Index of content:
Volume 80, Issue 2, February 2009
- PARTICLE SOURCES, OPTICS AND ACCELERATION; PARTICLE DETECTORS
80(2009); http://dx.doi.org/10.1063/1.3069291View Description Hide Description
We present the results of experiments leading to improvement in bulk plasma uniformity of a constricted-arc discharge system with electron injection. The steady-state discharge was in argon, at a gas pressure of 0.5 mTorr, and operated with a main discharge voltage between 20 and 100 V and current between 3 and 15 A. The radial plasma distribution was measured with a movable Langmuir probe. We find that geometric modification of the intermediate electrode exit aperture and the main dischargecathode add little to the plasma uniformity. Improved bulk plasma uniformity is observed when a special distributing grid electrode is used and the main discharge voltage is less than 20–30 V. The application of a weakly divergent magnetic field in the region of the intermediate electrode exit aperture decreases the plasma nonuniformity from 20% to 14% over a radial distance of 30 cm. The plasma uniformity was further improved by compensating the magnetic self-field of the injected electron beam by a reverse magnetic field produced with a special electrode compensator. It is shown that an increase in dischargecurrent causes a proportional increase in back current in the distributing electrode. The approach allows a decrease in plasma nonuniformity from 20% to 13% over a radial distance of 30 cm.
80(2009); http://dx.doi.org/10.1063/1.3080555View Description Hide Description
The energy spectrum of relativistic electrons is an important characterization of high intensity laser-matter interactions. We present a technique that utilizes Čerenkov radiation to measure the time-resolved energy distribution of electrons. Electrons escaping from targets irradiated by high-intensity laser pulses were measured, demonstrating the feasibility of such a novel diagnostic. Limitations on the time resolution of this diagnostic are also discussed.
Robust, easily shaped, and epoxy-free carbon-fiber-aluminum cathodes for generating high-current electron beams80(2009); http://dx.doi.org/10.1063/1.3086728View Description Hide Description
This paper presents the construction of carbon-fiber-aluminum (CFA) cathode by squeezing casting and its applications for generating high-current electron beams to drive high-power microwave sources. The fabrication process avoided using epoxy, a volatile deteriorating the vacuum system. These cathodes had a higher hardness than conventional aluminum, facilitating machining. After surface treatment,carbon fibers became the dominator determining emission property. A multineedle CFA cathode was utilized in a triode virtual cathode oscillator (vircator), powered by a , pulse. It was found that 300–400 MW, microwave was radiated at a dominant frequency of 2.6 GHz. Further, this cathode can endure high-current-density emission without detectable degradation in performance as the pulse shot proceeded, showing the robust nature of carbon fibers as explosive emitters. Overall, this new class of cold cathodes offers a potential prospect of developing high-current electron beamsources.