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Fabrication of a high-speed, self-excited air-core rotor for a field based compulsator has begun and is well under way. The compulsator is to be used as a power supply for firing 9 MJ projectiles from a skid mounted electromagnetic launcher (railgun). The rotor flywheel is made of fiber reinforced epoxy composite and is supported with high strength metal stub shafts which qre shielded from the excitation field by water cooled copper sleeves. The rotor features separate windings for selfexcitation and railgun firing, and a two-pole configuration for pulse length considerations. The rotor is designed to store 210 MJ at 8,600 rpm, with a rating of 3.2 MA peak current and 20 GW peak power into a 9 MJ railgun load.The concentric fiber-reinforced epoxy composite rings that make up the rotor flywheel are filament wound on steel mandrels, cured, and interference fit together. The main and excitation armatures and output conductors leading from the armatures to the shaft conductors are constructed of epoxy impregnated aluminum and copper Litz wire. The rotor is approximately 75% assembled; the metal shafts, the excitation winding with its output conductors completed, and several flywheel rings assembled. The main armature has been preformed on a mandrel and is ready for assembly onto the rotor.A detailed description of the compulsator rotor with design considerations and fabrication techniques are reviewed in this paper, and the current status of the project is discussed. The compulsator stator is being constructed in parallel with the rotor and is discussed in a companion paper presented at the 6th EML conference [l]. ELECTRICAL DESIGN AND PERFORMANCECompulsators are excellent power supplies for railguns because power system functions of energy storage, electrical pulse generation, and pulse preconditioning prior to delivery to the gun are combined in a single device [2,31. This results in a high efficiency system that is able to recover the inductive energy in the gun before the projectile exits the muzzle. Furthermore, burst firing is possible because sufficient energy can be stored in the rotor for multiple shots, allowing prime power to be averaged over several shots and substantially reducing system peak power requirements. Other important advantages of compulsators include a naturally occurring current zero at projectile exit, pulse shaping capability, and high energy and power densities The work was supported by U.S. Army ARDEC, contract no. DAAA21-86-C-0215.relative to other power supply options. For this particular mission a two-pole, self-excited air-core machine was selected based on weight and size constraints. Also, to accommodate relatively low projectile acceleration limits a selectively-passive compensation scheme [4,5] is incorporated in the design which results in a flat current wave form ( fig. 1) from the compulsator into a railgun load. The selectively-passive compensation scheme results in a peak projectile acceleration of 980,000 m/s2 (100 kgees). A crosssection of the rotor is shown in fig. 2 and...

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