A Cathode Test Utilizing Noise Measurements

The well-known effect of full shot noise of current saturated parts of a cathode and shot-noise suppression under spacecharge-limited conditions is shown to be very useful for evaluation of cathode quality. A test equipment and a practical test performance are described. Test results and their comparison to other methods of cathode evaluation demonstrate the high sensitivity of the proposed test. Alterations of the cathode quality by the method itself are very small. The test has been used in the laboratory for activation studies and cathode life tests during the past three years.