"Confinement in the Madison Plasma Dynamo Experiment" by Chris Cooper (University of Wisconsin-Madison)

Tuesday, June 25, 2013 - 1:00pm to 2:00pm
Plasma Seminars

Plasma Seminar

Tuesday, June 25, 2013
BAPSF Auditorium (15-17 Rehab Building)

Guest Speaker: Chris Cooper (University of Wisconsin-Madison)

Talk Title: "Confinement in the Madison Plasma Dynamo Experiment"


First measurements of plasma temperature, density, and flow have been made on the Madison Plasma Dynamo Experiment (MPDX) that allow the particle and energy confinement as well as the plasma conductivity (eta) and viscosity (nu) to be estimated.  The MPDX is designed to create large flowing plasmas with high magnetic Reynolds number Rm=vL/eta>>1000, and an adjustable fluid Reynolds number 10<Re=vL/nu<1000, in the regime where the kinetic energy of the flow exceeds the magnetic energy (MA=v/vA>>1).  Simulations show that these parameter ranges should generate large scale “slow” dynamos and small scale “fast” dynamos to be studied.  The 3 m diameter vacuum vessel is lined with rings of alternately oriented 3 kG Samarium Cobalt magnets to create a multicusp magnetic confinement scheme.  Lanthanum hexaboride (LaB6) stirring rods and molybdenum anodes inserted into the vessel are biased < 450 V at 40 A each, ionizing a fill gas and heating it.  Even at these initial low powers (<55 kW), the 2.6 m diameter unmagnetized sphere of helium plasma has Te < 10 eV, ne < 5x10^11 /cm^3 at with edge flow speeds vp < 3 km/s for Re = 60 and Rm = 225.  A model for particle and energy balance in MPDX is developed to predict Te, Ti, and ne (therefore Re, Rm, and MA) over a scaling of input power and neutral density.  This model is compared to data from the initial MPDX plasmas and a PIC code simulating cusp losses to predict the laboratory settings for dynamo onset.