[en] In the screw-pinch device SP IV a plasma is produced inside a non-circular quartz vacuum vessel which is enclosed by a conducting wall. The experiments performed in this device show that force-free currents surrounding the plasma column permit compression towards a highly elongated equilibrium state that does not exhibit fatal instabilities. It was found that an axisymmetric vertical instability is excited during the formation of the plasma. Since this 'hourglass' instability does not fully develop, it does not terminate the confinement. Apart from the very useful diamagnetic loop, also a vertical and a horizontal magnetic probe, a He-Ne interferometer, a set of pick-up coils, and a streak camera are used for diagnosing the plasma behaviour. Analytic equilibrium calculations support the findings that force-free currents largely increase the attainable compression ratios of an elongated, magnetically closed, geometry. (Auth.)

[en] It is shown that the stability of axisymmetric diffuse profile tokamaks is always governed by that of the straight cylindrical screw pinch if one assumes small deviations from circular flux surfaces and small inverse aspect ratio epsilon, regardless of the ordering of β in epsilon. Unstable modes with very small growth rates or those which are very highly localized are excluded from this treatment. Suydam-type modes are included. The sharp boundary and diffuse profile results are compared and commented on

[en] SPICA is a large toroidal screw-pinch device with torus dimensions R=60 cm, r=20 cm. The device has been designed to test earlier predictions that a screw pinch can be stable and in equilibrium up to β values of 20% at q-values of 0.75 and 1.4. These tests can be carried out at higher temperatures and during longer times than was possible in previous machines. The design of SPICA is such that the force-free currents in the outside region can flow for a long time. The decay times of the primary circuits are 1.2 ms for Isub(theta) and 2.1 ms for Isub(z). - The experiments have not yet been done under ideal conditions, the main reason being the low value of the bias field which leads to a β which is too high for stability. Also the base pressure and the correction for the stray fields in the gap region have not been optimized yet. Under these conditions we find 1/e-decay times of the plasma current of a few hundred μs. The equilibrium behaviour of the main plasma column is very good. Stability is still poor, as expected, but improves with increasing bias field. Theoretical analysis shows that the equilibrium position is little affected by loss of current in a wide plasma layer near the wall. - The high amplitude of the longitudinal plasma current (up to 400 kA) shows that the force-free currents in the outside region are induced. Current densities are approximately 280 A/cm² for qsub(wall)=1.4. (author)

[en] A high-beta plasma of β_t∼0.1 and εβ_p>2 is produced and its confinement properties are studied in a screw pinch of moderately elongated cross section. The initially constricted high-beta plasma column is surrounded by a force-free current layer and expands radially. The energy confinement time is much less than that from the empirical scaling of an ohmically heated tokamak, but it gradually improves as β_p decreases. The fast plasma-energy decay and the fast boundary diffusion are considered to be caused by the ballooning mode. (author)

No abstract available

[en] Some results of the assembling, electrical tests and performance of the screw pinch device TPE-2, with a non-circular cross-section are presented. The main object of the experiments is to attain the long confinement of the fat and high beta plasma produced by the fast shock heating in the screw pinch mode with a force free current and the high beta tokamak mode. plasma, we chose the fat torus and non-circular The another object is to develop the high voltage engineering with the aim of a high beta pulsed reactor

[en] The stability of a screw-pinch plasma with radial motion is explored. The linear theory of ideal magnetohydrodynamic (NHD) stability for stationary equilibrium has been generalized to include radial motion. This generalization results in the force operator, F, being non-self-adjoint and the widely used energy principle being no longer useful in this case. Because of this, a set of seven complex, first-order, simultaneous ordinary differential equations needs to be solved to determine the stability. The equations are solved subject to appropriate boundary conditions using the Runge-Kutta-Fehlberg. The eigenvalues for the set of equations are also complex, with the imaginary part of the eigenvalue corresponding to the exponential growth or decay of the instability. While the method derived can be used for any cylindrical equilibrium profiles, the results will be presented for imploding screw-pinch plasmas

[en] The sharp-boundary model of a high-beta tokamak surrounded by force-free currents (FFC) should yield a good description of the magnetohydroynamic stability of a screw-pinch: a tokamak with uniform q-profile. To arrive at the relationship between the equilibrium parameters giving rise to such a q-profile in the FFC region the poloidal field outside the plasma (with a prescribed cross-section) must be determined. An analytical solution has been derived for this field from which the desired relationship can be obtained by numerical means. From the results of a number of cross-sections it is evident that an approximation can be made that leads to this relationship more readily. Based on the latter the stability of a screw-pinch with a number of different cross-sections has been analyzed

[en] The interest in dynamic pinch stabilization by an external H_z field was kindled by the observation that the region outside the pinch column generally contains, not a vacuum, but rather a dilute plasma of good conductivity. As a result, the H_z external to the pinch column proper does not distribute itself as first anticipated, but actually assumes a much more favorable distribution. The theory of the Screw-Dynamic pinch has been checked

[en] The effects of current and pressure profiles, and the effect of the shape of the cross-section on the stability of a screw-pinch plasma with respect to global MHD modes are investigated. (H.W.). 3 refs.; 4 figs