Plasma Physics Seminar ( Phys 769)

Dr. Darren Garnier, MIT Observation of plasma convection and transport in the Levitated Dipole Experiment The magnetic dipole plasma confinement concept was first proposed by Akira Hasegawa after observing two curious features of planetary magnetospheres. The first is that, while consisting of a topology with bad magnetic curvature, magnetospheres maintain stability due to plasma compressibility. The second, and more curious, property is that magnetospheres exhibit naturally peaked radial density and pressure profiles. These profiles form in response to violent magnetospheric storms that drive particles and energy up these gradients. The Levitated Dipole Experiment (LDX) is investigating the confinement and stability of plasma in a dipole magnetic field configuration. Experiments with the floating coil fully levitated began in 2007. As compared to previous studies in which the internal coil was supported, levitation results in improved particle confinement that allows high-density, high-beta discharges to be maintained at significantly reduced neutral gas fueling. Elimination of parallel losses coupled with reduced neutral gas leads to improved energy confinement, with a majority of plasma stored energy now contained by the bulk plasma. Removing parallel losses allows plasma profiles to be dominated by radial transport. Experimental evidence of interchange convection leading to naturally peaked plasma profiles will be presented. The role of observed low frequency turbulence in this convection will also be discussed. Return to main page