Heating tokamaks via the ion-cyclotron and ion-ion hybrid resonances

Abstract

The ion-ion hybrid resonance can occur at high plarma• densities in tokamaks and thereby absorb energy from the fast magnetosonic mode which would otherwise propagate freely. Ion-cyclotron resonance regions, although they occur in the low density peripheral plasma, can nonetheless cause sufficient absorption to compete with fundamental cyclotron resonance damping by ions. For the ion-ion hybrid resonance it is shown that: (1) The energy absorption occurs via a sequence of mode conversions. (2) A poloidal field component normal to the ion-ion hybrid mode conversion surface strongly influences the mode conversion process so that rough ly equal electron and ion heating occurs in the present proton-deuterium experiments, while solely electron heating is predicted to prevail in deuteriumtritium reactors. (3) The ion-ion hybrid resonance suppresses toroidal eigenmodes. (4) Wave absorption i~ minority fundamental ion-cyclotron heating experiments will be dominated by ion-ion hybrid mode conversion absorption for minority concentrations exceeding roughly 1%.

Recent H majority inverted radio frequency heating scheme experiments in JET-ILW

“…At low 3 He concentrations, the deposition is close to the centre and highly peaked. When the concentration increases, the peak of the power deposition moves outward, reflecting the moving of the ion-ion hybrid layer whose position critically depends on the minority concentration and at which efficient localised absorption of the Bernstein wave by electrons takes place [12]. When X[ 3 He]~10%, the maximum of the power deposition has dropped by a factor 6 and its location has shifted to half-radius.…”

On all-FLR order numerical modelling of RF wave propagation and damping

“…Also the fact that the electrons do not take part at all in the absorption is highly unusual. Electron absorption scaling with k⊥ 2 when adding the electron Landau and transit time magnetic pumping contributions [9,10], the absence of electron absorption suggests that the considered spectrum not containing high enough k x -modes. More in depth analysis confirms this is indeed the case: see the inset for the corresponding evaluation using the TOMCAT differential equation solver [11] which shows a small but finite electron absorption exhibiting both long (fast wave) and short (Bernstein wave) wavelength structure.…”

A block-tridiagonal solver with two-level parallelization for finite element-spectral codes

“…If the distance between the cut--off layer and the resonance layer is small enough for tunneling of the wave as shown in Fig. 8, a large portion of the fast wave is not reflected but converted to either the ICW mode [30] or the IBW mode [31]. The wavelength of both converted modes is small, on the order of the ion gyroradius (ICW: a few millimeters, IBW: sub--millimeter).…”