Long implosion experiments and simulations on the Saturn and Z machines
By increasing the implosion time for Z-pinches from the canonical 100 ns to 200--300 ns, the complexity and power flow risks can be reduced for future higher current generators, assuming that the implosions still produce high energies and powers. The recent success of high wire number arrays and nested configurations have permitted load designs to be considered that could provide the necessary performance at the longer implosion times, i.e., can the authors challenge the conventional wisdom? At Sandia National Laboratory, two experimental campaigns (on Saturn and Z) plus two-dimensional MHD modeling have been performed to investigate the scaling of tungsten wire arrays to 150 to 250 ns implosion times. For the Saturn experiments 25 mm diameter, 240 tungsten wire arrays of increasing mass were used. A comparison with short pulse data shows similar powers, risetimes, final pinch diameters, and instability mode structure. For the same final implosion velocity, measured risetimes were faster than the equivalent short pulse. Fall times were much longer and correlated to late time on-axis dynamics. Simulations using the Mach2 code incorporated a cell-to-cell random density to initiate a Raleigh-Taylor instability, believed to dominate the implosion dynamics. The results of these simulations show that the rise time of the x-ray power correlates to the FWHM of the sheath and has a strong dependence on perturbation level. The mode evolution is similar to the short pulse simulation and experimental results are reproduced. Both simulations and theory suggest that in the long pulse mode, the wires have time to merge and form a more uniform shell prior to acceleration. Modeling of the long pulse Z data is in progress.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (US)
- OSTI ID:
- 20067641
- Country of Publication:
- United States
- Language:
- English
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Radiative Properties of High Wire Number Tungsten Arrays with Implosion Times up to 250 ns
Radiative properties of high wire number tungsten arrays with implosion times up to 250 ns