[en] Both the preheat and turbulent phase plasmas produced in the Texas Turbulent Torus discharge have been studied using microwave interferometry, Langmuir probe scans, Thompson scattering, microwave radiation detection, and an E vector x B vector velocity analyzer to obtain a picture of the evolution of the plasma during both phases of the discharge. A cool, uniform, well understood preheat plasma is produced which is subjected to a large toroidal electric field during the turbulent phase. The electron velocity distribution is measured during turbulent heating using an E vector x B vector velocity analyzer. A turbulent skin arises on the plasma edge which penetrates into the higher density (> 3 x 10¹²cm^-3), interior portion of the plasma on a microsecond time scale. Large drift velocities (v/sub d/ > v/sub Th/) and non-Maxwellian temperatures of several KeV are characteristic of the turbulent plasma. During the turbulent phase of the discharge large heating rates (12KeV/μs) are observed together with rapid energy losses from the edge of the plasma and less rapid losses from the interior. The non-Maxwellian velocity distributions provide an explanation for observed inconsistencies between laser, x-ray, and magnetic probe measurements while showing agreement with each measurement individually

[en] We have conducted experiments on Sandia National Laboratories' Mite accelerator (2 MV, 4.8 ohms) to study the effect of geometric transitions on power flow in a magnetically insulated power feed. The effect of both changing gaps (electric convolutes) and changing line widths (magnetic convolutes) was studied. These geometric transitions caused electron losses which depended on both the abruptness of the transition and the downstream load impedance. These losses, due to perturbation of the orbits of the magnetically insulated electron flow in the anode-cathode gap, are called kinetic losses. Temporally and spatially resolved measurements of these losses were made using Faraday cups and filtered, 4-chlorostyrene, radiochromic dosimeters. The effect of an anode plasma on magnetically insulated electron flow was also studied. The kinetic losses measured in these experiments can be significant in some situations

[en] An electron trajectory code is used to study the design of the injector and field coil system for a prototype of Delphi. For a 1 kA beam, fields of about 1 kG can keep the angular divergence to less than 1⁰

[en] The PBFA II vacuum insulator was originally designed for optimum coupling to a proton ion diode with minimum inductance. In July 1983 it was decided that lithium ions at 30 MeV would be the baseline for PBFA II. This requires the use of Plasma Opening Switches (POS) and vacuum inductor to reach 30 MV. To achieve this, the vacuum magnetically insulated transmission lines had to be redesigned as an inductive energy store. To gain optimum coupling to this vacuum inductor, the output impedance of the water section was increased by the use of a water-dielectric transformer. The calculations leading to the final design will be discussed

[en] This paper discusses injector losses on the Mite accelerator at the Sandia National Laboratories. Topics considered in the paper include energy losses, energy transfer, electron beam injection, and electron beams

[en] The absence of direct measurements of magnetically insulated line voltage necessitated reliance on inferred voltages based on theoretical calculation and current measurements. This paper presents some of the first direct measurements of magnetically insulated transmission line peak voltages. These measurements were made on the Sandia National Laboratories HydraMITE facility. The peak voltage is measured by observing the energy of negative ions produced at the line cathode and accelerated through the line voltage. The ion energy and the charge-to-mass ratio are measured using the Thomson Parabola mass spectrometry technique. This technique uses parallel E and B fields to deflect the ions. The deflected ions are detected using a microchannel plate coupled to a phosphor screen and photographic film. The Thomson Parabola results are compared to Faraday Cup measurements and to calculated voltages based on current measurements. In addition, the significance of observed positive ions is discussed

[en] Ion diode research at Sandia National Laboratories is performed on the PBFA II accelerator. The goal of this research is to deliver a lithium ion beam of approximately 100 TW and greater than 1 MJ to an inertial confinement fusion target. These parameters should be adequate to test ICF ignition physics. During this past year, over 500 kJ of beam energy was generated with peak voltages of over 5 MV. Experiments at 1/4 energy produced a focal spot with a FWHM of 5.7 mm diameter for the proton portion of the beam. Typical diode impedance lifetimes [-Z/(dZ/dt)] of 30-40 ns, and diode current efficiencies (I/sub ion//I/sub total/) of at least 80% were obtained in these experiments. Diode efficiency and impedance were found to be critically dependent on the details of magnetic field profiles in the diode. A new analytic theory of diode operation was developed which explains the operating voltage and current of applied-B diodes. The theory is based on the self-consistent equilibrium position of the virtual cathode. The theory explains the operating impedance of the PBFA II diode and the applied-B diodes fielded on Proto I, Proto II, and PBFA I during the past several years. Particle-in-cell code simulations of diode operation are consistent with the predictions of this theory. To facilitate diode design, a capability was developed to predict ion trajectories in the diode as a function of time and ion species based on the experimentally measured voltage and current, the diode geometry, and the magnetic field profiles in the diode region. This capability provides guidance in modifying the anode geometry and the applied magnetic field profiles for optimum focusing of either protons or lithium ions. 21 refs., 19 figs

[en] A new, magnetically insulated negative ion source has recently been discovered which can produce pulsed negative ion beams (H^-, Li^-, and C^-) with intensities of 100-300 A/cm² at 1-4 MeV. This source may provide the basis for a high energy neutral beam system for heating large tokamaks

[en] Quartz gauges have been used on the Sandia National Laboratories Proto II accelerator to measure current in the magnetically insulated transmission line at the 11 TW power level. The accelerator delivers 3.5 MA at 2 x 10¹⁴ A/s in a 40 ns pulse to a 0.0127 m diameter aluminum liner to produce a high density plasma. At this radius and dI/dt levels, the B-dot monitors no longer function for the measurement of load current because the monitor suffers electrical breakdown. Quartz pressure gauges mounted at a radius of 0.0086 m have successfully measured the magnetic pressure due to the load current with nanosecond temporal resolution

[en] A new water-plastic-vacuum interface has been designed for Sandia Laboratory's Supermite (2.8 MV, 2.2 ohm) accelerator. This design was based on the PBFA I vacuum interface. Electrostatic field plots show that in positive polarity the water feed to the PBFA I interface will fail at 2 MV on Supermite. This is confirmed by positive polarity experiments and field plots using the PBFA I style vacuum interface at the Naval Research Labs. Modifications to the water section geometry to increase the water breakdown strength in positive polarity result in equivalent electric field grading at the plastic-vacuum interface but allow positive polarity operation at voltages up to 3.1 MV. This is accomplished by incorporating a dielectric field shaper which significantly improves the electric field grading across the insulator