Observation of wall stabilization and active control of low‐n magnetohydrodynamic instabilities in a tokamak

The High Beta Tokamak‐Extended Pulse (HBT‐EP) experiment [J. Fusion Energy 12, 303 (1993)] combines an internal, movable conducting wall with a high‐power, modular saddle coil system to provide passive and active control of long wavelength magnetohydrodynamic (MHD) instabilities. Systematic adjustment of the radial position, b, of the conducting wall elements in relation to the surface of the plasma (minor radius a) resulted in the suppression of β‐limiting disruptions for discharges in which b/a