Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of intormation, including suggestions for reducing this burden to Department ot Defense, Washington Headquarters Services, Directorate for Information 14. ABSTRACT A deuterium gas-puff load imploded by a multi-MA current driver from a large initial diameter could be a powerful source of fusion neutrons, a plasma neutron source. Unlike the beam-target neutrons produced in Z-pinch plasmas in the 1950s and deuterium-fiber experiments in the 1980s, the neutrons generated in deuterium gas-puffs, with current levels achieved in recent experiments on the SNL Z facility, could contain a substantial fraction of thermonuclear origin. For recent deuterium gas-puff shots ont Z, our analytical estimates and I-D and 2-D simulations predict thermal neutron yields -5 x 1013, in fair agreement with the yields measured on Z. It is demonstrated that the hypothesis of a beam-target origin of the observed fusion neutrons implies a very high Z-pinch-driver-to-fast-ions energy transfer efficiency, 5 to 10%, which would make a multi-MA deuterium Z-pinch the most efficient light-ion accelerator. No matter what mechanism is eventually determined to be responsible for generating fusion neutrons in deuterium gas-puff shots on Z, the neutron yield is shown to scale as y~ I_4 where Im is the peak current of the pinch. Theoretical estimates and numerical modeling of deuterium gas-puff implosions demonstrate that the yields of thermonuclear fusion neutrons that can be produced on ZR and the next generation machines are sufficiently high to make Plasma Neutron Sources (PNS) the most powerful, cost-and energy-efficient laboratory sources of 2.5 to 14 MeV fusion neutron, just like Plasma Radiation Sources (PRS) are the most powerful sources of soft and keV x-rays. In particular, the predicted neutron-producing capability of PNS driven by ZR and ZX accelerators, from -6 x 1016 to _ 1 0 18 matches the projected capability of the NIF laser at thermonuclear energy gains of 1 and 20, respectively.

The Z accelerator [R. B. Spielman, W. A. Stygar, J. F. Seamen et al., Proceedings of the 11th International Pulsed Power Conference, Baltimore, MD, 1997, edited by G. Cooperstein and I. Vitkovitsky (IEEE, Piscataway, NJ, 1997), Vol. 1, p. 709] at Sandia National Laboratories delivers ∼20MA load currents to create high magnetic fields (>1000T) and high pressures (megabar to gigabar). In a z-pinch configuration, the magnetic pressure (the Lorentz force) supersonically implodes a plasma created from a cylindrical wire array, which at stagnation typically generates a plasma with energy densities of about 10MJ∕cm3 and temperatures >1keV at 0.1% of solid density. These plasmas produce x-ray energies approaching 2MJ at powers >200TW for inertial confinement fusion (ICF) and high energy density physics (HEDP) experiments. In an alternative configuration, the large magnetic pressure directly drives isentropic compression experiments to pressures >3Mbar and accelerates flyer plates to >30km∕s for equation of state (EOS) experiments at pressures up to 10Mbar in aluminum. Development of multidimensional radiation-magnetohydrodynamic codes, coupled with more accurate material models (e.g., quantum molecular dynamics calculations with density functional theory), has produced synergy between validating the simulations and guiding the experiments. Z is now routinely used to drive ICF capsule implosions (focusing on implosion symmetry and neutron production) and to perform HEDP experiments (including radiation-driven hydrodynamic jets, EOS, phase transitions, strength of materials, and detailed behavior of z-pinch wire-array initiation and implosion). This research is performed in collaboration with many other groups from around the world. A five year project to enhance the capability and precision of Z, to be completed in 2007, will result in x-ray energies of nearly 3MJ at x-ray powers >300TW.

Magnetically compressed plasmas initiated by a double planar wire array (DPWA) are efficient radiation sources. The two rows in a DPWA implode independently and then merge together at stagnation producing soft x-ray yields and powers of up to 11.5kJ∕cm and more than 0.4TW∕cm, higher than other planar arrays or low wire-number cylindrical arrays on the 1MA Zebra generator. DPWA, where precursors form in two stages, produce a shaped radiation pulse and radiate more energy in the main burst than estimates of implosion kinetic energy. High radiation efficiency, compact size (as small as 3–5mm wide), and pulse shaping show that the DPWA is a potential candidate for ICF and radiation physics research.

Experiments on the Z accelerator with deuterium gas-puff implosions have produced up to 3.7×1013 (±20%) neutrons at 2.34MeV (±0.10MeV). Although the mechanism for generating these neutrons was not definitively identified, this neutron output is 100 times more than previously observed from neutron-producing experiments at Z. Dopant gases in the deuterium (argon and chlorine) were used to study implosion characteristics and stagnated plasma conditions through x-ray yield measurements and spectroscopy. Magnetohydrodynamic (MHD) calculations have suggested that the dopants improved the neutron output through better plasma compression, which has been studied in experiments increasing the dopant fraction. Scaling these experiments, and additional MHD calculations, suggest that ∼5×1014 deuterium-deuterium (DD) neutrons could be generated at the 26-MA refurbished Z facility.

Laboratory are modeled with a two-dimensional radiation magnetohydrodynamic ͑MHD͒ code, showing strong growth of the magneto-Rayleigh-Taylor ͑MRT͒ instability. Modeling of the linear and nonlinear development of MRT modes predicts growth of bubble-spike structures that increase the time span of stagnation and the resulting x-ray pulse width. Radiation is important in the pinch dynamics, keeping the sheath relatively cool during the run-in and releasing most of the stagnation energy. The calculations give x-ray pulse widths and magnitudes in reasonable agreement with experiments, but predict a radiating region that is too dense and radially localized at stagnation. We also consider peaked initial density profiles with constant imploding sheath velocity that should reduce MRT instability and improve performance. Krypton simulations show an output x-ray power Ͼ80 TW for the peaked profile.