing four β=0.61 cavities and two β=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 β=0.61 cavities will be used for a cryomodule test at the end of 2001. Two cavities of each type have been fabricated and the first tests on both cavities exceeded the design values for gradient and Q value: E acc = 10.1 MV/m and Q = 5×10 9 at 2.1K for the β=0.61 and E acc = 12.5 MV/m and Q = 5×10 9 at 2.1 K for the β=0.81.

No abstract

The planned upgrade of the CEBAF electron accelerator includes the development of an improved cryomodule. Several components differ substantially from the original CEBAF cryomodule; these include: the new 7-cell, 1.5 GHz cavities with integrated helium vessel, a new, backlash-free cavity tuner, the waveguide coupler with its room-temperature ceramic window. In order to test the design features and performance of the new components, a horizontal cryostat (Horizontal Test Bed) has been constructed which allows testing with a turn around time of less than three weeks. This cryostat provides the environment for testing one or two cavities, with associated auxiliary components, in a condition similar to that of a real cryomodule. A series of tests has been performed on a prototype 7-cell cavity and the above-mentioned systems. In this paper the results of the tests on the cryostat, on the cavity performance, on its coupler, on the tuner characteristics, and on the microphonics behavior are presented.