分析了螺线管场下影响强流相对论电子束聚焦的主要因素,并给出了各影响因素所限制的最小焦斑。计算结果表明,当发射度和能散度的值分别控制在0.397mm*rad和1%以内,单个螺线管磁轴的偏心不大于0.54mrad;初始注入束偏心不大于1mrad时,对于20MeV、3kA的电子束和15MeV、2.5kA的电子束,最终打靶束焦斑均可小于1.5mm。

High-resolution X-ray photographing needs to focus intense relativistic electron beams of several thousand amperes on the bremsstrahlung converter target,thereon forming a small and stable spot.In the ideal case,electron beams cn be focused to a point.However,due to the influence of such factrs as the space charge effect,the beam emittance,the spherical aberration of the lens,and the chromatic aberration,the minimization of the spot size of electron beams is limited.Furthermore,the corkscrew oscillation of the beam centroid not only leads to the increase of the spot size but also to the distortion of the spot shape.The effects of solenoidal field on the spot size of intense relativistic electronic beams are analyzed and the minimal spot sizes limited by various factors are given.The results of the numerical calculation show that if the emittance ≤0.397mm*rad and the energy sweep ≤1%,the ultimate minimal spot size for 20MeV,3kA and 15MeV,3kA intense beams is less than 1.5mm when the tilt of each solenoid ≤1mrad and the injection tilt of beams ≤1mrad．