No abstract

The electron temperature of a quiescent plasma in a metal discharge chamber, where the walls serve as the anode, can be raised by introducing a second anode consisting of 0.0025-cm-diam tungsten wires held at potentials as high as 100 V with respect to the walls. Hot electrons orbit the wires and return to the plasma. Cold electrons are absorbed. Smooth temperature variation, without introduction of noise, has been achieved between 0.5 and 4.0 eV.

Few-joule table-top lasers can generate pressures up to the 100 kbar range in solid materials by propagating a low-intensity beam through a transparent dielectric, which confines the ablation pressure, onto an ablation layer in contact with the material of interest. This technique has application in studies of material dynamic behavior and material processing. Development and application of physically based models of this process have lagged experiment. In this article the particulars of a detailed computational model incorporated into a two-dimensional radiationhydrodynamics code are presented. The model accounts for the initial absorption onto a metal surface, low-intensity photoionization absorption in neutral vapor, collisional ionization, recombination, dielectric breakdown, band gap collapse, electron conductivity, thermal transport, and constitutive properties of the materials. The model shows that most of the laser energy is absorbed in the dielectric tamper, not the ablator. Good agreement is found between simulated and measured pressure histories for materials irradiated with several tens of joules using a single-beam neodymium-glass laser at the Lawrence Livermore National Laboratory.

A compact Ar−N2 excitation transfer laser pumped by a coaxial electron gun is demonstrated. This laser emits a 40-ns, 300-kW pulse at a nominal repetition rate of 1 HZ. With 45 J of energy delivered to the electron gun, 12 mJ of laser output at 3577 Å is obtained. A 2.8% laser efficiency is estimated from simple electron deposition calculations, and the over-all electrical efficiency is estimated to be 0.03%. Because the stored energy needed in previously reported Ar−N2 lasers has been reduced by more than an order of magnitude while maintaining a comparable laser energy output, this device represents a significant step forward in the study of high-pressure electron-beam-pumped lasers.

We report on

High-power laser emission has been observed from xenon fluoride (XeF) at 351.1 and 353.1 nm. A peak laser power of 0.5 MW was obtained by using a mixture of Ar, Xe, and NF3 in the ratio of 250 : 25 : 1 at a total pressure of 1.7 atm. The laser gas was excited by a 1-MeV 20-kA electron beam for a pulse duration of 20 nsec. Energy deposited in the gas by the electron beam was estimated to be 1 J which gives a laser efficiency of 0.5%. Using a coaxial electron gun, an 80-mJ 100-nsec pulse was obtained with an efficiency of 3%.

Large, quiescent, magnetized plasma for wave studies Rev. Sci. Instrum. 46, 1386 (1975;A reasonably uniform cylindrical plasma, 15-20 em diam, and collisionless for many wave experiments, is generated in fields up to 500 G by applying 200 V of rf at 80 Me' to a fine wire grid stretched across a diameter. Axial containment is provided by opposing sets of JL-metalstrips that gather lines of force and create multimirror fields. Drift waves are inhibited by a short range peripheral alternating shear field, produced by an azimuthal ring of bar magnets. Densities are lO B _109 ions/cm 3 in argon with electron temperatures up to 12 eV, with a noise level, an In ::::: 3 X 10-3 , over the ion acoustic frequency range.

Low-frequency electrostatic waves which propagate across the magnetic field are studied experimentally. The observed dispersion relation agrees with that of the ion cyclotron harmonic wave. Strong damping of the wave is observed.