Modeling of high power gyrotrons: Comparison with experiments

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:438842

Levush, B; Antonsen, Jr, T M; Cai, S Y; Saraph, G ^[1]; Guss, W C; Basten, M A; Kreischer, K E; Temkin, R ^[2]

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1. Univ. of Maryland, College Park, MD (United States). Inst. for Plasma Research
2. Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center

One would like to simulate the operation of gyro devices using Particle in Cell (PIC) computer codes. Unfortunately, the PIC simulations are not yet at a stage where they can be used effectively for gyrotron modeling. However, successful modeling of gyro-devices has been carried out over the years using reduced descriptions of the interaction. The key step in deriving the reduced description is representing the radiation field as a superposition of a small number of modes of the interaction waveguide whose amplitudes and phases evolve slowly in time and space on the scale of the frequency and wavelength of the radiation. The basic time scale for updating the radiation field is increased from a fraction of wave period, as it is in PIC codes, to a fraction of the cavity fill time, which is essentially the wave period times the quality factor, Q, of the cavity. Furthermore, the structure of the field in the direction transverse to the applied magnetic field is expressed as a sum of normal modes of the symmetric waveguide. This reduces the solution of Maxwell`s Equations to the solution of a coupled system of a relatively small number of one dimensional partial differential equations. As the amplitudes and phases of the cavity modes change on the cavity fill time scale, one can achieve a savings in computation time by periodically launching ensembles of beam particles, which transit the interaction region in a short time compared with the cavity fill time, and then updating the cavity fields taking relatively large time steps. Simulation results obtained with this method will be presented and compared with experiments conducted at the MIT.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• OSTI ID: 438842
• Report Number(s): CONF-960634--
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
COMPARATIVE EVALUATIONS
COMPUTERIZED SIMULATION
MATHEMATICAL MODELS
MICROWAVE AMPLIFIERS
OPERATION