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Property of LCP-GEM in Pure Dimethyl Ether under Low Pressure

Property of LCP-GEM in Pure Dimethyl Ether under Low Pressure. RIKEN / Tokyo Univ. of Sci. Yoko Takeuchi takeuchi@crab.riken.jp. T. Tamagawa A , T. Kitaguchi A , W. Iwakiri A , F. Asami A , B , A. Yoshikawa A.B , K. Kaneko A,B ,T . Enoto A,C , A. Hayato A , Y . Kohmura D ,

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Property of LCP-GEM in Pure Dimethyl Ether under Low Pressure

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  1. Property of LCP-GEM in Pure Dimethyl Ether under Low Pressure RIKEN / Tokyo Univ. of Sci. Yoko Takeuchi takeuchi@crab.riken.jp T. TamagawaA, T. KitaguchiA, W. IwakiriA, F. AsamiA,B, A. YoshikawaA.B, K. KanekoA,B,T. EnotoA,C, A. HayatoA, Y. KohmuraD, and The GEMS/XACT team RIKENA，Tokyo Univ. of Sci.B，NASA/GSFCC，KogakuinUniv.D 1 MPGD 2013 @Zaragoza

  2. 1-1.Cosmic X-ray Polarimetry Observation of cosmic X-ray objects image Polarization Energy time variation ？ Few significant detection of X-ray polarization. History of X-ray polarimetry year mission type 1972’ Sounding Rocket (Norvick+1972) Bragg 1976’ OSO-8 satellite(Weisskopf+1976, 78) Bragg ==No mission since 1970’s == Plan to mount polarimeter on sounding rocket • Cosmic X-ray Polarimeter Developed • Using GEM-TPC technique • Sensitivity with > 100 times higher than ever before. 2 MPGD 2013 @Zaragoza

  3. 1-2. XACT rocket Experiment Mirror Focal length 2.8 m • X-ray Advanced Concepts Testbed • NASA’s sounding rocket program • Scheduled to be launched in 2015 • Energy range : 1-10 keV • Observation time　：〜 6 min • Target : Crab Nebula XACT rocket 2.8 m [K. Gendreau + 2012] GEM-TPC polarimeter • One of the brightest X-ray objects • Only X-ray polarized source detected • by Bragg polarimeter so far • Strong X-ray emission around 2 keV • Using photoelectric effect 3 MPGD 2013 @Zaragoza

  4. 1-3. Photoelectric Effect • Photoelectric Effect • Direction of X-ray polarization : • E of the incident X-ray • distribution of photoE emission : • Polarization can be measured • by photoEdistribution. • Sensitive to only linear polarization X-ray E cos2Φ Φ PhotoE Track θ 4 MPGD 2013 @Zaragoza

  5. 1-3. GEM-TPC X-ray Polarimeter Trigger Drift Electrode [ Black +2007 ] GEM - Single GEM - Strip pitch : 121 μm - Readout ASIC: APV25 (20 MHz sampling) Photoelectron 2D photoE track image Readout strip Gas Electron Multiplier (LCP-GEM) y：strip [Tamagawa+ 2009] 70 um 140 um • About LCP-GEM, • See Tamagawa’sTalk (7/3 12:30). opt axis LCP x：time Thickness :100 um developed at RIKEN 5 MPGD 2013 @Zaragoza

  6. 1-3. GEM-TPC X-ray Polarimeter Trigger Drift Electrode [ Black +2007 ] GEM - Single GEM - Strip pitch : 121 μm - Readout ASIC: APV25 (20 MHz sampling) Photoelectron 2D photoE track image Readout strip requirement for property of target gas slow drift velocity …… coarse sampling with APV25 small diffusion.…… avoid blurring track image y：strip opt axis target gas: Pure Dimethyl Ether (DME) x：time 5 MPGD 2013 @Zaragoza

  7. 1-4. Requirement of Polarimeter DME pressure is optimized by calculating track length and count rate. • As pressure goes down, • -track length increases • -count rate decreases • We estimate optimum • pressure range by simulation. Track length (2 keV)[mm] Count Rate [/sec] Optimum pressure range : 50-150 Torr DME Pressure[Torr] LCP-GEM has NOTbeen operated under low pressure in DME. 6 MPGD 2013 @Zaragoza

  8. 1-4. Requirement of Polarimeter DME pressure is optimized by calculating track length and count rate. • As pressure goes down, • -track length increases • -count rate decreases • We estimate optimum • pressure range by simulation. Track length (2 keV)[mm] Count Rate [/sec] Optimum pressure range : 50-150 Torr Our study DME Pressure[Torr] Measure property of LCP-GEM in Pure DME under low pressure - Gain curve sufficient gain without discharge - Energy scale check linearity - Lower pressure limit of normal GEM operation LCP-GEM has NOTbeen operated under low pressure in DME. 6 MPGD 2013 @Zaragoza

  9. 2-1. Experimental Setup ・ Single LCP-GEM ( 30 mm x 78 mm x 0.1 mm ) ・ Constant drift velocity, 0.24 um/ns ex.) Ed = 196 V/cm at 190 Torr ・ To avoid electron amplification in the induction region, Ei is set suitable value. ・ Signals are read from pad & GEM anode ・ DME pressure: 10-190 Torr ・ X-ray beam from X-ray generator - Collimated with Φ200 μm - Parallel to LCP-GEM - Energy : * 6.4 keV (gain curve) * 4.5, 6.4, 8.0 keV (Energy scale) pure DME 10 ~ 190 Torr Vd Drift electrode Vc 20.5 mm Ed 10 MΩ X-ray LCP-GEM ΔVGEM 10 MΩ Ei 1 mm readout pad R3 preamplifier ORTEC 109PC ADC preamplifier AMPTEK A225 7 MPGD 2013 @Zaragoza

  10. 3-1. Gain Curve • One data : 30000 event • At 190 Torr • - Exponential function • Maximum gain :~ 20000 • (ΔVGEM=560 V) • w/o discharge rate of 0.1% • - ΔE/E(FWHM) ~20 % readout pad 190 Torr Effective Gain Next slide, gain curves <190 Torr Please check the point !! - function shape - maximum gain ΔVGEM 8 MPGD 2013 @Zaragoza

  11. 3-1. Gain Curve • One data : 30000 event • At 110 Torr • - Non exponential function • - Maximum gain :~ 20000 • (ΔVGEM=520 V) readout pad 110 Torr 190 Torr Effective Gain ΔVGEM 8 MPGD 2013 @Zaragoza

  12. 3-1. Gain Curve • One data : 30000 event • At 70 Torr • - Non exponential function • - Maximum gain :~ 10000 • (ΔVGEM=500 V) readout pad 110 Torr 190 Torr 70 Torr Effective Gain ΔVGEM 8 MPGD 2013 @Zaragoza

  13. 3-1. Gain Curve • One data : 30000 event • At 50 Torr • - exponential function • - Maximum gain :~ 5000 • (ΔVGEM=510 V) readout pad 70 Torr 110 Torr 190 Torr 50 Torr Effective Gain ΔVGEM 8 MPGD 2013 @Zaragoza

  14. 3-1. Gain Curve • One data : 30000 event • At 40 Torr • - Non exponential function • - Maximum gain :~ 2000 • (ΔVGEM=500 V) readout pad 70 Torr 110 Torr 190 Torr 50 Torr Effective Gain 40 Torr ΔVGEM 8 MPGD 2013 @Zaragoza

  15. 3-1. Gain Curve • One data : 30000 event • At 30 Torr • - Non exponential function • - Maximum gain :~ 1000 • (ΔVGEM=490 V) readout pad 70 Torr 110 Torr 190 Torr 50 Torr Effective Gain 40 Torr 30 Torr ΔVGEM 8 MPGD 2013 @Zaragoza

  16. 3-1. Gain Curve • One data : 30000 event • At 20 Torr • - Non exponential function • - Maximum gain :~ 300 • (ΔVGEM=470 V) readout pad 70 Torr 110 Torr 190 Torr 50 Torr Effective Gain 40 Torr 30 Torr 20 Torr ΔVGEM 8 MPGD 2013 @Zaragoza

  17. 3-1. Gain Curve readout pad 70 Torr 110 Torr 190 Torr • Difference of each gain curve • 1) Slope and offset of curve • 2) Non exponential<110 Torr 50 Torr Effective Gain 40 Torr 30 Torr 20 Torr • The pressure dependence of gain curve seems complex. • To understand this behavior of gain curve, • we derived the first Townsend coefficient α ΔVGEM 9 MPGD 2013 @Zaragoza

  18. 3-2. The First Townsend coef. α/p vs. E/p definition：　 ● α[/cm]・・・ ※Gain=Gainpad+GainGEMano. This is why we wanted to collect all of the amplified electrons in the GEM channels ● E [V/cm]・・・ ΔVGEM/GEM thickness (100 μm) α= ln (Gain)/xGEM 20Torr xGEM：100 μmfix (GEM thickness) 50Torr 70 Torr 30Torr ) ( 40Torr 110 Torr 190 Torr α/ p [ /cm/Torr] fitting by α/p = A × exp( -B p/E ) The data is well fitted by the empirical formula. E / p [V/cm/Torr] 10 MPGD 2013 @Zaragoza

  19. 3-3. Measured αvs. MAGBOLTZ MAGBOLTZ Experimental Data MAGBOLTZ parameters p=10 - 190 Torr E=10 - 60 kV/cm α/p[ /cm/Torr] [Sharma + 1993] • Experimentally-measured αgrossly agree with MAGBOLTZ’s result. • Although the GEM and parallel plate are different each other, • both results are well fit to the MAGBOLTZ estimation. E/p[V/cm/Torr] 11 MPGD 2013 @Zaragoza

  20. 3-4. Linearity of Energy Scale At 30 Torr incident Energy 4.5 keV (Ti) 6.4 keV (Fe) 8.0 keV (Cu) ● gain ~700 ● gain ~500 gain ~400 ● Measured Charge Q [fC] gain ~300 gain ~200 Incident Energy [keV] • Charge Q[fC]∝ incident Energy • Operated in proportional region • Linear energy scale above 30 Torr. 12 MPGD 2013 @Zaragoza

  21. 3-5. Odd Pulse Profile at 10 Torr We challenged to operate LCP-GEM at much lower pressure. Preamp-out signalcaptured by an oscilloscopefrom readout pad the signal profiledramatically changed above ΔVGEM= 437 V. ΔVGEM= 440 V ΔVGEM= 437 V ΔVGEM=430 V 10 us 5 sec 4 ms 4 mV 200 mV Normal signal 200 mV * duration: 1~10 ms * pulse height : ~200 mV * duration : ~10 μs * pulse height : 4 mV （gain ~40) * duration: 2~5 sec * pulse height: ~200 mV ※ No Signal when X-rays were stopped. ==> Those signals were triggered by X-rays. 13 MPGD 2013 @Zaragoza

  22. 3-6. GEM operated in Geiger region? We understand from those signal of oscilloscope, Proportional region Geiger region Ion chamber region 1)Change of pulse profile at 10 Torr - longer duration time - higher pulse height 2) As ΔVGEMgets higher, -longer duration -almost same pulse height Charge collected High voltage and/or low pressure E/ P[V/cm/Torr] Observation results suggest that GEM are probably operated in the Geiger region. The operation mode of gas chamber transits from the proportional region to the Geiger region. 14 MPGD 2013 @Zaragoza

  23. 4. Summary • We have developed Cosmic X-ray polarimeter using GEM-TPC. • Polarimeterrequirementof DME pressure : 50 – 150 Torr • We measured the properties of LCP-GEM in pure DMEat low pressure. • - gain curve (10-190 Torr) .. The data is well fitted by empirical formula. • - Energy scale (4.5-8.0 keV) … Linear from 30 to 190 Torr. • - Odd pulse phase at 10 Torr …GEM are probably operated in the Geiger region. • LCP-GEM can be operated in proportional region at pressure of 50-150 Torr. 15 MPGD 2013 @Zaragoza

  24. Thank you for your attention !!

  25. Backup side!

  26. LCP-GEM Performance Gain curve LCP-GEM (t100 um) is achieved higher gain than one of t50 um as same ΔVGEM. ArCO2(70%:30%) gas flow, 55Fe single double LCP-GEM(d/p/t: 70/140/100 um) Effective Gain ArCO2(70%:30%) gas flow, 55Fe LCP-GEM(d/p/t: 70/140/50 um) CERN GEM (d/p/t: 70/140/50 um) 500 700 800 600 relative gain LCP-GEM (d/p/t: 70/140/50 um) ΔVGEM/100 um (V) Time variation Gain of LCP-GEM does not change. 400 1000 800 200 600 elapsed time after HV ON (min)

  27. Drift Velocity of Electron (MAGBOLTZ Calculation) Ar-CO2(70%:30%) DME CO2 0.24 DME gas is very slow gas !!

  28. Drift velocity of electron and ion (Magboltz Calculation) electron Ar-CO2 Ar-CO2 DME Ion DME

  29. Discharge Point • ＊discharge point : • the highestΔVGEM • without discharge rate 0.1 % • ＊Paschen curve of DME is • non data. • ＊Discharge point is similar • with Paschen curve. Breakdown Voltage [V] P・d [Torr cm] ※calculation as d=100 μm(GEM thickness)

  30. Energy Resolution

  31. Energy Resolution

  32. Table of Ed & Ei Vd Drift electrode Vc 20.5 mm Ed 10 MΩ LCP-GEM 10 MΩ Ei 1 mm readout pad R3 preamplifier ORTEC 109PC ADC preamplifier AMPTEK A225

  33. Detection Efficiency in the DME gas & Effective Area of X-ray Mirror X-ray

  34. 2D Electron Track Image Direction of X-ray Polarization Strip (121 um pitch) photoE distribution - APV25 (20 MHz sampling) - Drift velocity : 0.24 um/cm

  35. Electron Track Length (Tabata + 1972 )

  36. Polarimeter Design for XACT Effective area : 31.6 cm Close chamber With MXS (Modulated X-ray Source)

  37. Gain Curve at 10 Torr • One data : 30000 event • At 10 Torr • Only one data point • - Maximum gain :~ 40 • (ΔVGEM=430 V) • Strange signal appear • at ΔVGEM> 437 V readout pad 70 Torr 110 Torr 190 Torr 50 Torr Effective Gain 40 Torr 30 Torr 20 Torr 10 Torr ΔVGEM

  38. Energy scale at 190 Torr incident Energy 4.5 keV (Ti) 6.4 keV (Fe) 8.0 keV (Cu) ● gain 7500 ● gain 4300 ● gain 2500 gain 600 gain 350 • charge Q[fC]∝ incident Energy • At 190 Torr, Operated in proportional region

  39. Townsend coef. vsEi at 190 Torr [Y. Takeuchi 2011] α[/mm] Ei [V/cm]

  40. CROSS SECTION of DME Ionization

  41. ADC Spectrum Incident energy: 6.4 keV At 70 Torr dVGEM= 460 V

  42. Future Works Linearity of Energy Scale at 30 Torr Future plan is measurement of the energy scale. In MPGD - below 30 Torr…. check linearity In XACT mission, X-ray emission of Crab Nebula is strong around 2 keV - with less than 4.5 keV X-rays at 10-190 Torr.

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