High Accuracy Measurement Of X-Ray Beam Position In The Front End Of BL18U1 Beamline At Ssrf

In synchrotron radiation facility, X-ray beam position is a key parameter to the debugging of storage ring and beamline, to the experiment on end stations and to the improvement of the beam stability. The beam position data is also important for experimental users to get to know the situation of beam center, these datum often be used as one of predict to the quality of experimental datum. The XBPM(X-ray Beam Position Monitor) in frontend is the nearest beam position measurement equipment of the beamline to the storage ring. In frontend, X-ray is clear and open-wide, almost have not any reflection or refraction made by optical elements. As might be the first "eye" of the beamline,the measured data of the XBPM can objectively indicate the stability of the light source point. The distance from XBPM to the light source point is generally about 10 meters, it makes XBPM is about 10 times sensitive to the disturbance of orbit than e BPM in the storage ring. So the XBPM is the most efficient beam position detecting device.In SSRF(Shanghai Synchrotron Radiation Facility), a new beamline construction project named "Shanghai protein crystal structure analysis system" is in progress. Began at BL18U1 beamline, many new designs have been applied to improve the characteristic of BBPM(Blade Beam Position Monitor, a kind of XBPM).In the new BBPM project, latest calculation has been conducted to obtain the optimized location of 4 blade-type detection electrodes, the mechanical structure has been adjusted to ensure the efficiency of the cooling method, the process of the installation of blade is also improved to reduce the electric noise. While a embeded processor Libera photon is used as the read out electronics equipment. For all of these improvements, the accuracy of BBPM eventually reach 1μm in the vertical, 2μm in the horizontal direction.In this paper, the assembling,optics calibration and the entire installation process about BL18U1- BBPM are stated in detail. The accuracy of the BBPM with 1μm vertically and 2μm horizontally can be proved by means of online calibration with small-step stage moving. Meanwhile, the test of partially shift of electron beam orbit proved that the BBPM can respond the electron beam orbit change in the same level with the e BPM in the storage ring. The data of the BBPM during the orbit fast feedback experiment imply that the resolution of the sensor indicated in RMS value can achieve sub-micron magnitude. This is further evidence of the feasibility that the BBPM signal can be taken into orbit feedback control system.