Article

# Optical measurements of plasma dynamics in carbon fiber Z-pinches

Blackett Lab., Imperial Coll. of Sci., Technol. & Med., London

IEEE Transactions on Plasma Science (Impact Factor: 0.87). 09/1998; DOI: 10.1109/27.725138 Source: IEEE Xplore

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**ABSTRACT:**Standard formulae for the electrical resistance and for the radiating properties of a fully ionized gas have been combined with pinch-effect relations to obtain the stationary state radial distribution functions and current-voltage characteristics of a radiation-cooled discharge, using a simplified model in which a stationary, axially symmetrical discharge is generated in a long straight tube. The validity of the diffusion conditions implied in the initial equations, the transport properties of the plasma, and the cyclotron radiation arising from thermal motion in the self-magnetic field, are considered. The calculations are applied to the requirements of a power-producing thermonuclear reactor. The chief results are that in a stationary state a pinched discharge will exist with radiation cooling, that the magnitudes of the voltages, tube diameters and initial gas pressure are within reasonable engineering limits, and that a maximum current of one to two million amperes will be encountered. This maximum is a characteristic current of an ionized gas and, slowly varying numerical factors apart, depends directly only on the fundamental constants e, m, h and c. While it is possible to present grounds for supposing these results to be independent of some of the assumptions, the work gives no guidance on the extent to which they will be invalidated by the instabilities of the current channel.Proceedings of the Physical Society Section B 12/2002; 70(1):11. - [Show abstract] [Hide abstract]

**ABSTRACT:**There is a critical current IPB of about 1 MA (the Pease-Braginskii current) at which Ohmic heating and Bremsstrahlung losses balance in a Z-pinch under pressure equilibrium. An analytic zero dimensional model shows the process of radiative collapse when the prescribed current exceeds the critical current. In particular for a linearly rising current radiative collapse is complete when the current is square root 3 IPB. However in practice the voltage limitation imposed by an external circuit prevents such a total collapse, and by including this in the model a maximum density ( approximately 1030-1032 m-3) can occur followed by an expansion and damped oscillation about an equilibrium at which the current equals the Pease-Braginskii current. In the absence of alpha-particle pressure the maximum density is limited by the resistance of the narrow column, the large voltage across which ( approximately 108 V) is balanced essentially by a large negative LI; it occurs when the current is IPB (( delta -1)/( delta -2))1/2 where delta =7/3+4/3 ln (Rw/a), where a is the pinch radius and Rw is the radius of the current return. The minimum current following maximum density is shown to be greater than IPB/ square root 2. Degeneracy effects can be included in the model.Plasma Physics and Controlled Fusion 12/2000; 31(5):759. · 2.37 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Dense z-pinch plasmas initiated from a single 25--100 [mu]m diam aluminum wire using a 100--350 kA, 100 ns current pulse have been studied with [le]1 ns time resolution. Rapid unstable expansion of a coronal plasma formed around the wire was observed with a subnanosecond pulsed nitrogen laser, while a dense core, which expanded more slowly and stably, was observed with 1--2 ns x-ray backlighting pulses. The core contained most of the initial wire mass, but there appeared to be little or no current flowing in it.Physical Review Letters 01/1994; 71(23):3806-3809. · 7.73 Impact Factor

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