Proportional Counter Used As The Monitor Of BESⅢ Drift Chamber

As a high precision gas detector, the performance of BESIII drift chamber is dependence on the component, temperature and pressure of gas, namely the gas gain. Therefore, the BESIII drift chamber must be monitored. Besides, the optimal gas flow rate for the BESIII drift chamber should be chosen, considering the stable of chamber and the cost of gas.Two proportional counters were installed at the inlet and outlet of aging chamber and full length prototype gas system to measure the gas gain used as the monitor of BESIII drift chamber. The results show that the optimal gas flow rate is 1.4 volume of chamber per day for aging chamber and is 1.0 volume per day for the full length prototype which was designed much closed to BESIII drift chamber was obtained. These providing primary data for choosing optimal gas flow rate in running BESIII drift chamber. The ratio of full energy photo electron peak position of ⁵⁵Fe 5.9 keV X-ray between inlet and outlet is a constant. We alsocan monitor the change of gas ratio efficiently.The traditional multi channel analyzer system was replaced by the ADVANTECH PCI-1716L data acquisition board to monitor the performance of BESIII drift chamber automatically. Adopting Visual C++ 6.0 as software developing kit, the real time data acquisition system of BESIII drift chamber was set up. By adopting simplex method algorithm, ⁵⁵Fe 5.9 keV X-ray full energy photo electron peak position was given automatically. Applied simplex method to the monitor system of BESIII drift chamber, it was proved to have a good converge properties and the chamber can be monitored automatically, real-timely and precisely.Coppery proportional counters were made for the running of BESIII drift chamber. Real-time data acquisition system of monitored proportional counter was test by cosmic rays in the BESIII drift chamber. The results shown that the system can monitor the chamber real-timely precisely, running stabilized and save the expense of instruments. The changes of gas and environment parameter are monitored efficiently; even the change is less than 0.2 percent. The peak position of full energy photo electron can be used in calibrating dE/dx,which its data was response to the gas gain.The results will be applied to the monitor of BESIII drift chamber.The contributions of the author as follows: (1) Monitoring the performance of BESIII drift chamber.(2) Developing real-time data acquisition system of monitored proportional counter in BESIII drift chamber.(3) Testing the monitor system by cosmic rays and providing primary data for runningBESIII drift chamber.