A new class of permanent-magnetic materials for high temperature applications in TWTs

The US Air Force and other branches within the US DoD have requirements for permanent magnets capable of operating at temperatures /spl ges/400/spl deg/C. A new class of Sm/sub 2/TM/sub 17/ type permanent magnetic materials has been developed to meet the needs of applications at high temperature. TM represents transition metals, which includes Co, Fe, Cu, Zr, and other elements. These magnets have high to moderate energy product (BH)/sub max/, high intrinsic coercivity /sub i/H/sub c/, with low temperature coefficient of /sub i/H/sub c/, and straightline extrinsic demagnetization curves up to 550/spl deg/C. A straightline extrinsic demagnetization curve provides greater design flexibility and facilitates reduced size and weight of magnetic circuits. A straight-line extrinsic demagnetization curve is important for dynamic and highly loaded applications where high demagnetization forces are encountered. Examples of dynamic applications include generators, motors, jet engine start generators, and electromagnet actuators. Highly loaded applications include the periodic arrangement of magnets in TWTs (traveling wave tubes). The high fields provided with relatively thin magnets allow minimizing of the magnetic period ratio. This ratio is a very important factor in the focusing and stability of a periodic permanent magnet focused, linear electron beam such as exists in a TWT. The combination of increased power and frequencies (higher temperatures) with smaller magnetic periods has contributed to the need to develop this new class of magnet materials that can operate at temperatures up to 550/spl deg/C.