Abstract
An experimental study of an intense current electron beam diode with a foil-free annular graphite cathode is carried out. The explosive emission images of a graphite cathode at discharging voltages of 240 kV and 780 kV and the attenuation images of cathode carbon ions at different magnetic fields are recorded using a 24-framing camera for the first time. The experimental results show that when the discharging voltage is 240 kV, the light spots of the plasma generated by the explosive emission process are randomly distributed over the annular cathode and the size and brightness of the light spots of the plasma are also randomly distributed; when the discharging voltage is 780 kV, if the background light generated by Čerenkov radiation is not taken into account, the light spots of the plasma generated by the explosion emission is more uniform than that when the discharging voltage is 280 kV and the brightness of the light spots of the plasma is higher, too. Meanwhile, when the axial magnetic field strength is less than 0.77 T, the plasma spots appear in the gap between the cathode and the anode. The smaller the axial magnetic field strength is, the higher the brightness of the plasma spots will be. In addition, when the discharging voltage is 780 kV/200 ns and the axial magnetic field strength is 0.77 T, a rough calculation indicates that the axial diffusion velocity of the cathode carbon ions ranges from 1.77 cm/μs to 2.1 cm/μs.
Highlights
High-power microwave (HPM) systems require an electron beam typically on the order of kiloampere
The experimental results show that when the discharging voltage is 240 kV, the light spots of the plasma generated by the explosive emission process are randomly distributed over the annular cathode and the size and brightness of the light spots of the plasma are randomly distributed; when the discharging voltage is 780 kV, if the background light generated by Cerenkov radiation is not taken into account, the light spots of the plasma generated by the explosion emission is more uniform than that when the discharging voltage is 280 kV and the brightness of the light spots of the plasma is higher, too
When the axial magnetic field strength is less than 0.77 T, the plasma spots appear in the gap between the cathode and the anode
Summary
High-power microwave (HPM) systems require an electron beam typically on the order of kiloampere. For O-type devices, annular graphite explosive emission cathodes (EECs) are usually used as the electron beam source of HPM systems. The characteristics of electron beams are related to the cathode plasma, such as the angular uniformity and the current density uniformity of the cathode plasma, which may affect the beam–wave interaction efficiency and the generation of microwaves and lead to excitation of other modes or even pulse shortening.. The characteristics of electron beams are related to the cathode plasma, such as the angular uniformity and the current density uniformity of the cathode plasma, which may affect the beam–wave interaction efficiency and the generation of microwaves and lead to excitation of other modes or even pulse shortening.2–8 Other characteristics such as the rise time, pulse width, and stability of the electron beam have significant impacts on the output characteristics of microwaves.. By analyzing the plasma luminescence and other luminescence phenomena that exist inside the diode, the generation, diffusion, and attenuation characteristics of the cathode plasma are investigated
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