The Emission Mechanism Of Carbon-Fiber Cathode And The Effect To The Output Pulse Width

Carbon-fiber cathode has lots of advantages over others in higher uniformity of electron emission, slower expansion velocity of cathode plasma, longer lifetime, lower out-gassing rate, lower threshold voltage of emission etc. By using the properly application of the carbon-fiber cathode, the output pulse width and efficiency of the the microwave source have both been evidently improved. Carbon-fiber belongs to semiconductor, and the carbon content is over 90%, therefore it is steady. It has strong sorption ability because it contains the configuration of the loosened layers and microcosmic voids. Its sublimation temperature is as high as 3650℃, which can increase the cathode lifetime.The carbon-fiber cathode we manufactured has our own feature in manufacture process and practicality. And some better results compared to the stainless steel have been obtained in the experiment of Vircator visual cathode oscillator of carbon-fiber cathode in TomaChan device. All the properties of carbon-fiber cathode have been attributed to the characteristic of carbon-fiber, the manufacture process, especially to the mechanism of its unique electron emission and working process. So it is very valuable to study the electron emission mechanism of carbon-fiber cathode.There may be multiple emission mechanisms in an optimized cathode, which made the cathode emission uniformly. The emission mechanism of carbon-fiber cathode has been studied in this thesis, the results show that the carbon-fiber cathode coated with CsI has the optimized and competitive emission mechannism. It is not only the mechanism of explosive electron emission in carbon-fiber tips, but also the flashover and tracking mechanism which expanded the area of electron emission and reduced the local current density and ohm heat on the surface of the carbon-fiber that functioned in the course of electron emission. Meanwhile, the carbon-fiber cathode coated with CsI, which improved the emission uniformity and slowed the plasma expansion velocities by producing heavy particles, is validated to have CsI photoelectric emission .The uniformity of the electron beam provided by the carbon fiber cathode has been proved by the bombarded target experiments and experimental investigations in the cathode light spots. The velocity of the plasma expansion has been measured by the electrical methods--the method of diode impedance fit and the temporal dependence of the diode gap and the method of the diode perveance, the results have showed the velocity of the plasma expansion using the carbon fiber cathode was about 1.0cm/μs, which was less than half of the velocity of the plasma expansion of the stainless steel. It is the compound mechanisms of the electron emission and the unique characteristic of carbon-fiber cathode that made the electron emission more uniformly...