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The DARHT-II linear-induction accelerator has been successfully operated at 1.2-1.3 kA and 12.5-12.7 MeV to demonstrate the production and acceleration of an electron beam. Beam pulse lengths for these experiments were varied from 0.5 [micro]s to 1.2 [micro]s full-width half-maximum. A low-frequency inductance-capacitance (LC) oscillation of diode voltage and current resulted in an oscillation of the beam position through interaction with an accidental (static) magnetic dipole in the diode region. There was no growth in the amplitude of this oscillation after propagating more than 44 m through the accelerator, and there was no loss of beam current that could be measured. The results of these initial experiments are presented in this paper. Index Terms--Accelerator, accelerator measurement systems, induction accelerators, particle beams, stability.

The spallation neutron source (SNS) is a next-generation high-intensity beam facility. The extraction kicker system is a high peak power, high average power, high-precision pulse-waveform, low beam impedance, and high repetition rate pulsed power system. It has been successfully designed and developed at Brookhaven National Laboratory, Upton, NY. The system consists of fourteen extraction magnet sections inside the ring vacuum chamber and fourteen identical high-voltage modulators located in the service building. The design features a Blumlein pulse-forming-network (PFN) based topology, a low beam impedance termination, a fast current switching thyratron, and low inductance capacitor banks. It has a maximum charging voltage of 50 kV, an open circuit output of 100 kV, and a designed maximum pulsed current output of 4 kA per modulator. The overall system output will reach multiple GW peak power with a 60 pulse/s repetition rate. A prototype modulator has been successfully built and tested well above the SNS requirement. The first batch of production modulators have passed all required tests at manufacture facility and delivered to Oak Ridge National Laboratory, Oak Ridge, TN, and the rest of the production units are under construction. The technical challenges and development results are presented in this paper. Index Terms--Accelerator power supplies, particle beam extraction, proton accelerators, pulse power systems.

The envelope oscillations of a cold-fluid corkscrewing elliptic beam in a uniform-focusing magnetic field are studied. In particular, by linearizing the generalized beam envelope equations, the eigenmodes of small-amplitude envelope oscillations are calculated for a cold-fluid corkscrewing elliptic beam oscillating about its equilibrium. All of the eigenmodes are shown to be stable. Index Terms--Focusing, particle beam stability, space-charge-dominated.

In this paper, we present a new scheme of injection into a plasma accelerator, aimed at producing a high-quality beam while relaxing the demands on the bunch length of the injected beam. The beam dynamics in the injector, consisting of a high-voltage pulsed photodiode, is analyzed and optimized to produce a [[Lambda].sub.p]/20 long electron bunch at 2.5 MeV. This bunch is injected into a plasma wave in which it compresses down to [[Lambda].sub.p]/100, while accelerating up to 250 MeV. This simultaneous bunching and acceleration of a high-quality beam requires a proper combination of injection energy and injection phase. Preliminary results from simulations are shown to assess the potentials of the scheme. Index Terms--Bunching, injector, plasma accelerator, pulsed photodiode.

Spatially resolved measurements of a supersonic [Ar.sup.+] ion beam are obtained using a movable retarding field energy analyzer positioned on the low potential side of a current-free helicon double-layer (DL). The DL is generated near the open end of the helicon source where the fairly 'collisionless' argon plasma is expanding in a diverging magnetic field for a radio frequency power of 250 W and a pressure of about 0.35 mtorr. The potential drop of the DL induces ion acceleration and the formation of an ion beam which propagates downstream of the DL. An image showing the ion beam spatial properties 12 cm downstream of the DL is presented. Index Terms--Double-layer, energy analyzer, expanding plasma, ion acceleration, ion beams, supersonic.

A current-free electric double-layer is created in a one-dimensional hybrid (particle ions and fluid electrons) plasma computer code by inserting a loss process along the axis of the simulation to mimic an expanding plasma. The image presented here shows a supersonic ion beam which has been accelerated downstream of the double-layer. Index Terms--Current-free double-layer, expanding plasma, hybrid simulation, ion acceleration, supersonic ion beam.

Insight into the interaction between plasma and the surface can be obtained from well-defined radical and ion beam studies using advanced surface diagnostics. Therefore, in this paper, a new ultrahigh vacuum setup is presented for a fundamental study of the plasma deposition process of hydrogenated amorphous silicon (a-Si:H). A first study of the surface diffusion process of plasma radicals is presented by visualizing the surface roughness evolution of the films as a function of bulk thickness and substrate temperature. Index Terms--Plasma deposition, surface diffusion, surface reactions.