M. M. Widner

WARP-10: a numerical simulation model for the cylindrical reconnection launcher

A fully self-consistent computer simulation code called WARP-10, used for modeling the reconnection launcher, is described. WARP-10 has been compared with various experiments with good agreement for performance and heating. Simulations predict that it is possible to obtain nearly uniform acceleration with high efficiency and low armature heating. There does not appear to be an armature heating limit to velocity provided the armature mass can be sufficiently large. Simulation results that show it is possible to obtain conditions needed for earth-to-orbit (ETO) launch applications (4.15 km/s and a 850 kg launch mass) are presented. This 3100-stage launcher has an efficiency of 47.2% and a final ohmic energy/kinetic energy equal to 0.00146. The mode of launcher operation is similar to a traveling wave induction launcher and is produced by properly timed and tuned discrete stages. Further optimization and much higher velocities appear possible. >

Design and performance of a multi-stage cylindrical reconnection launcher

A multistage launcher was designed and assembled by stacking six coil assemblies end-to-end in a support housing which also aligns the system. Each coil is powered by its own capacitor bank which is triggered when an optical sensor in each stage determines that the projectile is in the firing position. The induction launch technology is successfully demonstrated for multistage systems. A 5 kg projectile can be accelerated from 12 m/s to 335 m/s with an average of 200 kJ stored in each of six stages. Calculations of launcher performance with the digital simulation code, WARP-10, are in good agreement with experiments. >

Exploratory development of the reconnection launcher 1986-90

The exploratory development phase for the reconnection launcher is summarized. This is an induction launcher which features a contactless, solid armature with either flat-plate or cylindrical geometry. The strategy for successful design is discussed, emphasizing the way the issues of ohmic heating and high-voltage requirements for high velocity were resolved. The indispensable role of a fast-running, mesh-matrix code is stressed. The three multistage launcher are described. One of these achieved a muzzle velocity of 1 km/s with a 150 gram flat-plate projectile. The other two have launched cylindrical projectiles at 335 m/s, one with relatively heavy projectiles of 5 kg, the other with relatively light ones of 10 g. The cylindrical projectile scan be spin-stabilized prior to launch for improved flight. The potential of this technology for earth-to-orbit launch of small artificial satellites is outlined. >

Magnetohydrodynamic behavior of thermonuclear fuel in a preconditioned electron beam imploded target

Two‐dimensional magnetohydrodynamic numerical calculations have been performed to study the fuel behavior of a preconditioned relativistic electron beam target in which, experimentally, a portion of the beam current prepulse entered the target to provide fuel preheat and magneto‐thermoinsulation. The magnetohydrodynamic plasma model used includes radiation, thermal conduction, ionization, and resistive diffusion. The magnetohydrodynamic partial differential equations are solved by a computer code employing implicit finite‐difference methods. The fuel is shown to develop counter‐streaming vortices during the implosion phase. The computed neutron yield is in reasonable agreement with the experimental value, suggesting the origin of the neutrons to be thermonuclear. The effect of both magneto‐thermoinsulation and preheat is examined.

Self‐similar power‐driven expansion into vacuum

Planar, power‐driven expansion into a vacuum is found to be self‐similar for a power‐law driving source for the two ideal cases of a thick slab and a thin foil. For the thick slab expansion, an asymptotic solution for the far‐blowoff region is obtained and a numerical solution is present for the rest of the expansion wave. For the thin foil expansion, an analytical solution is obtained. In both cases, the solutions exhibit an unbounded flow field with velocities tending to infinity as a consequence of the continuum assumption, a finite temperature limit for the far‐blowoff material, and density profiles that decrease as a Gaussian in the far expanded material.

Ion sheath motion in plasma‐filled diodes

The time development of the ion space charge sheath in a plasma‐filled planar diode is considered in reference to the behavior of relativistic diodes used for electron and/or ion beam production.

Space applications for contactless coilguns

Two space applications are considered for (electrically) contactless coilguns: launch of small satellites into low-Earth orbit, and launch of lunar liquid oxygen (LLOX) from the Moon to the stationary Lagrangian point L2. For the Earth-to-orbit application, the baseline conceptual design consists of a 960-m-long gun sited in a tunnel at 25 degrees inclination. The gun launches an 1820-kg package that includes a 100-kg satellite and a 650-kg boost rocket for orbital insertion. For the lunar application, the launcher is 200 m long. A 100-kg load of LLOX is packaged in a 10-kg fiber-wrapped tank, accelerated at 2 kgees in an aluminum bucket (armature), and launched at 2.33 km/s at 30-min intervals. The canisters arrive at L2 2.97 days later and are captured by robotic tugs that deliver them to a fuel depot. The total mass of LLOX delivered per year is 867 Mg (metric tons). >

A 10-stage reconnection demonstration launcher

A small-scale, 10-stage cylindrical reconnection launcher has been designed, fabricated, and tested. Ten-gram projectiles are accelerated from rest to 317 m/s through the 0.44-m launcher assembly with a projectile kinetic energy to capacitor stored energy efficiency of 9%. Comparison of test results and computer code predictions are presented. Results of these studies have substantiated launcher scaling at small size and have provided a useful test bed for launcher components and diagnostics. >

Self‐generated magnetic fields in laser plasmas

Numerical simulation and analytic models are used to predict spontaneous magnetic field generation in laser‐produced plasmas. Calculations indicate magnetic fields are important for plasmas of controlled fusion interest.

Fuel preconditioning studies for e‐beam fusion targets

Fuel temperature and density conditions, achieved during the preheat phase of electron‐beam fusion compression experiments, must be accurately known to understand experimental results via numerical simulations. We present studies of discharge preheating in a simplified cylindrical geometry which compare measured quantities with results from the one‐dimensional Lagrangian CHARTB magnetohydrodynamic code. Experimental measurements included schlieren photography and ultraviolet through visible time‐ and space‐resolved spectroscopy in various configurations. It is seen that an 8‐kA 500‐ns heating pulse in 100 Torr of D2+10% O2 produces 10–12 eV temperatures, 1018 cm−3 electron densities, and 7×105 cm/s expansion velocities in the heated discharge channel. These results are consistent with previous claims for neutron‐producing targets, although the target geometry is different.