位于美国布鲁克海文国家实验室的相对论重离子对撞机RHIC计划于2019–2020年进行能量扫描二期实验项目,其主要科学目标是研究强相互作用物质的相结构并寻找相变临界点. STAR时间投影室内扇区丝室升级(inner TPC, iTPC)是该项目关键的探测器升级. iTPC升级将拓展STAR带电粒子测量的赝快度覆盖区间,并提高动量及能量损失测量的分辨率. iTPC升级将重新制作包括读出丝室和电子学在内的全部24块内扇区模块. iTPC丝室包括阳极丝、阴极丝、门极丝共3层丝面,丝张力及丝面的高度都需要高精度控制.我们设计了丝张力精密测量装置以及高精度丝面安装系统,高质量完成了全部iTPC丝室探测器的研制.实现了探测器增益均匀性1.5%(RMS)、能量分辨率25%(FWHM),及强辐射环境下稳定工作的出色性能,已在STAR实验安装并开始实验运行.
The second phase of the Beam Energy Scan(BES-II),has been scheduled at RHIC at Brookhaven National Laboratory during 2019–2020 and the major scientific task is to study the QCD phase diagram and search for the possible critical point in relativistic heavy ion collisions.The physics measurements rely on key upgrades on beam luminosity and the detector upgrades,for example the inner Time Projection Chamber(iTPC)upgrade at the STAR experiment.With the proposed iTPC upgrade at STAR,the pseudo-rapidity coverage will be extended and the precision of energy loss for particle identification will be improved significantly,resulting in a big improvement in the acceptance for the measurement.The iTPC upgrade will rebuild all 24 inner multi-wire proportional chamber(MWPC)readout sectors including new electronics.The STAR-China group is responsible for the MWPC R&D and mass production.The MWPC includes three layers of wires:anode,shield,and gated wire grids,above the PCB pad plane board.High precision of wire location and wire tension of the wire grids on Aluminum strong back are required during the assembly in order to meet the desired detector performance.A laser based wire tension measurement system has been designed and implemented to inspect the wire tension and pitch.A strict control of the mechanical tolerance of the components has also been realized with position precision of 10μm for wire pitch,and the distance between pad plane and wire planes using wire comb.The anode wire tension has been kept within 6%of desired value.With these quality control enforced,the gain uniformity and the energy resolution are around 1.5%(RMS/Mean)and 25%(FWHM/Mean)respectively,for all 28 produced sectors,tested using a55 Fe X-ray source.Comparing to the required values of 2%for gain uniformity and 30%for energy resolution by STAR,all sectors are qualified with good performances.The required 24 sectors have been installed at STAR experiment successfully.
Scientia Sinica(Physica,Mechanica & Astronomica)
time projection chamber
multi-wire proportional chamber