Studies of a vertically elongated screw pinch and a toroidal Z-pinch

Two types of toroidal pinch, a vertically elongated screw pinch and a toroidal Z-pinch based on spontaneous generation of toroidal field flux, are described. The equilibrium of a non-circular screw pinch plasma is numerically examined. A limiting beta is obtained from optimization of the plasma cross section and is 18 % for a plasma of elongation of 2. The equilibrium of a toroidal Z-pinch plasma, with toroidal field and plasma current profiles vanishing at the boundary, is also examined. Screw pinch experiments have been carried. A quasi-stationary plasma of elongation of about 3 is obtained as far as the plasma current is sustained. Mhd stability of the plasma is investigated in terms of field perturbations and the palsma is less stable for lower filling pressure and is always unstable below a critical filling pressure. Radiative loss is dominant during implosion and later sustainment stage, and conduction loss is dominant during transition stage and early sustainment stage. A toroidal Z-pinch experiment without initial toroidal magnetic field is carried out. In the toroidal Z-pinch, toroidal field flux is spontaneouly generated from the axial plasma current. More field flux is generated for lower filling pressure, and field flux needed to form a force free field configuration is obtained. Magnetic field measurements indicate that a force free field configuration is established. Design studies of the toroidal Z-pinch are carried out including adiabatic compression. Power supplies are significantly reduced by means of adiabatic heating. (author)