Test on RPC Veto Detector Model Anticoincidence Detector
- Slides: 22
Test on RPC Veto Detector Model —— Anticoincidence Detector for Daya Bay Neutrino Exp. Speaker: Jiawen Zhang 5 June 2006 1
Outline u. RPC Introduction u. RPC R&D in IHEP Of CAS Ø RPC Performance Study Ø RPC Mass Production for BESIII u. RPC for Daya bay Neutrino Exp. Ø Precondition and requirement Ø Test Design Ø Test Result u. Summary 2
RPC Introduction What is RPC? RPC is composed of two resistive plates with gas flowing between them. High voltage is applied on the plates to produce a strong electric field in the gas. When a cosmic-ray passes through the gas between the two plates, a signal will produce, which is then picked up by the pickup strip and sent to the DAQ system. Advantages: u. Simple structure u. Cheap to make a larger area detector 3
RPC R&D in IHEP Of CAS l The RPCs for the BESIII Muon tracker detector were constructed by using a new type of phenolic rosin laminates developed in IHEP of CAS. l The methods of improving surface quality is similar to other bakelite plates, and have been used to construct RPCs elsewhere. Oscilloscope traces of 100 triggered cosmic ray registered in a RPC prototype at 8 k. V. The average signal amplitude from a pickup electrode is about 400 m. V with a 50 Ω termination. No secondary streamers were recorded 4
Bakelite surface 5
R&D —— prototype performance 1. 18 0. 044 96 -98% 7
R&D ---- long-term stability other neutron irradiation experiments Beam test Max: 98. 8% Average: 97. 2% Min: 95. 3% 8
R&D ---- Humidity effect • During the R&D test, we added water vapor into the gas for about one month. No effects were observed. • All the HV connectors to the RPC are covered with insulation glue. Last summer, the humidity was about 80 -90% lasting about 2 week in Beijing. We tested the RPC bare chambers and the assembled modules, no problem was found, and we will do more test soon. 9
R&D---Flammability gas • The flammability Iso-butane of the mixture gas maybe catch fire, if its proportion is more than 15%. • We used the gas mixture of argon: F 134 a: Iso-butane = 50: 42: 8, Therefore the problem won’t be avoided with the ventilation requirement for Radon removal. 10
RPC mass production for BESIII • Single layer RPC (bare chamber) efficiency ε>95% Barrel 7. 5 Kv Min. 85. 6% Max. 99. 02% Aver. 95. 39% Barrel 8. 0 Kv Min. 90. 38% Max. 99. 2% Aver. 96. 4% 11
RPC mass production for BESIII • A new bare chamber single counting rate is below 1000 Hz/m 2( only training 1 -3 days), if training for a long time, the single counting rate will be below 500 Hz/m 2 Barrel 7. 5 Kv Min. 0. 016 Max. 0. 599 Aver. 0. 095 Barrel 8. 0 Kv Min. 0. 022 Max. 0. 872 Aver. 0. 130 12
RPC mass production for BESIII • 2 layers of RPCs form a super layer, ε >98% Mean 0. 98 Average eff: 0. 99 13
The requirements of Daya bay Neutrino Exp. u The anticoincidence detector is used to decrease the cosmic ray background to improve measurement precision Table 1. Neutrino instance and Cosmic ray flux Near Site Far Site Neutrino rate (/day) 560 80 Muon Flux (Hz/m 2) ~1 0. 045 According to the design, we know the radius of central detector is 1. 6 m. And by calculation, the cosmic ray through the detector is 8 Hz near site, and 0. 36 Hz far site. Taking example of far site, the cosmic ray through 4 modules every day is 4× 0. 36 Hz× 3600 s× 24 h=125000 >>80 14
• Anticoincidence detector ε~99. 9%, 125(>80) cosmic ray won’t be removed • Anticoincidence detector ε~99. 99%, 12(~15%) cosmic ray won’t be removed Most of cosmic ray can be removed by spectrum & time relation of later neutron signal So the result is acceptable! 15
The design of detector u. Requirement Ø Higher efficiency Ø Less noise But these two factors are contradictions, so the key problem is how to balance the two factors. A fact is that a water Cherenkov may be used. (efficiency is ~ 95%[1] , noise <0. 1 Hz. [2] ) 16
The design of detector(2) u. Outer detector scheme • • Adopt 2 dimension readout RPC operate in streamer mode The gas mixture used as Ar: C 2 H 2 F 4: C 4 H 10 =50: 42: 8 HV: +4000 V,-4000 V ü Single gap, 3 layers in one module ü Each layer overlapping assembly, no dead space. ü Each module overlapping assembly too, so between modules no dead space. 17
detector(3) u Efficiency and noise ü Efficiency of each layer is ε ~95%, and adopt choose 2 out of 3 as a hit, their coincidence efficiency is εeff =ε 3+C 32 ε 2(1 - ε)=0. 953+3× 0. 952×(1 -0. 95)=99. 3% The efficiency of the module with the water Cherenkov is 1 -(1 - εeff )(1 - ε)=1 -(1 -0. 99)(1 -0. 95)=99. 95% ü The RPC bare chamber noise rate ~800 Hz/ m 2 , the shaped signal width is τ=100 ns=10 -7 s, so the module noise rate is 3 C 32 r 2 τ=3 × 3 X(800)2× 10 -7=0. 576 Hz/m 2 since the module has 3 layers RPC, so we can do the track for itself. By using the track information, the noise can be reduced to <0. 05 Hz/m 2. If we reduce RPC noise rate to 300 Hz/m 2, the noise can be reduce to more lower. In addition, Because the noise of the water Cherenkov is very small, the total noise is not more than 1 Hz ! 18
The design of detector(4) • Electronics and readout l the same as BESIII Muon detector. l Each FEC can handle 16 channels,and a total of 16 FEC composed a data chain. l All the data chains are connected to the VME readout system. l A fast-OR signal from each FEC is sent to the trigger system. l The primary bitmap signal are transferred from parallel to serial, hence reduce significantly the cables. l The width of the shaped signal is 100 ns. 19
Test Result(1) • Group 1 (have been used as a telescope sys. ) 99. 5± 0. 25% 20
Test Result(2) • Group 2(haven’t used) 99. 3± 0. 4% 21
Summary u RPC is economical for a larger area detector u The RPC performance developed by IHEP is excellent, single gap RPC efficiency>95%, noise rate <800 Hz/m 2, dark current <2μA/m 2 u Adopt 3 layers, 2 dimension readout, RPC and module overlapping assembly, no dead space. Adopt choose 2 out of 3 as a hit, their coincidence efficiency >99%, the noises <0. 05 Hz/m 2 u Electronics and readout are same to BESIII Muon detector. 23
Reference 1. 2. Determination of Neutrino Mixing-Angle θ 13 Using the Daya Bay Nuclear Power Facilities,version 3. 1 Preliminary study of Daya Bay reactor neutrino experiment, Yaxuan Sun, Ph. D thesis The end Thanks! 24
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