Reconnection and Ion Heating in a Laboratory Plasma


S. Prager, S. Choi, D. Craig, D. Ennis, G. Fiksel, S. 
 Gangadhara, V. Mirnov, V. Svidzinski and the MST Team

In the reversed field pinch laboratory plasma, two types of 
reconnection occur: spontaneous reconnection arising from tearing 
instabilities and driven reconnection. Driven reconnection arises from 
the nonlinear coupling of two tearing instabilities, producing a 
perturbation at a location that otherwise does not experience 
reconnection.  In the MST experiment we are measuring, with probes in 
the plasma edge, the linear and nonlinear terms in the MHD equations 
that are expected from theory to be responsible for the reconnection.  
Reconnection often occurs suddenly in time.  During reconnection the 
ion temperature increases strongly: from about 200 eV to 600 eV in 100 
microseconds in the plasma core.  The temperature increases everywhere 
in the plasma.  Both minority ions (measured by active Doppler 
spectroscopy) and majority ions (measured by Rutherford scattering of 
an injected beam of neutral atoms) are heated.  The cause of the ion 
heating remains unknown.  Under theoretical study is viscous damping of 
flow velocity fluctuations associated with tearing instabilities.  The 
energy source for the heating is likely the decrease in total magnetic 
energy that accompanies reconnection.  The viscous damping is possibly 
the mechanism by which the energy is transferred.