Sheet Electron-Beam Transport Analysis Through Closed Short PCM for Vacuum Subterahertz Devices

Closed short periodic cusped magnets consisting of miniature permanent magnets of material NdFeB 35H have been designed for transporting the sheet electron beam suitable for vacuum subterahertz devices. The aspect ratio of the magnetic tunnel is selected as 2 to provide proper focusing force in both horizontal and vertical directions. Numerical analysis performed by CST Particle Studio shows that both the peak value of the magnetic field and the nature of variation of the transverse components of the magnetic field along their respective transverse directions depend on the transverse thickness of the magnets. The peak value of the magnetic field increases by increasing the transverse thickness of the magnets. When the magnetic period, axial thickness, and transverse thickness of the magnets are 3.4, 1.3, and 8 mm, respectively, the simulated peak value of the magnetic field is 0.131 T. Under the tunnel of the aforementioned structure, the sheet electron beam of size 3 mm (width) x 0.15 mm (height), current density 100 A/cm(2), and kinetic energy 20 keV transports up to a 60-mm distance without any significant instability through the drift tube of tunnel size 5 mm (width) x 0.3 mm (height). When the magnetic period, axial thickness, and transverse thickness of the magnets are 2.8, 1, and 8 mm, respectively, the simulated peak value of the magnetic field is 0.181 T. Under the tunnel of this structure, the sheet electron beam of size 2 mm (width) x 0.1 mm (height), current density 120 A/cm(2), and kinetic energy 20 keV transports up to a 60-mm distance without any significant instability through the drift tube of tunnel size 3 mm (width) x 0.2 mm (height).