JOINT MAE-CER SEMINAR
Electromagnetic turbulence and transport in increased-beta LAPD plasmas
The LArge Plasma Device (LAPD) at UCLA is a 17~m long, 60~cm diameter magnetized plasma column with typical plasma parameters ne ~ 1012 cm -3 , Te ~ 5 eV, Ti < 1 eV, and B ~ 1kG when plasmas are produced using the primary BaO cathode source. A new secondary plasma source has been installed, a 20cm LaB6 cathode that allows the production of much hotter (Te ~ 12 eV, Ti ~ 6 eV) and denser (ne ~ 5 x 1013 cm-3) plasmas. This hundredfold increase in plasma pressure combined with lowered magnetic field allows LAPD to be utilized to study the physics of magnetized, high β plasmas. We will report the variation of turbulence and transport driven by edge pressure gradients in LAPD with increasing plasma β (up to ~15%). Density fluctuations are observed to decrease slightly with increasing β while magnetic fluctuations increase. Surprisingly, parallel magnetic fluctuations dominate at the highestβ values with δB||/δB⊥ ~ 2 and δB/B ~ 1%. The measurements are consistent with the linear excitation of a recently theoretically predicted instability, the Gradient driven Drift Coupling mode or GDC. This instability is flutelike (k|| = 0) and grows in finite β plasmas due to density and temperature gradients through the production of parallel magnetic field fluctuations and resulting łB|| drifts. Linear and nonlinear calculations using LAPD parameters indicate the instability should grow in these experiments. Comparisons between experimental measurements and theoretical predictions for the GDC will be shown. Direct experimental measurements of electrostatic flux have been performed and show a strong reduction with increasing β. At the same time, no evidence is found (e.g. in density profile shape) of enhanced confinement, indicating that other transport mechanisms, perhaps electromagnetic, are active. These observations and future plans for direct evaluation of magnetic transport will be discussed. In addition, a brief overview of the Basic Plasma Science Facility and current user research will be provided.
Troy Carter is a Professor of Physics in the Department of Physics and Astronomy at the University of California, Los Angeles. He earned a B.S. in physics and nuclear engineering from North Carolina State University in 1995, and a Ph.D. in Astrophysical Sciences (plasma physics) from Princeton University in 2001. His research interests involve experiments in laboratory plasmas and seeks to understand phenomena relevant to magnetic confinement fusion energy and to space and astrophysical plasmas. In particular his work focuses on nonlinear wave interactions, turbulence, and turbulence-induced transport in magnetized plasmas. He is a member of the Center for Multiscale Plasma Dynamics (CMPD), which is a DOE Fusion Science Center led by UCLA and University of Maryland. View his personal website here.