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 °C_B with the cathode current density of 0.6 A/cm². 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