Free-electron masers vs. gyrotrons: prospects for high-power sources at millimeter and submillimeter wavelengths

MW gyrotron development for fusion plasma applications

“…This condition is satisfied if a bunching mechanism exists to generate electron density variations of a size comparable to the wavelength of the imposed EM wave. To achieve such a mechanism, a resonance condition must be satisfied between the periodic motion of the electrons and the EM wave in the interaction region [1,[7][8][9][10][11]…”

“…The strength of the magnetic field determines the radiation frequency. Gyrotron oscillators (gyro-monotrons or simply gyrotrons) are devices that usually utilize only weakly relativistic electron beams (E beam < 100 kV, γ < 1.2) with high transverse momentum (velocity ratio α = v ⊥ /v z ≈ 1.3) [1,[7][8][9][10][11]. The wavevector of the radiation in the cavity is almost transverse to the direction of the external magnetic field (k ⊥ k z , and the Doppler shift is small) resulting, according to equations ( 2) and (3), in radiation near the electron cyclotron frequency or one of its harmonics:…”

“…At present, gyrotrons are mainly used as high power millimetre (mm)-wave generators for electron cyclotron heating (ECH) and diagnostics such as collective Thomson scattering in magnetically confined plasmas for controlled thermonuclear fusion research [1], where robust long-pulse mm-wave sources are required. ECH has become a well established method for tokamaks [2,3] and especially for stellarators [4].…”

Long pulse operation of 170GHz ITER gyrotron by beam current control

“…The intensive development of the 170 GHz gyrotron with 1 MW, continuous wave (CW) operation and 50% efficiency has been carried out to satisfy the requirements of the ITER [3][4][5][6]. Japan Atomic Energy Agency (JAEA), formerly JAERI, initiated the development of a highpower gyrotron with the 100 GHz band in order to apply it to fusion devices from 1980s [7].…”

Recent Developments on High-Power Gyrotrons—Introduction to This Special Issue

“…The possible applications of gyrotrons and other gyro-type fast-wave devices span a wide range of technologies [11,[13][14][15][16][17][18]. The plasma physics community has already taken advantage of recent advances in producing high-power micro-and millimeter (mm) waves in the areas of RF plasma applications for magnetic confinement fusion studies, such as lower hybrid current drive (1)(2)(3)(4)(5)(6)(7)(8), electron cyclotron resonance heating and current drive , plasma production for numerous different processes and plasma diagnostic measurements such as collective Thomson scattering or heat-pulse propagation experiments.…”