A copper septum ma gnet of improved design has been developed to replace the existing FS septum deflector in the slow-extraction channel at the Brookhaven National Laboratory AGS. The new magnet has several novel desi gn features such as a solid rather than laminated core, a ball bearing suspended septum and a radiation resistant quick disconnect s ystem . The applic ation ca l ls for an 0.6 meter long magnet with a 17 mm gap operating at 0.15 Testa . The magnet is pulsed with a so~ duty factor

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... every 2.5 seconds. It must reach 99.5~ of full field in less than 100 msec. The septum is .75 mm thick and operates at 170 amps/mm2. Edge cooling is employed with monel tubes c arr y ing 8 liters per minute of water to handle the 2000 watts average septum power. Because of the relatively high current densit y , the septum expands and contracts .5 mm with each pulse or some 38 million times over three years of continuous operation. This thermally induced stress cycling along with the high radiation and high vacuum environment have been causes of frequent breakdowns in the past. For such a magnet, complexity and construction time can be reduced and reliabiit y correspondingly improved if a solid rather than laminated core can be used. Simple eddy current considerations suggest that a lamination thickness of the order of 1 em is needed. Since the required field, 0.15 T, is small compared to t he sacuraticn induction of the 1006 steel core, a solid core with the cross-section shown in Fig. 1 was used. Here the effective lamination thickness is 1.2 em. Measurements showed that the rise and fall time of such a core are quite good, as shown also in Fig.