Session K5: Plasma Physics in the Laboratory

Research Opportunities at the Basic Plasma Science Facility

The Basic Plasma Science Facility (BAPSF) at (UCLA) is a user facility sponsored by the Department of Energy and the National Science Foundation. The purpose is to provide access, free of charge, to qualified national and international scientists to a state-of-the art, large plasma device (LAPD) which, permits the exploration of frontier topics in plasma science under controlled conditions. Some of the research activities are related to space plasma investigations, others explore fundamental issues of interest to fusion research. The operation is centered on the LAPD device developed by the UCLA research team. The machine produces quiescent and reproducible plasma discharges having typical duration of 10 msec (t$_{rep}$ = 1 Hz), accessible throughout the day. The plasma column is 18 meters in length and 60 cm in diameter. The magnetic field can be varied continuously up to 2.5 kG. Fully ionized discharges in He, Ar, and Ne are available. Representative parameters are: The machine has 360 access ports. Qualified users have access to all of the machine diagnostics. Each user group is assigned a staff scientist who runs the machine and provides the necessary technical expertise to implement their research project. To obtain access a prospective user contacts the director and then submits a white paper. Instructions for this can be found at http://plasma.physics.ucla.edu/bapsf. The white paper is reviewed by an external committee. There are currently 11 active projects. This talk will give details of the device and briefly describe some of the experiments in progress.   

First Plasma Results from the Levitated Dipole Experiment

On August 13, 2004, the first plasma physics experiments were conducted using the \urllink{Levitated Dipole Experiment(LDX)}{http://www.psfc.mit.edu/ldx/}. LDX was built at MIT's Plasma Science and Fusion Center as a joint research project of Columbia University and MIT. LDX is a first-of-its-kind experiment incorporating three superconducting magnets and exploring the physics of high-temperature plasma confined by dipole magnetic fields, similar to planetary magnetospheres. It will test recent theories that suggest that stable, high-$\beta$ plasma can be confined without good curvature or magnetic shear, instead using plasma compressibility to provide stability. (Plasma $\beta$ is the ratio of plasma pressure to magnetic pressure.) In initial experiments, 750 kA of current was induced in the dipole coil which was physically supported in the center of the 5 m diameter vacuum chamber. Deuterium plasma discharges, lasting from 4 to 10 seconds, were formed with multi-frequency ECRH microwave heating of up to 6.2 kW. Each plasma contained a large fraction of energetic and relativistic electrons that created a significant pressure that caused outward expansion of the magnetic field. Reconstruction of the magnetic equilibrium from external magnetic diagnostics indicate local peak plasma $\beta \approx 7 \%$. Along with an overview of the LDX device, results from numerous diagnostics operating during this initial supported campaign measuring the basic plasma parameters will be presented. In addition, observations of instabilities leading to rapid plasma loss and the effects of changing plasma compressibility will be explored.   

Creating High Energy Density Jets in Laboratory Environments

A new experimental platform for the investigation of high Mach-number, high energy-density jets has been developed at the University of Rochester's Omega laser facility. Assuming the scalability of the Euler equations, the resulting mm-sized jets should scale to astrophysical objects such as Herbig-Haro objects and jet-driven supernovae that may involve jets with similar internal Mach numbers. This scalability still holds in the presence of radiation as long as the relative importance of radiative cooling is similar. In these experiments, either direct or indirect laser drive is used to launch a strong shock into a 125 micron thick titanium foil target that caps a 700 micron thick titanium washer. After the shock breaks out into the 300 micron diameter cylindrical hole in the washer, a dense, well-collimated jet with an energy density of more than 0.1 MJ per cc is formed. The jet is then imaged as it propagates for 100s of ns down a cylinder of low-density polymer foam. The experiments are diagnosed by point-projection with a micro-dot vanadium backligher. The field of view is several mm and the resolution is 15 microns. The X-ray radiographs show the hydrodynamically unstable jet and the bow shock driving into the surrounding foam. Such complex experimental data provide a challenge to hydrocodes and so are being used to test the hydrodynamic simulations of these types of flows. Initial comparisons between the data and LANL and AWE simulations will be shown. However, the high Reynolds numbers of both the laboratory and astrophysical jets suggest that, given sufficient time and shear, turbulence should develop; this cannot be reliably modeled by present, resolution-limited simulations. Future work concerning the applicability of the Omega experiments to astrophysical objects and the quantitative study of turbulent mixing via subgrid-scale models will be discussed.