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Update on SBS Back Tracker GEM @ UVa

Update on SBS Back Tracker GEM @ UVa. K. Gnanvo , N. Liyanage , V Nelyubin , K . Saenboonruang , Seth Saher , Nikolai Pillip (visiting from Univ. Tel Aviv, Israel). Preliminary tests and results Improvements for the next two prototypes. Design of 50 ×50 cm 2 Back Tracker GEM.

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Update on SBS Back Tracker GEM @ UVa

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  1. Update on SBS Back Tracker GEM @ UVa K. Gnanvo, N. Liyanage, V Nelyubin, K. Saenboonruang, Seth Saher, Nikolai Pillip(visiting from Univ. Tel Aviv, Israel) • Preliminary tests and results • Improvements for the next two prototypes

  2. Design of 50 ×50 cm2 Back Tracker GEM • Module of 50 × 50cm2to replace the 40 × 50cm2 • 32 modules to be built instead of 40 for the 8 SBS Back Tracker GEM chambers Reduce the overall cost and dead area • No protective resistors on the GEM foils  external resistor board • Individual HV test of all the sectors at different stages of the assembly and safer to operate during the assembly • Wider GEM frames and readout honeycomb support along x-axis • 30 mm instead of 8 mm, alignment holes away from active area • Room for strips connectors and GEM HV sectors electrodes • Holes for mechanical positioning of the chamber on the frame Triple GEM module 4 Triple GEM modules in a SBS Back Tracker chamber

  3. SBS Back Tracker GEM module Proto 1 HV divider Apv25-SRS FE cards Spark protection resistors Board

  4. Pedestal RMS noise • For 50 × 50 cm2 COMPASS-like readout, typical rms after common mode correction of the baseline is on average of 6-7 adc counts for apv25-SRS • @ 230 e-/adc  ~ 1200 to 1500 ENC • a cut at 5 sigma for zero suppression  ~ 6000 e- Pedestal RMS noise distribution over 16 APV y-strips (340 mm) x-strips (80 mm) ADC Ch counts

  5. Preliminary test with cosmic data X-Y strips charge sharing ratio Hit in X and Y strips Good S/N ratio at 4200 V X (adc) / Y (adc) = 1.34 Cluster ADC sum distribution X/Y strips charge sharing correlation

  6. Preliminary test with cosmic data Hit count distribution on Y-strips Event cluster position 2D map Event counts Hit count distribution on X-strips counts

  7. Non uniformity from the scintillator counters We use 2 set of 3 scintillators paddle in coincidence for the trigger on cosmic Changing the arrangement of the paddles in the set up lead to a big changes in the hit distribution profiles Main source of the non uniformity here

  8. Gain (non) uniformity of the chamber X • Gas flow uniform in Y direction  gas inlet and outlet • We suspects a non uniformity of the gain due to the gas flow in the X direction • The gas flow in X is facilitated by groove in the spacer but not sure if it is Y window Groove Mean cluster adc counts 2D map Drift cathode GEM foil 1 GEM foil 2 GEM foil 3 ADC counts Y X

  9. Suggestions for improvements for the next two prototypes

  10. Faraday cage shielding using GEM foil common electrode window Drift cathode GEM foil 1 GEM foil 2 GEM foil 3

  11. Safe area around the frame on GEM foil Current design • Problem • No space between the GEM Frame (inner part) and the GEM foil active area • Glue can leak onto the foil during assembly  Sector will spark at high rate  but Can be cured Proposed modification • Solution • We propose 1 mm clearance between the frame (inner part) and the GEM foil active area  Kapton foil with no holes

  12. New Gas distribution scheme for the chamber Current gas distribution scheme window Entrance window foil Drift cathode Drift cathode foil GEM foil 1 Proposed gas distribution scheme 3 GEM foils Frame_GEM GEM foil 2 Frame_GEM out GEM foil 3

  13. Charge sharing and 2D readout strips width old design 40 x 50 cm2 new design 40 x 50 cm2 Top strips: 140 mm Bottom strips: 360 mm Top strips: 90 mm Bottom strips: 360 mm X/Y ratio = 1.104  GOOD X/Y ratio= 1.34  BAD

  14. BACKUP

  15. APV25 Gain: MPD vs SRS

  16. HV test of the GEM sectors • We use an Iseg EHS 6 kV HV module in a Wiener crate, HV controlled through an internet protocol. • Fast ramp up mode at a rate of 1200 V/s. • The leakage current in the GEM is measured using a Keithley 6487 picoammeter, at sampling rate of 120 mswith a Labview interface and saved in txt file. • HV GEM sector ~ 2 nF and with a resistance the HV module is ~ 50 M, (once the voltage is achieved this resistance is shunted automatically within the supply). • HV of 550 V, the initial current is a couple of mA, then quickly drops and stabilizes to less 1 nAleakage. • We leave the HV for about 2 min and if no spark  sector is good Initial current with the HV ramping up and down

  17. HV test of the GEM sectors • Distribution of leakage current over all the 72 sectors (24 sectors per GEM foil and 3 foils per chamber) • HV Test is performed at 550V in N2 for naked, framed foils and in chamber foils • Average leakage current < 1 nA for all the tests naked GEM foils ~ 0.55 nA Framed GEM foils ~0.68 nA GEM foils in SBS Proto1 ~ 0.72 nA

  18. Recovering of a bad HV sector Excess of glue leaked onto the sector during assembly  sector recovered after curing on N2 or at 50 degree First test after assembly Second test one day later 4rd test three days later 3rd test two days later

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