Plasma is the most common state of matter in the universe and plays important roles in astrophysics. For example, the Earth’s magnetosphere plasma surrounds the planet, protecting it from high-speed solar wind – the plasma that is ejected from the sun. The properties of these plasmas play a key role in determining the “space weather”. As a complement to space-based observations and satellite measurements, it is important to study plasmas in well-diagnosed laboratory experiments. This is the basis of laboratory astrophysics – creating space plasmas in the lab where they can be studied in great detail.
The dipole magnetic field is the simplest and most common magnetic field configuration in the universe. It is the magnetic field generated by a single, circular current loop. A breakthrough in our capability to create and study dipole plasmas in a laboratory was achieved using the Levitated Dipole Experiment (LDX) located at MIT and the RT-1 at the University of Tokyo. These experiments rely on superconducting magnets – a specialty of the PSFC – to create the dipole field.
In the LDX at MIT, a half-ton, high-current superconducting ring is "levitated" for hours inside a 5-meter diameter vacuum vessel using feedback control. When the magnet is levitated, a large laboratory magnetosphere is created. Plasma threads the loop in the coil, avoiding contact with any material’s surface and allowing it to reach very high plasma pressure. In addition to studying the Dipole field, this allows general studies of complex turbulent dynamics relevant for many plasmas in astrophysics, space physics, and fusion energy research. LDX upgrades include adding auxiliary heating systems to increase the temperature of the plasma, which will allow access to new plasma regimes relevant for the study of magnetospheres around Jupiter and Saturn.
Additional experimental facilities allow access to the low-density plasmas in the solar wind with high-fidelity measurement systems to study the physics of magnetic reconnection, an important phenomenon in plasmas throughout the universe.
Mike Mauel, Dept. of Applied Physics and Applied Math, Columbia University
Anne White, Department of Nuclear Science and Engineering, MIT