Applied Mathematics and Applied Physics

Plasma Physics Colloquium

Deepak Kumar, California Institute of Technology
"Experimental investigations of magnetohydrodynamic plasma jets"

Spheromak formation consists of a series of dynamic steps whereby highly localized plasma near the electrodes evolves towards a Taylor state equilibrium. The dynamical evolution stage has been modeled as a series of equilibrium states in the past. However, the experiments at the Caltech spheromak facility have revealed that unbalanced J x B forces drive non- equilibrium Alfvenic flows during these preliminary stages.

The Caltech spheromak experiment uses co-planar electrodes to produce a collimated plasma jet flowing away from the electrodes. The jet formation stage precedes the spheromak formation and serves as a mechanism for feeding particles, magnetic helicity, energy and toroidal flux into the system. I will present detailed density and flow velocity measurements of hydrogen and deuterium plasma jets. These measurements show that the jets are extremely dense with  B thermal - 1. Furthermore, the flow velocity of the jets is Alfvenic with respect to the the toroidal magnetic field produced by the axial current within the plasma. I will also describe a magnetohydrodynamics (MHD) model which successfully predicts the effect of plasma current on the jet's density and  flow velocity.

These laboratory jets are often compared to collimated bipolar astrophysical jets associated with active galaxies, young stellar objects, etc. I will conclude the talk by highlighting the similarities and differences between these laboratory jets and some common models for the astrophysical jets.

Host: Michael Mauel