2020同步年報

Facility Status 115 Fig. 2 : (a) Thermal equilibrium period of DCM. Red and black lines represent vertical and horizontal beam positional variations, respectively. (b) Energy resolution. (c) Difference of energy drift. One of the most common issues that causes beam instability is the X-ray heat load on the double-crystal monochromator (DCM) that results in a loss of parallelism of its two crystals. At TPS 07A , the heat-load test showed that the period required to attain thermal equilibrium of the DCM upon X-ray exposure is about 22 min ( Fig. 2(a) ). The period of thermal equilibrium was subsequently decreased to about 2 min using a feedback system to correct the beam position continuously. Thermal drift and vibrational problems that also lead to beam instability will be analyzed in future commissioning. Regarding the energy resolution and energy stability, the results are as follows. The energy resolution (∆ E / E ) varies from 1.85 × 10 -4 to 1.95 × 10 -4 as the energy alters from 5.7 to 20 keV ( Fig. 2(b) ); the energy drift is about 1 eV within 10 h (0.1 eV/h) ( Fig. 2(c) ). Taken together, TPS 07A has effective energy resolution and stability for SAD/MAD experiments. To achieve a rapid and effective data collection from many micro-crystals or large inhomogeneous crystals with a raster/grid or helical scan, the endstation of TPS 07A is equipped with two state-of-the-art devices -- area detector Eiger2 X 16M and vertical axis micro-diffractometer MD3. Compared with MX300HS (at TPS 05A ), the major benefits of Eiger2 X 16M are the increased frame rate, a superior point-spread function and no readout noise. This detector hence becomes more suitable for efficiently obtaining diffraction data from micro-crystals. Many PX synchrotron beamlines worldwide, including TPS 05A , utilize a horizontal-axis diffractometer to rotate the crystal for data collection. In this geometry, polarization effects caused by the horizontal polarization of synchrotron radiation could cancel the Lorentz factor, but a diffractometer with a vertical spindle has superior mechanical stability (smaller sphere of confusion) for micro-crystals. After thorough consideration, our group chose a vertical-axis MD3 diffractometer to install at TPS 07A . In so doing, the necessary marginal cost is that the average intensity of symmetry-equivalent reflections decreases about 10% in a 2 Å bin using 1 Å radiation. 1 In addition, an ISARA high-capacity sample changer (29 UniPucks/464 samples) will be installed; it changes samples within tens of seconds to increase the efficiency of data collection for many micro-crystals. Finally, TPS 07A will be embedded with powerful software, MeshBest , that automatically analyses the results of the raster scan from a loop with many micro-crystals. The strategy of whether and how to collect those crystals will be given. The ultimate goal is to provide an automatic work- flow to make multi-crystal data collection even more efficient. In conclusion, TPS 07A with a high-flux mode and special features will be useful for the toughest crystallographic projects, such as those with large amounts of micro-crystals and those with large inhomogeneous crystals (Reported by Chung-Kuang Chou, Chia-Liang Lin and Chun-Hsiang Huang). Reference 1. J. M. Holton, K. A. Frankel, Acta Cryst. D66 , 393 (2010).