No abstract

The neutral-ablation model describing ablation of solid hydrogen fuel pellets in thermo-nuclear plasmas has been extended to determine the species composition of the ablatant consistent with the fluid profiles, and has been used to assess pellet shielding mechanisms. Aside from neutral-ablation shielding, none of the shielding mechanisms studied is very effective. Dissociation of hydrogen molecules extends pellet lifetimes by 10-20%. Ionization reduces the temperatures in the ablation by about a factor of three, but extends pellet lifetimes by only a few per cent. Excitation of atoms is not important because the fraction of excited atoms does not exceed a few per cent anywhere in the ablation. Bremsstrahlung and recombination radiation are negligible energy losses. Where emitted abundantly, line radiation is trapped within the optically thick ablatant. Incident electron heat is reduced by less than 10% in overcoming the electric potential of the pellet. Magnetic shielding is treated elsewhere.

We show that a Fabry-Perot interferometer filled with a Kerr medium has a multiple-valued transmission-intensity characteristic. ’’On’’ and ’’off’’ field for bistable operation are estimated, and a simple but accurate approximate theory is described.

Evidence is presented that an axial magnetic field of 100 kG has been compressed to 42 MG by an imploding neon gas-puff Z pinch on a 800 kJ, 7.5 MA, 60 nsec pulsed power generator. Machine electrical diagnostics and x-ray pinhole photographs indicate that this 420-fold field compression was produced by imploding plasma at high magnetic Reynolds number.

C:0ntrolled, ultrahigh axial :naglletic fields have been produced and measured in a gas-puff Z pmch. A O.S-MA. 2-cm-radlus annular gas-puff Z pinch with a 3-min repetition rate was imploded radially onto an axial seed field, causing the field to compress. Axial magnetic field com~ressions up to 180 and peak ~agnetic fields up to 1.6 MG were measured. Faraday rotation of an Argon laser (5154 A) in a quartz fiber on-axis was the principal magnetic field diagnostic. Other diagnostics included a nitrogen laser interferometer, x-ray diodes, and magnetic field probes, The magnetic field compression results are consistent with simple snowplow and self-similar analytic models, which are presented here. Even small axial fields help stabilize the pinches, some of which exhibit several stable radial bounces during a current pulse. The method of compressing axial fields in a gas-puff Z pinch is extrapolable to the order of 100 MG. Scaling laws are presented. Potential applications of ultrahigh axial fields in Z pinches are discussed for x~ray lasers, inertial confinement fusion, gamma-ray generators, and atomic physics studies. 3831