"Creating a Spinning, Unmagnetized Plasma to Study Astrophysical Accretion Disks and Dynamos," by Cami Collins (UC Irvine and DIII-D)

Date: 
Friday, January 31, 2014 - 1:00pm to 2:30pm
Series: 
Plasma Seminars

Plasma Seminar

Friday, January 31
1-2:30pm
PAB 4-330

Guest Speaker: Cami Collins (UC Irvine and DIII-D)

Talk Title: "Creating a Spinning, Unmagnetized Plasma to Study Astrophysical Accretion Disks and Dynamos"

Abstract:

A technique for creating a large, steady-state, fast flowing, sufficiently hot plasma which is weakly magnetized has been demonstrated experimentally. This marks an important first step towards laboratory studies of phenomenon such as the generation of magnetic fields through self-excited dynamos, or the magnetorotational instability (MRI), the mechanism of interest for its role in creating the turbulence necessary for efficient outward transport of angular momentum in accretion disks. In a prototype experiment, called the Plasma Couette Experiment (PCX), plasma is confined in a cylindrical, axisymmetric, multicusp magnetic field, with Te< 10 eV, Ti<1 eV, and n<10^11 cm-3. Azimuthal flows (up to 12 km/s) are driven by JxB torque using biased, heated filaments at a single toroidal position in the magnetized edge. Measurements show that momentum couples viscously from the magnetized edge to the unmagnetized core, and that collisional ion viscosity must overcome the drag due to ion-neutral collisions for the plasma to rotate. Since the plasma is partially ionized, flow speeds seem to be limited by the Alfvén critical ionization velocity. PCX has achieved magnetic Reynolds numbers of Rm~65 and magnetic Prandtl numbers of Pm~0.2-10, which are approaching regimes shown to excite the MRI in local linear analysis and global Hall-MHD numerical simulations. The stirring technique developed on PCX is now being implemented in the larger Madison Plasma Dynamo Experiment, which has been designed to produce flowing plasma in spherical geometry with Rm>1000, ideal for dynamo studies. The current status of both of these UW-Madison experiments will be presented.