Comparison of electric dipole and magnetic loop antennas for exciting whistler modes

Abstract

The excitation of low frequency whistler modes from different antennas has been investigated experimentally in a large laboratory plasma. One antenna consists of a linear electric dipole oriented across the uniform ambient magnetic field B 0. The other antenna is an elongated loop with dipole moment parallel to B 0. Both antennas are driven by the same rf generator which produces a rf burst well below the electron cyclotron frequency. The antenna currents as well as the wave magnetic fields from each antenna are measured. Both the antenna currents and the wave fields of the loop antenna exceed that of the electric dipole by two orders of magnitude. The conclusion is that loop antennas are far superior to dipole antennas for exciting large amplitude whistler modes, a result important for active wave experiments in space plasmas. Published by AIP Publishing.

Whistler waves with angular momentum in space and laboratory plasmas and their counterparts in free space

“…Groundbased radiation sources require too much power since the coupling of free-space electromagnetic waves into whistler modes is not very efficient. Active whistler wave injections from satellites using efficient antennas [44] have not yet been performed.…”

“…Whistler instabilities by anisotropic distributions have also been observed [76]. Many nonlinear phenomena have been studied in the laboratory which are not found in space [13] Comparison of electric dipole antennas and magnetic loops show that the latter have a much higher radiation efficiency for low-frequency whistlers than dipoles [44].…”

Kinetic study of instability growth rate in a helicon plasma discharge source

“…Moreover, whistler mode waves are right‐hand circularly polarized helicon waves propagating in free unbounded spaces. Normally, the whistler wave modes are observed in solar wind, cometary foreshocks, upstream of planetary bow shocks, upstream of interplanetary shocks, and magnetosphere …”

“…On the other hand, the propagation of electromagnetic waves inside in plasma discharges has the capability of enhancing the technological applications of high-density plasma media. [1][2][3][4][5][6][7][8][9][10][11][12] These technological applications mainly include semiconductor manufacturing, spacecraft based on helicon plasma discharges, material surface modification, material processing, and basic and applied laboratory research. [13,14] Helicon waves are right-hand-polarized electromagnetic waves.…”

“…Moreover, whistler mode waves are right-hand circularly polarized helicon waves propagating in free unbounded spaces. Normally, the whistler wave modes are observed in solar wind, [2] cometary foreshocks, [3] upstream of planetary bow shocks, [4] upstream of interplanetary shocks, [5] and magnetosphere. [6] Stenzel and Urrutia [7] showed that the three-dimensional (3D) field topology of whistler modes will remain unchanged in a uniform plasma discharge where there are no specific geometric boundaries.…”