From the Director - Plasma Science and Fusion Center - MIT

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theory (JOULE) milestone of the US Department of Energy. They also worked extensively on simulating the radial and velocity space structure of non-thermal fast electrons produced in LH current drive experiments on Alcator C-Mod. The simulated profiles of current density have been found to be in quantitative agreement with measurements from a Motional Stark Effect (MSE) diagnostic on the experiment, but the predicted profiles of hard x-ray emission have been found to be narrower than the measured profiles. Physics explanations for the broader measured emission include fast electron diffusion or broader deposition than what is predicted from ray tracing, perhaps due to diffraction effects. These effects are under investigation. PSFC theorists are also participating in the Fusion Simulation Project “Simulation of Wave Interactions with MHD (SWIM),” where they have completed work on coupling a full-wave field solver to a general framework known as the integrated plasma simulator. An analytical description correctly including relativistic effects on the propagation and damping of electron Bernstein waves was formulated for the first time by collaborative work between PSFC theorists and their counterparts in Cadarache, France. They have recently shown that the physics of electron Bernstein wave propagation and damping in spherical tori is similar to that of ordinary electromagnetic wave propagation and damping in ITER plasmas. Thus, the results for electron Bernstein waves (EBW) may be useful in understanding electron cyclotron current drive in ITER. In addition, a model for mode conversion to EBWs in the presence of sharp gradients in the edge region of the plasma was developed for the first time. The MHD interchange mode is thought to set the pressure limit in dipole confinement devices like LDX. A Z-pinch provides a large aspect ratio approximation to a dipole and in this limit finite beta nonlinear modeling indicates the development of a stiff pressure gradient limit accompanied by convective cells that reduce particle, but not necessarily energy, confinement. Recent theoretical work indicates that toroidal flow has only a weak effect on the MHD stability limit. A quasi-linear MHD theory developed showed that the density as well as the pressure may be expected to attain a stiff profile. Finally, PSFC theorists have completed a study of equilibrium beta limits in dipole configurations with toroidal rotation and pressure anisotropy. The existence of an equilibrium limit was proven with the use of numerical and analytical tools. They are continuing their analytic study of magnetic confinement devices in the presence of flow and resistive walls, with the purpose of formulating the problem in a form attractive for code development. Levitated Dipole Experiment (LDX) Physicists at the PSFC are exploring novel magnetic confinement configurations that are fundamentally different from the tokamak. These may lead to alternate reactor concepts, and in addition may provide insights into space and astrophysical plasma phenomenon. One such approach, which uses a levitated current-carrying superconducting ring, is being pursued as a collaboration with Columbia University. Such a current ring generates a dipole type magnetic field geometry, which in Plasma is confined around a floating superconducting coil in LDX. 15
turn confines a torus of hot plasma. Dipole confinement is observed in nature to be robust (e.g., in the magnetosphere around the planet Jupiter). This Levitated Dipole Experiment (LDX) will improve our understanding of dipole confinement in a laboratory setting. LDX is a joint collaborative project with Columbia University at MIT. The principal investigators of this project are Dr. Jay Kesner (MIT) and Professor Michael Mauel (Columbia University). During the initial experimental campaign, which began in 2004, the dipole coil was mechanically supported within the LDX vacuum chamber. These experiments provided a database for supported operation to be compared with future levitated experiments and have provided an opportunity to test the coil operation, the diagnostic set and the control system. During the supported experiments plasma was primarily lost to the supports. LDX cross-section showing plasma heating zone, with ECH microwaves. The experiments with the floating coil fully levitated began in 2007. The loss channel to the supports was eliminated by the levitation Principal investigators, Michael Mauel (above) from Columbia University, and Jay Kesner (below) of the PSFC, guide the LDX project with the help of Columbia University scientist Darren Garnier (right, atop LDX). 16
Page 2 and 3: Contents From the Director ••
Page 4 and 5: Founded in 1976, the Center consoli
Page 7 and 8: Alcator C-Mod Background The Alcato
Page 9 and 10: day-by-day operation can be found o
Page 11 and 12: Alcator C-Mod Basics 1 2 6 3 4 5 1.
Page 13 and 14: Physics Research Background The goa
Page 15: Existing nonlinear gyrokinetic and
Page 19 and 20: Frequency [kHz] a. Phase Contrast I
Page 21 and 22: High-Energy-Density Physics Backgro
Page 23 and 24: laser-plasma interactions and to ob
Page 25 and 26: Waves & Beams Background The Waves
Page 27: that occurs at these bends. Recentl
Page 30 and 31: The Division has contributed in man
Page 32 and 33: In a different area of research, wo
Page 34 and 35: other waste treatment technologies.
Page 37 and 38: Educational Outreach Background The
Page 39: Night” at the MIT Museum, and the

From the Director - Plasma Science and Fusion Center - MIT

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