IMPROVEMENT OF X-RAY BEAM POSITION STABILITY FOR BL4-2

这个子项目是许多利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 在BL 4 -2启动和初始调试后，对X射线束在箱中焦点处的位置进行了数天的测量。测量结果表明，光束的水平位置稳定在140微米以内，光束的垂直位置移动到400微米，具有明显的昼夜特征。因此，与聚焦光束的尺寸（1.2mm水平和0.3mm垂直）相比，水平移动是可忽略的，但是需要解决垂直光束位置的变化。 聚焦镜的间距变化被确定为观察到的光束运动的主要贡献者。 在2008年初夏安装了反射镜冷却水的局部温度控制，以减少反射镜冷却水的温度变化，从而最大限度地减少由于热漂移引起的反射镜位置的可能依赖性。确实观察到减少（至250微米），但未达到所需水平。 当前的方法包括实现反射镜俯仰运动的电子主动反馈。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. After the start-up and initial commissioning of BL4-2, the position of the x-ray beam at the focal point in the hutch was measured for several days. The measurements showed that the horizontal beam position was stable within 140 microns and the vertical position of the beam moved up to 400 microns with clear diurnal characteristics. Thus, compared to the size of the focused beam (1.2 mm horizontal and 0.3 mm vertical) the horizontal movement is negligible, but the changes in the vertical beam position needed to be addressed. Variations in the pitch of the focusing mirror were identified as the major contributor to the observed beam motion. Local temperature control of the mirror cooling water was installed in early summer 2008 to reduce the temperature variation of the mirror cooling water and thus minimize the possible dependence of the mirror position due to thermal drift. A reduction was indeed observed (to 250 microns) but not to the required level. Current approaches include implementation of electronic active feedback of the mirror pitch motion.