The influence of multiple ion species on Alfvén wave dispersion and Alfvén wave plasma heating

In this paper, the effects of light impurities, such as deuterium, helium, or carbon, on Alfvén wave dispersion characteristics are explored. It is shown that a small population of light impurities in a hydrogen plasma modify the dispersion of the global Alfvén waves and the Alfvén continuum in such a way that the wave frequency depends weakly on the toroidal wave number. It is also shown that the global Alfvén wave enters into the Alfvén continuum. Under these conditions, it is possible to heat plasma efficiently by employing an antenna with a broad toroidal wavelength spectrum. The relationship between impurity concentration and the efficiency of Alfvén wave heating is explored. Under appropriate conditions, the results indicate that in the presence of impurities, Alfvén waves can heat electrons predominantly in the central part of the plasma. This effect is explored via a series of numerical calculations of the heating specifically for the Phaedrus‐T Alfvén wave heating experiment [Phys. Fluids B 5, 2506 (1993)].