Curvature of the cathode and electron emission

An experiment was carried out to investigate the relationship between the initial electron emission and the effective field strength under a nonuniform field, as in the case of the cathode-anode needle-plane and hemisphere-plane geometries. The curvature of the cathode was altered to change the characteristics of the surface field strength, and the initial electron current was measured. The curvatures were 1.2 mu m to infinity (plane). The range of the current was 1*10/sup -19/ A to 1*10/sup -14/ A in a high vacuum (2*10/sup -7/ torr). The effect of the effective field strength on the initial electron emission under nonuniform and uniform fields was evaluated. The effective field strength is mostly constant at 10/sup 8/ V/cm, irrespective of the cathode shape. In the case of gas adsorption, the effective field strength of the inception of the electron emission is mostly constant.<>