Helicon wave excitation with helical antennas

Abstract

Components of the wave magnetic field in a helicon discharge have been measured with a single-turn, coaxial magnetic probe. Left- and right-handed helical antennas, as well as plane-polarized antennas, were used; and the results were compared with the field patterns computed for a nonuniform plasma. The results show that the right-hand circularly polarized mode is preferentially excited with all antennas, even those designed to excite the left-hand mode. For right-hand excitation, the radial amplitude profiles are in excellent agreement with computations.

Axial propagation of helicon waves

“…reasons not yet known, as reported earlier 10 . The N antenna was expected to give a plane polarized wave, created by a linear combination of the +1 and -1 modes; but in practice it excites only the +1 mode in both directions 10 .…”

“…2. A detailed explanation of the proposed coupling mechanism 16 for these antennas has been given by Light and Chen 10 . Since the free space wavelength at the frequency of interest for this experiment is much larger than any dimension of the antennas, we can assume that the current reaches all parts of the antenna simultaneously.…”

“…The N antenna was expected to give a plane polarized wave, created by a linear combination of the +1 and -1 modes; but in practice it excites only the +1 mode in both directions 10 . In order to keep track of the relation between wave propagation and magnetic field direction, the following nomenclature was adopted.…”

“…They have been subsequently used for a variety of applications [2][3][4][5][6] . Radial amplitude profiles of helicon waves in uniform and nonuniform plasmas have been studied extensively by Chen et al [7][8][9] Azimuthal mode content in a high aspect ratio helicon discharge was investigated by Light and Chen,10 who found that the m = +1 (right-hand polarized) mode was preferentially excited in a variety of antenna and static magnetic field configurations. Though the high ionization efficiency of these helicon discharges is not yet completely understood, Landau and collisional damping 7 , and cyclotron damping 11 have been suggested as possible mechanisms.…”

Nonlinear Phenomena Associated with Large Amplitude Whistler Pulses

“…Applications include plasma opening switches [2], pulsed ion beam propagation across Bo [3], helicon waves [4], electrodynamic tethers in space [5], dissipation processes in narrow current sheets undergoing reconnection [6], plasma releases [7], and wings behind small asteroids in the solar wind [8]. Basic physics experiments have demonstrated that pulsed EMHD currents in magnetized plasmas are transported by whistler waves [9-111.…”