The magnetic circuit of a typical crossed-field microwave tube represents a significant part of the mass and weight of the complete device. The magnetic field. B, required for the SSPS Amplitron is illustrated in Figure 61. At the higher frequencies, higher magnetic fields are required. With the development of a new magnet material, samarium-cobalt, new light-weight magnetic circuits can be developed. FIGURE 61. - MAGNETIC FIELD VERSUS FREQUENCY The significant advantage realized with samarium-cobalt is illustrated by the design of an ultra light-weight magnetic circuit for an S-band 8129-type Amplitron utilizing samarium-cobalt (Sm-Co) permanent magnets (as shown in Figure 62). The Sm-Co magnet weighs 10 pounds. The present Alnico V magnetic circuit weights 89 pounds. Using the Sm-Co magnetic circuit, the weight of the S-band 8129-type CFA can be reduced from 114 pounds to 35 pounds. A computer program was utilized to design Sm-Co magnetic circuits for the SSPS Amplitron at the main frequencies of interest, 2.0, 2.45, and 3.3 GHz. The design of the magnetic circuit is important in achieving a light-weight tube. Also, the heat flow path of the cathode will depend upon the size of the magnet, since the cathode cooling radiator will extend beyond the magnet. The computer program was used to calculate the coordinates of all points at which the equipotential lines and flux lines crossed the grid. This information was then fed to a cathode-ray tube plotter which generated a field plot. Radially gaussed samarium-cobalt magnets were investigated for an SSPS Amplitron which is to operate at 2.0 GHz. The equipotential surfaces and flux lines calculated in Figure 63 are for one quadrant of the magnetic circuit. The ordinate of the plot is the tube axis and the abscissa is the tube's mid-plane. This magnetic circuit develops the required 2700 gauss in the interaction region with a 6.08-oz. Sm-Co magnet. A pole piece is utilized for field shaping, and a steel flux return path is used.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==