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AbsfracePerformance of an electromagnetic induction launcher is considered for three types of armatures. These are: solid, l-element wound and 16-element wound aluminum armatures. The one element wound armature has uniform current density throughout and thus can withstand field reversal (working against embedded armature flux) and still maintain low temperature. Slingshot simulations were performed for several configurations. Best performance was obtained for a single element wound armature with two field reversals. For a 60 kg projectile, 10.5 cm coil inner radius and 5.5 cm coil build, the velocity after 50 meters of launcher length (670 stages) exceeded 3.5 Wsec with an overall efficiency of about 45%. For the same parameters the solid and 16-element wound armatures reach a velocity of about 3.3 kmlsec after 800 stages (60 meters of launcher length) but without field reversal. A velocity of 3.5 km/ sec is possible after 60 meters of launcher length with the 16-element wound armature with one field reversal, but the temperature is close to the melting temperature of aluminum. In all simulations with a solid armature, melting of some of the surface material occurs. However, it is shown that most of the melting occurs after contribution has been made to the forward going pressure, that is, melting does not affect the electrical performance of the launcher. The effect of coil firing time jitter on launcher performance is also considered and is found to be very small for realistic perturbations. For f 2 p-secs random jitter, the reduction in the final velocity for a 60 meter launcher with a solid armature is less than 0.1% and the increase in temperature is only 2%. This holds for all types of armatures. I. WIXODUC~ONThe electromagnetic induction coil launcher accelerates a conducting armature by inducing armature current opposite to coil c m n t s . The armature current is induced in an attempt to exclude magnetic flux from the armature. The interaction of the net radial magnetic field with the azimuthal armature current results in an axial force that accelerates the armature [l-21. If the launcher geometry, the coil firing times and current rise lengths are adjusted properly, a near constant acceleration can be maintained. A snapshot of coils. armature and magnetic field lines for a typical induction launcher is shown in Fig. 1.Because of the finite resistivity the armature current decays and the magnetic field diffuses into the armature. For a solid armature, if the firing position of the coils is advanced (slipped) to account for field diffusion, near constant axial acceleration can be maintained 133. For a 1-element wound armature, no slipping is needed, but there is still field diffusion due to the finite resistivity. A multiple element wound armature with many elements behaves in a similar manner to This work was supported by the U.S. Department of Energy under Contract NO. DE-AC04-94ALS.5000.a solid armature with the exception that the current is distributed uniformly in the radial direction.After a period ...
We present results which are encouraging for a multibeam approach to relativisticeleetron-beam-induced pellet fusion. A self-pinched relativistic electron beam with nominal parameters of 1.1 MV, 200 kA, and 5-mm radius has been propagated at atmospheric pressure over distances of up to 1 m. Gross beam stability and reasonable energy transport efficiency have been achieved. A simple Alfv6n-type calculation corroborates the propagation result, and a self-consistent particle simulation indicates the possibility of scaling to very high-iVy beams.The relativistic-electron-beam (REB) approach to inertial-confinement fusion 1 * 2 requires powers in excess of 100 TW delivered to a target. 3 However, pinched-flow REB generators and diodes presently operate below the 10-TW level. One conceptual solution to this problem consists of propagation of many, several-terawatt, pinched REB's to a single target. This approach would allow the REB accelerator to be located at a large distance from the pellet explosion and would require relatively little improvement over presently available diode operation. Establishment of the feasibility of this scheme has two elements:(1) demonstration of "long-distance" propagation of a pinched, high-v/y REB, and (2) demonstration of the superposition (overlapping) of many beams at a pellet. In this Letter, we report the propagation of a pinched REB over distances of up to 1 m and the observation of complete beamcurrent neutralization. This latter result implies that the superposition problem may be reducible to one involving considerations only of singleparticle orbits in the preformed magnetic field of a plasma discharge. The propagation technique employed in this experiment would allow the use of a high-density gas blanket surrounding a thermonuclear target which would be useful for reactor shielding. Previous work has been done on beam propagation and combination in plasma channels. 4 However, the present work employs techniques which might be extrapolated to the currentdensity and geometry requirements of pellet fusion.In the experiments, a pinched REB from the Hydra accelerator 5 was extracted through a 25jutm Mylar vacuum window into the atmosphere. The beam was collimated to 10 mm diameter by an aperture and, after propagation of a few millimeters, it entered the end of a preformed plasma channel (see Fig. 1). The diode parameters were typically 1.1 MV, 250 kA, i//y~5, 100 ns full width at half-maximum (FWHM), and 25 kJ. The hollow cathode was 75 mm o.d. by 25 mm i.d. and a 6-mm anode-cathode gap was used. X-ray measurements made with collimatedp-i-n diodes (described below) indicated that the initial 25 ns of the beam pulse was not incident on the apertured region, but that once the pinch was fully developed (after 35 ns), over 90% of the beam was available for propagation. We estimate that 15 kJ at peak electron current of 200 kA were injected into the channel region. (A 20% allowance for ion current flow has been included.)The beam propagation channel was preformed by exploding 6 tungste...
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