Fluctuations 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 ∼ 250 G toroidal field and a ∼ 6 G vertical field. Typical plasma density is ne ∼ 10 cm−3 and typical electron temperature is Te ∼ 10−20 eV. Observed fluctuations are characterized and compared with theories of drift waves and interchange modes.