J-PARC での高輝度 ビームに向けた GEM トラッカーの 開発 小沢 恭一郎 ( 東大・理 ) KEK 測定器開発室 Supported by 科研費

2007/12/14 MPGD K. Ozawa Contents Tokai New J-PARC Tokyo Summary

2007/12/14 MPGD K. Ozawa Linac Do you know J-PARC? Cascaded Accelerator Complex: 3GeV Rapid Cycling (25Hz) Synchrotron 50GeV Synchrotron Materials and Life Science Facility Hadron Hall (Slow Extracted Beams) Neutrino Beamline to Super-Kamiokande

2007/12/14 MPGD K. Ozawa Performance of the 50-GeV PS Beam Energy ： 50 ＧｅＶ (30GeV for Slow Beam) (40GeV for Fast Beam) Repetition: 3.4 ~ 5-6s Flat Top Width ： 0.7 ~ 2-3s Beam Intensity:3.3x10 14 ppp, 15A (2×10 14 ppp, 9A) E Linac = 400MeV (180MeV) Beam Power: 750kW (270kW) Numbers in parentheses are ones for the Phase 1.

2007/12/14 MPGD K. Ozawa Hadron Hall NP-HALL 56m(L)×60m(W)

2007/12/14 MPGD K. Ozawa 50GeV-15μA 、 Ni-54mm 、 BL-Length=50 m 、 Acceptance:2msr% Beam Intensity By H. Noumi

2007/12/14 MPGD K. Ozawa Counting Rate Interaction rate itself is 10 6 Hz However, beam halo can not be ignored What is actual condition at KEK? –350 kHz at the most forward cell of Drift Chamber At radius of 200 mm and the horizontal angle of 6° 3.5mm width and 220 mm height –Mostly from beam halo Extrapolate to J-PARC –10 times higher beam intensity –shorter beam-extraction duration –3.5 MHz is expected. –10 times finer segments are required 0.7 mm pitch x 100mm height That ’ s the main issue for spectrometer design. We have to develop the detector which cope with 10 times larger rate.

2007/12/14 MPGD K. Ozawa Proposed new spectrometer Side view Plain view

2007/12/14 MPGD K. Ozawa GEM Tracker Similar to COMPASS detector –Use 3 layers in magnetic field Extended to cover large acceptance Challenge : –Work properly –Long term stability –Mechanical support with low radiation length –Readout Collaboration with KEK COMPASS detector (NIM A535, 314) Rate issue: COMPASS detector is working Up to 25 kHz/mm 2 (400 m pitch) 5 kHz/mm 2 is expected at J-PARC with 700 m pitch x 100mm height GEM detector may work

2007/12/14 MPGD K. Ozawa Detectors in high counting MWPC limitation –Wire spacing: 1~2 mm –Gain high rate Micro strip gas chamber –Discharge problem Micromegas –Another candidate GEM –Flat gain over 10 5 Hz/mm 2 –I like flexibility of configuration –Good characteristics of signal Signal is generated by electron Not by ion No ion tail and pole cancellation electronics Collaboration with KEK I took these ideas and figures from F. Sauli ’ s presentation at XIV GIORNATE DI STUDIO SUI RIVELATORI Villa Gualino Febbraio 2004 GEM MWPC

2007/12/14 MPGD K. Ozawa Read out configuration Collaboration with KEK Figures from F. Sauli ’ s presentation at XIV GIORNATE DI STUDIO SUI RIVELATORI Villa Gualino Febbraio 2004 Developed by KEK –Ideas by Prof. S. Uno –Use both sides 2-D strip readout configuration NIM A425(1999)254 Developed by CERN

2007/12/14 MPGD K. Ozawa Tokyo Purpose: Develop a GEM tracker Evaluate specifications Position resolution Efficiency Rate dependence Current Configuration: 3 GEM foils p-10 gas 2-D strip Both side 0.8 m pitch Copy of KEK ’ s

2007/12/14 MPGD K. Ozawa Signals We can see signals from both sides. Signal from bottom surface is distorted. Already known problem by KEK group. Strips on top surfaceStrips on bottom surface TOP Bottom Bottom2 Bottom1 TOP1 TOP2

2007/12/14 MPGD K. Ozawa Sum Sum of 3 strips looks reasonable distribution. Position distribution is almost reasonable. Position Charge Distribution (Top) Strip1Strip2Strip3 Fe-55 X-ray Source

2007/12/14 MPGD K. Ozawa New GEM foils SciEnergy GEM foils are very good!! But it ’ s expensive. We ’ d like to use 700 foils Cheaper is better Cheaper foils are being developed by wet-etching method. (Raytech Co., Ltd)

2007/12/14 MPGD K. Ozawa Comparisons Time 100m-GEM + 50 m-GEM (SciEnergy) 340V/50m 50m-GEM - 3 foils (Raytech all 3 lines) p10-gas

2007/12/14 MPGD K. Ozawa Summary At J-PARC, beam line tracker will be GEM based one. In addition, a GEM based spectrometer is proposed to cope with high interaction rate experiment. R&D has started for J-PARC at Tokyo and KEK. GEM tracker with 2-D strip read out is being developed. First brief result of R&D is appeared. New GEM foil is developed to reduce costs. It used wet-etching method and shows similar characteristics with CERN ’ s one.