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Radiation Detectors Based on Gas Electron Multipliers. A. Buzulutskov. Budker Institute of Nuclear Physics, Novosibirsk. Outline - Principles and basic properties of GEMs - Cryogenic avalanche detectors - Tracking detectors - Other detectors - Summary.

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Radiation Detectors Based on Gas Electron Multipliers

A. Buzulutskov

Budker Institute of Nuclear Physics, Novosibirsk


- Principles and basic properties of GEMs

- Cryogenic avalanche detectors

- Tracking detectors

- Other detectors

- Summary

A. Buzulutskov, Instr08, 1/03/08


Gas Electron Multiplier (GEM) properties

GEM: Gas Electron Multiplier,

invented by F.Sauli in 1996

[F.Sauli, NIM A 386(1997)531]

  • High rate capability
  • High gain
  • Low discharge rate
  • High space resolution
  • High time resolution
  • Reasonable energy resolution
  • Low ageing rate
  • Low material budget
  • Geometrical flexibility
  • Variety of readout structures
  • Ion backflow reduction
  • Photon feedback reduction
  • Operation in pure noble gases
  • Operation at cryogenic temperatures
  • Operation in two-phase mode
  • Low noise
  • Coupling to photocathodes

A. Buzulutskov, Instr08, 1/03/08


Operation principles

Real gain

Effective gain

Field strength along hole axis at different hole diameters [GDD-CERN]

Effective and real GEM gain [GDD-CERN]

Field pattern [GDD-CERN]

Triple-GEM structure[Novosibirsk & Weizmann]

A. Buzulutskov, Instr08, 1/03/08


Double mask process requires +-2 mm accuracy and therefore is possible for up to 40x40 cm2 area

A. Buzulutskov, Instr08, 1/03/08


Other hole-type structures:Micro-hole and strip plate (MHSP) [Coimbra]

[Veloso et al., Rev. Sci. Instr. 71(2000)2371]

  • -Amplification occurs first in thehole and then near the microstrip anode
  • MHSP:
  • is two-stage structure and therefore has higher gain than single GEM
  • has lower ion backflow
  • can be usedboth independently and as stages of a multistage GEM

A. Buzulutskov, Instr08, 1/03/08


Other hole-type structures:Thick GEM (THGEM) [Weizmann, CERN]


Hole diameter d = 0.3 - 1 mm

Pitch a = 0.7- 7 mm

Thickness t = 0.4 - 3 mm

See A. Breskin talk

30 mm

[Shalem et al. NIM A558 (2006) 475]

Manufactured by standard PCB techniques of precise drilling in G10 (and other materials) and Cu etching.

  • Easy to produce
  • Higher gain in a single stage structure due to larger thickness and rim
  • Higher resistance to discharges due to smaller hole number and larger hole length
  • The possibility of cascading
  • THGEM can replace GEM when the high space resolution and high rate capability is not necessary

A. Buzulutskov, Instr08, 1/03/08


Other hole-type structures:Thick GEM with resistive electrodes (RETHGEM) [CERN]

Photo of RETHGEM made of resistive kapton

[Oliveira et al. NIM A 576 (2007) 362]

Photo of RETHGEM produced using screen printing technology [Peskov et al.]

RETHGEM has the same properties as that of THGEM + even higher resistance to discharges due to lower discharge energy and higher resistance of electrode material evaporated on hole surface during discharge

A. Buzulutskov, Instr08, 1/03/08


Gain characteristics

Triple-GEM vs. double- and single-GEM gainDischarge probability induced by alfa-particles[GDD-CERN]

Triple-GEM gain in mixtures with quenching additives [Novosibirsk & Weizmann]

A. Buzulutskov, Instr08, 1/03/08


Space, time and energy resolution

5.3 ns

9.7 ns

  • = 2 ns
  • = 40 µm

200mm pitch

4.8 ns

4.5 ns

  • = 69.6 µm

400mm pitch

Space resolution [GDD-CERN]

Time resolution for tracks [Frascatti]

Time resolution for photons in 3GEM-based GPM in CF4[Weizmann & Novosibirsk]

Energy resolution [GDD-CERN]

Space resolution [COMPASS]

A. Buzulutskov, Instr08, 1/03/08


Rate capability and ageing


Triple-GEM [Frascatti]

A. Buzulutskov, Instr08, 1/03/08

Triple-GEM [Frascatti]


Discharge rate

Efficiency and signal-to-noise ratio as functions of gain in triple GEM with 2D readout at PSI pion beam [Novosibirsk]

Discharge probability as a function of gain in three-stage structure, 3GEM, and two-stage structures, 2GEM and GEM+m-Groove. Test at PSI 300 MeV/c pion beam.[Novosibirsk & CERN]

- Two-stage structures do not provide efficient operation beforethe onset of discharges

- Only the triple-GEM satisfies this criterion

A. Buzulutskov, Instr08, 1/03/08


Operation in pure noble gases: GEMs

Unique ability of GEM-like structures No other gas avalanche detectors can do this !

Triple-GEM gain at high pressures: - High gain in light noble gases up to 15 atm- High gain in heavy noble gases at 1 atm- Fast gain decrease with pressure in heavy noble gases [Novosibirsk]

High gain of the triple-GEM in Ar-based mixtures at 1 atm [Novosibirsk & Weizmann]

High gain of the triple-GEM in noble gases at cryogenic temperatures [Novosibirsk & Columbia Un.]

A. Buzulutskov, Instr08, 1/03/08


Operation in pure noble gases: MHSPs and THGEMs

See A. Breskin talk

RETHGEM gain in pure Ar at 1 atm: - High gain both at room and cryogenic temperatures[Peskov et al. IEEE TNS 50(2007)1784]

MHSP gain in pure noble gases at high pressures: - High gain in Ne at all pressures- High gain in heavy noble gases at 1 atm- Slower gain decrease with pressure in heavy noble gases compared to the triple-GEM[Coimbra & Weizmann]

THGEM gain in pure Ar and Xe: - High gain at 1 atm- Fast gain decrease with pressure[Weizmann & Coimbra]

A. Buzulutskov, Instr08, 1/03/08


Ion backflow (IBF)

See A. Lyashenko talk

Reduction of ion backflow in high magnetic field in the triple-GEM. Gain 104, drift field 0.2 kV/cm, asymmetric transfer fields [Aachen]

  • IBF is independent of gas mixture - IBF is linear function of the drift field- IFB is a polynomial function of the gain[Novosibirsk]

A. Buzulutskov, Instr08, 1/03/08


GEM in current, ready for operation and future experiments

Cryogenic experiments for neutrino and dark matter physics:E-bubble ArDMSLICECoherent neutrino scattering

Tracking experiments:COMPASSLHCb muon detectorSystem of Tagged Electrons for KEDRTOTEM telescopeNA49 upgradeCLOE2 vertex detectorILC TPC

Cherenkov detectors:Hadron Blind Detector forPHENIX experiment at RHIC

Current R&D:Two-phase avalanche detectorsHigh-pressure detectors MHSPTHGEMRETHGEMPixel readoutGas PMTMedical applications

Synchrotron radiation experiments:OD4

A. Buzulutskov, Instr08, 1/03/08


Cryogenic two-phase Ar or Xe avalanche detectorsMotivation: dark matter search and coherent neutrino scattering

ArDM: Two-phase Ar detectors for dark matter search using THGEM readout

[A.Rubbia et al., Eprint hep-ph/0510320]

Need for detector recording both ionization and scintillation signal with a threshold of ~10 keV (200 electrons)

Two-phase or high-pressure Ar or Xe detectors for coherent neutrino-nucleus scattering

[Hagmann & Bernstein, IEEE TNS 51 (2004) 2151]

Need for noiseless (1 event/hour/kg)

detector with a threshold of 1 e (single-electron counting)

A. Buzulutskov, Instr08, 1/03/08


Two-phase avalanche detectors The concept and experimental setup [Novosibirsk]

The concept of two-phase avalanche detector with detection both ionization and scintillation signals, using multi-GEM multiplier with CsI photocathode on top of first GEM

A. Buzulutskov, Instr08, 1/03/08


GEM-based two-phase avalanche detectors: properties [Novosibirsk]

See D. Pavlyuchenko talk

See F. Balau poster

Triple-GEM gain in two-phase mode:

- In Ar: rather high gains are reached, of the order of 104

- In Kr and Xe: moderate gains are reached, about 103 and 200 respectively

Triple-GEM pulse-height spectra in two-phase Ar for 60 keV X-rays, neutrons+gammas from 252Cf and single electrons at gains~4000-5000

Triple-GEM with CsI PC in two-phase Ar:

Distribution of events in the plane “ionization (S2) vs. scintillation (S1) signal” amplitudes at gain~2500 and drift field 0.25kV/cm. Most events are of the “S1+S2” type where S1 and S2 are observed and correlatedto each other.

Triple-GEM single electron spectra in two-phase Ar:

- At gains>4000 good separation from electronic noises

- Described by exponential function

A. Buzulutskov, Instr08, 1/03/08


Triple-GEM vs. double-THGEM in two-phase Ar avalanche detectors [Novosibirsk & Weizmann]

See D. Pavlyuchenko talk

Typical signal of thin triple-GEM induced by 60 keV X-ray. Fast and slow emission through liquid-gas interface is distinctly seen.

Typical signals of double-THGEM induced by 60 keV X-ray, corresponding to 1000 e prior to multiplication, and by cluster of 50 e prior to multiplication. Fast component is not seen due to slow ion movement through holes.

Stable operation in two-phase Ar:

- Thin triple-GEM with gains reaching 104

- Double-THGEM with gains reaching 3x103

A. Buzulutskov, Instr08, 1/03/08


Cryogenic He and Ne avalanche detectors at low T

Motivation: E-bubble project for solar neutrino detection

[Columbia Un. & BNL]

  • 10 tons mass of He or Ne- Excellent (sub-mm) spatial resolution for low energy tracks- To maintain this, need very low diffusion, namely electrons localized in bubbles (e-bubbles)- Need for some gain, obviously in gas phase

A. Buzulutskov, Instr08, 1/03/08


Cryogenic avalanche detectors at low T: experimental setup

- Developed at Columbia Un. & BNL

- Operated in He and Ne

- 1.5 l cryogenic chamber

- Several UV windows

- 3GEM inside [Novosibirsk]

- Gas filling through LN2 or LHe reservoir

A. Buzulutskov, Instr08, 1/03/08


Cryogenic avalanche detectors at low T: gain drop problem

[Columbia Un. & Novosibirsk]

In He:

- High gains in 3GEM at T > 78 K

- At 2.6-20 K the maximum gain drops considerably: it is only few tens at 0.5 g/l and drops further at higher densities

In Ne:

- High gains in 3GEM at room T

- At cryogenic T GEMs could not work at all

High gains observed in He and Ne above 78 K are most probably due to Penning effect in uncontrolled impurities, which freeze out at lower T

A. Buzulutskov, Instr08, 1/03/08


Cryogenic avalanche detectors at low T: solution of the gain drop problem using Penning mixtures in H2

Ne and He forms Penning mixtures with H2 at low T:

- H2 boiling point (20 K) is below that of Ne (27 K)

- Energy of metastable Ne state exceeds H2 ionization potential

This is a solution of the gain drop problem at low T in Ne. Unfortunately, this does not work for two-phase He, since H2 vapor pressure is too low at He boiling point (4.2 K)

[Columbia Un. & Novosibirsk]

  • Gains in Ne+H2 at 55-57 K
  • - at density 9 g/l, corresponding to saturated vapor density at Ne boiling point
  • Rather high gains are observed, as high as 2*104. The maximum gains are not reached here
  • [Columbia Un. & Novosibirsk]

Observation of alfa-tracks in Ne+10-3H2 using CCD optical readout from a single-GEM at 77 K, density of 22g/l (!) and gain>1000

[Galea et al. IEEE NSS Conf. Rec. 2007]

Initial ideas based on two-phase detector is transformed to single-phase supercritical fluid due to insufficient gain in vapor phase for He and long trapping time at liquid-gas surface for Ne [Columbia Un. & BNL]

A. Buzulutskov, Instr08, 1/03/08


Tracking detectors: COMPASS [CERN]

- 22 triple-GEM chambers- 31x31 cm2 active area- Mixture Ar/CO2- 2D readout: perpendicular strips- 400 mm strip pitch- Space resolution 70 mm- Time resolution 12 ns- 25 kHz/mm2- Operation in 2002-2006

Uniformity of tracking efficiency

A. Buzulutskov, Instr08, 1/03/08


Tracking detectors: LHCb muon trigger system [Frascatti]

- 12 triple-GEM chambers in innermost region of M1- 20x25 cm2 active area- Foil stretching – no spacers- Fast mixture Ar/CO2/CF4 (45/40/15)- Time resolution 4.5 ns- Rates up to 500 kHz/cm2- Radiation hardness 1.8 C/cm2 in 10 years- Gain ~ 6000

Efficiency at test beam

A. Buzulutskov, Instr08, 1/03/08


Tracking detectors

See L. Shekhtman talk

See D. Attie talk

System of Tagged Electrons for KEDR- 8 triple-GEM chambers - Active area up to 25x10 cm2- 2D readout with small angle stereo strips


A. Buzulutskov, Instr08, 1/03/08


Tracking detectors: TOTEM [CERN]

  • 40 half-moon triple-GEM chambers- 30 cm diameter- 2D readout with radial strips and pads

Forward tracker in CMS

A. Buzulutskov, Instr08, 1/03/08


Tracking detectors: cylindrical GEMs

NA49 upgrade [CERN]

CLOE2 vertex detector [Frascatti]

- 5 concentric layers of cylindrical triple-GEM detectors- Diameter 300 mm, active length 350 mm- 1000x350 mm2 GEM active area patch- 3 GEM foils glued together- ~1500 strips

  • COMPASS 31x31 cm2 GEM foils- 2D readout with orthogonal strips- Special tools

A. Buzulutskov, Instr08, 1/03/08


Cherenkov detector at PHENIX: Hadron Blind Detector [BNL & Weizmann]

  • Windowless Cherenkov counter- CsI PC coated GEMs- CF4 radiator - 24 triple-GEM detectors 23x27 cm2- Pad readout[Woody et al. IEEE NSS Conf. Rec. 2006]

A. Buzulutskov, Instr08, 1/03/08


Pixel readout

See D. Attie talk

MPGD with ultimate space resolution using integrated pixel electronic readout

[Bamberger et al. / NIM A 573 (2007) 361]

Medipix2 image of the electron track from 106Ru source in Ar-CO2 (70:30). Primary ionization clusters are seen

Schematics of triple-GEM detector with Medpix2 chip readout

- Medpix2 chip: 256x256 pixels 55 µm pitch- Originally developed for X-ray imaging- Digital readout: preamp / discriminator - Pixel noise 150 e

A. Buzulutskov, Instr08, 1/03/08


Pixel readout

MPGD with ultimate space resolution using integrated pixel electronic readout

[Bellazzini et al. / NIM A 572 (2007) 160]

Concept of pixel readout for X-ray polarimetry by tracking the photoelectron direction

Single-GEM detector with CMOS chip readout

- Dedicated CMOS readout- 300x352 pixels 50 µm pitch hexagonal pads of 15x15 mm2 active area - Digitals readout: pre-amplifier, shaping amplifier, sample and hold, multiplexer- Pixel noise 50 e

A. Buzulutskov, Instr08, 1/03/08


Photoelectric gate to reduce ion backflow

Photoelectric Gate [Buzulutskov & Bondar JINST 1 (2006) P08006]

- Signal transfer efficiency through the gate is 1/30-1/50 in He and Kr and much lower in CF4

Photon Assisted Cascaded Electron Multiplier (PACEM) [Veloso et al., JINST 1 (2006) P08003]

- Signal transfer efficiency through the gate is 1/50 in Xe

- Since scintillations should be provided, the gate can effectively work in pure noble gases only

- At the moment signal transfer efficiency through the gate is not high enough

A. Buzulutskov, Instr08, 1/03/08


GEM-based gas photomultupliers (GPM)


A. Buzulutskov, Instr08, 1/03/08



  • The amount and variety of radiation detectors based on GEMs is amazing. The fields of most active investigations are the following:
  • - Tracking detectors for colliding beam experiments: high rate and with high space resolution
  • - Cryogenic avalanche detectors for neutrino and dark matter search experiments, including two-phase detectors
  • Photon detectors, including Cherenkov detectors
  • - Micro-pixel electronic readout for precise tracking
  • - Synchrotron radiation detectors
  • We may conclude that GEM is the most fruitful successor of previous generations of gas detectors !

A. Buzulutskov, Instr08, 1/03/08


GEM physics: physical processes

A. Buzulutskov, Instr08, 1/03/08


GEM physics: ionization coefficients

Obtained due to unique GEM ability to effectively operate in pure noble gases at high pressures and low temperatures

- Ionization coefficients for ultrapure He and He “purified” by low T (< 20 K) correspond to literature data - That means that the principal avalanche mechanisms at room and low T are the same, namely electron impact ionization - High gains observed in He and Ne above 78 K are most probably due to Penning effect in uncontrolled impurities [Novosibirsk & Columbia Un. & BNL]

  • Big difference between heavy and light noble gases- Good agreement between high and low pressure data for heavy noble gases- Ionization coefficients in He and Ne obtained at high pressures strongly exceed the coefficients at low pressures available in the literature[Novosibirsk]

A. Buzulutskov, Instr08, 1/03/08


High pressure detectors [Novosibirsk]

  • In mixtures with molecular quenchers the maximum gain decreases quite rapidly with pressure- In the triple-GEM, high gain in light noble gases (He, Ne) up to 15 atm (due to Penning effect on uncontrolled impurities?)- In the triple-GEM, fast gain decrease with pressure in heavy noble gases (due to ion feedback between GEM elements)- However in single-GEM, slow gain decrease with pressure in heavy noble gases: gains of the order of 100 are reached at 10 atm- Very high gains, up to 106 at 10 atm, in Penning mixtures Ar+Xe, Ne+H2, He+N2, He+Kr- MHSP and THGEM are more promising for high pressure detectors?

A. Buzulutskov, Instr08, 1/03/08



Cryogenic two-phase Ar or Xe avalanche detectors

Motivation: medical applications

GEM-based two-phase Xe or Kr avalanche detector for PET

- Solving parallax problem

- Superior spatial resolution if to use GEM readout

Budker Institute: CRDF grant RP1-2550 (2003)

Two-phase Xe detector for PET

Chen & Bolozdynya, US patent 5665971 (1997)

  • GEM-based two-phase Ar or Kr avalanche detector for digital radiography with CCD readout
  • - Robust and cheap readout
  • Thin (few mm) liquid layer is enough to absorb X-rays
  • - Primary scintillation detection is not needed
  • Budker Institute: INTAS grant 04-78-6744 (2005), Presented at SNIC06,

A. Buzulutskov, Instr08, 1/03/08


Electron emission through liquid-gas interface [Novosibirsk]

Emission characteristics in Xe

- Anode pulse-height as a function of electric field in liquid Xe induced by pulsed X-rays, in 3GEM at gain 80.

Emission characteristics in Ar and Kr

- Anode pulse-height as a function of electric field in the liquid induced by beta-particles: in Ar – in 2GEM at gain 1500; in Kr – in 3GEM at gain 250.

- Electron emission from liquid into gas phase has a threshold behavior

- Electric field for efficient emission: in Ar by a factor of 2-3 lower than that in Kr and Xe

A. Buzulutskov, Instr08, 1/03/08