title: Simultaneous use of camera and probe diagnostics to unambiguously identify and study the dynamics of multiple underlying instabilities during the route to plasma turbulence.
abstract: We use multiple-tip Langmuir probes and fast imaging to unambiguously identify and study the dynamics of underlying instabilities during the controlled route to fully-developed plasma turbulence in a linear magnetized helicon plasma device. Langmuir probes measure radial profiles of electron temperature, plasma density and potential; from which we compute linear growth rates of instabilities, cross-phase between density and potential fluctuations, Reynold's stress, particle flux, vorticity, time-delay estimated velocity, etc. Fast imaging complements the 1D probe measurements by providing temporally and spatially resolved 2D details of plasma structures associated with the instabilities. We find that three radially separated plasma instabilities exist simultaneously. Density gradient driven resistive drift waves propagating in the electron diamagnetic drift direction separate the plasma into an edge region dominated by strong, velocity shear driven Kelvin-Helmholtz instabilities and a central core region which shows coherent Rayleigh-Taylor modes propagating in the ion diamagnetic drift direction. The simultaneous, complementary use of both probes and camera was crucial to identify the instabilities and understand the details of the very rich plasma dynamics.
authors.affiliation: Center for Momentum Transport and Flow Organization, San Diego, California 92093, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Thakur
authors.affiliation: Center for Energy Research, University of California at San Diego, San Diego, California 92093, USA.
authors.forename: C
authors.initials: C
authors.lastname: Brandt
authors.affiliation: Center for Integrated Plasma Studies, Department of Physics, University of Colorado at Boulder, Boulder, Colorado 80309-0390, USA.
authors.forename: A
authors.initials: A
authors.lastname: Light
authors.affiliation: Center for Energy Research, University of California at San Diego, San Diego, California 92093, USA.
authors.forename: L
authors.initials: L
authors.lastname: Cui
authors.affiliation: Center for Energy Research, University of California at San Diego, San Diego, California 92093, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Gosselin
authors.affiliation: Center for Momentum Transport and Flow Organization, San Diego, California 92093, USA.
authors.forename: G R
authors.initials: GR
authors.lastname: Tynan