Magnetosonic oscillations of thin plasma columns
- PDF / 453,383 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 20 Downloads / 235 Views
LLATIONS AND WAVES IN PLASMA
Magnetosonic Oscillations of Thin Plasma Columns A. V. Timofeev National Research Centre Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123182 Russia email: [email protected] Received May 5, 2014
Abstract—Oscillations of a plasma column in a longitudinal magnetic field are considered. It is found that eigenmodes with frequencies close to the ion cyclotron frequency can be excited in columns the radii of which are smaller than the characteristic wavelength of magnetosonic oscillations predicted by the theory of homo geneous plasma. The eigenmodes have the form of waves running around the column axis in the direction of electron gyration in the magnetic field. Magnetosonic oscillations can be excited as a side effect when using helical antennas for ion cyclotron resonance heating of plasma. These oscillations should enhance electron heating in the plasma core, as well as both electron and ion heating at the periphery of the plasma column. The spectrum of eigenmodes of inhomogeneous plasma columns includes oscillations of different nature. Comparative analysis of their properties performed in the present paper is useful for understanding the full picture of the physical processes occurring during ion cyclotron resonance heating and clarifying the charac teristic features of the magnetosonic oscillations under study. DOI: 10.1134/S1063780X14110063
1. INTRODUCTION Magnetosonic oscillations (MSOs), also called fast MSOs, are a fundamental phenomenon characteristic of magnetized plasma. In particular, they are used to heat plasma by the method of ion minority in fusion devices (see, e.g., [1]). These oscillations can also be excited as a side effect in other ion cyclotron reso nance (ICR) heating systems, such as systems for ICR isotope separation [2] and the VASIMR plasma thruster [3]. The MSO frequency can be varied in a wide range of 0 < ω ≤ ωi . In the highfrequency range ω Ⰷ ωi , MSOs transform into helicons, which turned out to be very efficient for plasma generation. For this reason, the latter are widely used in plasma technolo gies and have been thoroughly studied theoretically. In particular, it was found that, in a plasma column with a longitudinal magnetic field, there should pre vail oscillations that run around the column axis (along the azimuth) in the direction of electron gyra tion in the magnetic field [4, 5]. This agrees with the characteristic feature of helicons, namely, with their electric field being dominated by the circular compo nent rotating in the same direction as electrons. Since, as mentioned above, both helicons and MSOs belong to the same branch of oscillations, it may be expected that lowfrequency MSOs running in the direction of electron gyration should also be predom inantly excited in the plasma column. This indeed agrees with the results of the present work. As in the case of helicons, asymmetry of azimuthal rotation is caused by the radial inhomogeneity of the plasma col umn. The radial inhomogeneity leads to a substantial decrea
Data Loading...
