Research On The Technology Of The Channel Cut Crystal And Beam Position Monitor

Synchrotron radiation(SR) light source is another revolutionary force to human beings besides x ray source and laser source. It has been widely used in many fields as an essential instrument for its excellent character. In recent years, several improvements have been made in SR source and experiment techniques. And the beamline engineering, too, has been improved during recent years, especially for the key technique and hardcore. The improvements of the beamline are good for the amelioration of the light source performance.Some systemic research on key parts of the beamline, which include fix-exit channel cut monochromator with curved reflecting surfaces and photon beam position monitor, had been made by support of NSRL-XAFS beamline upgrading project. Design, manufacture, test and application of the two key parts were done. The main research contents are described as follows:1. Research on fix-exit channel cut monochromator with curved reflecting surfaces:Curving a crystal block to get two specific profiles, a channel cut monochromator is done. This new kind of crystal monochromator can accomplish energy scan as well as fixing exit beam position. It restrains high-order harmonic and improves the resolution of the beam. This kind of crystal simplifies the beamline, reduces the size of the vacuum chamber. A monolithic channel cut monochromator with curved surfaces was designed based on the parameters of the XAFS beamline at NSTL. The principle of energy scanning with single rotation movement, processing of the curved surfaces, measuring of the reflecting surfaces and the effects of the beam deviation from the center of the beam on diffracted performance were discussed in this paper. Performance of channel cut crystal with curved surfaces had been analyzed and measured. Comparing with the conventional symmetric double-flat-crystal monochromator, we found that the transfer efficiency of the beam, bandwidth and exit beam stability of the channel cut crystal were mainly affected by the asymmetric reflection of the extended beam and the Bragg rotation axis deviation from exact position. A conclusion could be made that the performance the channel cut crystal could be improved by enlarging the dimension of the reflecting surfaces, improving the precision of the two profiles machined on the crystal and the precision of the Bragg rotation axis of the channel cut crystal. The thermal load of the channel cut crystal at XAFS beamline was calculated, and the temperature and hot deformation of the crystal were simulated. Two cooling methods were brought forward and analyzed. Finally the side face cooling method was chosen to bate the thermal effects brought by high energy third light source.2. Research on monitoring of the beam position:Ascertaining the beam position is the basic requirement to estimate whether a source is good. A Precise beam position monitor is indispensable. Based on the parameters of the XAFS beamline, a double wire BPM was designed and manufactured. A monitor with two tungsten wires perpendicular to each other had been developed to simultaneously collect the data from each individual wire with one linear scanning motion. Using this monitor, the X-ray beam position detected from Wiggler radiation at NSRL had been performed by tracking the beam profiles in horizontal and vertical directions, and computing the beam drifts during electron stored period and the beam shifts from different electron injections for the storage ring in vertical direction. The result data allows the users to assess beam instability and take some compensation means. The monitor also possibly provides an accurate way of correcting electron orbit via real time observation of the incident photon beam position.The key work of this paper is research of key parts of the beamline, which including the fix-exit channel cut monochromator with curved reflecting surfaces and photon beam position monitor. Some conclusions could be made, which were shown as follows:1.Under existing conditions, the channel cut crystal manufactured can fulfill the experiment requirement on XAFS beamline at NSRL; the most convenient and efficient way to improve the performance of the channel cut crystal is to enlarging the size of the reflecting surfaces, reducing the size of the beam spot irradiating on the crystal, improving the precision of the two reflecting surfaces and side face cooling the channel cut crystal.2. A new double wire beam position monitor had been successfully designed and manufactured. The double wire monitor can obtain the position of the beam and the two-dimensional distribution of the beam density. The monitor results are veracious and believable, which indicate the stability of the Wiggler source at NSRL. And the beam position has been detected in vertical drift with 200μm as the electron current decays from 220 mA to 100 mA and vertical shifts within±250μm at the different electron stored periods. The short time deviation of the beam position is 30μm.