Experiments with coaxial plasma guns at currents in excess of ten megamperes have resulted in the production of high-voltage pulses (0.5 MV) and hard x radiation (10–200 keV). The x-radiation pulse occurs substantially after the high-voltage pulse suggesting that high-energy electrons are generated by dynamic processes in a very high speed (≳106 m/s), magnetized plasma flow. Such flows, which result from acceleration of relatively low-density plasma (10−4 vs 1.0 kg/m3) by magnetic fields of 20–30 T, support high voltages by the back electromotive force-u×B during the opening switch phase of the plasma flow switch. A simple model of classical ion slowing down and subsequent heating of background electrons can explain spectral evidence of 30-keV electron temperatures in fully stripped aluminum plasma formed from plasma flows of 1–2 × 106 m/s. Similar modeling and spectral evidence indicates tungsten ion kinetic energies of 4.5 MeV and 46 keV electron temperatures of a highly stripped tungsten plasma.

An electrostatic accelerator technique for microprojectiles is being developed based on a multistage system using the sequential application of moderate-voltage pulses (>or=100 kV). Preliminary experiments have shown that carbon fibers have adequate tensile strength and conductivity to achieve charge-to-mass ratios >or=1 C/kg, a value consistent with hypervelocity goals. The carbon microprojectiles have been used in a five-stage proof-of-principle prototype accelerator at stage voltages of 35 kV to attain velocities of 0.5 km/s. Through the use of schlieren imaging techniques, data have been obtained showing that good control of the projectile trajectory can be achieved with electrostatic aperture focusing methods. Information from these experiments is being used to design and construct a 10-20 km/s prototype accelerator. To obtain a relatively short accelerator, encapsulation techniques are being developed so that acceleration gradients approaching the high dielectric strengths of the encapsulants can be achieved. A reflex transmission line arrangement has been devised that permits the longitudinal accelerating field to follow the projectile motion along the multiple stages with minimal switch action and without reversing electric field vectors, which would degrade dielectric strength. Details on the accelerator concept, the experimental results, and hardware designs are presented. >

The acceleration of solid material to velocities > 100 km/s using reasonable length accelerators can best be accomplished if electrostatic techniques are utilized. An accelerator for nanogram microprojectiles is being developed to demonstrate the basic principles for a multistage system based on the sequential application of voltage pulses /spl ges/ 100 kV. Experiments have been performed stressing carbon material to electric fields > I.6x1O/sup 9/ V/m, a field adequate to attain charge-to-mass ratios (q/m) of 5.0 C/kg for micron-diameter projectiles. An injector for charging and launching the microprojectiles into an accelerator has been constructed and operated with q/m = 1 C/kg. Specialized diagnostics for recording the microprojectile's charge and trajectory include a Faraday cup, and a schlieren optical system coupled to an electronic streak camera and to a microchannel-plate framing camera. A five-stage system is presently being and tested to attain a microprojectile velocity of 1 km/s as a proof-of-concept demonstration.

The utilization of high voltage electrodes in vacuum environments is common in a number of pulsed power applications. A limitation to voltage amplitude and/or pulse duration is flashover across the insulator separating the electrodes. Most often in cases where external effects are not involved, the cause of flashover is due to electron emission from the triple point, i.e., the junction of the cathode, insulator, and vacuum region. An approach being developed, in particular for application to compact electrostatic accelerators, is the elimination of the triple point through the use of bulk or film encapsulation techniques. Data from experiments will be presented showing that under both DC and repetitive pulse conditions (200 - 400 Hz), a simple bare-electrode accelerator structure that breaks down at 75 kV/cm in vacuum can be made to operate at fields exceeding 500 kV/cm by encapsulation. Candidate encapsulation compounds with reported dielectric strengths as high as 13,250 V/mil (thin film) will be discussed.

The plasma flow switch utilizes the nonlinear and nonuniform dynamics of a plasma discharge in vacuum to accumulate magnetic energy in times of several microseconds and then release this energy to a load in times of a few hundred nanoseconds. Experiments have been performed with capacitor banks up to 6 MJ, providing currents in excess of 107 A and peak voltages over 0.5 MV. Theoretical models incl...

Using a 1313-μF, 3-nH, 120-kV, 9.4-MJ SHIVA Star capacitor bank, we have performed vacuum inductive store/plasma flow switch (PFS) driven implosions of low mass (200-400 μg/cm2) cylindrical foil liners of 2-cm height and 5-cm radius. This technique employs a coaxial discharge through a plasma armature, which stores magnetic energy over 3-4 μs and rapidly switches it to an imploding load as the pla...

Previous investigators have demonstrated the feasibility of using an ionizing electron beam to control the conductivity of a gaseous volume-discharge switch. We consider the possibility of using such switches repetitively at high-power levels (up to 1010 W), with switch opening and closing times as short as several nanoseconds. An analysis of the relevant gas chemistry indicates that these requirements can best be met by using a nonelectronegative base gas with a high electron mobility, diluted with a small percentage of an electronegative gas. Detailed chemistry simulations, using the nonelectronegative gas N2 and the electronegative gas O2, are presented to support the analysis.

: Recent progress in the development of key elements of high power inductive storage systems makes it possible to generate high power pulses using energy storage systems (other than explosive generators) that include single-pulse inductive systems, hybrids (inductor/pulse line and inductive devices for steepening of the capacitor output) as well as inductive systems for generation of high power pulse trains. Prospects for further development of opening switches and storage systems suggest potential near-term payoff. Improvements based on such developments can be expected to impact system efficiency, compactness and operational convenience.

The technology for producing an intense relativistic electron beam with particle energies of less than 10 MeV is higly developed and has been discussed extensively in the literature. Methods of generating intense electron beams with particle energies exceeding 10 MeV are linked with solving complex physics, enginneering and financial problems. A potentially simple and inexpensive approach for generating such a high kinetic energy electron beam is to use autoacceleration processes on a lower voltage beam. The autoacceleration processes are the result of the mutual interaction between the electron beam and passive structures which are inserted in a conventional drift tube. This interaction leads to the redistribution of energy within the beam such that the majority of the electrons transfer their energy to a small portion of the beam. Possible processes for autoacceleration were discussed as early as 1971 especially in the Russian literature. Experiments showed the feasibility of autoacceleration and the problems facing these mechanisms.

Investigation of inductive storage technology for powering 1011 to 1012 W relativistic electron beam accelerators is presented. Circuits for effective power amplification using inertial energy storage units a current sources for generating high voltage have been analyzed. The analysis, based on using economical, high current, opening switch modules w command triggering capability, indicates that good efficiencies can be obtained. Experimental results supporting the analytical projection are summarized. The experimental results include generation of 300 kV inductive voltage at the output of 85 kJ magnetic storage coil and demonstration of inductive charging of an 8 Ohm water-dielectric pulse line to 5 kV.