2020同步年報

114 ACTIVITY REPORT 2020 Current Status of TPS 07A T PS 07A , a micro-focus protein crystallography (PX) beamline, is currently under commissioning and ex- pected to be operational in December 2021. Different from TPS 05A , which is optimized for crystals with a large unit cell, TPS 07A is particularly optimized for micro-crystals (small ratio of signal to noise) and large inhomogeneous crystals (difficult to measure). In building a reliable micro- focus PX beamline, three main design guidelines for the op- tical system have been pursued: a small beam size, high-flux density and a highly stable beam. Based on these demands, beamline specifications and a simulation of beam perfor- mance appear in detail in Tables 1 and 2 , respectively. Table 2 : Simulation of beam performance of TPS 07A . Simulation energy at 12.39 keV, 3 m-IU22, 500 mA, min gap 5 mm, with heat load on first crystal. Fig. 1 : (a, b) Focused beam size at the sample position in vertical and horizontal directions. Black and red solid dots show the raw data and the derivative defining the beam profile, respectively. The red solid line shows the Gaussian fitting. (c) Range of beam size. The red and blue lines stand for ver- tical and horizontal positions, respectively. The red and blue lines show vertical and horizontal beam sizes at varied offsets from the focus point. The measurements were conducted under fully open horizontal secondary source slits. Table 1 : Beamline specifications of TPS 07A . Energy range 5.7−20 keV Beam size 1 x 1 to 30 x 30 µm 2 @ 12.4 keV (H x V, FWHM) Monochromatic flux ≥ 10 12 photons/s @ 12.4 keV @ 1 x 1 µm 2 Beam divergence < 1 mrad (in both directions) Energy resolution ≤ 1.7 x 10 -4 with Si(111) crystal Energy stability < 0.25 eV h -1 Because of the ongoing commissioning, some vital beam characteristics for PX experiments, including beam size, flux and sta- bility, have been measured at the sample position. The focused beam size at the sample position was measured on scanning a tungsten knife edge through the beam along the vertical and horizontal directions. Based on the Gaussian profile, it clearly shows that the focused beam size at the sample position is 1.7 × 3.7 μm 2 (V x H) ( Figs. 1(a) and 1(b) ). In addition, notably, TPS 07A can provide continuously adjustable beam sizes from 1.7 to 97 µm ( Fig. 1(c) ). The flux at the sample position can be determined with a Si-PIN photodiode and was found to be 6.6 x 10 11 photons s -1 at 12.7 keV and magnet gap 7.575 mm when normalized to current 400 mA in the storage ring. As mentioned above, it is reasonable that the measured flux is less than the expected flux ( Table 2 ) about one order. Second source H-opening /µm MD3 position /mm Beam size /µm 2 , V x H Beam flux /photons s -1 Flux density /photons s -1 µm -2 Interval to Henderson limit /s 2 2 0.7 x 1.5 1.4 x 10 12 1.3 x 10 12 0.031 4 11 3.3 x 3.2 2.8 x 10 12 2.7 x 10 11 0.15 6 15 5.0 x 5.3 4.1 x 10 12 1.5 x 10 11 0.27 12 25 10 x 11 7.9 x 10 12 7.0 x 10 10 0.57 25 46 21 x 24 1.4 x 10 13 2.9 x 10 10 1.38 >100 62 29 x 34 1.7 x 10 13 1.7 x 10 10 2.35 >100 82 40 x 45 1.7 x 10 13 9.5 x 10 9 4.21 >100 102 50 x 56 1.7 x 10 13 6.1 x 10 9 6.55