High Performance 2:17 Permanent Magnets for Traveling Wave Tubes

The objective of this effort is to develop high performance rare earth permanent magnets with essentially constant magnet properties over a wide temperature range of -50 to 350oC, and which can survive temperatures as high as 500oC, for TWT applications.The combination of a light rare earth (Sm) with heavy rare earths (Gd, Er, and Ho) provides very low temperature coefficients of magnetic properties over a wide temperature range. We propose to complete the development of new (Sm, Er, Gd, Ho) 2TMM17magnets that possess near zero temperature coefficients of magnetization over a broad range of temperature. Our approaches to extend the compensation temperature and to significantly improve the energy product of temperature compensated permanent magnetsare (1) to us Ho and Er to extend the temperature of peak magnetization (Tp) since Ho and Er compounds have a much higher Tp than Gd compounds used in current temperature compensated magnets; (2) to use Ho and Er to improve magnetization at hightemperature; (3) to use Gd to maintain useful high coercivity; and (4) make new sintered temperature compensated permanent magnets with (Sm,Gd,Er,Ho) TM13 as the main phase since this 1:13 phase has high magnetization, high Curie temperature, and high Tp.The payoff for DoD and commercial systems includes temperature compensated high temperature permanent magnets that permit TWTs to operated at higher temperatures and minimize the system cooling requirements and weight. The use of permanent magnets thatcan withstand the bakeout process will permit simplification of the permanent magnet designs, improve beam focusing, and reduce TWT manufacturing costs. Using magnets that provide a near-constant focusing field over broad temperature range will improvesystem performance and tube life, and reduce the final focusing and test labor costs.