Electron Beam Propagation in a PPM System

By using a 2.5 and 3-D particle-in-cell code, this paper reports on the electron beam propagation behavior, in a drift tube, under different acceleration potentials ranging from 15 kV to 125 kV in a PPM (periodic-permanent magnet) focusing structure. The investigation is carried out under two approaches. First, an electron beam with a constant electric current of Iomicron = 24 A is injected into a drift tube. Second, an electron beam with a constant perveance of 0.77 mu Perv is injected in the same drift tube. In both cases, the peak of axial component of the magnetic density flux is Bomicron = 173 mT and the PPM period is L = 24 mm. The analysis is centered on evaluating both the magnetic field parameter a, which determines the theoretical conditions for a satisfactory transmission of the beam through the drift tube and the azimuthal momentum of the electrons.