J.D. Graham

Compact toroid formation experiments

Summary form only given, as follows. A compact toroid (CT) formation experiment is discussed. The device has coaxial electrode diameters of 0.9 m (inner) and 1.25 m (outer) and an electrode length of ~1.2 m, including an expansion drift section. The CT is formed by a 0.1-0.2-T initial radial magnetic field embedded coaxial puff gas discharge. The gas puff is injected with an array of 60 pulsed solenoid driven fast valves. The formation discharge is driven by a 108-μF, 40-100-kV, 86-540-kJ, 2-5-MA capacitor discharge with ~20-nH initial total discharge inductance. The hardware includes transmission line connections for a Shiva Star (1300-μF, up to 120-kV, 0.4-MJ) capacitor bank driven acceleration discharge. Experimental measurements include current and voltage; azimuthal, radial, and axial magnetic field at numerous locations; fast photography and optical spectroscopy; and microwave, CO2 laser, and He-Ne laser interferometry. Auxiliary experiments include Penning ionization gauge, pressure probe, and breakdown gas trigger diagnostics of gas injection, and Hall probe measurements of magnetic field injection

New method of initiating multi-megampere, multi-megajoule plasma focus discharges using magnetized plasma flow switches

Summary form only given. We describe a novel dense plasma focus experiment at the Shiva Star facility (operated at 1 MJ-2 MJ capacitor bank energy), which uses a compact toroid (CT) magnetized plasma flow switch to initiate the focus implosion downstream from a shielded vacuum insulator. The CT armature stably and reproducibly translates up to 3 MA from the vacuum feed region through coaxial electrodes to a puffed-gas central load. The inertia of the 1 mg CT and the work that must be done in compressing the internal magnetic fields during the translation provide a delay in current delivery to the pinch of 5-/spl mu/s ps, which matches the bank quarter cycle time relatively well. Effectiveness of the current delivery was monitored by primarily by inductive probes in the PFS region, fast photography of the focus, and X-ray and neutron measurements of the pinch. No evidence of current loss was observed.

Solid liner compression of working fluid to megabar range

Summary form only given. We have used 12 megamp, 5 megajoule axial discharges to electromagnetically implode tapered thickness spherical aluminum shells, achieving peak implosion velocities above 20 km/sec inner surface, 10 km/sec thickness averaged. The shell thickness was proportional to the inverse of the square of the cylindrical radius. This causes the ratio of magnetic pressure to shell areal mass density (and spherical acceleration) to be independent of polar angle, so that the spherical shape is nominally maintained during the implosion. We have used these implosions to compress hot hydrogen plasmas with initial pressure about 100 atm and initial temperature above 1 eV. The hot hydrogen plasmas were injected beforehand using 1 megamp, 100 kilojoule range co-axial gun discharges through a circular array of vanes to strip away magnetic field. The imploding shell and the compressed hot hydrogen working fluids effect on a diagnostic compression target were observed with radiography.

Inverse-pinch flux compression generator

Summary form only given. In this work, a non-explosive flux compression generator was designed, built and tested. The device is based on an inverse-Z-pinch plasma discharge which is used as the piston field in compressing the seed poloidal magnetic field. The feasibility of non-explosive flux compression generators in driving high impedance loads was demonstrated in an earlier experiment where a coaxial plasma discharge was used in compressing a poloidal seed field.

Time Resolved Mass Flow Measurements For A Fast Gas Delivery System

point is sealed off with a fast closing valve within a time interval short compared to the mass flow time scale. If the injected mass is allowed to equilibrate in a known volume after being cut off from its source, a conventional static pressure measurement before and after injection, and application of the ideal gas law suffices. Repeating for many different values of fP, and assuming reproducibility, the injected mass time history M(t) characteristic of the system without the fast closing valve may be determined. The flow rate versus time &W(t)/& may then be determined by numerical differentiation. Mass flow measurements are presented for a fast delivery system for which the flow of argon through a 3.2mm-i.d., 0.76mm-thick copper tube is isolated by imploding (8 pinching) the tube using a single turn tungsten magnetic-field coil. Optical measurements of the tube’s internal area versus time indicate that the tube is sealed in 7 ,us. Results are correlated with piezoelectric probe measurements of the gas flow and 2D axisymmetric numerical simulations of the 6 pinch process.