Study on Dependence of Cathode Current on the Parameters of Helical Cathode Structure of a Coaxial Cylindrical Diode

Abstract

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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$r_{f}$ </tex-math></inline-formula> ), cathode height ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> ), helical pitch ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> ), and anode voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> ), respectively. The results show that the value of current is an increasing function of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$r_{f}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> , and a decreasing function of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> . The simulation results show that when the radius of the cathode filament is greater than or equal to 1.6 mm, the proposed model of this article is more suitable than Y. Koike’s model, and can be used in combination with Y. Koike’s model to estimate quantitatively the SCLC of helical cathode diode. Moreover, it also provides an effective basis for the design and optimization of the helical cathode structure of the microwave tube.