G. Cooperstein

Vacuum Inductive Store/Pulse Compression Experiments on a High Power Accelerator Using Plasma Opening Switches.

A new type of an opening switch which operates in vacuum and opens on a nanosecond timescale at voltages > 1 MV is described. This Plasma Opening Switch (POS) is able to conduct several hundred kiloamperes for approx. 50 nsec while a vacuum inductor is charged, then to open in < 10 nsec, delivering a large fraction of the stored energy to an electron-beam load. Preliminary experiments are described and a simple model of the POS operations is presented.

Impedance characteristics of diodes operating in the self−pinch mode

The impedance characteristics of large aspect ratio diodes employing hollow field emission cathodes operating in the self−pinch mode have been studied at electron kinetic energies between 400 and 800 keV and currents between 100 and 500 kA. The importance of correcting the anode−cathode gap spacing for closure due to plasma motion is recognized and taken into account in the definition of the diode aspect ratio in impedance calculations. With this correction, the impedance at peak diode voltage and current is found to be nearly independent of voltage and cathode surface area, and inversely proportional to the diode aspect ratio. Its amplitude is approximately 50% higher than that predicted by parapotential flow theory.

Production of intense light ion beams on a multiterawatt generator

The operation of a pinch‐reflex diode as an intense pulsed ion‐beam source has been scaled up to the multiterawatt PITHON generator. Ion beams with currents of 1 MA at 1.8 MeV have been extracted in a 130 kJ, 100‐ns pulse. The corresponding ion production efficiency is 60%. Power losses were observed in interfacing the coaxial diode to the biconic vacuum feed of the generator. By using smaller area diodes, the average current density at the anode source was increased to 20 kA/cm2. Proton and deuteron beams were studied in both planar and spherical diode geometries. The ion beam is focused predominantly by self‐magnetic fields for planar diodes and predominantly by electrode shaping for spherical diodes. Current densities exceeding 150 kA/cm2 were achieved with spherical diodes. The spatial evolution of the anode and cathode plasmas was studied by laser holographic interferometry. As the peak of the power pulse is approached, plasmas were observed to expand from the electrodes in fairly uniform profiles wi...

High‐impedance ion‐diode experiment on the Aurora pulser

Proton beams with currents ⩾50 kA at 5 MeV in a ≲160‐ns FWHM pulse have been extracted from an ion diode operated on the Aurora pulser. This current corresponds to an efficiency (proton currrent/total current) of 20%, which compares favorably with numerical simulation. The simulation indicates that the ion current is enhanced over the Child‐Langmuir value due to increased electron lifetime in the diode. The proton beam directed onto a LiCl target provides a source of 1.8×1012 neutrons/sr/pulse in the forward direction from the 7Li(p,n) 7Be reaction.

Status of Light Ion Inertial Fusion Research at NRL

Abstract : High-brightness proton beams have recently been extracted from axial pinch-reflex diodes (PRD) mounted on the Gamble II generator. The source power brightness that was measured exceeded 10 TW/sq cm sq rad. Analysis of a modular Inertial confinement fusion system using such diodes shows that an operational window for transport of light-ion species exists. Multi-terawatt beams can be transported a few meters in channels a few centimeters in diameter. A proof-of-principle experiment for the required final focusing cell has been successfully carried out on Gamble II. A new barrel-shaped equatorial PRD that can be coupled to PBFA II as a single diode has also been operated on Gamble II and has demonstrated 50% ion efficiency with predominantly azimuthally-symmetric charged-particle flow. Preliminary experiments using vacuum inductive storage and plasma opening switches have demonstrated factor-of-three pulse compressions, with corresponding power and voltage multiplications for pulse durations of interest to PBFA II. In other experiments the stopping power of deuterons in hot plasmas was measured. Results show about 40% enhancement in stopping power over that in cold targets when the deuteron beam is focused on the target to about 0.25 MA/sq cm. (Author)