CLASSE, Ithaca
A 1300 MHz deflecting cavity will be used for beam slice emittance measurements, and to study the temporal response of negative electron affinity photocathodes in the ERL injector currently under construction at Cornell University. A single-cell TM110-mode cavity was designed to deflect the beam vertically. The paper describes the cavity shape optimization procedure, its mechanical design and performance at low RF power.
CLASSE, Ithaca
Based on the encouraging results of the first 1300 MHz 70 mm aperture single cell re-entrant cavities*, we continue the high gradient studies for ILC with new re-entrant cavities made of fine-grain as well as large-grain niobium. These new cavities have smaller aperture of 60 mm, providing a further reduced Hpk/Eacc or a further improved ultimate gradient. Four 1300 MHz 60 mm aperture re-entrant cavities are made, two out of fine grain niobium and the other two out of large-grain niobium. In addition, two elliptical shape 1500 MHz cavities are also made out of large-grain niobium. We present the testing results of these cavities.
* R. L. Geng et al., PAC2005, p.653.
CLASSE, Ithaca
Six 1300 MHz superconducting niobium 2-cell cavities are manufactured for the prototype of Cornell ERL injector to boost the energy of a high current, low emittance beam produced by a DC gun. Designed for high current beam acceleration, these cavities have new characteristics as compared to previously developed low-current cavities such as those for TTF. Precision manufacture is emphasized for a better straightness of the cavity axis so as to avoid unwanted emittance dilution. We present the manufacturing, processing and vertical test performance of these cavities. We also present the impact of new cavity characteristics to the cavity performance as learnt from vertical tests. Solutions for improving cavity performance are discussed.
CLASSE, Ithaca
Cornell University is developing and fabricating a SRF injector cryomodule for the acceleration of the high current (100 mA) beam in the Cornell ERL prototype and ERL light source. Major challenges include emittance preservation of the low energy, ultra low emittance beam, cw cavity operation, and strong HOM damping with efficient HOM power extraction. Prototypes have been completed for the 2-cell niobium cavity with helium vessel, coaxial blade tuner with piezo fine tuners, twin high power input couplers, and beam line HOM absorbers loaded with ferrites and ceramics. Axial symmetry of HOM absorbers, together with two symmetrically placed input couplers per cavity, avoids transverse on-axis fields, which would cause emittance growth. A one-cavity cryostat has been designed following concepts of the TTF cryostat, and is presently under fabrication and assembly. The cryostat design has been optimized for precise cavity alignment, good magnetic shielding, and high dynamic cryogenic loads from the RF cavities, input couplers, and HOM loads. In this paper we report on the status of the assembly and first test of the one-cavity test cryostat.
Cornell University, Ithaca, New York
The introduction of reentrant shape for superconducting cavities has made it possible to achieve record high gradients. In this paper it is shown that lowest losses in the cavities are also achievable employing the reentrant shape. Influence of the cavity wall slope angle on the extreme gradient and losses is analyzed.