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Recent Status of GEM at IHEP Beijing

This article discusses the recent status of the Gas Electron Multiplier (GEM) technology at IHEP Beijing, focusing on its application in neutron beam monitoring at the China Spallation Neutron Source (CSNS) project and Beijing Synchrotron Radiation Facilities project. It covers the background, physical design, performance test, and prospects for development of neutron source reactor spallation.

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Recent Status of GEM at IHEP Beijing

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  1. Recent Status of GEM at IHEP Beijing Zhijia SUN, Huirong Qi sunzj@ihep.ac.cn 6th Workshop RD-51, Bari, Oct 8, 2010

  2. Outline • Application of GEM in neutron beam monitor ( China Spallation Neutron Source project ) Yuanbo CHEN, Yigang XIE, Zhijia Sun, Yubin ZHAO, Rongguang LIU, Dong JING, Jianrong ZHOU, Guian YANG, Yanfeng WANG • Status of 2D GEM Detector with Strip Readout( Beijing Synchrotron Radiation Facilities project ) Yuanbo CHEN, Qun OUYANG, Huirong Qi, Xinyu LV, Yubin ZHAO, Hongyu ZHANG, Huayi SHENG, Jian ZHANG, Rongguang LIU, Mingyi DONG, Yigang XIE, Dong JING

  3. Application of GEM in neutron beam monitor (CSNS project) • Background & History • Physical Design • Performance Test • Prospects

  4. Development of Neutron Source Reactor Spallation CSNS

  5. China Spallation Neutron Source (CSNS) CSNS, with the power of 100kW and the pulse repetition frequency of 25Hz, is scheduled to begin operation in September, 2016.

  6. Neutron Beam Monitor Sample • Intensity fluctuations of the incident beam due to the accelerator or reactor power changes • Need beam monitor to correct the experimental data of each neutron scattering instrument • Requirements to meet the need of new generation neutron facilities • Timing resolution(~1μs) Wavelength resolution • Spatial resolution(~1mm) More accurate corrections • High transmission(>95%) & low efficiency(~1‰) least perturbation • Gamma to neutron separation(<10-6)γ insensitivity • High counting rate(~106Hz) High intensity (>108n/ cm2﹒s) Neutron Beam Neutron Guide Neutron Beam Monitor Neutron Detector

  7. History

  8. Why GEM? • Fast signal: ~100ns • High counting rate: 10MHz • Flexible readout: pad, strip, CCD • Convenient to use neutron convertor • Spatial resolution: ~1mm • γ insensitivity • Radiation endurance • Long life • Cost less

  9. Physical Design

  10. Object for Detection • Beam monitor for Spallation or Reactor Neutron Source • Size of Beam: ~4cm*4cm • Flux at Guide Exit CSNS: ~108n/cm2.s(MS, HIPD), ~107n/cm2.s(SANS) Reactor: ~ 107n/cm2.s • Repeated Pulse ~ms, CSNS: 40ms • Wavelength Cutoff with Choppers/Velocity Selector Custom Extent: SANS 0.4~8 angstrom HIPD 0.3~4.8 angstrom MS 1.9~6.2 angstrom

  11. Design Structure neutron Gas ： Ar/CO2 = 70:30 n+10Bα+7Li+2.79MeV 7% Eα=1.78MeV ELi=1.0MeV n+10Bα+7Li* + 2.31MeV 93% τ=73fs α+7Li+γ+2.31MeV Eα=1.47MeV ELi=0.84MeV Cathode plane coatedwith 10B 7Li or α 10B: easy to get, cost less, chemical stability Gain: ~103 Charge input: 0.1~1 pC Pulse: ~100ns wide Drift -e GEM1 With the thin conversion layer, the time and the location of the emitted α or 7Li can be just treated as those of incident neutron. Transfer GEM2 Induction Active area: 50mm*50mm Readout pad: 4mm*4mm, 1mm gap

  12. Neutron Convertor--10B • Due to the multiple Coulomb scattering: • 1) Range of 1.47 MeV α : 3.6μm • Range of 1 MeV 7Li : 2μm (SRIM) • Maximum efficiency (~5%) for thermal neutrons: ~2.5 μm • Low efficiency5‰: ~0.1 μm coated on Cu using evaporation • or sputtering techniques. • Energy of charged particles is extended down. • Thin foil can improve capacity of γ discrimination • 4) Cone emission of α & 7Li Neutron 7Li or α Cu cathode plate 10B 99% α or 7Li 0.1μm 10B 1μm 10B Geant4 Simulation for Thermal Neutron η=3.7% η=5.2‰

  13. Double GEM is enough to α or 7Li (~1MeV) S. Bachmann et al, Nucl. Instr. Meth. A479 (2002) 294

  14. M.C. Simulation(Garfield +Geant4) Geant4 Garfield Root Direction & energy of ions Single electron avalanche Sigma : ~200um

  15. GEM detector • Operation in flow mode with Ar /CO2 (70/30) mixtures at atmospheric pressure to avoid ageing effects . • Range of 1.47 MeV α in the mixture gas is about 6 mm (SRIM). • 3) If the drift gap is chosen corresponding to the range of the ions so as to energy deposited completely in the drift gas volume, the neutron can be detected with maximal pulse-height related to good γ discrimination. • 4) Range of ions and emission direction determine spatial resolution. CERN Standard GEM: 50 µm Kapton 5 µm Copper 70 µm holes at 140 µm pitch

  16. Readout electronics • Pad readout In order to fulfill counting rate 1MHz/cm2 for fast readout, an array of pads is used and the special electronics is being designed in IHEP, each channel of which is independent completely. • Electronics & DAQ • The best solution is ASIC FPGA DAC DAC Counting individually Counting individually Pad Preamplifier +Shaper Discriminator Ethernet &USB Pad Preamplifier +Shaper Discriminator DAQ PC Timing counting Timing counting All channel All channel

  17. Readout

  18. Shielding & Background • Shielding • Al shell  electromagnetism • Boron-rich plastic and Cd  absorbing neutrons • Background • Due to low-Z materials used, counting gas with low density and thin  low probability • Hardly secondary charged particles • Al without neutron activation • High energy of charged conversion products: α and 7Li • Insensitive to γ background

  19. Efficiency Linearity : Flux of incident neutron, : Reaction rate, η: Conversion efficiency S : energy spectrum of incident neutron σ(E) : Cross section with energy Energy Linearity: n : Atomic density of 10B, d: Thickness of 10B Spatial Linearity: Cathode plate 10B d △d Uniform d: if energy spectrum S(E) is uniform in 2-dimensional cross section, Conversion η is constant. Intensity Linearity: Determined by counting rate of detector and readout speed of electronics

  20. PerformanceTest

  21. Prototype Chamber Active area 100mm*100mm The enrichment 92% of boron-10 (mass thickness 1mg/cm2) is coated on one surface of aluminum cathode plate as the neutron convertor with electrophoresis in Beijing 261 Factory so as to obtain the maximum conversion efficiency for irradiation tests. The signal collection plane is a printed circuit board with 96 square pads with each area 8mm×8 mm.

  22. Signals of neutron ~1.5μs A channel directly connected to charge sensitive amplifier (made in IHEP) with sensitivity 500mV/pc. The majority of amplitude is about 100mV. The minority is above 200mV. Noise <3mv 241Am(Be)

  23. Signal induced by α 239Pu α source (1.0×106 Bq , 5.2 MeV α-ray) ~150ns One channel with a current preamplifier (FBPANIK). pulse ~150ns wide. noise <30mV.

  24. Image Test by scanning 239Pu source Discriminator Scaler CAMAC DAQ Pad Pre-amplifier PC A block of 3mm thick steel with a hole of diameter 2mm is used to collimate the emitted α. It is hoped that the spatial resolution about 10mm (FWHM) can be obtained easily with each pad 4mm×4mm

  25. New Prototype Chamber

  26. Next plan • Development of GEM Monitor • Spatial resolution: ~1mm • Active area: custom size. 100mm*100mm, >104channels • ASIC readout • Insensitive to γ • Calibration for energy, intensity and location • Stable for long time • Native GEM, THGEM

  27. Status of 2D GEM Detector with Strip Readout( Beijing Synchrotron Radiation Facilities project ) • 2D GEM Detector • Strip Readout and DAQ • Some Results • Discussion

  28. 50 µm 2D GEM Detector • Standard GEM from CERN • 3- Stages Amplification • Active Area: 200mmX200mm • Reduce the Risk of Damage • Top layer: Four Separate Sectors • Bottom layer: One Sector • Working Gas: Ar/CO2-90/10 • Readout CH: 704 • Working Voltage: ~360V Standard GEM

  29. X-ray Trigger Strip Readout 2D GEM Detector • Trigger Signal from the bottom of third GEM • Drift Distance: 14mm • Transfer Space: 2mm • Induction Space: 2mm • Two Methods for HV • Seven Channels Independent • Resistance Division Seven Channels HV Resistance Division HV

  30. 2 3 3 1 2 1 4 4 2D GEM Detector • 2D GEM Detector Support • Collimator Support • Source Support • X-tube • 55Fe • Synchrotron Radiation • Mounted Support bracket • Distance of 1, 2 and 3 can be adjusted by PC Experimental Platform of 2D GEM Detector

  31. b. Detector and DAQ a. GEM Detector with PreAMP 2D GEM Detector Mounted the 2D GEM Detector System • All of GEM Detector, Experimental Platform, DAQ hardware and DAQ software assembled in May,2010. • Experimental research has been continued to the present.

  32. X Y X Y X Strip Readout • X Direction • Channels of Strips Readout: 267 • Width: 0.193mm • Pitch: 0.752mm • Y Direction • Channels ofStrips Readout: 437 • Strip with PADs connected at bottom layer of PCB • Width: 0.355mm • Pitch: 0.457mm • PAD: 0.355mmX0.355mm Diagram of Y-Strip with PADS

  33. DAQ • DAQ Gate Pulse • Signal from the third GEM • -> PreAMP + Discriminator • -> input to GCAC Board and the output as DAQ gate • GQ Modules • 16 Channels/Module • FPGA +Amplifier/Module • All DAQ Boards mounted in 6U VME crate • Data transfer with PowerPC, Network and Serial Server to PC • DAQ software with LabView and C++ Program Trigger Generation

  34. DAQ Schematic Diagram of All DAQ • 2D Detector System: • GEM Detector • Four VME Crates • Acquisition Computer • GQ Boards: 11×4 • PowerPC: 1×4 • One common Trigger • Preamplifier Boards: 11×4 • Trigger Preamplifier Board: 1 • Fan IN/OUT Boards: 3×4

  35. Some Results • Light Green line • Signal of One trip (x) from Preamplifier1@IHEP • Red line • Signal of Trigger from Preamplifier2@IHEP • Test with 55Fe Source • Source: 55Fe • Energy: 5.9keV • Detector: Triple GEM • Voltage: 360V/360V/360V • PAD of Readout: 30mmX30mm • Collimator: Φ2mmX12mm - Cu • Energy Resolution:~24%

  36. Some Results Select the Optimum Time Windows to Involve All the Pulse Peaks Peak of FADC Time windows Selection of Optimum Time Windows for Pulse Peak Out of time window DAQ Sequence of Signal, Trigger • Yellow line • Signal of One trip (x) with PreAMP and Main AMP • Red line • Signal of Trigger with Preamplifier and Discriminator • Search peak of Pulses Window starting time VS Peak of Pulses

  37. 55Fe X-ray Source(Gause Distribution) Comisc Ray(Landau distribution) Count Rate: 7~8/s Count Rate: ~720/s Some Results Energy Spectrum of 2D GEM Detector Energy Resolution: ~22%@ 5.9 keV 55Fe Source GEM Detector GEM Detector Count Count Charge(fc) Charge(fc)

  38. Count Number of Strip in X Count Number of Strip in Y Some Results Hit profile of One Event@55Fe X-ray Source X Y 55Fe Source Position Resolution: δx ~162um@ ; δy ~211um

  39. Count Number of Strip in X Count Number of Strip in Y Some Results Hit profile of One Event@Cosmic Ray X Y Cosmic Ray

  40. Some Results 2D GEM Detector testCluster Size - Charge Distribution on Adjacent Strips Chamber Number of the strip per Event • Average of Cluster Size: ~Φ2.5mm • Effective Trigger: 99.7±0.01% • GAS: Ar-CO2(90-10) • GEM1/GEM2/GEM3:330V/330V/320V • Drift/Tran.1/Tran.2/Indu.: 1.8/3/3/5kV/cm • To get the true particle position: • The centre of gravity of the recorded charge profiles • More fire numbers of Y than X

  41. 751.8 193 558.8 101.6 457.2 355.6 Some Results Unit:mm Cluster Size Profile on Readout PCB (Based on the real size) • Various cluster locations cover different X and Y strip numbers • See Red and Blue circles • To increase the cluster size, • Select large transverse diffusion working gas • Optimized electric field of drift region

  42. Some Results 2D GEM Detector Image with 55Fe Source • 55Fe X-ray Source located on the Detector with Cu Collimator • GAS: Ar-CO2(90-10) • GEM1/GEM2/GEM3:330V/330V/320V • Drift/Tran.1/Tran.2/Indu.: 1.8/3/3/5kV/cm Hole of Cu Collimator Φ2mmX12mm Cross of Cu Collimator 0.5mmX20mm/0.5X20mm More Experiments are continuing……

  43. Voltage of X-Tube Discussion HV • Two Methods for HV • Seven Channels Independent (Working with X-tube is ok!) • Resistance Division (Saturation effect working with X-tube) R1 R2 R3 R4 R5 R6 R7 R8 GND Current meter *R=R1=R2=R3=R4=R5=R6=R7=R8=30MΩ Setup of 2D GEM Detector with X-tube Saturation effect happened here, but the anode current is too small?

  44. Discussion • Anode Current with different value of Resistance • Value–R : 30MΩ -> 5MΩ -> 2MΩ -> 1MΩ • Saturation effect: Serious->………………………..-> Less • Under very high rate or high beam conditions, saturation effect obvious. • Positive ion accumulation serious causing high voltage deduction and gain decrease. • Reduce the recovery time to dissipate the positive ions

  45. Summery • Application of GEM in neutron beam monitor ( China Spallation Neutron Source project ) • Prototype was studied by neutron source and  source. The results show the detector could get our physical design. • Plan to upgrade the electronics to ASIC • Status of 2D GEM Detector with Strip Readout( Beijing Synchrotron Radiation Facilities project ) • All of GEM Detector, Experimental Platform, DAQ hardware and DAQ software assembled in May,2010 • Experimental research has been continued to the present. • Several main parameters was obtained • Many ideas and works in our future schedule

  46. Thank you very much ! Grazie !

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