No abstract

Abstract-A theoretical investigation of high-pressure discharges ionized by an external electron beam (e-beam) was conducted. Only when secondary emission from the cathode and electron-impact ionization of metastable states were included in the analysis did calculated current-voltage (I-V) characteristics for argon and methane discharges compare well with experimental data. The I-V characteristics obtained reveal a sharp rise in the current at a certain threshold voltage. This threshold voltage and the entire I-V characteristic are shifted to lower voltages when metastable ionization is significant. Below the threshold voltage and at low external ionization source strengths, a region of negative differential conductivity is obtained. In the high-current region, the I-V slope is controlled by the secondary emission coefficient. The additional cathode sheath ionization from secondary emission and ionization from metastable states significantly reduces the discharge voltage. This important effect can be used to reduce e-beam switch losses and increase lifetime through judicious gas mixture selection and proper cathode conditioning. INTRODUCTION R IGH-PRESSURE DISCHARGES ionized by the externalelectron beam (e-beam) offer unique advantages for use as high-power switches. They are capable of switching, both on and off, large currents at high voltages. Initial experiments [1], [2] using very high e-beam current densities, have proven the feasibility of this concept. Recent experiments [31, which used very low e-beam current densities, achieved a much higher current gain, i.e., the ratio of the discharge current switched to the e-beam current. In these experiments, discharge current densities of more than 1 A/cm2 have been achieved and current densities of 10 A/cm2 are considered to be obtainable. The e-beam current density required to control the switch is low, ranging from 1.5 to 50 mA/cm2. Thus using a moderate power electron gun (e-gun), "on" operation time of 10-5-10-4 s are achieved without being limited by overheating of the foil which separates the e-gun vacuum and the discharge gas.The repetition rate of these switches is limited only by the cooling characteristics of the gas volume. It is, therefore, de- In order to improve e-beam switch design through judicious gas mixture selection and enhancement of cathode sheath ionization processes, a better theoretical understanding of these discharges is required. The theory of e-beam ionized discharges has been treated by numerous authors and the effect of cathode sheaths has been investigated in [41, [5]. A particularly clear treatment was presented by Lowke and Davies [6]. They investigated externally ionized discharges at the very low gas pressure and electron density usually associated with charged particle counters. They also considered the intermediate gas pressure and electron density case for an e-beam ionized discharge. This paper, based on their theoretical development, analyzes an externally ionized discharge at higher current densities and considers the i...

The Chemical Oxygen-Iodine Laser (COIL) has been studied for several industrial applications. Recent demonstrations have shown that lasers can be highly effective for size-reduction cutting of radioactivelycontaminated structures.

No abstract

The interaction of a high power (infrared) laser beam with samples of rock encountered in hard-rock metal mining operations was experimentally investigated. These tests were intended to explore the feasibility of using high power lasers to improve the speed, performance, accuracy, and safety of rock cutting and drilling in mining operations. The current results were compared to similar tests, performed with the same laser, of materials typically encountered in gas and oil well drilling. Suggestions are made for the next steps in exploring how laser systems could possibly revolutionize drilling and cutting operations in the mining and oil/gas industries, particularly by augmenting other drilling hardware and techniques.