GEM Detector Shoji Uno KEK

2 Wire Chamber Detector for charged tracks Popular detector in the particle physics, like a Belle-CDC Simple structure using thin wires

3 Gas amplification near anode wire High electric field (>30kV/cm) can be obtained easily due to using thin wire (diameter ~0.03mm) Energy of electron become higher for high electric field near wire. Electron can produce another electron for ionization. Number of electrons increases due to multi steps of this process. (gas amplification 、 electric avalanche) Gas gain up to ~10 5 can be obtained easily. Electron Anode wire

Recent gas chamber Requirement –High incident rate One wire covers wide region. –Wire spacing > ~1mm – Length >~10cm Need more space –Pure two-dimensional readout –Wire has some limitation due to straight wire LHC ATLAS

Limitation of wire chamber

New development Development MPGD （ Micro Pattern Gas detector) –Gas multiplication in high electric field with other than wire – 3 types MSGC （ Micro Strip Gas Chamber ） MICROMEGAS （ Micromesh Gaseous Detector ） GEM （ Gas Electron Multiplier ）

GEM (Gas Electron Multiplier) Hole diameter 70  m Hole pitch 140  m Thickness 50  m Cu thickness 5  m Electric field Developed by F.Sauli (CERN) in NIMA 386(1997)531 Double side flexible printed circuit board

Flexible shape Fabio Sauli

Configuration for GEM detector Readout

Multi-layer

High counting capability ワイヤーチェンバー GEM

Application of GEM Feature of GEM –Pure two-dimensional readout → Image –Multi-layer structure Stable operation Multi-conversion-layer (Neutral  Charged) –High counting capability GEM can be applied for many other fields, not only high energy physics.

TPC

X-ray detector X-ray absorption tomography Crystal structure analysis using X-ray

Photon sensor Same function for photomultiplier Usable in Magnetic field Fine segmentation in readout Cheap and Larger Key issue is photo-electric surface in gas volume. Under developement

Basic property of GEM chamber

Test Chamber GAS Ar-CH 4 (90/10) (P-10) Ar-CO 2 (70/30) 2200pF ～ 2 mm 10 mm GEM1 GEM2 GEM3 ～ 2 mm 55 Fe (5.9 keV X-ray) DRIFT TRANSFER 1 TRANSFER 2 INDUCTION PCB 36 ＝ 6×6 1mm □15mm×15mm PCB

Pulse shape Signal from Readout pad Signal from GEM foil 200ns 130mV

Effective gas gain and resolution Ar-CO 2 P10 Number of events Sigma/Mean = 8.8%  V GEM =325V E drift = 0.5kV/cm E transfer = 1.6kV/cm E induction = 3.3kV/cm 55 Fe ADC counts Pedestal=104.6 Ar-CH 4 (90/10)

Gas gain vs various parameters P10 Ar-CO 2 P10 Ar-CO 2 EDED EIEI ETET EIEI

ΔV GEM =360V E T =1.6kV/cm E I =3.6kV/cm ΔV GEM =360V E T =1.6kV/cm E I =3.6kV/cm Electric field dependence in drift region 55 Fe (5.9 keV X-ray) EDED Ｄｒｉｆｔ region E D =3000V/cm E I =1000V/cm E D =500V/cm E I =1000V/cm In case of weak field In case of strong field Δ Ｖ ＧＥＭ ＝３２０Ｖ Ionization occurs in drift region Electrons enter into GEM holes. Collection Efficiency Electric field (kV/cm)

Charge distribution ADC counts 0 63 Channel One event ｄ X （各 strip － C.O.G) σ ＝ 359.7±0.4 μm P10 ΔVgem ＝３３０ V Ed= 0.5 kV/cm Et=1.65 kV/cm Ei= 3.3 kV/cm ΔVgem ＝３３０ V Ed= 0.5 kV/cm Et=1.65 kV/cm Ei= 3.3 kV/cm ADC SUMADC Normalized ADC counts ｍｍ ΔVgem ＝３７０ V Ed= 0.5 kV/cm Et=2.59kV/cm Ei=5.18 kV/cm ΔVgem ＝３７０ V Ed= 0.5 kV/cm Et=2.59kV/cm Ei=5.18 kV/cm σ ＝ 181.2±0.3 μm Ar-CO 2 (70/30) Normalized ADC counts ｄ X （各 strip － C.O.G) ｍｍ dX (each strip – C.O.G)

P10 Ar-CO mm/√cm 0.258mm /√cm Charge spread Diffusion is dominant factor. P10 Ar-CO 2 MagBoltz

Application of GEM Shoji Uno (KEK-DTP)  Neutron detector  X-ray detector  Soft X ray  Hard X ray  Light

Application to Neutron Detector Normal GEM B10 coated GEMs Readout board Cathode plate With B10 Ar-CO 2 Expensive 3 He Gas is not necessary. –No pressure vessel Free readout pattern High resolution –Position and Time Insensitive against g-ray Capability against high counting rate

Chamber structure 1 mm ( 0.5mm ) Readout strip 2 mm 1 mm E I = 4.0kV/cm GEM 2 E T = 2.2 kV/cm E D = 1.5 kV/cm Ar/CO 2 = 70:30 GEM 1 1 mm 2 mm B GEM 1 B GEM 2 E T = 1.5 kV/cm Al - 10 B cathode 150V (75V) 150V 240V 150V 400V 440V 370V 800V X(120) +Y (120) strips 0.8mm pitch Thickness of Boron-10 : 4.4  m 2.0  m  m ×4 8 mm

Ethernet GEM Chamber I/F –One HV cable –Three LV cables –One Ethernet cable Electronics –8 ASIC chips + 1 FPGA FE2009 ASIC : KEK-DTP Data transfer and Control through Ethernet –SiTCP by T. Uchida （ KEK ） –Using Note-PC Present Detector System Low Voltage Electronics Compact and Portable System T.Uchida et. al., "Prototype of a Compact Imaging System for GEM detectors," was published on IEEE TNS 55(2008)2698.

(Å ) 11 Data samples (Å) L = mm ~ 18.8 m L: distance from the source to the detector The beam profile and its TOF distribution An image of a cadmium slit and its TOF distribution L = mm 27 mm 60 mm The thickness of the slit ~0.5 mm This image is produced with a wavelength cut. Events from 1.5 Å to 8 Å are selected Our system can obtain a 2D image and its TOF at the same time. Cd cutoff

Energy Selective Neutron Radiography Bragg Edge region (Thermal and cold) Resonance absorption region (E>1eV)

Resonance absorption imaging By T. Kai (JAEA) et al. at BL10 in J-PARC

One more demonstration EURO coin TEST Sample gold coin Ratio of ToF spectrums with/without sample Imaging data with around 450  sec ToF