We have formed dense Z pinches from frozen deuterium fibers ranging in diameter from 80 to 125 ^m and at peak currents of up to 640 kA. The pinch remains stable for the entire 130 nsec of the current rise. This anomalously long stable period corresponds to about 100 magnetohydrodynamic growth times. As soon as the current peaks, i.e., when dl/dt =0, the pinch goes rapidly m =0 unstable and produces nearly 10 n neutrons in a 30-60-nsec-wide pulse. The instability occurs only at dl/dt =0 and is independent of either the current magnitude or the time to peak.PACS numbers: 52.55.EzAs an alternative to the conventional magnetic-confinement approach to fusion, where the plasma density is limited by the strength of an externally applied magnetic field, the linear Z pinch, which is confined solely by its self-field, can in principle confine a much higher-density plasma, and should thus require a correspondingly shorter containment time for net energy production. Because of this, as well as its attractive simplicity, the Z pinch was investigated extensively in the early days of controlled-fusion research. However, all the early experiments were plagued by seemingly intractable magnetohydrodynamic (MHD) instabilities, 1 and the simple Z pinch has long since been abandoned as a candidate for a fusion system. This negative view may need revision in the light of new results from dense Z pinches formed from frozen deuterium fibers, through which rapidly rising currents are driven by means of modern lowimpedance pulse generators. This novel formation technique was first proposed in simultaneous articles by

New laser-driven shock experiments have been used to study the equation-of-state (EOS) properties of liquid deuterium. Reflected shocks are utilized to increase the shock pressure and to enhance the sensitivity to differences in compressibility. The results of these experiments differ substantially from the predictions of the Sesame EOS. EOS models showing large dissociation effects with much greater compressibility (up to a factor of 2) agree with the data. By use of independent techniques, this experiment offers the first confirmation of an earlier observation of enhanced compressibility in liquid deuterium.

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