The effect of a sheared axial How on the m = 1 kink instability in Z pinches is studied numerically by reducing the linearized magnetohydrodynamic equations to a one-dimensional displacement equation.An equilibrium is used that is made marginally stable against the m = 0 sausage mode by tailoring its pressure profile. The principal result reveals that a sheared axial flow stabilizes the kink mode when the shear exceeds a threshold that is dependent on the location of the conducting wall. For the equilibria studied here the maximum threshold shear (v, '/kVq) was about 0.1. PACS numbers: 52.55.Ez, 52.35.Py, 52.65.KjThe m = 1 kink instability is well known, both theoretically and experimentally, to plague Z-pinch plasmas [1,2].(In this paper we refer to a Z pinch as having only axial plasma current. ) Certain notable exceptions occur, mainly in Z pinches with a flow velocity, where the flow state is observed to be stable [3,4]. We have been led to reexamine the effects of flow on stability because of the profound implications a stable, high-density Z pinch would have for magnetic confinement thermonuclear fusion [5].By tailoring the pressure profile of a static Z-pinch equilibrium the m = 0 sausage mode can be stabilized, but the equilibrium remains unstable to the internal kink mode [6,7]. The introduction of an axial magnetic field

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We have demonstrated acceleration of magnetically confined plasma rings in a coaxial accelerator, with acceleration of 0.02-mg ring masses to 1.4x 10^ cm/sec at > 30% efficiency. In some cases lowmass rings have reached a velocity of 2.5 x 10^ cm/sec. When the accelerated rings translate into conical electrodes, we have observed focusing of rings by a factor of -3 in radius, with a factor of >: 4 magnetic field amplification. A reasonably complete accounting of ring mass, momentum, and energy confirms the basic concept of acceleration of stable, well-confined magnetized plasma rings.

Conceptual DT and DD fusion reactors are discussed based on magnetic confinement with the high-plasma-density Z-pinch. The reactor concepts have no “first wall”, the fusion neutrons and plasma energy being absorbed directly into a surrounding lithium vortex blanket. Efficient systems with low re-circulated power are projected, based on a flow-through pinch cycle for which overall Q values can approach 10. The conceptual reactors are characterized by simplicity, small minimum size (100 MW(e)) and by the potential for minimal radioactivity hazards.

Experimental data are presented on the production of field-reversed deuterium plasma by a modified coaxial plasma gun. The coaxial gun is constructed with solenoid coils along the inner and outer electrodes that, together with an external guide field solenoid, form a magnetic cusp at the gun muzzle. The net flux inside the inner electrode is arranged to be opposite the external guide field and is the source offield-reversed flux trapped by the plasma. The electrode length is 145 cm, the diameter of the inner (outer) electrode is 15 cm (32 cm). The gun discharge is driven with a 232-/lF 40-k V capacitor bank. Acceleration of plasma through the magnetic cusp at the gun muzzle results in entrainment offield-reversed flux that is detected by magnetic probes 75 cm from the gun muzzle. Field-reversed plasma has been produced for a variety of experimental conditions. In one typical case, the guide magnetic field was Bo = 4.8 kG and the change in axial magnetic field .::iB, normalized to Bo was .::iB,/Bo = -3.1. Total field-reversed flux (poloidal flux) obtained by integrating .::iB, profiles is in the range 2 X 10 3 kG cm 2 • Measurement of the orthogonal field component indicates a sizable toroidal field peaked off axis at r~ 10 cm with a magnitude of roughly one-half the poloidal field component that is measured on magnetic axis. Reconnection of the poloidal field lines has not been established for the data reported in the paper and will be addressed in future experiments which attempt to trap and confine the field-reversed plasma in a magnetic mirror.