Title :
Effect of the radial thickness of electron beams on mode coupling and stability in gyrotrons
Author :
Nusinovich, G. ; Sinitsyn, O.V. ; Yedulla, M. ; Velikovich, L.
Author_Institution :
IREAP, Maryland Univ., College Park, MD, USA
Abstract :
In the development of gyrotrons for controlled fusion experiments (electron cyclotron resonance plasma heating and current drive, suppression of plasma instabilities), one of the most important problems is to provide a stable, highly efficient operation in the desired mode. So far this problem was considered under the assumption that the RF field in a gyrotron cavity is excited by an annular, ideally thin, cylindrical electron beam. However, as the wavelength shortens and the beam power increases, the spread in radii of electron guiding centers, Rb, becomes more important for gyrotron operation. First, this spread reduces the efficiency because electrons with different guiding center radii have different coupling impedance to the RF field with a certain radial structure. Second, in the case of simultaneous interaction with several modes with different radial structures, the spread in guiding center radii may result in simultaneous excitation of these modes (a so-called "weak" coupling of modes, which extract energy from different fractions of the beam). The effect of the beam radial thickness on the mode interaction and stability is analyzed.
Keywords :
Q-factor; coupled mode analysis; gyrotrons; particle beam stability; plasma radiofrequency heating; Q-factor; RF field; beam radial thickness; controlled fusion; current drive; electron beams; electron cyclotron resonance plasma heating; gyrotrons; hard excitation; highly efficient operation; mode coupling; mode interaction; mode stability; saturation effects; soft self-excitation; Cyclotrons; Electron beams; Gyrotrons; Heating; Optical coupling; Plasma stability; Plasma waves; Radio frequency; Resonance; Temperature control;
Conference_Titel :
Vacuum Electronics Conference, 2002. IVEC 2002. Third IEEE International
Print_ISBN :
0-7803-7256-5
DOI :
10.1109/IVELEC.2002.999409