Eugene K. Tsikis

An experiment on the plasma expansion into a wake

Experiments on the expansion of a plasma into the wake region behind an object inserted in a flowing plasma are described. The dominant expansion mechanism that fills in the wake is determined to be a self‐similar expansion. Accelerated ions with a velocity greater than the local ion‐acoustic velocity are detected ahead of the self‐similar expansion front. In a plasma with two species, two groups of accelerated ions are detected.

Propagation of an ion-acoustic soliton in an inhomogeneous plasma

Experiments on the propagation of an ion‐acoustic soliton into a region of inhomogeneous plasma density are described. It is found that the local amplitude and velocity decrease and the width increases as the soliton propagates into a region of lower density. The results are in good agreement with a model based on the KdV equation and with the recent study of Kuehl and Imen [Phys. Fluids 28, 2375 (1985)].

On the Reflection of Ion-Acoustic Solitons from a Bipolar Potential Structure

A potential structure consisting of a negatively biased screen placed in front of a positively biased plate and inserted in the target chamber of a double-plasma machine is shown to be a reflector of ion-acoustic solitons. A simple model is proposed to explain the reflection mechanism pioneered by Popa and Oertl. This structure is also an efficient launcher of ion-acoustic waves.

Scattering of ion‐acoustic solitons

A series of experiments is described that is designed to ascertain the properties of the scattering of planar ion‐acoustic solitons from objects of various shapes. The scattered solitons are compared with those radiated from the same objects.

Propagation of ion-acoustic solitons in a non-quiescent plasma

The propagation of an ion-acoustic soliton from a quiescent plasma region into a localized non-quiescent region ( Delta n/n mod soliton approximately= Delta /n mod noise) is experimentally examined. Several of the soliton properties are preserved although the soliton undergoes an enhanced damping as it propagates in the noisy plasma.

On the evolution of an ion phase-space vortex

Conditions which allow the formation of a stable ion phase-space vortex in a double plasma machine are reported. A high frequency propagating signal with a frequency ~ fpi/2 which cannot be associated with a dispersing Airy function is observed on the trailing shoulder of the hole.

On grid launched linear and nonlinear ion-acoustic waves. III

For pt.II see ibid., vol.26, no.6, p.799 (1984). The authors extent their study on grid excited ion-acoustic solitons to examine far field radiation characteristics. In particular, for propagation distances greater than any launching grid dimension, the solitons propagate as spherically expanding shells.

Resonant interaction of ion-acoustic solitons in three-dimensions revisited

Using a launching structure consisting of four large diameter hemispherical grids located at the corners of a square, it is observed that the amplitude of a resonantly produced soliton is greater than ten times the value of an individual soliton. This observation extends to three dimensions Kaup’s conjecture that the two‐dimensional resonance‐soliton creation requires a finite interaction tune.

Comments on Probe-Excited Oblique Ion-Acoustic Waves in a Multidipole Plasma Device

Low-frequency noise (fci < f < fpi) excited by positively biased probes of various diameters near the magnets in a multidipole plasma device is investigated. It is concluded that the noise is due to the excitation of oblique ion-acoustic waves, i.e., the electrostatic ion-cyclotron waves in the low field limit propagating at large angles to the magnetic field.

Radiation of Ion Acoustic Waves from Finite Sources

ABSTRACT The radiation characteristics of a longitudinal ion acoustic wave in a plasma from several different sources are experimentally measured. Results are Interpreted in terms of the solution of an appropriate scalar-Helmholtz equation or where appropriate, in terms of the germane plasma physics phenomena.