Beam Test Result

Jeewon SEO

World lab fellow

T10 Beam Test 14. Oct. ~ 20. Nov. 2009ALICE 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)

Data Acquisition

Slewing Correction

Time = Tchamber – Tave Tave : average time of the timing scintillators

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 in-crease.

Breakdown at 11.8 kV with the pure freonBreak down at

11.8kVwith 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

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.