James L. Eddleman

Two‐dimensional radiation‐magnetohydrodynamic simulations of SATURN imploding Z pinches

Z‐pinch implosions driven by the SATURN device [D. D. Bloomquist et al., Proceedings of the 6th Institute of Electrical and Electronics Engineers (IEEE) Pulsed Power Conference, Arlington, VA, edited by P. J. Turchi and B. H. Bernstein (IEEE, New York, 1987), p. 310] at Sandia National Laboratory are modeled with a two‐dimensional radiation magnetohydrodynamic (MHD) code, showing strong growth of the magneto‐Rayleigh–Taylor (MRT) 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 consta...

Laser light forces and self‐focusing in fully ionized plasmas

A derivation is given for the nonrelativistic equation of motion of a fully ionized isothermal plasma in the presence of an intense electromagnetic wave, such as laser light. The result can be expressed in a form similar to an equation used in the microwave confinement of plasmas. Applications of the result are made to the evaluation of self‐focusing effects. The forces exerted on the plasma are found to be significant magnitude at contemporary intensity levels for neodymium laser radiation at λ = 1.06 μm.

Two-dimensional magnetohydrodynamic calculations of the plasma focus

Two‐dimensional magnetohydrodynamic calculations on plasma focus experiments in the Mather geometry are described. The properties of the two‐dimensional numerical solutions are discussed. Detailed results are given for a specific problem which compares favorably with experiment. The numerical solution for the plasma focus previously given by Potter has been rerun with substantial disagreement. Arguments are given to show that the Potter code is incorrect.

Experimental demonstration of compact torus compression and acceleration

Tests of compact torus (CT) compression on the RACE device [Phys. Rev. Lett. 61, 2843 (1988)] have successfully demonstrated stable compression by a factor of 2 in radius, field amplification by factors of 2–3 to 20 kG, and compressed densities exceeding 1016 cm−3. The results are in good agreement with two‐dimensional magnetohydrodynamic simulations of the CT dynamics. The CT is formed between a pair of coaxial conical conductors that serve as both a flux conserver for stable, symmetric formation and as electrodes for the compression and acceleration phases. The CT is compressed by J×B forces (poloidal current, toroidal field) when a 120 kV, 260 kJ capacitor bank is discharged across the electrodes. The CT reaches two‐fold compression to a radius of 8 cm and a length of 20–30 cm near the time of peak current, 10 μsec (many Alfven times) after the accelerator fire time, and is subsequently accelerated in a 150 cm straight coaxial section to velocities in the range 1.5–6.5×107 cm/sec. A new set of accelera...

Magnetohydrodynamic solution for a Z pinch showing the production of a hot spot

Two‐dimensional LASNEX [National Technical Information Service Document No. DE 81026329 (Zimmerman, Report No. UCRL‐74811, 1973)] calculations are made for a Z pinch on Saturn, the low‐impedance, low‐inductance electron accelerator at the Sandia National Laboratories [D. D. Bloomquist et al. Proceedings of the Sixth IEEE Pulsed Power Conference, Arlington, VA, edited by P. J. Turchi and B. H. Bernstein (Institute of Electronics and Electrical Engineers, New York, 1987), p. 310]. The experiment is characterized by a current of 6 MA with a tungsten wire load (4 mg) at 2 mm. Two‐dimensional calculations show the evolution of the Rayleigh–Taylor instability to the bubble and spike phase, causing high‐density islands to form in the pinch opposite the bubbles. The two‐dimensional energy flow causes a ‘‘hot spot’’ to evolve, which is shown to agree in its size and brightness with pinhole camera measurements. This is the first explicit calculation of a hot spot in two dimensions employing the full magnetohydrodyn...

The flow-through Z-pinch for fusion energy production

The authors discuss a high-density fusion reactor which utilizes a flow-through Z pinch magnetic confinement configuration. Assessment of this reactor system is motivated by simplicity and small unit size (few hundred MWe) and immunity to plasma contamination made possible at high density. The type reactor discussed here would employ a liquid Li vortex as the first wall/blanket to capture fusion neutrons with minimum induced radioactivity and to achieve high wall loading and a power density of 200 W/cm{sup 3}.

Nonthermal X-ray emission from a tungsten Z-pinch at 5 MA

Summary form only given. The generation of intense bursts of warm X-rays (10 to 100 keV) with power in the 1-TW regime are of interest for the study of in-depth nuclear radiation effects. Results from high-atomic-number single-wire experiments carried out at 0.8 MA on Gamble II in the 1970s showed 0.25% efficient production of nonthermal, bremsstrahlung-like lines and continuum in the 5- to 100-keV regime. This high efficiency in combination with suggested Z/sup 2/ and I/sup 2/ scaling of the nonthermal radiation motivated the present experiment to measure and model the radiation from the Z pinch formed from compact high-Z wire arrays at high current. In the experiment, tungsten wire arrays of length 20 mm on a mounting radius of 2 mm were imploded over the mass range 1 to 16 mg on the Saturn accelerator operating with a peak discharge current of 5 MA. As in the Gamble-II experiments, bright spots were observed to form at /spl sim/1-mm intervals along the z axis at the time of a first implosion and to be the source of the hard radiation measured. Maximum radiation occurred for masses less than or approximately equal to 4 mg. The experiment was simulated using the LASNEX and TIP numerical codes with a nonthermal model.

STUDIES OF THE GAS-EMBEDDED Z-PINCH

Numerical modeling and experimental investigations of the gas-embedded Z-pinch are reported. One dimensional MHD calculations, including ionization, are extended to include α-particle heating effects for very dense pinches. Heating from 10 to 50 keV is dominantly due to α-heating and in consequence the pinch expands radially. Experimental studies of the gas-embedded Z-pinch were conducted using a relativistic electron beam to provide an initial ionized channel. Both pinch and expanding discharge channel modes are observed depending on pressure. The observed growth of a helical deformation driven by the kink instability is compared with a nonlinear theory. The theory is found to over-estimate the observed helix radius by roughly a factor of 10.