B. Szapiro

Electron emission from glow-discharge cathode materials due to neon and argon ion bombardment

We have measured the electron yields of 7 glow‐discharge cathode materials under bombardment by neon and argon ions with energies between 1 and 20 keV. The surfaces of the samples were conditioned by operating the materials as cold cathodes in a high‐voltage glow discharge before the electron yield measurement. The materials studied are oxidized magnesium, oxidized aluminum, a molybdenum‐aluminum oxide sintered composite, molybdenum, stainless steel, copper, and graphite. The dependence of electron yield on ion velocity was found to be approximately linear for all materials and gases, with the slopes being strongly material dependent. The corresponding glow‐discharge current intensities were observed to have a supralinear dependence on the electron yield. The results are relevant to the design and modeling of cold cathode high‐voltage glow discharges.

Discharge‐pumped soft‐x‐ray laser in neon‐like argon

Starting with the discovery of x‐ray lasers in 1984, laser‐created plasmas remained for almost a decade, the only medium in which large amplification of soft‐x‐ray radiation could be obtained. In this paper the recent first demonstration of large soft‐x‐ray amplification in a discharge‐created plasma column, realized utilizing a fast capillary discharge to collisionally excite the 46.9 nm transition of Ne‐like, Ar is reviewed. Results of the parametrization of the Ar IX discharge‐pumped amplifier, the study of the dynamics of its plasma column, and the measurement of the time history of the laser pulse are reported. Prospects for laser operation at shorter wavelengths are also discussed.

Electron yield of glow discharge cathode materials under helium ion bombardment

The secondary electron emission coefficient of materials for helium ion bombardment in the energy range 0.5–20 keV was measured for the surface conditions of cathodes in high voltage glow discharges. The materials studied are oxidized aluminum, oxidized magnesium, a molybdenum‐aluminum oxide sintered composite, molybdenum, stainless steel, copper, gold, and graphite. Each sample was surface conditioned by operating it as cathode of a helium glow discharge shortly before the electron yield measurement. The results are relevant to the modeling of glow discharges and the design of cold cathode electron guns.

Study of Intense Electron Beams Produced by High-Voltage Pulsed Glow Discharges

We report the generation of high-current-density (20 A/cm2) pulsed electron beams from high-voltage (48-100 kV) glow discharges using cathodes 7.5 cm in diameter. The pulse duration was determined by the energy of the pulse generator and varied between 0.2 ¿s and several microseconds, depending on the discharge current. The largest electron beam current (900 A) was obtained with an oxidized aluminum cathode in a helium-oxygen atmosphere. An oxidized magnesium cathode produced similar results, and a molybdenum cathode operated at considerably lower currents. A small-diameter (<1 mm) well-collimated beam of energetic electrons of very high current density (>1 kA/cm2) was also observed to develop in the center of the discharge. Electrostatic probe measurements show that the negative glow plasma density and the electron beam current have a similar spatial distribution. Electron temperatures of 1-1.5 eV were measured at 7 cm from the cathode. The plasma density (8.5 · 1011 cm-3 at 450 A) was found to depend linearly on the discharge current. In discharges at high currents a denser and higher temperature plasma region was observed to develop at approximately 20 cm from the cathode. We have modeled the process of electron beam generation and predicted the energy distribution of the electron beam. More than 95 percent of the electron beam energy is calculated to be within 10 percent of that corresponding to the discharge voltage.

High current density hollow cathode electron beam source

An electron beam with current density greater than 30 A/cm2 and total current of 92 A has been generated in 5 μs pulses by accelerating the electrons from a glow discharge in a narrow gap between two grids. The ratio of the extracted electron beam current to discharge current is approximately 1. The gun also operates in a dc mode.

Modeling of fast capillary discharge for collisionally excited soft x-ray lasers: comparison with experiments

In this paper we report results of a model of a fast capillary discharge (FCD) and discuss them in comparison with experiments. The overall good coincidence between theory and experiment and the observation of stable reproducible compression are beneficial properties of FCD which open the possibility for achieving X-ray laser action in a compact discharge device. The required discharge parameters for lasing in different atomic elements have been calculated.

Experiments on soft x-ray laser development in a tabletop capillary discharge

The possibility of achieving soft X-ray amplification by collisional recombination in a capillary discharge plasma is being investigated. The results of the soft X-ray spectroscopy study of carbon capillary plasmas excited by a 40 kV, 108 ns FWHM discharge are discussed. The first spectra corresponding to a fast 25 ns FWHM, 600 kV discharge are also reported.

Soft X‐ray Laser Interferometry/Shadowgraphy of Exploding Wire Plasmas

We present the first results from soft x‐ray laser interferometry measurements of current‐driven thin wire explosions obtained using a capillary discharge pumped 46.9 nm laser and an amplitude division interferometer based on diffraction gratings. We have obtained series of high‐resolution soft x‐ray interferograms/shadowgrams that depict the initial stage of the evolution of exploding Al wires 15 μm and 25 μm in diameter. The images show a dense vapor core that completely absorbs the probe beam during the initial part of the explosion, and a surrounding plasma shell where both a shift of the interference fringes and partial absorption of the soft x‐ray laser probe beam are observed. The excitation of the 25 μm diameter wires at a current rate of 30 A/ns is observed to result in the uniform expansion. However, an increase of the rate of energy deposited per unit mass is observed to give rise to significant instabilities. The expansion velocity of the wire core was determined from the variation of the meas...

Study of fast capillary discharge plasma columns for soft x-ray amplifiers

The efficient generation, by a fast discharge, of capillary plasma channels containing Ne-like and Ni-like ions for collisionally excited soft-x-ray lasers is reported. Rapid pulse excitation of capillary channels 1.5 mm in diameter with currents of less than 70 kA produced Ca and Ti plasmas in which atoms are ionized up to the F-like state. Line emission at the wavelengths corresponding to the 3p - 3s and 3d - 3p transitions of Ne-like Ca has been observed.

Electron beam generation by electron multiplication

We have demonstrated that intense pulsed electron beams can be created by multiplication of lower current electron streams impinging on a high electron yield target. A 17 A electron beam of 1 μs pulse width was generated from a 2.5 A beam bombarding an activated Ag‐Mg target 2.5 cm in diameter.