A 2-kW multioctave TWT focused with samarium cobalt magnets

The most severe and fundamental performance limitation of the PPM focused TWT has been excessive thermal heating of the RF propagating structure due to some fractional interception of the electron beam. The quality of beam focusing has largely been determined by the characteristics of permanent magnets in the Alnico series. With the introduction of the cobalt-rare earth alloys, a breakthrough in the performance of PPM focused TWTs can be expected. A samarium cobalt focused TWT yielding an output power of 2 kW at 10 percent duty is described. Utilizing a conventional helix slow-wave circuit, the tube covers a multioctave frequency range from 3.5 to 10.6 GHz. Successful operation has been achieved into a load VSWR of 10:1. The magnets are fabricated from powdered cobalt-rare earth alloys by a process sequence that includes powder preparation, magnetic alignment, pressing, sintering, and magnetizing. Energy products in excess of 15×10⁶gauss-oersteds (MGOe) have consistently been achieved for use on this tube.