1. Gas Quality Checks Maria Luisa Porto Oriented by: Burkhard Schmidt 23/02/2009

2. Summary 23/02/2009Gas Quality Checks2 1. Introduction 2. Experimental setup 3. The procedure 4. The software 5. Temperature and Pressure 6. Next steps

3. Introduction 23/02/2009Gas Quality Checks3  The LHCb muon system is composed of five detection stations with are equipped with Multi-Wire-Proportional- Chambers (MWPC).  The MWPC performances are heavily dependent on the gas gain.  Our purpose was to develop a software that could help us compare the gas gain results from different measurements.

4. Experimental setup 23/02/2009Gas Quality Checks4 The experimental setup was installed in the UXA zone. The experiment consists in comparing signals from the MWPC produced by a 241 Am source in two configurations, both with the CO 2 /Ar 60/40 gas mixture: 1. the chamber is flushed with gas from the supply line. 2. the chamber is flushed with gas from the return line. The chamber is held inside a wooden box to stabilize the ambient conditions, such as temperature and pressure.

5. Experimental setup 23/02/2009Gas Quality Checks5  Gas lines and panel The chamber inside the box and de 241 Am source

6. The procedure 23/02/2009Gas Quality Checks6 CAEN to monitor the high voltage applied on the chamber. Current produced by the radioactive source measured with an OPERA current meter (~1 nA precision). Controlled ambient conditions (temperature and pressure measured). Nine measurements are taken. Two minutes of data are acquired for each value of HV. High Voltage (V) 241 Am Source 2800No 2800Yes 2750Yes 2700Yes 2650Yes 2600Yes 2550Yes 2800Yes 2800No

7. The procedure 23/02/2009Gas Quality Checks7 Two options for the procedure: 1. From 2550 V up to 2800 V

8. The procedure 23/02/2009Gas Quality Checks8  From 2800 V down to 2550 V

9. The software 23/02/2009Gas Quality Checks9  The software for the gas quality checks was written in C++ language and runs in the root.  It is installed in the LHCb control room, which makes possible to acquire the data in UXA zone e analyze it in the control room.  Its inputs are the text files with the data corresponding to the current and voltage plus the text file corresponding to the temperature and pressure.

10. The software 23/02/2009Gas Quality Checks10  The plots:

11. The software 23/02/2009Gas Quality Checks11  The output file:

12. Temperature and Pressure 23/02/2009Gas Quality Checks12  The gain depends on the gas density and therefore on the gas temperature and pressure.  According Diethorn’s formula, for small temperature and pressure variations, the gain variation is: Where α is a constant parameter that depends on the chamber geometrical parameters and on the gas mixture.

13. The software 23/02/2009Gas Quality Checks13  Checking the points:

14. Next steps 23/02/2009Gas Quality Checks14  Continue the study of the temperature and pressure variations and how they effect the gas gain.  Make changes in the high voltage values accordingly to the variation of temperature and pressure in order to keep the gas gain constant.