为了减少软X射线谱学显微光束线开光后光栅单色器系统光通量漂移的稳定时间,通过有限元分析开光后超环面镜转动机构的瞬态温度,得到2 h后推杆方向总的线性热膨胀量,以及由此引起聚焦光斑在出射狭缝中心处的水平偏移量。结果显示：超环面镜推杆方向热膨胀量为0.97μm,聚焦光斑的水平偏移量达到141μm,而狭缝水平开口仅为50μm,由此推断光通量漂移产生的主要原因是超环面镜吸收的热负载缓慢传导至正弦机构引起Pitch角持续变化。据此设计了超环面镜间接水冷结构,通过对结构优化后的超环面镜箱开光测试,将稳定时间由2 h以上缩短到30 min左右,有效地提升了用户机时的利用效率。
[Background] Rotation mechanism of the toroidal mirror is a main part of the grating monochromator system, which is a key equipment of the soft X-ray spectromicroscopy beamline. Flux stabilization is essential to every experiment. However, a long stabilization time exceeding 2 h causes a serious waste of beamline time. [Purpose] This study aims to reduce the flux stabilization time of grating monochromator system by optimized design of rotation mechanism of the toroidal mirror. [Methods] By analyzing the temperature increase of the toroidal mirror（TM）, the total linear thermal expansion along the bar direction is calculated to be 0.97 μm after 2 h, which causes a 141 μm horizontal deviation of the focusing spot from the exit slit center while the horizontal size of the slit is only 50 μm. Hence the rotation of the sin-bar mechanism is caused by the absorption heat load of TM with continuous change of incidence angle, which is the main reason of the flux drift. This problem could be solved by adding an indirect water cooling system on both sides of the TM. [Results] The flux stabilization time has been reduced to about 30 min from more than 2 h after adding the cooling system. [Conclusion] The experiment result shows that the optimized design for reducing the flux stabilization time is feasible and effective, and the efficiency of the beamline could be improved greatly.
Grating monochromator system
Linear thermal expansion
Indirect water cooling