Electron-beam Sustained Discharge Research Articles

Characterization and Switching Performance of Electron-Beam Controlled Discharges

The electron-beam sustained discharge switch is an attractive concept for repetitive pulsed power switching because it has a demonstrated capability to interrupt direct current and because it is inherently scalable. We report on experiments with this type of switch in a 4-kV dc circuit. A wire-ion-plasma (WIP) electron-beam (e-beam) gun is used to irradiate and sustain a switch discharge with a 100-cm2 cross-sectional area in 1 atm of N2 or CH4. Interruption of 8-10-μs pulses of up to 1.9 kA, and of 100-μs pulses of 150 A has been demonstrated in methane, and interruption against higher recovery voltages (11 kV) has been performed at 1.2 kA by adding series inductance to the circuit. These values represent power supply limitations rather than limitations of the switch itself. A comparison of the measured discharge characteristics with theoretical predictions shows that the measured switch conductivities are higher than the predicted values for given e-beam current values. A qualitative explanation for this observation is offered by considering the effects of electron reflection from the discharge anode and of nonlinear paths for the beam electrons across the discharge gap. We conclude that the switching performance of the e-beam controlled discharge switch corresponds to its design parameters, and that for a given switch size a lower voltage drop during the on time can be expected compared with the voltage drop predicted by previously published theory.

On electron energy distribution functions in low-pressure magnetic multicusp hydrogen discharges

Following the approach which was used in a previous paper for the calculation of the EEDF for an electron-beam sustained discharge in a magnetic multicusp geometry, the authors examine the influence of some physical processes such as energy sharing between free electrons issuing from ionisation and superelastic collisions associated with vibrational deexcitation. Particular attention is devoted to low-pressure conditions which are commonly used for the production of intense beams of H- ions. Even for high current values the EEDF is proved to be largely non-maxwellian. On the basis of their results the authors prove that the influence of vibrational excitation on the EEDF is weak, allowing the calculations of the EEDF without any precise knowledge of the vibrational populations.

The use of attachers in electron-beam sustained discharge switches—theoretical considerations

Electron-beam sustained discharges can be used in opening and closing switch applications for producing bursts of energy in pulsed power systems. The incorporation of admixtures of attachers with low attachment rate at low values ofE/Nand high attachment rate at high values ofE/Nin the gaseous switch dielectric has been proposed to achieve low forward voltage drop in the conduction phase as well as rapid opening when the sustaining e-beam is terminated. This paper presents model calculations on the characteristics and transient behavior of an electron-beam sustained discharge in the high current density regime in N2. The influence of an attacher (N2O), with the property described above, and of the circuit parameters on the discharge is investigated as an illustrative example. The advantage of using such an attacher is demonstrated for the steady state conduction phases and for the opening phase, while the closing process is obstructed by the attacher. Additional possible control mechanisms, such as photodetachment to aid the closing process are discussed.

Electron-ion dissociative recombination rate constant for the reaction e + H +n

Rate constant determinations for the reaction e + H + n are reported as a function of E/N (where E is the applied field and N is the total number density of the gas). These measurements were made in an electron beam sustained discharge device operating at room temperature with total hydroge pressures of one atmosphere. Although these experiments were performed without mass identification, for these operating conditions, the likely principal ion is H + 5.

Threshold power density measurements for electron-beam sustained discharge excitation of XeF and KrF

Threshold power densities for electron-beam-stabilized discharge excitation of XeF and KrF lasers are reported for Ar+Kr+F2 and Ar+Xe+NF3 gas mixtures at 1 atm. Stable discharges were obtained with these gas mixtures for times greater than 0.5 μsec with lasing pulse width as long as 0.5 μsec. An analysis of data for several different pump power densities is presented which indicates that the threshold pump power density varies inversely with the cavity buildup time.

Vibrational excitation of HCl by electron impact

Measurements have been made of the vibrational excitation rate constant of HCl excited by electron impact. The experiments were performed in a uniform electron beam sustained discharge over the range of average electron energies from 0.8 to 1.7 eV. A mean value of (1.2±0.4)×10−8 cm3/sec was obtained corresponding to a cross section of several A2. It was also determined that the vibrational excitation by electron impact was predominantly to the first vibrational level with only 20% probability of exciting the second or higher levels.

Vibrational excitation of HCl by electron impact

Measurements have been made of the vibrational excitation rate constant of HCl excited by electron impact. The experiments were performed in a uniform electron beam sustained discharge over the range of average electron energies from 0.8 to 1.7 eV. A mean value of (1.2±0.4)×10−8 cm3/sec was obtained corresponding to a cross section of several Å2. It was also determined that the vibrational excitation by electron impact was predominantly to the first vibrational level with only 20% probability of exciting the second or higher levels.

Results of the time-dependent gain with a high-current electron-beam sustained discharge in CO2

A large-aperture cold-cathode electron beam with 150 kV and 0.4 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> has been used to sustain 1-μs discharges in a CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -laser mixture of 3/(1/2)/1. The electron density produced in the gas was approximately <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.9 \times 10^{13}</tex> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and thus for 1 atm a discharge power density of 150 J/1μs was achieved at 5.4 kV/cm for the sustainer electric field. The time-dependent gain for the 001-100 transition has been measured. Taking the experimental values of the discharge power, the gain has also been calculated using a kinetics program and a solution of the Boltzmann equation for the fractional power transfer. The good agreement between the experimental and calculated results gives confidence that the performance of cold-cathode electron-beam sustained-discharge CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> lasers can be predicted.