E. Chojnacki

Design of a high average power waveguide window

A study has been performed to design a waveguide vacuum window capable of propagating >1 MW average power operating at 500 MHz. This would extend current technology by about a factor of 2 in average power for stand-alone windows, made possible by advances in available ceramic size and quality. The work to be presented comprises the RF design and corresponding thermo-mechanical analysis.

The cornell erl superconducting 2-cell injector cavity string and test cryomodule

Cornell University is developing and fabricating a SRF injector cryomodule for the acceleration of the high current (100 iriA) 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 fer- rites 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.

Development of superconducting RF for CESR

After the successful CESR beam test of August 1994 the continued development of a superconducting RF system for the CESR luminosity upgrade is in progress at the Laboratory of Nuclear Studies, Cornell University. The system description as well as recent results are presented.

Upper hybrid wave collective accelerator studies

The authors report progress in the development of a low-repetition-rate modulator for use in an upper-hybrid-wave collective accelerator project as well as initial results on wave excitation on a 400-kV, 150-400-A beam driven by a single-shot Marx-Blumlein pulser. Waves are excited as the beam propagates through a cavity where an interaction develops between the rotating beam and electromagnetic waves in the cavity. The cavity is tapered into a uniform guide in which all electromagnetic modes are cut off for the frequencies of interest while the cyclotron body wave on the beam continues to propagate. Measurements of the body wave downstream of the cavity are reported. It is pointed out that the accelerator concept is of interest for a variety of reasons, one of which is that it allows for the development of an accelerator in which the need for coupling circuits between the RF source and the accelerated beam is eliminated. A corollary of this is that the acceleration field is a maximum at the location of the beam being accelerated and not at the structure boundaries where breakdown may occur. A second important reason for the study is that the system is simple and eliminates the need for complex structures while retaining the essential features of an RF accelerator.<<ETX>>

A high power X-band relativistic klystron

Intrinsic klystrons have been proposed as an RF drive for future high-gradient accelerator structures. Presented are details of experiments in which a 400 keV, 250-500 A electron beam is propagated through X-band TM/sub 020/ cavities to demonstrate high-beam-energy, high-frequency klystron operation. A magnetron supplies microwave power to the initial cavity for amplification. Profiles of the downstream RF magnetic field have indicated that space charge oscillations dominate the klystron beam behavior. Previous small signal experiments are correlated to present high-power results in order to compare gain measurements, beam loading effects, and output RF pulse quality.<<ETX>>