Characteristics of radio frequency wave propagation in bounded plasma under the various magnetic field configurations

Abstract

Detailed characteristics of radio frequency (rf) waves with pulsed modes in the whistler wave range were studied in a cylindrical rf-produced plasma, where the plasma boundary lay in the intermediate regime between infinite whistler wave propagation and bounded geometry helicon wave propagation. Excited magnetic field amplitudes and phases with three components in two-dimensional space were measured for different experimental conditions. Three magnetic field configurations were used and the diameter of the excitation loop antenna was also varied. Numerical calculation by the finite element method, which has been demonstrated to be a powerful means for this analysis, showed good agreement with the observed results, satisfying the dispersion relation and wave structures of helicons in the semisteady state and also satisfying the dispersion of whistlers with a short pulsed mode. The excited waves propagated nearly along the magnetic field lines within a small angle of less than 10°. Furthermore, in the low (high) collisionality regime, domination of standing (propagating) waves was found from the wave analysis.

Whistler modes in highly nonuniform magnetic fields. III. Propagation near mirror and cusp fields

“…14 Experiments on cyclotron absorption have been done in several laboratory experiments. [15][16][17] However, the topic of wave propagation in highly nonuniform magnetic fields (B=jrBj < k) has received little attention since it is not amenable to ray tracing. It has been addressed in the present work and its preceding Papers I and II.…”

“…Such predictions cannot be made for whistler modes in lunar crustal magnetic fields 35 or for low frequency whistlers at the bowshock 36 or near reconnection regions. 37,38 Nonuniform magnetic fields also exist in the exhaust region of helicon thrusters 14,16,39 or toroidal plasma devices [39][40][41][42] with the focus on plasma production rather than wave refraction. Refraction in nonuniform magnetic fields destroys the cylindrical geometry of helicons.…”

Characteristics of low-aspect ratio, large-diameter, high-density helicon plasmas with variable axial boundary conditions

“…Plasmas can be produced very efficiently by using helicon waves, or whistler waves propagating in a bounded plasma region, whose frequency is x ci ( x ( x ce , where x ci and x ce are the ion-and electron-cyclotron frequencies, respectively. [1][2][3][4] Because it is possible to easily obtain high-density ($10 13 cm À3 ) plasmas with high ionization rate (several tens of percent) under a wide range of magnetic field strength in helicon-wave discharge, helicon plasma sources are suitable for various plasma applications, such as basic science experiments, [5][6][7] developing magnetoplasma rocket engines, 8,9 plasma processings, 10,11 and fusion related experiments. 12 A low-aspect ratio plasma source with uniform density profile is especially useful for such applications like plasma processings and plasma thrusters.…”

Development of high-density helicon plasma sources and their applications

“…High-density ͑ϳ10 13 cm −3 ͒ plasma experiments performed at Kyushu University 20,21 used a vacuum vessel, 45 cm in diameter and 170 cm in axial length, by using a spiral antenna. With this large device, in addition to the basic studies on helicon/whistler wave characteristics in the highdensity regime, [22][23][24][25][26] many fundamental and applied studies have been done in the low-density region by voltage biasing of the concentric electrodes located at the end of the vessel. These include the control of the radial density profile and the high azimuthal plasma rotation with a high velocity shear, [27][28][29][30][31][32] a proof of principle experiment on ion mass separation, 33 and the self-excited, density-transition phenomenon in the bistable system.…”