Detailed measurements of the trapped magnetic fields and currents in plasma structures generated by conical theta-pinches are reported. Studies of these structures interacting with a magnetic barrier, and with each other in a collision at the centre of a magnetic mirror, are reported. The magnetic well formed by the collision has been studied by simultaneous use of several diagnostic techniques. The measurements are in agreement with a force-free, collinear magnetic field configuration (Wells 1972). Arguments relating superposability and collinearity of flow fields to these observations are given.

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out, however, that no correction for ExB drifts has been made, because the plasma potential is not known for these discharges.Attempts were made to compare the experimental results with the predictions for the m = 1 internal kink mode. 4 * 5 Pictures like Fig. 3 suggest an experimental growth rate y « 3x 10 3 sec" 1 . The theoretical linear growth rate depends on the exact radial dependence of q. For parabolic temperature profiles (n e = const, j~T e 3/2 ) we derive from Eq. (13) of Ref. 5where v A is the Alfven velocity, R the major radius, p z0 the toroidal j9 in the center of the column, and r s the radius of the singular surface (q = 1). This formula gives a value of y^e oT equal to 2x 10 4 sec" 1 , which is larger than the experimental growth rate by a factor of about 7.We can also compare the radial profile of the oscillation amplitude [Fig. 2(d)] with the prediction for the internal kink mode, i.e., displacement | = const for rr s . The x-ray signal is the integral over the x-ray sources along a line of sight. To obtain the x-ray radial profile a set of scans at different lines of sight have been inverted. Without going into the details, we state that the shape of the profile is in reasonable agreement with the theoretical prediction. The experimental displacement |, however, seems to be larger than the predicted non-Over the past fourteen years, an extensive series of experiments concerned with naturally occurring stable plasma states has been performed. 1 " 6 We have intensively studied, both theoretically and experimentally, a whole new field of plasma physics concerned with the problem of production, heating, and application of these states.linear displacement of Ref* 5 by approximately an order of magnitude. Experimentally we obtain £/r 5 « 0.2. It should be pointed out that resistivity is not included in the present theory and that it is likely that a tearing-mode version of this instability exists (Ref. 5, p. 1899) which might lead to smaller growth rates and larger displacements.The technical assistance of W. Mycock and the ST tokamak operating crew is gratefully acknowledged.A theory has been developed which predicts a spectrum of naturally occurring stable states. 5,7,B The particular stable state studied at the University of Miami consists of a closed plasma structure produced by conical theta-pinch guns. This state is the force-free collinear vortex ring or spheroid first described by Wells. 1 ' 2 Plasma vortex structures generated by conical theta-pinch guns have been successfully compressed and amplified by secondary adiabatic compression. A pair of vortex rings meet at the center of a primary magnetic mirror. A secondary mirror starts to compress them as soon as the collision has occurred. Peak ion temperatures of 170 eV have been obtained at an nr of 10 12 sec/cm 3 by utilizing a capacitor bank that stores 250 kJ.1203