Beam Test Result Jeewon SEO World lab fellow. T10 Beam Test 14. Oct. ~ 20. Nov. 2009 ALICE TOF 10...
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Transcript of Beam Test Result Jeewon SEO World lab fellow. T10 Beam Test 14. Oct. ~ 20. Nov. 2009 ALICE TOF 10...
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 ㎜ⅹ 10 ㎜ beam spot
(130 triggers/spill in every 20 seconds)
Time Resolution
σres = √( σch2-σsc
2)
σres : time resolution
σch : measured time of signals
σsc : jiter of scintillators
Ave(S1,S2)-Ave(S3,S4)
Efficiency and Streamer Plateau
SF6 0 % 2 % 4 % 6 % 8 % 10 %
Streamer free and ef-ficient >90%
operation range
10.6~11.6 kV
10.8~13 kV
11~13.2 kV
11.2~13.4 kV
11.4~13.6 kV
11.6~13.8 kV
1 kV 2.2 kV 2 .2kV 2.2 kV 2.2 kV 2.2 kV
The knee of the effi-
ciency 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
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
Tdiff = (Tmean)MRPC1-(Tmean)MRPC2
The best resolution is 20.8 ps
with pure freon and 19.1 ps
with added 5% SF6.
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)
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.