Magnetized Target Fusion (MTF) requires the fast compression of hot, dense plasmas by a conducting liner. We have used two-dimensional MHD calculations to study the electromagnetic implosion of metallic liners driven by realistic current waveforms. Parametric studies have indicated that the liner should reach velocities of 3-20 k d s , depending on the magnetic field configuration, and reach convergence ratios (initial radius divided by final radius) of at least 10. These parameters are accessible with large capacitor bank power supplies such as SHWA or ATLAS, or with magnetic flux compression generators. One issue with the high currents that are required to implode the liner is that Ohmic heating will melt or vaporize the outer part of the liner. Calculations have shown that this is a realistic concern. We are currently addressing questions of liner instability and flux diffusion under MTF conditions. Another issue is that the magnetic fields needed to inhibit thermal losses to the walls will also heat, melt, or vaporize the inner wall surfaces. For initial fields between 5-50 Tesla, the wall heating is significant but does not result in rapid melting. As the implosion evolves, flux compression leads to fields in excess of 100 Tesla. Calculations which include flux diffusion, Ohmic heating, and realistic material properties show that a significant fraction of the inner surface of an aluminum liner will have melted and vaporized in the final microsecond of implosion. It is not clear at this time that such material mixes will the hot plasma. We are conducting studies to determine the extent of wall-plasma interaction under these conditions. Magnetized Target Fusion (MTF) is an approach to fusionwhere a preheated and magnetized plasma is adiabatically compressed to fusion conditions. Successful MTF requires a suitable initial target plasma with a magnetic field of a1 least 5 T in a closed-field-line topology, a density of roughly 10l8 ~m -~, a temperature of at least 50 eV but preferably closer to 300 eV, and must be free of impurities which would raise radiation losses. The goal of these experiments is to demonstrate plasma conditions meeting the requirements for an MTF initial target plasma. The plasma is produced by driving a z-directed current of 1-2 MA through either a static gas fill or a 38 pm diameter polyethylene fiber. The data obtained from an array of filtered photodiodes is used to estimate the plasma temperature. The filter material and thickness for each diode is chosen such that the lowest absorption edge for each is at a successively higher energy, covering the range from a few eV to 5 keV. The analysis assumes a fully stripped optically thin plasma which radiates as either a blackbody, a bremsstrahlung emitter, or a group of emission lines (gaussian-like). 288

No abstract

The development of plasma-based propulsion thrusters for spacecraft has seen a rapid growth over the past few decades, with the number of spacecraft including small satellites and Cubesats increasing exponentially. Although traditional chemical propulsion is still widely employed in space flights, it cannot meet the more challenging requirements for deep space travel due to low specific impulse. Electric propulsion thrusters have already helped humans travel further from Earth and have the potential to be developed for interstellar flights due to their advantages such as high velocity increments, long operational lifetimes, high impulse-to-weight ratios and high impulse-to-power ratios. The electrodynamic thrusters have significant potential for applications in the remote regions of space, and several types of electrodynamic plasma thrusters are currently under investigation. In this paper we present conceptual experiments to study a miniaturized Rotamak-type device initially proposed for the controlled thermonuclear fusion, with a view to assess its potential for the application as a small space thruster. An outline of the physical characteristics of the experiments that has been carried out, and measurements were done to try to elucidate the important mechanisms at work in the Rotamak, which will help design next-generation thruster capabilities. A discussion is also presented about the Rotamak systems and the opportunities they present for space applications.

No abstract