IMPROVEMENT OF X-RAY BEAM POSITION STABILITY FOR THE BL4-2 SAXS FACILITY

该子项目是利用 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来源获得主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 中心，不一定是研究者的机构。 我们继续缓解去年在新BL 4 -2位置发现的射束位置不稳定问题。今年初，我们确定了不稳定的主要原因，其幅度往往高达1.5倍的全宽半最大垂直梁大小在24小时内，最有可能是逐步热漂移的几块厚混凝土地板移动在不同的速度，以响应昼夜温度波动。我们开始采用一种与SSRL其他插入装置站上成功运行的系统非常相似的反射镜俯仰反馈系统。 第一个版本涉及一个标准束流位置监测器的直接副本，铍信号叶片涂有一层薄的钛工作在氦气氛下。这种方法导致了光束稳定性的改善，在16小时内实现了10微米的稳定性，而在同一时间段内的典型总体漂移为0.2 mm。然而，由于Ti涂层在小散射角下提供的高背景水平，其使用仅限于较短的样品到检测器距离。我们最近修改了这个设计，以尽量减少散射背景。一个新的真空兼容的外壳已经建成，不同的叶片材料进行了测试。结果发现，未电镀，抛光铍叶片提供了一个适当的信号水平的反馈系统的工作，同时保持不必要的寄生散射在一个可容忍的水平。新的刀片现在正在制造和最终版本的设备将安装和测试的新刀片成为可用。

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. We continue to mitigate the beam positional instability issue, which were found last year at the new BL4-2 location. Earlier this year, we identified the major cause of the instability, whose magnitude is often as much as 1.5 times the full width half maximum vertical beam size in 24 hours, to be most likely the gradual thermal drifts of a few pieces of thick concrete floor moving at different rates in response to diurnal temperature fluctuation. We began adopting a mirror pitch feedback system very similar to those operating successfully on other SSRL insertion device stations. The first version involved a straight copy of the standard beam position monitor with beryllium signal blades coated with a thin layer of Ti working under helium atmosphere. This approach resulted in an improvement in beam stability, achieving ten micron stability over a 16 hour period, down from typical 0.2 mm overall drifts over the same period. Its use is, however, limited to shorter sample-to-detector distances due to the high back ground level given by the Ti coating at small scattering angles. We have recently modified this design to minimize scattering background. A new vacuum compatible housing has been built and different blade materials have been tested. It was found that un-plated, polished beryllium blades give an appropriate level of signal for the feedback system to work while keeping unwanted parasitic scattering at a tolerable level. The new blades are now being fabricated and finial version of the device will be installed and tested as the new blades become available.