An accelerated life test method for highly reliable on-board TWT's with a coated impregnated cathode

An accelerated life-test method is established for on-board TWT's with an M-type cathode. This method is shown to be effective to predict the TWTs reliability. The M-type cathode has two life-limiting factors: impregnant reduction and surface coating degradation. The theoretical calculations of these factors under the accelerating conditions are confirmed by the life-test results. The highest acceleration is obtained at the cathode temperature of 1100 /spl deg/C/sub B/ with the cathode current density of 0.6 A/cm/sup 2/. In this case the acceleration factor is derived to be 31. The lifetime distribution of TWT's at the optimum cathode temperature is predicted using the derived acceleration factors. The Weibull distribution of BTTs (beam test tubes) fits a line with a slope of 3.2. From this result, TWT's with an M-type cathodes at optimum cathode temperature show wear-out failure and their cumulative failure rate is under 0.5% during a useful life of 100 000 h.<
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