Further study should be considered in the following areas: • Materials — low circuit loss, higher temperature; • Lighter weight magnetic circuits; • Field shaping for higher efficiency; • Space environment — vacuum and thermal; and • Higher temperature performance of Sm-Co magnets. The ambient temperature for the cathode pyrolytic graphite radiator can be higher than that for the anode. The cathode utilizes high-temperature metals such as platinum and molybdenum; therefore, the cathode temperature may be 600-800°C. This would put the pyrolytic graphite radiator at a temperature of about 500°C. The temperature of the anode would be limited by the silver solder to approximately 450°C. The samarium-cobalt magnets would probably limit the temperature at which passive cooling may take place. The upper operating temperature on the Sm-Co magnet material is in the order of 350°C because of the loss of gauss with temperature. RF Spectrum Considerations for the SSPS Amplitron. — The cross-field amplifier (Amplitron) can produce the following microwave energy emissions: (a) the main RF signal which carries the power; (b) harmonic energy which relates to the main signal and is produced by slight distortion in the generating process; (c) energy that occurs during the turn-on and shut-down sequence; (d) random background energy that is intrinsic to the electron interaction mechanism in the tube; and (e) spurious signals, unrelated to the others, which may arise as a result of the specific design. The main signal energy is the primary energy produced by the tube for the system function. This signal is locked onto the RF drive signal, and, under DC or CW conditions, its spectrum would be characterized by a single frequency, phase-locked or controlled by the drive signal. Any movement, variability, or modulation of this signal would be related entirely to the drive signal source quality. Any additional variability or spectrum components produced by the amplifier would arise only from instability of the de power source. With regard to harmonic energy, we expect, that all harmonics produced by the tube would be at least 45 dB below the main signal amplitude. Harmonic energy occurs because of the nonlinearity of the high efficiency saturated interaction process within the tube. Spectrum components are exact multiples of the main signal frequency, and their intensity is influenced in part by the properties of the various elements of microwave plumbing through which the signal passes. The most complete data on harmonics applicable to the crossed-field amplifier (CFA) were taken on a radar system built by ITT-Gilfillan. The system consists of a chain of two Amplitrons and a traveling-wave tube driver (Figure 67). Typical data presented (Figure 68) show the strength of the second and third harmonics under several operating conditions. The harmonics measured at the output with the final and driver-stage Amplitrons off are lower, partly because the passband of the circulator and the Amplitrons pe form a filter function as the signal passes through. When the entire chain is on, least filtering occurs o i the final stage and the harmonics are strongest, although as low as 45 dB down. These data were
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