Santwana Raychaudhuri

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.

Study of particle transport to the tokamak edges and the drift-wave-like instability occurring in the SOL region

Particle transport towards the scrape-off layer (SOL) region and the low-frequency instabilities occurring in the edge plasma have been studied in a small research Tokamak. The results obtained show that there exists enhanced particle transport in the plasma. The drift-wave-like instabilities observed in that region are related to this enhanced particle transport to the edge region.

Ion-acoustic solitons in a multi component plasma: comparison of different theoretical models

Conditions for the existence of ion-acoustic solitons have been derived and studied for a warm multi-ion component plasma with two electron temperatures. The models: (a) reductive perturbation method (using KdV equation), (b) warm ion fluid theory based on a method by Sakanaka (1972) and (c) kinetic theory approach have been compared.

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.

Propagation of ion-acoustic solitons into a weak localized magnetic field II - longitudinal field

Experiments on the propagation of an ion-acoustic soliton from an isotropic plasma into a region containing a weak mirror magnetic field are described. An anomalous focusing of the soliton is detected. The magnetic field also allows us to separately observe reflected ions from the soliton and the ions involved in the excitation of the soliton.