5.3 MAGNETRON The magnetron is a well-developed technology, and is used in microwave ovens. The best demonstrated efficiency for a magnetron is 84%; the best attainable efficiency is probably about 902.(16) The starting point for the magnetron analysis is the design presented on pages 7-3 and 7-27 in Reference 16. This magnetron has an output of 3.2 k’ and a mass of 1.018 kg. The mass elements are listed in Table 5.3-1. TABLE 5.3-1 PRELIMINARY MASS STATEMENT FOR MAGNETRON Several changes were made to the composition of the magnetron to decrease the mass of non-lunar materials. The changes are detailed below. Change #1: Replace pyrolytic graphite in the radiator with iron oxide coated aluminum. Mass increases to 1510 grams for this component, since aluminum has a lower thermal conductivity. Change #2: Replace samarium-cobalt permanent magnets with Alnico 5 permanent magnets. Alnico-5 has a composition of 51% Fe, 24% Co, 14% Ni, 8% Al, 32 Cu. The main field magnets weigh 328 grams instead of 103. The voice coil magnet weighs 80 grams instead of 25. Change #3: Change buck-boost coil composition to aluminum. Mass decreases from 200 grams to 100 grams. This is comprised of 90 grams of aluminum and 10 grams of fiberglass insulation. Change #4: Replace copper parts with copper coated aluminum parts. It was decided to use copper coated aluminum rather than pure aluminum because of the severe thermal environment inside the magnetron. The parts changed are
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