Reflection Of Ion Acoustic Waves Research Articles

On reflection of ion acoustic waves

Reflection of ion acoustic waves from a bipolar potential structure was studied in a double plasma device. The existence of a reflected signal, even when no external bias was applied on the bipolar reflector, could be detected, although with much lower velocity than the incident wave. Application of proper bias on such a reflector resulted in an additional reflected image with greater velocity than the reflection obtained without bias. The experiment was also extended to study negative ion plasma waves.

Reflection of Ion Acoustic Waves from a Dusty Plasma with a Dust Size Distribution

A general dispersion relation for ion acoustic waves in a plasma containing charged dust grains is obtained taking an account of dust size distribution. The dust size is given by a power law distribution. Assuming that the duty plasma is well separated from the dust free plasma, the influence of this distribution is studied on the calculated reflection coefficient. On the basis of this reflection coefficient we have tried to interpret the maintenance of large scale dust structures in the plasma environment.

Excitation and reflection of ion-acoustic waves by a gridded plate and a metal disk

Reflection coefficients and excitation efficiency of a gridded plate (a bipolar potential structure where the grid is separate but parallel to the juxtaposed plate) and a metallic disk for ion-acoustic waves have been measured experimentally. When the grid is biased negatively with respect to the plasma potential, reflection in phase with the incident wave and excitation of an outgoing wave are observed only when the bias of the plate is positive. When the bias of the gridded plate is positive, reflection occurs when the grid bias is either negative or positive. For the metal disk, reflection and excitation are observed when the bias is positive. The small reflection detected when the bias is negative is found to be due to scattering of the incident wave at the edge of the disk.

Effect of a high-frequency field on the reflection of ion acoustic waves from the sheath at a grid

Experiments are described which show that the reflection coefficient for ion acoustic waves (IAW) from the sheath at a grid is affected by an HF electric field with a frequency f/sub HF/<or approximately=5f/sub pi/(f/sub pi/=ion plasma frequency). For peak-to-peak amplitudes of the HF voltage drop across the sheath Phi /sub 0/<or approximately=k/sub B/T/sub e//e and f/sub HF/>f/sub pi/, the energy distribution of the ions passing through the grid develops a hot tail and the reflected wave suffers enhanced Landau damping. If Phi /sub 0/>or approximately=k/sub B/T/sub e//e and f/sub HF/<f/sub pi/, a large-amplitude IAW is excited at the grid; a well-defined ion beam is formed; and local growth of the reflected wave is observed. Test waves launched from the grid show the same propagation characteristics as the reflected waves.<<ETX>>

Reflection of ion-acoustic waves from bipolar potential structures

Reflection of ion-acoustic waves from the ion sheath in front of the separation grid in a double-plasma device has been investigated experimentally. The plasma potential φ of the source plasma was controlled relative to that of the target plasma. When eφ &lt; κΤe, where Τe is the electron temperature, no reflection was observed. The reason for this is that ions are drifting towards the grid with the Bohm velocity, i.e. the ion-acoustic velocity. When eφ &gt; κΤe the reflected wave consists of the ion-acoustic wave and the ion beam mode. The reflection coefficient for the ion-acoustic wave is about unity. This high efficiency is due to reflection of the ions themselves.

Single and multiple reflection of ion-acoustic waves and solitons from a bipolar wall

Reflection of ion-acoustic waves and solitary signals at a wall consisting of a grid and a plate is demonstrated in a DP-machine plasma. A velocity comparison is made between the signals supporting the identification of the nonlinear solitary pulses as solitons. The reflection coefficient for both kinds of signals is found to lie near 100%.

Reflection of ion-acoustic waves from an ion sheath at a grid

The reflection of continuous sinusoidal waves from a grid is investigated experimentally. It is found that the reflection coefficient has a distinct maximum in contrast to the prediction of the theory. The electron components of the incident and reflected waves are observed to vanish within the quasineutral layer close to the grid where the plasma density rapidly drops. Furthermore it is shown that the reflected wave is a downstream wave that propagates on the ion beam that originates on the other side of the grid.

Experimental Observations of Ion-Acoustic Wave Reflection from Discharge-Tube Walls

We have experimentally observed the reflection of ion-acoustic waves from the walls of a discharge tube by a very simple technique. We first excite intense spontaneous oscillations, then rapidly switch to a quiescent mode of operation. The ion-acoustic waves are observed to persist after the transition, but damp away with time.

Reflection of ion acoustic waves by the plasma sheath

The reflection coefficient R for linear monochromatic ion acoustic waves incident on the transonic layer and sheath from the plasma interior is calculated. The treatment differs from previous analyses in that (1) the exact zero-order ion density and velocity profiles for a planar, bounded plasma are used, and the zero-order charge separation is not neglected, and (2) the first-order quantities near the transonic layer are considered in detail, including first-order charge separation, whereby it is found that no coupling to the beam modes exists, and that the functional form of the first-order solution is completely determined. It is shown that the upper bound for ‖R‖ is (1)/(3) . The largest reflection occurs for frequencies which are small compared with the ionization frequency, and generally decreases with increasing frequency. By Fourier superposition, the reflection of a pulse is computed. For a narrow incident pulse, the reflected pulse is greatly distorted and is small compared with the incident pulse. For a broad pulse, the reflected pulse is similar in shape to the incident pulse, and has a magnitude which is approximately (1)/(3) of the incident pulse.

Reflection of ion acoustic waves from positive and negative space charge sheaths

Experimental evidence is presented showing that externally excited ion acoustic waves are reflected from positive and negative space charge sheaths around a cylindrical wire.

Ion Wave Reflections as Observed in a “Perturbed” Plasma

The experimental observation of the reflection of ion acoustic waves from a negatively biased grid immersed in a plasma is reported. Reflection is detected only in the region where the plasma is “perturbed.”

Damping and reflection of ion-acoustic waves

Reflection of ion-acoustic wave pulses from sheaths in argon plasmas was observed for normal and 45° incidence angles. Two rates of exponential spatial damping were found for parallel-plane electrode geometry in both argon and xenon.