The helical cathode is one of the classical structures of the cathode for the microwave tube, and has a wide application in pulse transmission tube. In this article, we propose a quantitative expression of the space charge limited current (SCLC) of the helical cathode diode through improve the theoretical model of Japanese distinguished scholar Y. Koike, and study the dependence of the SCLC of the helical cathode diode with radius of the cathode filament ( $r_{f}$ ), cathode height ( $H$ ), helical pitch ( $d$ ), and anode voltage ( $V$ ), resp...
