Seungjun Yi

On the origin of the ion acoustic soliton

The excitation of ion acoustic solitons by a grid modulated near the ion plasma frequency is studied computationally in a plasma of kinetic ions and Boltzmann electrons. It is found that a large-amplitude, pulse-like, ion acoustic wave is launched from the grid and then amplified via inverse Landau damping. This wave is unstable and decays nonlinearly into an ion acoustic soliton and an ion acoustic wave packet. The model reproduces features observed in the experiment of Yi et al. [Phys. Plasmas 4, 2436 (1997)], confirming its essential correctness. The results are also consistent with Korteweg–de Vries theory.

Reflection of modified Korteweg–de Vries solitons in a negative ion plasma

Reflection of modified Korteweg–de Vries solitons from the sheath in front of a negatively biased metal disk is experimentally investigated in a negative ion plasma. Both rarefactive and compressive solitons are reflected and the polarity of the reflected solitons is the same as that of the incident solitons. The points of reflection for the rarefactive and compressive solitons are at different locations. As the magnitude of the negative bias potential that is applied to the reflector is increased, the two reflection points move away from the reflector. An interpretation in terms of the sheath characteristics is presented.

Ion acoustic soliton excitation using a modulated high-frequency sinusoidal wave

Experiments on the excitation of ion acoustic solitons using a fine mesh grid in a normal two component plasma are described. The excitation is novel in that a modulated high-frequency sinusoidal wave voltage signal is applied to the grid. The carrier frequency of the high-frequency sinusoidal wave is above the ion plasma frequency. An interpretation of the velocity modulation and bunching of free streaming ions that pass through the grid to which the signal is applied is given.

Expansion of a negative ion plasma into a vacuum

The expansion of a plasma consisting of positive ions, negative ions, and electrons into a vacuum is solved numerically. In addition to the expected self‐similar expansion found in a quasineutral plasma expansion model, a burst of positive ions is accelerated into the vacuum and a burst of negative ions is accelerated into the plasma. These accelerated ions arise since quasineutrality is not imposed in the simulation.

Reflection of modified Korteweg-de Vries solitons in a plasma having negative ions

The variable coefficient modified Korteweg-de Vries (mKdV) equations for incident and reflected solitons are derived and solved to study the reflection of compressive and rarefactive ion acoustic solitons at the critical density in an inhomogeneous negative ion plasma. The polarity of the incident compressive and rarefactive solitons is not altered during the reflection process. Increasing the density gradient reinforces the reflection of both compressive and rarefactive mKdV solitons, whereas enhancement of the unperturbed plasma density weakens the reflection.

Two‐dimensional sheath evolution in a negative ion plasma

The spatial and temporal evolution of the components of a plasma surrounding a 90° convex and a 90° concave electrode whose potential is suddenly decreased in a three‐component plasma is numerically investigated. The quasineutral plasma consists of positive ions and various proportions of negative ions and electrons. The results are compared and contrasted with those that are obtained in a normal two‐component plasma. The transient or ion matrix sheath is identified and its subsequent evolution is investigated. Effects of perturbations in the electrode are investigated.

Expansion of a dusty plasma into a vacuum: effects of charge nonneutrality

Abstract The nonlinear expansion of a dusty plasma into a vacuum region investigated without imposing a quasi-neutrality assumption. The nonlinear expansion is obtained using numerical methods. Electrons and positive ions are found to initially escape into the vacuum region creating an electric field that accelerates a small group of massive dust particles into the vacuum ahead of the dust expansion.

Rarefactive ion acoustic soliton excitation using a modulated high-frequency sinusoidal wave in a negative ion plasma

Experiments on the excitation of rarefactive ion acoustic solitons using a fine mesh grid in a negative ion plasma are described. The excitation is novel in that a modulated high-frequency sinusoidal wave voltage signal is applied to the grid. An interpretation of the velocity modulation and bunching of free-streaming ions that pass through the grid to which the signal is applied is given.

Positive ion current to a spherical electrode in a negative ion plasma

Critical parameters for the development of the plasma‐source ion implantation process are the ion implantation current and the sheath expansion characteristics. Recently, Xia and Chan [J. Appl. Phys. 73, 3651 (1993)] have investigated these parameters for small spherical electrodes inserted in a two component positive ion‐electron plasma. This investigation is extended to a plasma that consists of three components: positive ions, negative ions, and electrons.

Plasma sheath evolution from perturbed electrodes in a negative-ion plasma. Part 2. Experiment and PIC simulation

The two-dimensional spatial and temporal evolution of a plasma surrounding an electrode whose potential is suddenly decreased is experimentally investigated. The electrode contains a localized convex or a localized concave perturbation. The quasineutral plasma consists of positive ions and various proportions of negative ions and electrons. The results are compared and contrasted with those that are obtained numerically using a particle-in-cell (PIC) simulation and those that had previously been obtained using a fluid-model code.