Performance of a compact, cascade FCG system

A system of two FCG´s coupled via ¿flux-trapping¿ is described. The driver FCG, designated SAM, was custom-designed for this application. The output of SAM is a single-turn loop that is tightly coupled to the first winding section of a larger FCG, designated JILL. The single-turn driver loop, coupled to 35 turns of the input winding of JILL, provides a calculated flux gain of 28. For the first experimental test of the SAM/JILL system, the SAM generator was seeded with 1.0 kA (flux 0.29 Wb) and produced a current of 472 kA (flux 0.10 Wb) in the coupling loop at crowbar time of the JILL generator. Based on the calculated mutual inductance of 5.95 ¿H, the JILL generator began operation with a seed flux of 2.81 Wb. With this seed flux, the expected output current for JILL driving a 0.8 ¿H load is 1.8 MA. The measured output current was 884 kA, roughly one half of the expected current. Analysis of the I-dot data from the test shows that this low performance was due to multiple electrical breakdowns in the JILL generator during the interval when the armature-stator contact point was underneath the coupling loop. Subsequent analysis suggests that the electrical breakdowns were the result of flux compression in the coupling loop. Details of the experiment and analysis will be presented. A modification to the SAM/JILL apparatus is proposed to eliminate electrical breakdown.