On RF heating of inhomogeneous collisional plasma under ion-cyclotron resonance conditions
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ODS OF PLASMA HEATING
On RF Heating of Inhomogeneous Collisional Plasma under Ion-Cyclotron Resonance Conditions A. V. Timofeev Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123098 Russia e-mail: [email protected] Received May 26, 2015
Abstract—During ion-cyclotron resonance (ICR) heating of plasma by the magnetic beach method, as well as in some other versions of ICR heating, it is necessary to excite Alfvén oscillations. In this case, it is difficult to avoid the phenomenon of the Alfvén resonance, in which Alfvén oscillations transform into lower hybrid oscillations. The latter efficiently interact with electrons, due to which most of the deposited RF energy is spent on electron (rather than ion) heating. The Alfvén resonance takes place due to plasma inhomogeneity across the external magnetic field. Therefore, it could be expected that variations in the plasma density profile would substantially affect the efficiency of the interaction of RF fields with charged particles. However, the results obtained for different plasma density profiles proved to be nearly the same. In the present work, a plasma is considered the parameters of which correspond to those planned in future ICR plasma heating experiments on the PS-1 facility at the Kurchatov Institute. When analyzing the interaction of RF fields with charged particles, both the collisionless resonance interaction and the interaction caused by Coulomb collisions are taken into account, because, in those experiments, the Coulomb collision frequency will be comparable with the frequency of the heating field. Antennas used for ICR heating excite RF oscillations with a wide spectrum of wavenumbers along the magnetic field. After averaging over the spectrum, the absorbed RF energy calculated with allowance for collisions turns out to be close to that absorbed in collisionless plasma, the energy fraction absorbed by electrons being substantially larger than that absorbed by ions. DOI: 10.1134/S1063780X15110094
1. INTRODUCTION Ion-cyclotron resonance (ICR) heating is used to heat plasma in nuclear fusion devices, plasma systems for isotope separation, plasma propulsion engines, etc. There are different versions of ICR heating. Heating based on the excitation of Alfvén oscillations (AOs) (in particular, heating by the magnetic beach method) is inseparable from the phenomenon of the Alfvén resonance (AR) (see, e.g., [1]). In the AR, AOs with the predominant transverse polarization of the electric field (with respect to the external magnetic field) transform into lower hybrid oscillations (LHOs), whose electric field has an appreciable longitudinal component. For this reason, most energy deposited in AOs can be spent on electron heating (see, e.g., [2]). During ICR plasma heating in a nonuniform magnetic field by the magnetic beach method, AOs should be excited far from the ICR region and absorbed by ions when approaching the resonance zone. This process can be inhibited by the AR, due to which the AO energy is transferred to electrons. Ion heating by the mag
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