Beam Test Result JeewonSEO World lab fellow
T10 Beam Test • 14. Oct. ~ 20. Nov. 2009 • ALICE TOF 10 gap chamber and 24 gap MRPC was tested with different percentages of SF6. • SF6 • Property : Highly electronegative • Disadvantages • Expensive cost • Global warming gas
10 Gap MRPC • Gap size : 250 ㎛ • Aluminum box volume : 200ℓ • Gas flow rate : 20ℓ/h (O2 content was kept at 100 ppm)
Beam Test Setup • -5GeV/c beam of π-, μ- . • Trigger selected 10㎜ⅹ10㎜ beam spot (130 triggers/spill in every 20 seconds)
Slewing Correction • Time = Tchamber – Tave Tave : average time of the timing scintillators
Time Resolution Ave(S1,S2)-Ave(S3,S4) • σres = √( σch2-σsc2)σres : time resolution σch : measured time of signals σsc : jiter of scintillators
Efficiency and Streamer Plateau • The knee of the efficiency plateau moves to high voltage when the percentage of SF6 increase. • Breakdown at 11.8 kV with the pure freon Break down at 11.8kV with pure freon
Time resolution with various percentage of SF6 • Time resolution is independent of the fraction of SF6.
24 Gap MRPC • 160㎛ gaps (total thickness : 3.84㎜) • Gas flow rate : 20ℓ/h (box volume : 30ℓ)-> O2 content was kept at 20 ppm • Threshold : 40 fC
Data Acquisition • NINO mounted on chamber inside gas volume
Compare time of one MRPC with another • Time resolution obtained by measuring time difference between two chambers • Timing scintillators are not used.
Efficiency and Time resolution • Efficiency plateau is shifted to a lower voltage with the pure freon. • The streamer-free and efficient operation range • Pure freon : 1.6 kV (10.6kV ~ 12.2kV) • 5% SF6 : 2 kV (11kV ~ 13 kV) • Tdiff = (Tmean)MRPC1-(Tmean)MRPC2 • The best resolution is 20.8 ps with pure freon and 19.1 ps with added 5% SF6.
Conclusion • 10 gap MRPC • Break down at 11.8kV with pure freon. • Work with 2% SF6, obtaining the time resolution below 50 ps with a 2.2 kV range.-> Seems to need the SF6 to avoid breakdown • 24 gap MRPC • Work satisfactorily with pure freon • SF6 effect • Shift the efficiency plateau to a higher voltage • Shift in streamer production to higher voltage • For 24 gap MRPC, the efficient operation range without streamer is broader when SF6 added. • Time resolution is independent of SF6 fraction.