Active-Feedback Control of the Magnetic Boundary for Magnetohydrodynamic Stabilization of a Fusion Plasma

Stable operation with control on magnetohydrodynamic modes has been obtained in the modified reversed field experiment employing a set of 192 feedback controlled saddle coils. Improvements of plasma temperature, confinement (twofold), and pulse length (threefold) and, as a consequence of the magnetic fluctuation reduction, strong mitigation of plasma-wall interaction and mode locking are reported.

Figure 1

Linear $m=1$ growth rates normalized to the wall time vs $n$. The equilibrium parallel current is defined as: $\mu =\mu (o)(1-r^{\alpha })$. Empty diamonds correspond to $\mu (o)=3.42$, $\alpha =3$ and black circles to $\mu (o)=3$, $\alpha =5.8$.

Figure 2

RFX-mod standard and VS (squares) discharges: (a) plasma current; (b) toroidal loop voltage; (c) equilibrium axisymmetric shift.

Figure 3

(a) Ion (squares and circles) and electron temperature (lines); (b) electron temperature profiles.

Figure 4

Mode amplitudes (radial magnetic field) vs $n$ (a) at the edge and (b) in the core.

Figure 5

Mode amplitudes ($m=1$ toroidal magnetic field) and electron temperature (SXR double filter) vs time (ms) during “sawtoothlike” oscillations with VS operation.

Figure 6

Frequency vs time as measured by fast magnetic probes at the plasma edge. The $m=0$ mode activity is given by the superimposed white line.