Beam Test Result

Jeewon SEO

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 ㎜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

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

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.