D. Parks

Decade quad monolithic POS modeling

The decade quad (DQ) was initially fielded as a large area bremsstrahlung (LAB) source. This utilized the four decade modules (DM) triggered simultaneously but each driving a separate hard X-ray bremsstrahlung radiation source (BRS). Recently, water convolute hardware was installed that combines the power from the four Decade modules to drive a soft X-ray plasma radiation source (PRS). The water convolute configuration also enables the use of a monolithic plasma opening switch (MPOS) for driving a common BRS or PRS load. The work reported here was performed in support of the use of an ACE 4 type POS on DQ. The modeling included equivalent circuit and DELTA-CREMIT magneto-hydrodynamic (MHD) simulations. The circuit analysis extracted equivalent circuit parameters from ACE 4 data and applied them to the planned DQ MPOS-BRS configuration. The MHD analyses evaluated strategies to optimize the DQ MPOS.

Implementation of the ACE 4 plasma opening switch on the Decade Quad

Summary form only given, as follows. This paper reports on the initial implementation of a monolithic plasma opening switch (MPOS) on the Decade Quad (DQ). The recent installation of a water convolute combining the power flow from the four DQ modules to drive a plasma radiation source (PRS) enables a MPOS configuration for driving a bremsstrahlung radiation source (BRS). The conduction phase requirement for the DQ MPOS is roughly 8 MA for 300 ns. Numerical simulations and experimental results on ACE 4 suggest that the dominate parameter controlling the POS operation is the conduction phase I*T product. The ACE 4 POS design, characterized at an I*T product of 2.4 MA-/spl mu/s, was installed and tested on the water-convoluted DQ configuration. The work reported here will contrast the observed performance of the unoptimized ACE 4 POS on DQ with that expected based on scaling from ACE 4. Optimization of the DQ monolithic POS is planned for a later phase of the present work.

Magnetic diffusion effects on electrically driven flux compression schemes

Summary form only given, as follows. Power amplification in vacuum utilizing electrically driven magnetic flux compression has been introduced and researched recently for efficient drive of z-pinches and other loads operating at sub-100 ns times and very high magnetic fields (tens of megamperes at radii below 1 cm). We present the results of 1 D MHD calculations, in the 1 microsec regime, corresponding to the ECF2 pulsed power generator being built at CEG, France, and the 100 ns regime, corresponding to the Z machine at SNL. These calculations purport to assess the role of magnetic field diffusion through the plasma armature. To evaluate numerical accuracy the equations are solved both in Lagrangian and Eulerian reference frames. We utilize analytic approximations for the equation of state, resistivity and opacity of the Al armature, and compare with results obtained employing SESAME tables. The magnetic field diffusion equation is solved using a mixed finite element algorithm employing an edge-based electric field vector representation.

2-D MHD calculations for argon double shell experiments on Double Eagle and Saturn

Summary form only given. 2-D MHD calculations for argon double puff Z-pinch implosions in the 200 ns regime are compared with experimental results. The experiments were conducted on DOUBLE EAGLE at about 4 MA peak currents at Maxwell Physics International, and on Saturn at SNL at about 6 MA peak currents. To do the calculations the 2-D MHD code DELTA is employed. DELTA operates on a triangular unstructured mesh. Initial conditions for the implosion are either taken directly from the interferometric measured r,z. profile and/or calculated using a module of DELTA, NOZZLE. The NOZZLE code solves the Navier-Stokes equations for the supersonic transient flow in the actual geometry from plenum to exit. The full 2-D MHD DELTA is then used to follow the implosion dynamics of this initial density profile. A Collisional Radiation Equilibrium Model (CREMIT) is employed to calculate radiation self-consistently. The results of these calculations are compared with the experimentally measured K-shell radiation yield and power, as well as with filtered X-ray pinhole images designed to observe zippering and final pinch radius. Calculations studying the sensitivity of the final implosion to variations in the initial gas density conditions are presented.

MHD modeling of the plasma source and conduction phase of the ACE4 plasma opening switch

Summary form only given. We have used the two-dimensional MHD code, Mach2, to develop a deeper understanding of the flashboard plasma sources and the conduction phase of plasma opening switch experiments performed on the ACE4 facility.

The effect of neutrals on the performance of plasma opening switches

Summary form only given. We address the question of the limitations on voltage and current transfer to loads in magnetic storage systems utilizing microsecond conduction time plasma opening switches. We propose that the limitation of performance results from neutral atoms that are not entrained into the ionized material that is driven by the magnetic field of the rising generator current. Evidence in support of this proposition is gathered from experiments performed on the Ace-4 and Hawk generators. We set forth a theory to describe the effect of neutrals on the electrical performance of plasma opening switches. The neutral gas in assumed to be present in the region between the moving plasma mass and the generator, primarily in the region in which the plasma is injected initially. The essential elements of the theory are a weak photoionization source to seed the gas with a low concentration of electrons, and joule heating accompanied by further ionization and breakdown of the gas as voltage develops across the switch.

Operation and empirical modeling of the plasma opening switch

Summary form only given, as follows. Plasma opening switch (POS) experiments have been conducted on the DNA BLACKJACK 5 and ACE accelerators at Maxwell Laboratories. On BLACKJACK 5 one of the switch geometries increased the value of dI/dt delivered to a ring e-beam load by a factor of 5 to a value of 2×1014 A/s. Bremsstrahlung pulse shapes indicate a power pulse compression of greater than a factor of 2. Work on the ACE accelerator has demonstrated the capability of the POS to perform as a final opening switch in an inductive energy storage system. BLACKJACK 5 and ACE POS experiments have been designed to allow comparison of switch operation over three distinct switch conduction time regimes: 50 to 100 ns for BLACKJACK 5, 200 to 400 ns for a fuse-driven configuration on ACE, and 500 to 2000 ns for a capacitor-bank-driven configuration on ACE. The data from these different experiments were compared with the predictions of a plasma erosion and an ion piston switch model