The rod-pinch diode consists of an annular cathode and a small-diameter anode rod that extends through the hole in the cathode. With high-atomic-number material at the tip of the anode rod, the diode provides a small-area, high-yield x-ray source for pulsed radiography. The diode is operated in positive polarity at peak voltages of 1 to 2 MV with peak total electrical currents of 30–70 kA. Anode rod diameters as small as 0.5 mm are used. When electrode plasma motion is properly included, analysis shows that the diode impedance is determined by space-charge-limited current scaling at low voltage and self-magnetically limited critical current scaling at high voltage. As the current approaches the critical current, the electron beam pinches. When anode plasma forms and ions are produced, a strong pinch occurs at the tip of the rod with current densities exceeding 106 A/cm2. Under these conditions, pinch propagation speeds as high as 0.8 cm/ns are observed along a rod extending well beyond the cathode. Even faster pinch propagation is observed when the rod is replaced with a hollow tube whose wall thickness is much less than an electron range, although the propagation mechanism may be different. The diode displays well-behaved electrical characteristics for aspect ratios of cathode to anode radii that are less than 16. New physics understanding and important properties of the rod-pinch diode are described, and a theoretical diode current model is developed and shown to agree with the experimental results. Results from numerical simulations are consistent with this understanding and support the important role that ions play. In particular, it is shown that, as the ratio of the cathode radius to the anode radius increases, both the Langmuir–Blodgett space-charge-limited current and the magnetically limited critical current increase above previously predicted values.

No abstract

PHYSICAL REVIEW LETTERS 6 DECEMBER 1976 eration in He and Ne to extend the range of coherent wavelengths to 53.2 nm. Conversion is in the range of 10" 5 to 10" 6 with further optimization believed to be possible. This work represents the first application of frequency upconversion to the extreme ultraviolet with use of optical nonlinarities of higher order than third, and indicates the feasibility of using such processes to extend the range of available coherent wavelengths ever closer to the soft x-ray range. The authors would like to thank T. N. Lee for advice and assistance with VUV photography, W. Hunter for advice on VUV equipment, M. Fink for preparation of the Al filters, and E. Tiedemann for laboratory assistance.

A plasma erosion opening switch, coupled to a small capacitor bank, conducts 120 kA for 400 ns before opening in 40 ns. Voltages above 170 kV are produced through the use of an electron beam diode. These voltages exceed the initial capacitor bank voltage by a factor of 4. Current and magnetic field measurements indicate that the same current conduction and opening processes observed in earlier erosion switch experiments are involved here at tenfold greater conduction times, verifying the current controlled nature of plasma erosion switch operation.

No abstract