Studying a kind of portable ultra-bright microfocus x-raysource

This paper studies the properties of a kind of portable ultra-bright microfocus x-ray source with the Monte-Carlo method in detail. The new x-ray source consists of an electron-emission system, an electrostatic focusing system and a metal target. A crystal Lanthanum Hexaboride cathode, a Wehnelt grid and an extracted electrode compose the triode electrode electron-gun system. Two equal radius cylinder electrodes form the focusing system. The key factors determining the focus properties of the electron beam such as the ratio $D_{\rm w}/H$, grid bias $V_{\rm g}$, and the properties of the extracted electrode are numerically studied. The calculated results reveal that when $D_{\rm w}$/$H$, $V_{\rm g}$, the length of the extracted electrode, and the distance between the grid and the extracted electrode equals 5, --0.6~kV, 10~mm, and 8~mm respectively, the electron beam focal spot can be concentrated down to 9~$\mu $m in radius and a reasonable focal length about 72.5~mm can be achieved, at the same time, the cathode emission currents can be as high as 30~mA.