DYNAMIC CONTROL OF THE REVERSED-FIELD PINCH IN NUMERICAL MAGNETOHYDRODYNAMIC SIMULATIONS

First results from a numerical test of dynamic chaos control for the r eversed-field pinch are presented. A control scheme, using a control s ignal in the form of a small time continuous perturbation, is implemen ted into a magnetohydrodynamic simulation code. The control signal, co nstituting the difference between a periodic external signal and the a ctual toroidally applied electric field, multiplied by an adjustable w eight factor, is added to an existing code equation. This equation det ermines the loop voltage for a desired plasma current, and would corre spond to modulations of the applied loop voltage in an experiment. The main effect of the dynamic control on the dynamics of the reversed-fi eld pinch is an increase in the magnetic helicity with an unchanged va lue of the magnetic energy. The helicity increases in a stepwise manne r, and occurs when the loop voltage undergoes a pi phase shift. (C) 19 97 American Institute of Physics.