1. Quality Assurance procedures for the construction of ALICE TOF detector VIIIth Workshop on Resistive Plate Chambers and Related Detectors 10-12 October 2005 Seoul - Korea Andrea Alici University of Bologna – I.N.F.N. Bologna On behalf of ALICE TOF Group (INFN and University, Bologna – INFN and University, Salerno – ITEP, Moskow – Kangnung University)

2. Andrea Alici RPC 2005 Seoul 10-12 October 2005 1 Outline  Introduction to the ALICE experiment and to the Time-Of-Flight detector;  Motivation of Quality Assurance tests;  Description of the most relevant tests;  Results and comments.

3. Andrea Alici RPC 2005 Seoul 10-12 October 2005 2 PID in ALICE Time Projection Chamber dE/dx Inner Tracking System dE/dx @ low p t Time-Of-Flight High Momentum Particle Identification PID @ high p t PHOton Spectrometer , π 0 ID Transition Radiation Detector electron ID Time-Of-Flight

4. Andrea Alici RPC 2005 Seoul 10-12 October 2005 3 TOF requirements  Large area ~ 160 m 2 ;  High segmentation, with about 160000 channels of ~ 10 cm 2 readout pads to limit the occupancy at the level of about 15%;  High efficiency > 99%;  Good rate capability > 50 Hz/cm 2 ;  Excellent global time resolution < 100 ps to efficiently separate π/K up to 2.5 GeV/c (and k/p up to 4 GeV/c). Gaseous detectors Multigap Resistive Plate Chambers

5. Andrea Alici RPC 2005 Seoul 10-12 October 2005 4 MRPC performances Test with a beam of charged particles @ CERN PS during summer 2004 over 18 MRPC of the pre-production (76 pads in total) Time Resolution (ps)Efficiency (%) H.V. (kV) ε > 99.9 % mean ~ 50 ps rms ~ 5 ps For other results see talk by G. Scioli

6. Andrea Alici RPC 2005 Seoul 10-12 October 2005 5 Quality Assurance tests Tests applied to the single MRPC components:  tests of planarity on the rigid components of the MRPC;  measure of surface resistivity of the electrodes. Test applied to the assembled detector:  measure of the gaps size;  pulsing tests;  high voltage tests;  study of the performances of the MRPCs with cosmic rays;  all the MRPCs will be tested in a dedicated Cosmic Ray Facility @ CERN (HV tests, efficiency and time resolution estimation). 1638 MRPCs for the whole TOF  Q.A. procedures are mandatory! Locations:  Bologna  CERN

7. Andrea Alici RPC 2005 Seoul 10-12 October 2005 6 The MRPCs for ALICE TOF Reminder for the next slides:  the 4 electrodes are obtained with 0.55 mm thick glasses painted with a specially developed acrylic paint loaded with metallic oxides of chromium and zinc;  these external glasses are 1 mm larger than the internal ones;  the connectors for signal trasmission to the FE cards are placed on the middle PCB.

8. Andrea Alici RPC 2005 Seoul 10-12 October 2005 7 Mechanical tests 10 mm Honeycomb panels for mechanical rigidity Printed Circuits Boards with readout pads All the rigid components of the detectors are checked in order to reject those wich are not planar enough and which show construction faults.

9. Andrea Alici RPC 2005 Seoul 10-12 October 2005 8 Measure of resistivity pA 4 glasses with acrylic paint are needed for each MRPC 6592 glasses in total! The surface resistivity of all the glasses is measured in 5 different positions to check the uniformity of the applied paint. We use a V o source and a picoammeter to measure the resistance of an element of the paint. With the selection of a square part of the glass, the measure of resistance is equivalent to the measure of the surface resistivity.

10. Andrea Alici RPC 2005 Seoul 10-12 October 2005 9 Measure of resistivity resistivity (M  / G ) distance from the border (cm) The value of surface resistivity can range from 2 to 10 M  / G. For each MRPC, 4 glasses with most similar values point- by-point are chosen. 1.Values of resistivity within an acceptance range.

11. Andrea Alici RPC 2005 Seoul 10-12 October 2005 10 Measure of resistivity mean resistivity (M  / G ) Average value for each glass 1.Values of resistivity within an acceptance range.

12. Andrea Alici RPC 2005 Seoul 10-12 October 2005 11 Measure of resistivity mean resistivity (M  / G ) std. dev./mean resistivity cut for values greater than 0.25 1.Values of resistivity within an acceptance range; 2.Uniformity along the glasses.

13. Andrea Alici RPC 2005 Seoul 10-12 October 2005 12 Gap size measure - setup CCD camera Navitar Zoom 6000 lens system (0.5x+6.5X+0.5x) NI IMAQ 1409 frame grabber for data aquisition + LabVIEW software for image processing and user interface program The MRPC for ALICE TOF will be work in avalanche mode but with a very high Townsend Coefficient (E ≈ 100 kV/cm)  the gaps width is an important feature. The width of each gap is then measured in 4 different position along the MRPC.

14. Andrea Alici RPC 2005 Seoul 10-12 October 2005 13 Gap size measure - setup N.A.= sen α Resolution  N.A. Depth of field Depth of field  1/ (N.A.) 2 It’s not possible to focus all the glass edges and to have a resolution less than 10 μm. For the gaps between the external and the internal glasses (external gaps in following slides) we need to change the focus. This kind of measure is very sensitive to the alignment of the MRPCs with respect to the microscope axis. 5 mm α

15. Andrea Alici RPC 2005 Seoul 10-12 October 2005 14 Gap size measure We focus the external edges The presence of the gap spacers between the microscope and the light source cause a non uniformity of the background luminosity. The image is thesholded using a different threshold value for each glass edge. Luminosity profile

16. Andrea Alici RPC 2005 Seoul 10-12 October 2005 15 Gap size measure 3 measures corresponding to 2 gaps in 2 MRPC strips are outside mean value  15 μm 7 measures corresponding to 3 gaps in 2 MRPC strips have cleary failed also the optical tests More than 100 MRPCs tested frequency gap size (μm)

17. Andrea Alici RPC 2005 Seoul 10-12 October 2005 16 Pulsing tests 1664 soldering for each MRPC A trace has been implemented in order to induce a signal pulse directly on the readout pads 15mm GND Anode signal Cathode signal Each MRPC has 96 readout pads arranged in two rows of 48. The MRPCs have 32 connectors to bring the signals from the strip to the FE cards (3 pads per connector).

18. Andrea Alici RPC 2005 Seoul 10-12 October 2005 17 Pulsing tests National Instruments™ PXI – 1052 1. A signal pulse is induced on the MRPC pads. 2. The output signals from the MRPC pads are aquired with NI DAQ, sampled and analyzed with LabVIEW During the experiment with this same trace will be possible to check all the readout chain, i.e. readout pads FE electronics channels LVDS signal cables TDC channels

19. Andrea Alici RPC 2005 Seoul 10-12 October 2005 18 High Voltage tests universal multichannel power supply CAEN SY3527 current (μA) In this preliminary phase we tests all the MRPCs with HV in air up to 3 kV for few minutes.

20. Andrea Alici RPC 2005 Seoul 10-12 October 2005 19 Tests with cosmic rays – HW setup The facility consist of a stack of 5 MRPCs; the signals of each chamber are amplified and discriminated by front- end electronics which allows to retrieve also the OR of the signals for each MRPC. The trigger is formed by taking the coincidence of at least 4 of the OR signals. The 2 external MRPCs was tested in the summer of 2004 at the CERN PS. They are used as reference. The pads structure of the devices allow to perform the track reconstruction. The time resolution of each MRPC is obtained using the other 4 detectors as time reference. VME crate with TDCs CAMAC crate with coincidence unit and dual timer PC with slow controls and DAQ CAEN SY127 HV power supply

21. Andrea Alici RPC 2005 Seoul 10-12 October 2005 20 Tests with cosmic rays Time Resolution (ps) Efficiency (%) Same MRPC tested @ CERN PS (~50 ps of time resolution) Comparable results, but with cosmic rays: full area of the pads illuminated; data taking of more than one week.

22. Andrea Alici RPC 2005 Seoul 10-12 October 2005 21 Tests with cosmic rays – efficiency pads Results of about 5% of assembled MRPCs ε ~ 99.6%

23. Andrea Alici RPC 2005 Seoul 10-12 October 2005 22 Tests with cosmic rays – time resolution pads Results of about 5% of assembled MRPCs time resolution/time resolution of reference MRPC

24. Andrea Alici RPC 2005 Seoul 10-12 October 2005 23 Tests with cosmic rays @ CERN scintillators array 5 ALICE TOF modules (91 MRPC strips) will be tested at the same time: HV tests in gas at the operating voltage, study of efficiency and time resolution (ITEP).

25. Andrea Alici RPC 2005 Seoul 10-12 October 2005 24 Conclusion  A set of Quality Assurance procedures has been developed in order to take the assembly of the MRPC under control;  At this moment the Q.A. tests are going in parallel with the MRPC construction;  The failure rate is very low, it means that the assembly procedure is well optimazed.