Fluctuations and Turbulence in the Enormous Toroidal Plasma Device at UCLA

Turbulence and transport across magnetic field lines disrupt plasma confinement, which is particularly troublesome in toroidal geometries potentially useful for fusion energy. We investigate fluctuations of a helium plasma in the Enormous Toroidal Plasma Device (ETPD) at UCLA using 4-tip Langmuir probes to measure potential and ion saturation current. ETPD is a simple magnetized torus with major radius 5 m. The toroidal vacuum chamber has a rectangular cross section that is 3 m tall and 2 m wide. Plasma is generated by a lanthanum hexaboride (LaB6) cathode discharge into a helical magnetic field produced by a $\sim 200$ G toroidal field and a $\sim 6$ G vertical field. Typical plasma density is $n_e \sim 10^{13}$ cm$^{-3}$ and typical electron temperature is $T_e \sim 10-20$ eV. Observed fluctuations are characterized and compared with theories of drift waves and interchange modes.