Investigation on focus and transport characteristics of high transmission rate sheet electron beam

The investigation on focus and transport characteristics of sheet electron beam has been a key technique for the development of high-power microwave and millimeter-wave vacuum electronic devices. Compared with the period permanent magnetic system to transport the sheet electron beam, the uniform magnetic focusing system has many advantages, such as easily adjusting and matching the magnet with the beam, focusing the intensity electron beam, no cut off beam voltage restriction, etc. However, the Diocotron instability of the sheet electron beam in the uniform magnetic field can produce the distortion, deformation, vortex and oscillation to destroy the beam transportation. In this paper, the single-particle model and the cold-fluid model theory and calculation are used to indicate that if the electron optics system parameters of the sheet beam are designed more carefully, the magnitude of uniform magnetic field and the filling factor of the beam in transport tunnel are increased appropriately, the Diocotron instability can be reduced, even vanished completely to transport the sheet beam effectively in a long distance. To verify the above conclusion, the electron gun with the ellipse cathode and the electron optics system are designed and optimized with the three-dimensinal simulation software in detail. After the complex assembly and weld process with the small geometry and high precision, the W-band sheet electron beam tube is manufactured and tested. The sheet beam cross section of 10 mm×0.7 mm is achieved experimentally with the one-dimensional compression and formation of electron gun. Also, with a beam voltage of 20-80 kV, and beam current of 0.64-4.60 A, the experimental transmission rate of sheet beam electron tube manufactured is more than 95% with a drift length of 90 mm, which is higher than the periodic cusp magnetic field transport experiment result of 92% obtained recently.