High average power and high peak power gyrotrons: present capabilities and future prospects†

Abstract

We survey work in the U.S.A. High average power gyrotrons (1 MW at 100-150GHz) are required for ECRH of magnetic fusion plasmas. Even though gyrotrons have superior mode stability compared with other tubes, they must be so grossly overmoded to handle 1 MW CW that mode control does become an issue. Studies of gyrotron-oscillator cavity designs with enhanced mode stability properties are described, including complex and Fabry-Perot cavities. In the complex cavity concept, two cavities each operating in a different mode are strongly coupled. Exploitation of this concept in a 60 G Hz TED I/TE 0 1 gyrotron has already resulted in power greater than 200kW CWo Designs of TE 0 3jTE 0 4 and TE 0 3/TE 0 6 gyrotrons which promise to extend performance are discussed. A 115GHz gyrotron using a Fabry-Perot cavity has been successfully demonstrated at power levels above 50 kW and prospects of extending performance are considered. Study of high peak power gyrotrons is stimulated by the perceived requirement for 300 MW RF sources at i. -3 cm to drive very high energy (I TeV) linear electron accelerators. For this application, the phase of the microwave signal must be precisely controllable. These demanding requirements have led to renewed interest in gyro-klystron amplifiers, and studies of relatively low power gyro-klystrons will be reviewed. Finally, a design of a 300 MW gyro-klystron is presented.

A quasi-optical electron cyclotron maser for fusion reactor heating

“…High power microwave and millimeter sources, such as the quasi-optical electron cyclotron maser (QOECM) are important in fusion research[II [2], as welI as in high-energy physics [3] and in other applications. The interaction between the electromagnetic modes of a Fabry-Perot resonator and an electron beam gyrating through a magnetic field has been studied for both the cases of beams parallel and perpendicular to the resonator.…”

Phase noise reduction in a gyroklystron amplifier

“…Alternatively, -100MW peak power and a -1·6 Ils pulse length would be acceptable assuming the use of pulse compression between the microwave tube and the accelerator (Farkas 1986). High power microwave tubes that are being explored with the linear collider application in mind include the gyroklystron (Granatstein 1984) and conventional klystrons with multiple gaps in the output cavity. The gyroklystron project at the University of Maryland is initially aiming to demonstrate 30-50 MW of output power in I IlS pulses with a gain in excess of 50dB at ).=3 em (Chu et al 1985, Granatstein andVitello 1984).…”

Experiments on space-charge waves in electron beams propagating through a resistive-wall channel

“…Transport and acceleration of intense charged particle beams with high quality is an important issue in advanced accelerator applications such as colliders for high-energy physics, 1,2 induction linacs as drivers for heavy-ion inertial fusion, 3,4 high intensity linacs and synchrotrons for spallation neutron sources, 5,6 free-electron lasers and high-power microwave generators, 7,8 etc. Due to the requirement of ever increasing beam intensity in these applications, space-charge effects and collective behavior among charged beam particles play a crucial role in the beam dynamics, which may limit the maximum transportable beam current and/or deteriorate beam quality.…”