Takeshi Nagasawa

Excitation of ion‐acoustic rarefactive solitons in a two‐electron‐temperature plasma

Rarefactive ion‐acoustic solitons have been observed in a two‐electron‐temperature plasma. Some of the characteristics can be interpreted by the solution of the Kortweg–de Vries (K–dV) equation. The Mach number of the solitons is a function of the temperature ratio of hot and cold components.

Refraction and reflection of ion acoustic solitons by space charge sheaths

It has been found that ion acoustic solitons tunnel through the space charge sheath in front of the reflector, without time delay, but they are absorbed resonantly when the spatial width of the wave is close to the characteristic gradient scale length of the sheath. The empirical scaling laws for the reflection and transmission rates have been obtained as functions of (i) the bias voltages on the reflector, (ii) the wave width, and (iii) the density gradient scale length. The theoretical model for interpreting the observed phenomena is discussed to show the existence of the electrostatic tunnel effect in the space charge sheath area. In this model, the absorption of wave energy by the sheath, which is strong in the present experiments, was not taken into account.

Effects of space charges in gridded energy analyzer

When a gridded energy analyzer is used for energy analysis of plasma particles, it is experimentally found that the characteristics of the analyzer can be heavily affected by the space charge of particles accumulating behind its entrance grid. In this experiment, using a large model analyzer, the current profiles of accumulating ions in the analyzer and the effects of the space charges on ion energy distributions are directly measured in detail. Finally, problems related to the ion accumulation and the space charge effects in a gridded energy analyzer are generally discussed on the basis of the above experimental results.

High-Energy Electron Production by Vp × B Acceleration in Microwave-Plasma Interaction Experiments

Detailed experimental observations on the microwave plasma interaction in a nonuniform plasma with weak magnetic field (¿/¿ ¿ 10-2) have revealed that high-energy electrons are produced by a process of the VP × B acceleration, where ¿ and ¿ are, respectively, electron cyclotron and microwave frequencies. The maximum energy of hot electrons increases almost linearly to about 1 keV with the RF power up to 8 kW. Hot electrons are produced from typically two regions; one in the underdense region (several centimeters down the critical layer for the resonance absorption) and the other in the resonance absorption area. The theoretical predictions have interpreted the experimental results in reasonable agreement.

Effects of fast beam ions on ion-acoustic solitons and shocks excited in a double plasma device

The limitation in amplitude of ion-acoustic solitons or laminar shocks excitable in a double plasma device is clarified to result from the effect of pulsed fast beam ions, generated by the pulse externally applied for wave excitation. Beam ions faster than the soliton, which suppress the growth of the proto-soliton amplitude at an early stage of wave excitation, are always generated in the case of the double plasma (DP)-excitation, when a pulse high enough is applied so as to excite a large amplitude soliton. Controlling the generation of such fast beam ions by adjusting the rise time of the applied pulse, ion-acoustic solitons or laminar shocks of high Mach numbers up to M≃1.4 are observed to be formed even in a plasma with a finite ion temperature such as Ti≃Te/20.

Chaotic phenomena of a periodic ion-acoustic soliton system

Chaotic phenomena of a periodic ion-acoustic solitons system that is composed of a series of ion-acoustic solitons have been observed in a double-plasma device. Periodic ion-acoustic solitons become unstable by the energy gain and energy loss of the solitons, and they become chaotic. Taking account of a pair of solitons in the system, the front soliton gains energy from the reflected ions from the rear soliton, which is controllable by the rear soliton amplitude or the interval between the solitons. The energy loss of solitons results from collisions with neutral particles that vary with changing gas pressure.

Effects of the ion-beam density and velocity on the excitation of multimode soliton

Multimode solitons are observed to be excited in an ion‐beam–plasma system. But, the excitation of some mode solitons of these is found to be suppressed under a certain condition depending on the density and velocity of a low‐energy ion beam, produced by the applied negative pulse. Furthermore, weak interaction between the slow‐beam soliton and ion‐acoustic soliton is also observed to cause small time lags in their trajectories on the distance–time plane.

Resonance absorption of transmitted ion acoustic solitons by space charge sheaths

Abstract Ion acoustic solitons tunnel through the sheath area without time delay and the wave is resonantly absorbed when D ∼ L , where D is the spatial width of the wave and L the characteristic gradient scale length of the sheath in front of the reflector. The experimental results show the existence of a new mechanism in the reflection and transmission of ion acoustic solitons from space charge sheaths, and a model describing the phenomena is discussed.

Observation of reflex klystron oscillation phenomena in a plasma

Reflex klystron electron oscillation, occurring in a plasma potential well formed in a system consisting of plasma and two electrodes (filaments and a mesh grid which is at floating potential), was observed in a very simple device with only filaments and a mesh grid. This oscillation mechanism consists of three elements: 1) an acceleration region on the side in which filaments are located, which accelerates primary electron beams emitted from filaments; 2) a deceleration region on the side in which the mesh grid is located, which causes the reflection of the beams; and 3) a plasma region. In addition, the velocity modulation of primary electron beams is given by the electron plasma oscillation at the presheath on the filament side. The maximum amplitude and frequency of an oscillation obtained by this mechanism were V/sub pp/=210 mV 210 mV and f=200 MHz, respectively. These values can be controlled by the discharge potential.

Study of PM Removal Through Silent Discharge Type of Electric DPF Without Precious Metal Under the Condition of Room Temperature and Atmospheric Pressure

© 2013 Chuubachi and Nagasawa, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Study of PM Removal Through Silent Discharge Type of Electric DPF Without Precious Metal Under the Condition of Room Temperature and Atmospheric Pressure