c. Constant power output and depressed collector of varying potential, At maximum voltage, the excess power is then dissipated as heat in the collector. This has the disadvantages of increasing the required weight of the radiator, and using the collector efficiently only at minimum voltage. At peak source voltage the collector is undepressed and efficiency is at its minimum. Figure 4-29 summarizes the alternatives. The unregulated klystron has a clear overall advantage. When the source voltage falls by 5 percent, 7-1/2 percent of the available source power is unused. Tubes designed for 5.6 kW, 16 kW and 43 kW maximum output power, respectively, will have annual minima of 4. 9 kW, 14 kW and 37. 5 kW. A grid-controlled tube maintains constant current so that beam power varies only directly with the source voltage. Under imperfect focusing conditions the beam ripples about an equilibrium radius (8) . The cathode magnetic field and the gun must be designed for a fixed voltage; simple estimates (Reference 8, Appendices G and H) suggest that an 11 percent voltage reduction may increase the ratio of beam-to-tunnel radius from 0. 65 to 0. 74, with ripple to 0. 83, accounting for the fall of solenoid power in an unregulated tube. Current regulation increases the charge density in the beam and may cause instability. The effects of saturated drive are best determined by actual measurement in order to decide whether solenoid power must be regulated. Electronic efficiency depends both on the beam size and on the normalized gap voltages , which can be optimized at only one beam voltage. An estimated efficiency loss of one-half percent for each percent fall of voltage may occur through the fall of output-gap voltage below optimum, but, as several mechanisms are involved, experimental measurements should be made on existing tubes to confirm this. The cavity loadings and tunings must, of course, be fixed as the voltage varies so as to simulate the conditions in the satellite tube. At the input cavity the impedance and resonant frequency are partly determined by the beam-loading impedance, which changes with beam voltage (Appendix E). However, the effects are small. The voltage standing-wave ratio increases from unity by about 0. 0025 for each percent fall of beam voltage, while the resonant frequency changes by only 0. 003 MHz. In either unregulated or constant-current
RkJQdWJsaXNoZXIy MTU5NjU0Mg==