In the case of the Amplitron detailed thermal design considering such approaches as biasing the thermal flow path in the region of H&L (Figure 6-27) to conduct more heat to the L side of the waveguide should be undertaken. The goal would be to minimize the average temperature gradient along the length of the waveguide which in turn would lead to smaller thermal distortions. This as well as detailed considerations of thermal coatings, blankets and shields should be the subject of in-depth thermal materials and structural technology development. Such a development program may lead to lighter wraveguides than the 0. 0508 cm assumed here and the goal in this regard should be to develop the waveguide with its interfaces to the tube, neighbor’s waveguides and the supporting structure to make it producible and functional with high efficiency, low weight and low system cost. A preliminary layout of a complete subarray for fully packed amplitrons and composite material is given in Figure 6-34. The screwjacks shown (three) provide for attitude and translation adjustments at installation and at periodic intervals as may be required. The primary means of beam control is electronic, as described in the next section. 6.7.2 MATERIALS A search for information on graphite epoxy and graphite polyimide composites showed considerable data had been generated but for very specific conditions and for short time periods relative to the 30-year life needed by MPTS. Some data are shown in Figures 6-35 through 6-37 as reported by R. Poloti of American Cyanamide Co. The composites offer high specific stiffness (modulus of elasticity/density) and have very low thermal expansion coefficients, and the graphite polyimides offer the additional advantage of high temperature stability, as indicated by the figures. There is no question of the ability to manufacture composites with the required dimensional tolerances, and surface finishes (500| in and 50. in have been achieved) and to obtain good adhesion of a silver conductive liner for the waveguide [References 6-1, 6-2]. Graphite epoxy reflectors have been made for spacecraft microwave application, and a number of structural components for the Space Shuttle will be of graphite epoxy. However, composites are relatively costly, and the long term stability in the space environment and
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