Joseph Thomas Bradley

Diagnostics and analysis of incident and vapor shield plasmas in PLADIS I, a coaxial deflagration gun for tokamak disruption simulation

Tokamak disruption simulation experiments have been conducted at the University of New Mexico using the PLADIS I plasma gun system. Earlier work had characterized the plasma-surface interaction in terms of parameters such as incident energy from bucket calorimeter measurements and rough measurements of beam area from flat damage targets. A variety of new plasma diagnostics have been used to further investigate the characteristics of the incident plasma beam and vapor shield plasma in a simulated tokamak disruption. These diagnostics have included laser interferometry, two-color pyrometry, emission spectroscopy, and other methods to quantify the characteristics of the incident and vapor shield plasmas of a simulated tokamak disruption. The synthesis of different beam area measurement techniques is used to determine the radial structure of the plasma beam. Vacuum ultra violet spectroscopy is used to determine the thickness and internal structure of the vapor shield plasma. Results from two-color optical pyrometry and surface pressure measurements are used to determine the dynamics of vapor shield formation.

Test wire for high voltage power supply crowbar system

The klystron microwave amplifier tubes used in the low energy demonstration accelerator (LEDA) and to be used in the accelerator production of tritium (APT) plant have a strict upper limit on the amount of energy which can be safely dissipated within the klystrons vacuum envelope during a high voltage arc. One way to prevent damage from occurring to the klystron microwave amplifier tube is through the use of a crowbar circuit which diverts the energy stored in the power supply filter capacitors from the tube arc. The crowbar circuit must be extremely reliable. To test the crowbar circuit, a wire that is designed to fuse when it absorbs a predetermined amount of energy is switched between the high voltage output terminals. The energy required to fuse the wire was investigated for a variety of circuits that simulated the power supply circuit. Techniques for calculating wire length and energy are presented along with verifying experimental data.

Pulsed power diagnostics on the PLADIS I plasma gun

Tokamak disruption simulation experiments are being conducted at the University of New Mexico (USA) using the PLADIS I plasma gun system. PLADIS I is a high power, high energy coaxial plasma gun configured to produce an intense plasma beam. The inductance and capacitance of the PLADIS I gun circuit are adjusted to produce a current pulse with a full width half max (FWHM) time of 100 /spl mu/s. Candidate materials are placed in the beam path to determine their response under disruption relevant energy densities. Various diagnostics have been used to determine the characteristics of the incident plasma and the vapor shielding plasma. Calorimeter arrays provided by the Japan Atomic Energy Research Institute were used to determine the profile of energy density deposited in the array material. A fast, two color optical pyrometer was used to determine the surface temperature of the sample as a function of time during initial plasma/surface interaction, before the vapor shield plasma becomes optically thick and obscures the surface. A time resolved target surface pressure diagnostic using a commercially available, fast response polyvinylidine fluoride pressure sensor has been built and is used to determine the pressure pulse of the plasma as a function of position and time. Data from this diagnostic regarding plasma beam spot size and pulse width are compared to results from other diagnostics. Initial results from the pressure diagnostic agree very well with the risetime of the surface temperature and the FWHM time of the gun current pulse. Further results regarding total absorbed energy, time resolved target surface temperature and time resolved target surface pressure in PLADIS I as a function of incident power and energy are presented.

Crenulation-­1 Flash Report

We briefly report on the first of PHELIX driven Crenulation experiments diagnosed with proton radiography. PHELIX is a 300 kJ capacitor bank located at the LANL LANSCE pRad facility. It is capable of delivering a 4 MA, 10 us current pulse to a low inductance cylindrical load. Using a magnetically driven cylindrical liner, we have shocked a concentric tin cylindrical shell to melt-on-release and compared to theory and calculations. The inner surface of the tin cylinder has three sectors of single-mode perturbations, which are subject to Richtmyer-Meshkov Instability (RMI). Recent theoretical work on the EOS of tin has modified both the Hugoniot and the isentropes for release into various states in tabular data. The new multiphase EOS for tin, SESAME 2161, includes the beta and gamma solid phases as well as a liquid phase. It predicts a lower pressure boundary for release to pure solid (~20 GPa) and a higher pressure boundary for release to pure liquid (~35 GPa) than the existing SESAME 2160 table.

Quantitative evaluation of magnet hysteresis effects at LANSCE with respect to magnet power supply specifications

The proton beam in the LANSCE accelerator is guided and focused almost exclusively by electromagnets. Magnet hysteresis has had significant impacts on the tuning of the LANSCE accelerator. Magnet hysteresis can also have an impact on magnet power supply (MPS) control, regulation and repeatability requirements. To date, MPS performance requirements have been driven by the requirements on the magnetic fields as determined by the accelerator physicists. Taking hysteresis effects into account can significantly change MPS requirements, as some requirements become more stringent and some are found to be over specified. Overspecification of MPS requirements can result in significant increases in MPS cost. Conversely, the use of appropriate MPS requirements can result in significant cost savings. The LANSCE accelerators more than three decades of operation provide a wide variety of MPS technologies and operational experience. We will survey the LANSCE MPS history and determine how performance specifications can be refined to both reduce costs and improve the operators abilities to control the magnetic fields.