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Self-magnetic-pinched diode behavior at 1.5-2 MV was diagnosed using a variety of electrical, radiation, and optical diagnostics. Results are compared with predictions of the LSP particle-in-cell code, and shown to be in good agreement. A practical diagnostic of electron incidence angles is demonstrated. A quadrature interferometer is shown to be capable of measuring the time-dependent position of the effective electrode-plasma boundaries. Both one-dimensional (1-D) and two-dimensional (2-D) interferometry show the importance of anode plasma expansion in such diodes with high anode-power concentration. Not only does the anode plasma contribute significantly to gap closure, but there is evidence that anode plasma expansion results in a distortion of the effective anode shape, which can significantly affect the diode performance. Index Terms--Electron beams, particle beams, pinched-beam diodes, pulsed power, radiography.

A plasma-filled diode (PFD) technique is described for producing high dose-rate bremsstrahlung over small areas. A PFD was developed for this purpose using the Gamble II generator. For maximum dose-rate conditions, the short-circuit phase duration was 40 ns, after which the voltage increased to 1.8 MV and the total current in the diode was 0.5 MA. The X-ray pulsewidth was 8 ns, much less than the typical 50 ns pulsewidth with a vacuum diode. This PFD was adapted to the higher-current Saturn generator at 6-8 MA by making a 10-cm diameter circular array of 6, 9, or 12 isolated PFDs. Higher dose rates were obtained using fewer PFDs; about 1 x [10.sup.12]rad/s with the 12-PFD array, 2 x [10.sup.12] with nine PFDs and 4 x [10.sup.12] with 6 PFDs. Analyses based on electrical and radiation diagnostics indicate that 40%-77% of the electrical current produces radiation at the time of maximum dose rate. The X-ray pulsewidth was typically 13-16 ns, less than the pulsewidth for standard (vacuum) bremsstrahlung diodes on Saturn. This system, with improvements in reproducibility, could provide a high dose-rate, small-area bremsstrahlung capability for high current generators. Index Terms--Bremsstrahlung, dose rate, plasma-filled diode (PFD), pulsed power.

The K-shell radiated energy (yield) from neon Z-pinch implosions with annular, gas-puff nozzle radii of 1, 1.75, and 2.5 cm was measured for implosion times from 50 to 300 ns while systematically keeping the implosion kinetic energy nearly constant. The implosions were driven by the Hawk inductive-storage generator at the 0.65-MA level. Initial neutral-neon density distributions from the nozzles were determined with laser interferometry. Measured yields are compared with predictions from zero-dimensional (O-D) scaling models of ideal, one-dimensional (l-D) pinch behavior to both benchmark the scaling models, and to determine their utility for predicting K-shell yields for argon implosions of 200 to >300 ns driven by corresponding currents of 4 to 9 MA, such as envisioned for the DECADE QUAD. For all three nozzles, the 0-D models correctly predict the Z-pinch mass for maximum yield. For the 1- and 1.75-cm radius nozzles, the scaling models accurately match the measured yields if the ratio of initial to final radius (compression ratio) is assumed to be 8:1. For the 2.5-cm radius nozzle, the measured yields are only one-third of the predictions. Analysis of K-shell spectral measurements suggest that as much as 70% (50%) of the imploded mass is radiating in the K-shell for the 1-cm (1.75-cm) radius nozzle. That fraction is only 10% for the 2.5-cm radius nozzle. The 0-D scaling models are useful for predicting 1-D-like K-shell radiation yields (better than a factor-of-two accuracy) when a nominal ([approximately equal to] 10:1) compression ratio is assumed. However, the compression ratio assumed in the models is only an 'effective' quantity, so that further interpretations based on the 0-D analysis require additional justification. The lower-than-predicted yield for the 2.5-cm radius nozzle is associated with larger radius and not with longer implosion time, and is probably a result of two-dimensional effects. Index Terms - Inductive energy storage, plasma pinch, X-ray production.

K-shell x-ray measurements were obtained for aluminum x-pinch plasmas using the LION generator. X-pinch scaling experiments were performed wherein a 280 to 470 kilo-ampere peak current, 80 nanosecond full width at half-maximum pulse was delivered to an aluminum x-pinch wire load. The K-shell yield measurements were then extended to higher current using the Gamble II generator. Results indicate that the K-shell x-ray yield is directly proportional to the intensity of the applied current.

The “Compton–Hall” voltmeter is a radiation-based voltage diagnostic that has been developed to measure voltages on high-power (TW) pulsed generators. The instrument collimates photons generated from bremsstrahlung produced in the diode onto an aluminum target to generate Compton-generated electrons. Permanent magnets bend the Compton electron orbits that escape the target toward a silicon pin diode detector. A GaAs photoconductive detector (PCD) detects photons that pass through the Compton target. The diode voltage is determined from the ratio of the electron dose in the pin detector to the x-ray dose in the PCD. The Integrated Tiger Series of electron–photon transport codes is used to determine the relationship between the measured dose ratio and the diode voltage. Variations in the electron beam’s angle of incidence on the bremsstrahlung target produce changes in the shape of the photon spectrum that lead to large variations in the voltage inferred from the voltmeter. The voltage uncertainty is minimized when the voltmeter is fielded at an angle of 45° with respect to the bremsstrahlung target. In this position, the photon spectra for different angles of incidence all converge onto a single spectrum reducing the uncertainty in the voltage to less than 10% for voltages below 4 MV. Higher and lower voltages than the range considered in this article can be measured by adjusting the strength of the applied magnetic field or the position of the electron detector relative to the Compton target. The instrument was fielded on the Gamble II pulsed-power generator configured with a plasma opening switch. Measurements produced a time-dependent voltage with a peak (3.7 MV) that agrees with nuclear activation measurements and a pulse shape that is consistent with the measured radiation pulse shape. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Describes the use of a differential phase shift interferometer for measuring axisymmetric gas distributions for high-power Z-pinch plasma research. Measurement of the line-integrated gas density; Determination of radial density distributions via Abel inversion; Accuracy of the instrument; Comparison of the differential technique with standard laser interferometry.

Presents two interferometric methods used in measuring gas preionization for plasma radiation sources. Measurements of a flashover ultraviolet photoionization scheme; First technique's use of a single laser wavelength to probe a chord of the cylindrical gas puff; Wavelengths used by the second technique to determine neutral and free electron densities using a single gas puff event.

Describes the development of a simple technique to image intense pulsed proton beams with radiochromic film and to measure their spatial distribution. Optical density of the thick film; Increase in optical density linearly with fluence up to 0.25 cal/centimeter; Use of the film to measure the uniformity of large-area beams as well as the detector in a multiple-pinhole camera.

Describes absolute calibration of an annihilation-radiation sodium iodide (NaI) coincidence detection system for short-lived ion-induced radioactivity. Incident proton intensity; Comparison of absolute fluences of pulsed proton beams with ion beam fluences measured by carbon calorimetry.