Focusing an electron-beam array with a multi-hole permanent magnet

A simulation study was performed to confirm the technical feasibility of a magnetic lens consisting of a multi-hole permanent magnet to focus a two-dimensional electron beam array. The permanent magnetic lens has a simple structure, and its interference with the deflection electric field is low. In contrast to expectations, the magnetic field intensity is substantially flat in the central region of the multi-hole permanent magnet with a diameter of 6 mm. Only a slight nonuniformity is observed in the radial direction in this region. Although the outer edge of the magnet strongly distorts the intensity distribution in the peripheral region, the area of the influence is only 1 mm wide. The beam convergence rate in the uniform area is approximately 1/10 for a simple model, and 1/40 for an improved model. This technology is applicable to ultra-high-speed imaging with a temporal resolution of the order of picoseconds. The number of recorded signals is expected to be M2 with 1/M convergence with the deflection in two directions. Therefore, a speed-up of 1600 times is achievable.