Monte Carlo Study on Focus Properties of Portable Ultrabright Microfocus X-Ray Sources

The construct and electrode potential of emitting systems are very important for the portable ultrahigh brightness microfocus x-ray sources. The ratio of D_w/H (D_w is the diameter of Wehnelt grid aperture and H is the setting height of the cathode) and the grid bias are determinative parameters for the emission current and focus properties of an electron beam. The Monte Carlo method is used to numerically calculate the electron beam trajectories within a microfocus x-ray tube. The calculated results indicate that an optimum source system with the electron beam focal spot diameter smaller than 10μm at the anode, reasonable short focal length of about 76mm and the cathode emission current of more than 30mA can be attained under conditions of D_w/H =5 and grid bias V_g= -0.6kV.