Evaluation of emission inhomogeneity of gyrotron scandate cathodes

The efficiency of gyrotrons is significantly affected by the emission inhomogeneity of the cathode. The current-voltage characteristics (CVCs) of the cathode, which can be used for the evaluation of emission inhomogeneity, is a promising method for daily diagnosis of gyrotrons. In this paper, the CVC evaluation method considering a semiconductor emission model is proposed to evaluate the emission inhomogeneity of the scandate cathode whose emission characteristics are different from the traditional M-type cathode. The experiments of a scandate-cathode gyrotron that has been run for two months, as well as a scrapped scandate-cathode gyrotron are carried out on a specially designed data acquisition (DAQ) system. The CVCs obtained in the experiments are fitted by using genetic algorithm. The calculated emission inhomogeneity of the cathode successfully reveals the efficiency change of the gyrotron to be diagnosed. The Miram curves are measured to calculate the Longo model and the practical work function distribution (PWFD) curves considering the semiconductor emission model. These results can also verify the rationality of the proposed evaluation method of scandate cathodes.