A New Microwave Harmonic Generator

IF my estimate 1 of up to 10 7 amp./cm. 2 for the emission current density of free cathode ‘spots’ on a clean mercury surface is accepted, the mercury arc may be regarded as an indestructible point-contact rectifier with interesting microwave properties. At high rates of growth of current (that is, in excess of 6 × 10 7 amp./sec.) the cathode emission appears to be unable to follow the rising current by its normal method of increasing size 1 and presumably (at microwave frequencies) must either change its emission density or become unstable, or both. In either case a ‘non-linear’ current-voltage relationship is still to be expected.