A rectangular pulse vertical field circuit for a small tokamak

A rectangular pulse vertical field circuit of transistor type was devised and assembled as a substitute for the usual crowbar type. The circuit is composed of 10 units, each consisting of a capacitor, a transistor, and a comparator. The current rise time, the maximum field, and the current duration of the circuit are 750 A/ms, 18 G, and 2.5 ms, respectively. When the pulse vertical field of the circuit having a short current fall time is applied to a plasma, the horizontal displacement of the plasma is reduced, the plasma is stably confined around the center of a vacuum vessel, and the duration of the plasma current is elongated. The rapidly rising pulse vertical field can clarify the effect of the vacuum vessel as a thin‐casing shell. © 2000 Scripta Technica, Electr Eng Jpn, 133(4): 19–27, 2000