Driving large magnetic Reynolds number flow in highly ionized, unmagnetized plasmas

Abstract

Electrically driven, unmagnetized plasma flows have been generated in the Madison plasma dynamo experiment with magnetic Reynolds numbers exceeding the predicted Rm crit ¼ 200 threshold for flow-driven MHD instability excitation. The plasma flow is driven using ten thermally emissive lanthanum hexaboride cathodes which generate a J Â B torque in helium and argon plasmas. Detailed Mach probe measurements of plasma velocity for two flow topologies are presented: edge-localized drive using the multi-cusp boundary field and volumetric drive using an axial Helmholtz field. Radial velocity profiles show that the edge-driven flow is established via ion viscosity but is limited by a volumetric neutral drag force, and measurements of velocity shear compare favorably to the Braginskii transport theory. Volumetric flow drive is shown to produce larger velocity shear and has the correct flow profile for studying the magnetorotational instability.

High ionisation fraction plasmas in a low temperature, multidipole cusp plasma

“…(2016) and Weisberg et al. (2017). As a result, the He line emissivity ratios should also be constant.…”

“…The vessel is equipped with an array of 16 grounded molybdenum anodes fixed in the bulk plasma. The cathodes can be retracted into the cusp in order to apply a torque to the plasma during the discharge (Collins et al 2012;Weisberg et al 2017). Gas is injected into the vessel with a piezo-electric puff valve located at the wall of the chamber.…”

“…2012; Weisberg et al. 2017). Gas is injected into the vessel with a piezo-electric puff valve located at the wall of the chamber.…”

“…2014, 2016; Weisberg et al. 2017), part of the Wisconsin Plasma Physics Laboratory (WiPPL). This facility has recently demonstrated the ability to produce Helium plasmas with strong neutral depletion in the core.…”

“…Generating these instabilities in a laboratory plasma requires sufficient input power and confinement that the resulting plasmas are sufficiently hot to be highly conducting and sufficiently ionised to reduce the role of neutrals in the plasma dynamics (Holland et al 2006;Collins et al 2012). These conditions are realised in a large, spherical ring-cusp device referred to as the Big Red Ball (BRB) (Cooper et al 2014(Cooper et al , 2016Weisberg et al 2017), part of the Wisconsin Plasma Physics Laboratory (WiPPL). This facility has recently demonstrated the ability to produce Helium plasmas with strong neutral depletion in the core.…”