Numerical studies of confinement scaling in the conventional reversed field pinch

Scaling laws for reversed field pinch (RFP) confinement parameters versus plasma current and density are found from computer simulations. The RFP dynamics at high Lundquist numbers approaching 106 is studied using a high resolution, 3-D, resistive MHD numerical code. Optimum plasma conditions are attained by assuming that the transport coefficients are classical, and by ignoring radiation losses and resistive wall effects. Anomalous global transport results from classical parallel heat conduction along stochastic field lines in the plasma core. The pinch parameter is Q = 1.8 and the aspect ratio is R/a = 1.25. Poloidal beta is found to scale as bq µ (I/N)-0.40I-0.40 and energy confinement time as tE µ (I/N)0.34I0.34. On-axis temperature scales as T(0) µ (I/N) 0.56I0.56. Experimental results from T2, RFX and MST agree well with the above numerical results and also with the obtained magnetic fluctuation scaling µ S-0.14, where S is the Lundquist number. Thus stochastic core field lines appear to persist also at higher, reactor relevant currents and temperatures in the conventional RFP, indicating the need to further pursue confinement enhancement techniques.