Reversed Field Pinch Historical Review (1)

In a gas the flow of an unidirectional current produces an azimuthal self generated magnetic field that tends to constrict (or pinch) the same current channel. W.H. Bennet first developed the theory of the constricted gas current in 1934. A few years later (1937) L. Tonks resumed the Bennett studies and proposed the term "Pinch Effect" in the sense it is employed at the present time.

The pinch effect is a phenomenon where a magnetic field keeps a plasma away from its container walls, increases the plasma density and heats the plasma by adiabatic compression; in the meantime the plasma is heated by the Joule effect too.

Cousins and Ware, in Great Britain, used the pinch in 1951 for the confinement of a plasma inside a small toroid. They observed that the plasma column was highly unstable and was rapidly destroyed by magnetohydrodynamic (MHD) instabilities, which were fast-growing.

In the USSR and in the USA the studies of the Pinch Effect began in 1952 - 53.
Fig.1 - The ZETA device worked in 1954 - 58 at Harwell. It was a toroidal device, whose metal liner had a minor radius of 0.48 m and a major radius of 1.5 m. ZETA reached an electron temperature of 150 eV, an energy confinement time of 1 ms and 'Beta' greater than 5%.
The devices were linear. The discharges were fast linear pinches between two electrodes and researcher's objectives were to heat a plasma by shock heating and to produce thermonuclear reactions before the instabilities, found by Cousins and Ware, could destroy the column.

For damping the instabilities of the pinch discharges, in the late 1950s research concentrated on the so-called "Stabilized Pinches", usually in toroidal geometry. The discharges were stabilized by an applied toroidal magnetic field Btor, such that Btor= Bpol; the poloidal magnetic field Bpol was produced by the plasma current itself. Following the theoretical predictions of the physicists, Btor could suppress m = 0 and inhibit
m = 1 MHD instabilities, where m is the harmonic order along the poloidal coordinate.

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