First Plasma Results in Levitated Configuration Achieved on 11/8/07

On 11/8/07, scientists at MIT and Columbia University created and confined a high-temperature plasma that completely surrounded a large floating superconducting electromagnet. The half-ton, one million ampere circular magnet was magnetically levitated in a 5 meter diameter plasma
chamber using a state-of-the-art laser detection system and real-time control computer. With all supports removed, the scientists conducted the world's first experiments that investigated plasma heating and fueling processes of high-pressure plasmas confined by a levitated dipole magnet. Initial results were reported last week at the Annual Meeting of the APS Division of Plasma Physics.

DOE's Office of Fusion Energy Sciences launched the Levitated Dipole Experiment (LDX) to investigate whether the physics of plasma confined by planetary magnetospheres could be applied in the laboratory to better understand how high temperature and high pressure plasma can be used for fusion energy. As was pointed out by Akira Hasegawa, plasma confined by planetary dipole magnetic fields, like those surrounding Earth and Jupiter, are naturally peaked and attain plasma pressures comparable to the confining magnetic field pressure. The late John Dawson pointed out that the dipole could exhibit large scale convective flows which would transport particles without transporting energy, also an advantageous property for fusion energy.

The LDX project is a joint research effort between Columbia University and MIT and is the only operating fusion experiment in the U.S. that uses superconducting magnets. The floating dipole magnet was designed by the MIT engineering group using a NbSn superconductor based on the conductor developed for ITER. The coil is inductively charged using another large superconducting magnet that was designed and built in Russia.

Initial experiments with LDX began in 2004 when the floating coil was mechanically supported by thin rods. These experiments achieved a peak pressure that was 20% of the magnetic field pressure and established the operation of cryogenic, diagnostic, and plasma heating and control systems. When the coil is mechanically supported, heat and particles escape to the supports, distorting the radial plasma profiles that are natural to a dipole. When the coil is fully levitated, plasma particles can only escape across the magnetic field. Indeed, measurements with the levitated coil indicate a dramatic change in the plasma density profiles.

These first experiments with a levitated dipole magnet mark the beginning of a series of experiments that aim to measure plasma confinement, transport, and dynamics. A picture of the floating coil levitating ans surrounded by plasma appears below. The LDX project benefits from considerable theoretical and experimental collaborations with scientists located at a number of institutions including MIT, Columbia, Dartmouth, University of Washington, University of Tokyo, IFS, UCLA, PPPL, LLNL and Kurchatov.