Antenna radiation patterns of balanced electric dipoles and shielded magnetic loop antennas are obtained by measuring the relative wave amplitude with a small receiver antenna scanned around the exciter in a large uniform collisionless magnetized laboratory plasma in the whistler wave regime. The boundary effects are assumed to be negligible even for many farfield patterns. Characteristic differences are observed between electrically short and long antennas, the former exhibiting resonance cones and the latter showing dipole-like antenna patterns along the magnetic field. Resonance cones due to small electric dipoles and magnetic loops are observed in both the near zone and the far zone. A self-focusing process is revealed which produces a pencil-shaped field-aligned radiation pattern.

Antenna radiation patterns in the whistler wave regime measured in a large laboratory plasma

An experimental investigation of current‐driven ion sound turbulence in a collisionless magnetized plasma column is presented. Frequency and wave vector spectrum of the saturated instability are analyzed. The cross‐power spectral density of probe signals shows that waves are localized in k space both in the electron drift direction and along the instability cone of angle ϑ=arc cos(cs/vd) ≲90°. In spite of good plasma uniformity, azimuthal asymmetries in wave propagation are noticed. The self‐consistent electron distribution function deviates from a shifted Maxwellian.

Ion sound turbulence in a magnetoplasma

The ion acoustic wave response to an impulse disturbance is experimentally examined for two different exciting mechanisms. The differences and similarities are noted for the double-plasma (D-P) and plate excitation methods. The observed response agrees well with that predicted from a self-similar study of a fluid equation model which includes the effects of Poisson's equation.

https://iopscience.iop.org/article/10.1088/0032-1028/15/11/008/pdf

Ion-acoustic wave response to an impulse disturbance

The authors describe a series of experiments performed in a positive ion-negative ion plasma that were designed to study the reflection and focusing properties of solitons. The nonlinear wave was compared with a theoretical model using linear waves. The two-dimensional soliton was created by reflecting an incident planar soliton from a concave hemispherical surface. The experimental results are interpreted in terms of the linear waves that can exist in a focused Fabry-Perot resonator. >

A two-dimensional soliton in a positive ion-negative ion plasma

The literature on the subject is reviewed under the headings: anisotropic (cold) electron plasma, isotropic (warm) electron plasma, loop antennas, resonance rectification, and ion effects. Though the gap between theory and experiment has narrowed for most of these topics, understanding is still unsatisfactory at lower frequencies where ion motion cannot be neglected.

Antennas in Plasma: Characteristics as Functions of Frequency

This paper describes experiments designed to measure the radiation patterns of a longitudinal wave excited in a warm plasma by both monopole and dipole antennas. The longitudinal wave used in this experiment is the low-frequency ion acoustic wave that propagates with a phase velocity [γkTe/M/i]½. Experimental results agree well with the theoretical predicted radiation pattern.

S. Aksornkitti

Papers

Radiation Characteristics of Longitudinal Waves From an Antenna in a Plasma