为了测量更广能量范围的等离子体辐射的硬X射线轫致辐射光谱,以获得激光等离子体超热电子能谱的特性,基于柱面弯曲晶体的分光原理,提出了透射晶体谱仪。为满足实验中光源到谱仪距离不同的需要,设计了Johann型可调节透射晶体谱仪。谱仪中的会聚狭缝设计成可移动的,位置随着光源到谱仪距离的变化而改变。通过理论计算获得了会聚狭缝位置变量与光源距离变化之间的关系,得出小角度(小于0.2 rad)入射时能够保证入射光线经过晶体后近似会聚于一点,并对谱仪具体设计时遇到的一些问题,给出了初步的理论分析和看法。该谱仪中会聚狭缝的可调节解除了谱仪到光源距离固定的限制；前端晶体的可更换,也增加了谱仪测量的灵活性。

Based upon the dispersion principle of cylindrically bent crystal, a transmissioin crystal spectrometer has been presented primarily to characterize the hotelectron energy distribution of laser generated plasma by registering the hard Xray Bremsstrahlung spectrum emitted by hot plasma in a larger energy range. Actually according to the different experimental requirements and variety of the distance between source and crystal, Johann adjustable Xray transmission spectrometer is designed. The focal slit of the spectrometer is planned to be movable, and its place can be changed when the distance between the source and crystal is changed. By the theoretical calculation the relation is acquired about the position of the focal slit and the distance from source to crystal, and the consequence can also be reached as long as Bragg angle is less than 0.2 rad that the incident light will approximately focus on one point. Furthermore, the primary theoretical analysis and conclusion on the questions of designing the device are illustrated.In conclusion, the adjustable focal slit breaks the limit of fixed distance from source to crystal; moreover, the frontal replaceable crystal makes the spectrometer more flexible.