Go Imada

Experimental demonstration of relativistic magnetron with modified output configuration

A modified configuration of relativistic magnetron with diffraction output has been investigated experimentally by using repetitive pulsed power generator “ETIGO-IV” (400kV, 13kA, 120ns, 1Hz). The purpose is to verify the improved microwave conversion efficiency predicted by numerical simulations [M. Daimon and W. Jiang, Appl. Phys. Lett. 91, 191503 (2007)]. The experiments have concentrated on comparison between the output microwave powers obtained by using the modified and the conventional configurations of relativistic magnetron. The results have been in general agreement with that obtained by the simulations.

Pulsed Power Technology and Its Applications at Extreme Energy-Density Research Institute (EDI), Nagaoka

Recent activities conserning pulsed power technology and its applications are reviewed. Using high-density ablation plasma produced due to the short range of an ion beam in targets, we have successfully prepared crystallized B4C thin films by ion-beam evaporation, which are characterized by hardness, wear resistance, and stability at high temperatures. Fullerenes have been prepared as well. Ultrafine nanosize powders were synthesized by pulsed wire discharge. Flue gas treatment of NOx was achieved by intense pulsed relativistic electron beam. Foil acceleration was observed to be ~8 km/s at the ablation pressure of 13 GPa. Pulsed laser deposition was used to prepare (Cr1-x, Alx)N films. The AlN solubility limit was found to be 77 at.% AlN. The hardness of the films increases with x up to 0.75, and decreases rapidly due to their being amorphous in structure. A highly repetitive, new pulsed power generator is operational, with the specifications of 400 kV, 13 kA, 120 ns, and 1 pps.

Flue Gas Treatment by Intense Pulsed Relativistic Electron Beam

Diesel-flue-gas treatment has been demonstrated by using an intense, pulsed relativistic electron beam (IREB). A flue gas treatment chamber, 1.6-m isolated from the IREB source, is filled up with the diesel flue gas with the pressure of 200 kPa, and is irradiated by IREB (2 MV, 0.12 kA, 65 ns (FWHM)). The maximum kinetic energy of IREB injected into the gas chamber is experimentally estimated to be -0.23 MeV. When the diesel flue gas is irradiated by firing 10 shots of the IREB, the concentration of NOx, SO2, and CO are decreased from 75, 14, and 770 ppm to 5, 11, and 690 ppm, respectively. It is found that - 93 % of NOx is removed by firing 10 shots of the IREB irradiation. We have obtained the energy efficiency of NOx removal of 256 g/kWh.

Influences of Shock Waves on High-Pressure, Pulsed Glow Discharge due to Excimer Laser Excitation

The high-pressure, pulsed glow discharge has been studied to gain a further understanding of the excitation discharge on application of excimer lasers. The influence of shock waves on the discharge has been investigated disregarding other factors which may affect the discharge instabilities, such as gas density depletion, discharge products, residual ions, halogen gas, and electrode heating. A shock wave of 1.2 in Mach number is produced by a shock tube with a gas mixture of helium and argon. It is found that if the shock wave, propagating across the discharge direction, does not reach the middle of the discharge region, glow discharge occurs only in front of the shock wave. Even if the shock wave passes through the middle of the discharge region, the glow discharge occurs only in front of the shock wave. However, an arc-like filament through the shock front is also produced. If the shock wave passes through the discharge region, the glow discharge can be produced again behind the shock front, however, a surface discharge is also produced between the main electrode and the pre-ionization pin electrode.

Generation and propagation of shocks in discharge-pumped excimer laser

Shock waves and disturbed gas generated by an excitation discharge in an excimer-laser cavity have been visualized by the shadowgraph technique. The influences of HCl and Xe concentration on the generation of shock waves have been investigated in a He/Ne gas mixture. At the higher HCl concentration, the distribution of gas density in the discharged region, where the gas is rarefied due to the expansion, seems to be strongly jagged, and the strong shock waves propagate toward the upstream and the downstream directions along the flow axis. At the lower HCl concentration even with the high Xe concentration, on the other hand, the density distribution in the heated column is fairly smooth and the shock waves are very weak. We have also successfully demonstrated the double-pulse glow discharge of a pulse interval of 200 microsecond(s) using a high-speed He-Ar gas flow of approximately 200 m/s. At the pulse interval of 100 microsecond(s) , however, the second discharge, which seems to be arc, occurs through the heated column which is swept downstream but still contains the waste products of the first discharge.

Removal of nitrogen oxide in spatially isolated chamber by pulsed intense relativistic electron beam

Nitrogen oxide (NO/sub x/) in a chamber spatially isolated from beam source has been removed by a pulsed, intense, relativistic electron beam (PIREB). The chamber is filled up with dry-air-balanced NO/sub x/, and is irradiated by the PIREB (2 MeV, 2.2 kA, 85 ns) passing through 1.6-m-long atmosphere. The NO/sub x/ concentration decreases from 88 to 25 ppm by ten shots of PIREB.

Growth of arc in high-pressure, pulsed glow discharge by gas density depletion

Effects of gas density depletion on arc formation of high-pressure, pulsed glow discharge have been investigated by eliminating the other factors which may affect the discharge stability, such as shock waves, residual ions, electrode heating, and discharge products. The gas density depletion has been simulated by utilizing a subsonic gas flow between the curved electrodes combined with a convergent nozzle and a divergent diffuser. A comparison has been made on the discharge in the aerodynamically created gas density depletion with the second discharge in the double-pulse discharge within a stable gas. We have found that the large gas density depletion, Δρ/ρ0∼−3.6% corresponding to a pulse repetition rate (PRR) of ∼50 Hz, tends to cause an arc-like filament or an arc without the shocks, ions, electrode heating, and products. However, the second discharge in the double-pulse discharge becomes an arc in much smaller gas density depletion (Δρ/ρ0∼−1.2% corresponding to PRR ∼3 Hz). Therefore, the collapse of hi...

Theoretical study on nonstationarity of electron energy distribution function for discharge‐pumped XeCl laser

The nonstationarity of electron energy distribution function (EEDF) has been studied for a discharge‐pumped XeCl laser, where a self‐consistent model is considered. The energy relaxation time has been observed by solving a time‐dependent Boltzmann equation. The importance of a nonstationary treatment in determining EEDF, electron average energy, electron‐impact rate coefficients, and species densities has been discussed. It has been found that a pronounced nonstationarity is likely to occur at a relatively low electric field (< 2 Td). The quasi‐stationary treatment tends to underestimate the electron average energy and some electron‐impact rate coefficients around the inversion points of the discharge voltage. Electron–electron collisions induce a strong nonstationarity when the electron density exceeds a certain value. The electron‐impact rate coefficients selected by neglecting the nonstationarity result in an incorrect determination of species densities.

Effects of secondary electrons due to ionization on model predictions of discharge‐pumped XeCl laser

A self‐consistent code has been utilized in modeling a discharge‐pumped XeCl laser. The electron energy distribution function (EEDF) has been calculated using a time‐dependent Boltzmann equation. The effects of the secondary electrons produced by ionization on EEDF, rate coefficients, species densities, laser energy, and breakdown delay time have been examined by comparing different models in a wide range of discharge parameters. Efforts have been made at explaining the discrepancy in the breakdown delay time between simulation and experiment. It is found that the secondary electrons due to ionization play an important role in determining the breakdown delay time. Furthermore, the measured breakdown delay time can be well reproduced using the model presented in this work instead of increasing the total excitation cross sections of xenon.

Effects of supersonic flow channel configuration on pulse discharge for excimer laser excitation

Several supersonic flow channel configurations chosen from the viewpoints of electric field and aerodynamics are constructed to evaluate their effects on the stability of a single pulse discharge for excimer laser excitation. First, two types of electrode with a flat or curved top are experimentally investigated in still gas and the electrode with a curved top is selected for discharge experiments in a supersonic flow. A Ludwieg tube with a two-dimensional shock-free nozzle is used to generate a supersonic flow with a Mach number of 2 in a discharge cavity. A shadowgraph technique is applied to visualize the gas density disturbance inside the discharge cavity due to shock waves and boundary layers. It is shown that discharge stability strongly depends on the flow channel configuration. Within the scope of this investigation, a channel configuration with an upstream cover and a downstream channel widened by 2 mm is the most suitable configuration for the excitation discharge preionized by UV pin spark in a supersonic flow.