cryogenic avalanche detectors based on gas electron ...ju/paper/talk/alexei-bnl.pdf · 2004nov 17...

Alexei Buzulutskov ,seminar at BNL ,17 Nov 2004 1

Cryogenic Avalanche DetectorsBased on Gas Electron Mulitipliers

A. Bondar, A. Buzulutskov, D. Pavlyuchenko, L. Shekhtman, R. Snopkov, Y. Tikhonov, A. Vasiljev

Budker Institute of Nuclear Physics, Novosibirsk

OutlineBasic part:

- Motivation: dark matter and solar neutrino detection and PET- GEM operation in gaseous He, Ar and Kr at cryogenic T- Two-phase cryogenic detector in Kr, based on GEMs

Some details: secondary effects in two-phase Kr; two-phase Kr + gas; ionization coefficients; ion-induced signals; photon feedback

Summary


J. Dodd, R. Galea, Y. Ju, M. Leltchouk, V. Radeka, P. Rehak, V. Tcherniatine, W. Willis

Nevis Lab & BNL

This work is carried out under CRDF grant RP1-2550-NO-03

in collaboration with


Two-phase detectors for solar neutrino and dark matter

Two-phase Xe detectors for WIMP search: ZEPLIN II-IV:UK Dark Matter Search Collaboration

Two-phase He detector for solar neutrino detection: Nevis Lab (Columbia Univ) & BNL


Medical applications: two-phase Xe or Kr detector for PET

LXe- LXe is comparable to NaI (Tl) in atomic number, density and scintillation yield - LXe price: $10.4/rad. length (2.6 cm) which is comparable with BGO- LKr price is much lower: $1.4/rad.length (4.6 cm)- Solving parallax problem


Principle of two-phase cryogenic avalanche detector based on GEMs

- For solar neutrino and WIMP, primary ionization signal is weak→ Signal amplification, namely electron avalanching in pure noble gases at cryogenic temperatures is needed

- Detection of scintillations in liquid is needed, to provide fast signal coincidences in PET and to reject background in neutrino and WIMP detection

- Electron avalanching at low temperatures has a fundamental interest itself.

Two-phase (liquid-gas) cryogenic avalanche detector using multi-GEM multiplier, with CsI photocathode on top of GEM

1. First results from cryogenic avalanche detectors based on GEMs, Buzulutskov et al. IEEE Trans. Nucl. Sci. 50(2003)2491; E-print physics/03080102. Cryogenic avalanche detectors based on GEMs, Bondar et al., NIM A 524(2004)130.


2000 2100 2200 2300 2400 2500 2600 2700 2800 2900 3000 3100 3200103

104

105

106

Ar+10%N2

Ar+1.3%CH4

Ar+1%Xe

Ar

Ar+50%Ne Ar+1.3%N2

3GEM + PCB

Visi

ble

gain

VG ( V )

GEM operation in noble gases: previous results

0 2 4 6 8 10 12 14 16100

101

102

103

104

105

3GEM+PCBKr

He

Ne

ArXe

Max

imum

gai

n

Pressure (atm)

Budker Inst & Weizmann Inst & CERN: NIMA 443(2000)164

Budker Inst: NIMA 493(2002)18; 494(2002)148; 513(2003)256

0 2 4 6 8 10 12 14 160

200

400

600

800

1000

1200

Xe

open points: 3GEM+PCBsolid points: 1GEM+PCB

Kr

Kr

HeNe

Ar

Max

imum

vol

tage

acr

oss G

EM (V

)

Pressure (atm)


Gaseous cryogenic avalanche detector:experimental setup


Gain-voltage characteristics at cryogenic T in He, Ar and Kr

100 150 200 250 300 350 400 450 500101

102

103

104

105Kr, 175K2.5*1019cm-3

Ar, 165K2.5*1019cm-3

Two-phase Kr118K, 5.3*1019cm-3

He,123K7.5*1019cm-3

Trip

le-G

EM g

ain

∆ VGEM ( V )

Rather high gains are reached in all the gases studied. The maximum gain exceeds 105 and few tens of thousands in He and Ar and Kr, respectively.


Temperature dependence of gain at constant voltage and constant gas density

120 140 160 180 200 220 240 260 280 300102

103

104

3GEM 70/140 µm

He, 7.5*1019cm-3

Ar, 2.5*1019cm-3

Kr, 2.5*1019cm-3

Trip

le-G

EM g

ain

Temperature (K)

- In He, gain is independent of temperature, ruling out effect of organic impurities on avalanche mechanism. - In Ar and Kr, gain increases by a factor of 1.5-5, in 3 GEM, and 1.1-1.8, in 1GEM, when decreasing temperature → modification of avalanche mechanism?

120 140 160 180 200 220 240 260 280 30050

100

150

200

250

300

Kr2.5*1019 cm-3

1GEM32/100 µm

Sing

le-G

EM g

ain

Temperature (K)

Single-GEM in KrTriple-GEM in He, Ar, Kr


He: anode signals at cryogenic T, induced by X-rays

T = 124 Kp = 1.26 atm , N=7.5*1019 cm-3

Gain~6000Stainless steel cathode

T = 295 Kp = 3 atm , N=7.5*1019 cm-3


We do not observe any unusual properties in the shape of anode pulses, induced just by cryogenic temperatures.


He and Kr: anode signals at cryogenic T, at high gains

He, T = 125 KN=7.5*1019 cm-3

Gain~25000Stainless steel cathodeX-ray tube with Re target

Kr, T = 180 KN=2.5*1019 cm-3

Gain~18000Stainless steel cathodeX-ray tube with Mo target


No charging-up effects at cryogenic T

100 120 140 160 180 200 220 240101

102

103

104

105

24 kV, 0.9*104 s-1mm-2

30 kV : 1*105 s-1mm-2

40 kV : 8*105 s-1mm-2

He3GEM3atm@22C144 KCurrent mode

Gai

n∆ VGEM ( V )

3.4 3.6 3.8 4.0 4.2 4.4101

102

103

104

solid: Ar, ∆VGEM=317Vopen: He, ∆VGEM=200V

Leak

age

curr

ent (

pA)

1000/T (1/K)

300 280 260 240 220

T (K)

σ ~ exp ( - EA / kT )


Two-phase cryogenic avalanche detector: experimental setup

- Liquefying starts when Kr pressure drops below 1.5 atm- Strong p-T dependence in two-phase mode → monitoring pressure to measure temperature


Two-phase cryogenic avalanche detector: experimental setup


+VG

R

R

R

R

R

R

GEM3

GEM2

GEM1

Cathode

C2

C1

E

-VC

High-voltage divider and readout

- Divider: three identical circuits connected in parallel, each GEM being connected to one of them:- Protection against discharges induced by ion feedback between GEMs: if even one GEM breaks-down, electrical potentials on others do not increase.


Two-phase Kr: formation of liquid phase

0 20 40 60 80 100 1200

1

2

3

4

5

Curre

nt (n

A)

Time (min)

0

2

4

6

8

10

12Gaseous Two-phase

p / T

Current

Temperature

p / T

(10-3

atm

/K)

100

120

140

160

180

200

220

240

260

280

300

The

rmoc

oupl

e te

mpe

ratu

re (K

)

- Liquefying starts when Kr pressure drops below 1.5 atm- Strong p-T dependence in two-phase mode

Cathode-GEM1 capacitance as a function of pressure during cooling/heating cycles

Anode current in the cathode gap, T and p/T as a function of time during cooling cycle


Two-phase Kr: electron emission from liquid into gas

0 1 2 3 40.0

0.1

0.2

0.3

0.4

Ano

de c

urre

nt in

two-

phas

e m

ode

(nA

)

EDRIFT (kV/cm)

0

1

2

3

4

5Anode current in the cathode gapsolid: two-phase mode at 122K and 1.23atm (left scale)open: gaseous mode at 137K and 1.67atm (right scale)

Ano

de c

urre

nt in

gas

eous

mod

e (n

A)

- Electron emission from liquid into gas phase has threshold behavior- Critical electric field ≥ 1.5 kV/cm

0.00.51.01.52.02.53.03.54.0

050

100150

200250

Two-phase Kr

120 K, 1 atm

3GEM

β-particles

∆VGEM= 417 V

Ave

rage

pul

se-h

eigh

t (m

V)

ELKr (kV/cm)

Anode pulse-height as a function of the electric field in liquid Kr, induced by beta-particles ([email protected]=250)

Anode current recorded in the cathode gap as a function of the electric field, induced by X-rays


Two-phase Kr: gain-voltage characteristics

Gaseous Kr:Change of slope at low T indicates that the avalanche mechanism is modified?

100

101

102

103

104

105

106

200 250 300 350 400 450 500 550100

101

102

103

104

6.2*1019 cm-3

189 K

295 K

2.5*1019 cm-3

195 K295 K

KrGaseous3GEM

Gai

n

123 K1.32 atm8.0*1019 cm-3

118 K0.84 atm5.1*1019 cm-3

KrTwo-phase3GEM

Gai

n

∆ VGEM ( V )

Two-phase Kr:Electron avalanching in saturated vapor does not differ from that of normal gas in general:- Gain and voltages are similar to gaseous mode at equal gas densities- Secondary processes at high gains are more pronounced


Two-phase Kr: anode signals induced by β-particles from 90Sr

0.8 1.0 1.2 1.4 1.6 1.8 2.01

10

100

Gaseous Kr295K

Two-phase Kr120-123K

3GEMβ-particlesDecreasing T

Ano

de c

urre

nt /

Gai

n (p

A)

p (atm)

The signal in two-phase mode is larger than in gaseous mode, because the energy deposited by β-particle in the liquid is much larger than in the gas

Pulsed mode Current mode


Two-phase Kr: towards PET applications. Anode signals induced by 0.51 MeV γ-quanta from 22Na in coincidences with BGO counter

- Triggered by GEM signal - Almost no background- GEM-BGO signal delay is t~2 µs: corresponds to electron drift in liquid and gaseous Kr in the gap and between GEMs

- No peak in pulse-height spectrum from 0.51 MeV gammas, due to domination of Compton scattering in LKr.


Two-phase Kr: analysis of GEM-BGO signal time spectra

2.5 3.0 3.5 4.0 4.50

1

2

3

LKr layer "thickness": v∆t

v ∆t

(m

m)

ELKr (kV/cm)

0.4

0.5

0.6

0.7

0.8

GEM-BGO signal time spread (FWHM): ∆t

∆t (µ

s)

Electron drift velocity in LKr: v

3.4

3.6

3.8

4.0

4.2

4.4

v (1

05 cm

/s)

- Left edge of time histogram is defined mostly by LKrlayer thickness - Fitting left edge by Gauss: getting time spread ∆t- ∆t and t decreases with E due to increase of v- Estimating LKr layer thickness: ∆x = v ∆t


0 20 40 60 80 100 120 140 160 180 2000

20

40

60

80

100

120

Ave

rage

pul

se-h

eigh

t (m

V)

Time (min)

5.60

5.65

5.70

5.75

5.80

5.85

solid: pulse-heightopen: capacitance

Gain = 120∆VGEM= 400 VELKr= 3.3 kV/cm

Two-phase Kr120 K, 1 atm3GEMβ-particles

Cap

acita

nce

(pF)

Two-phase Kr: stability of operation

- Relatively stable operation for 3 hours was observed, confirming possibility for stable GEM operation in avalanche mode in saturated vapor- Signal disappearance is correlated to drop of cathode-GEM1 capacitance, indicating disappearance of the liquid phase, and is due to not enough temperature stability of the cryostat


Two-phase Kr:secondary effects and maximum gain

300 350 400 450 500 550100

101

102

103

104

123K, 1.32atmcurrent mode

120K, 1atmPulse-countingmode

120K, 1atmCurrent mode

Two-phase Kr3GEM

Gai

n

∆ VGEM ( V )

- In pulse-counting mode, the maximum gain does not exceed 1000. - In current mode, secondary effects arise at higher gains. They are not observed in pulse-counting mode. Most probably they are induced by ion backflow, which at high fluxes might result in a) ion feedback between GEMs (enhanced in saturated vapor?)b) charging-up of kapton in GEM holes (enhanced in saturated vapor?)c) charging-up at phase interface (what happens to electrons not emitted from liquid?).- Secondary effects might also be dependent on liquid surface state (surface waves, boiling) and electric field. - Ways to increase the gain and suppress secondary effects should be looked for.


Two-phase Kr + Ar or He

200 250 300 350 400 450 500 550100

101

102

103

104

105

Kr(1.9atm)+Ar (0.2atm)

Kr(1.9atm)

Kr(1.9atm)+He (1.1atm)

Gaseous295K, 3GEMCurrent mode

Gai

n

∆ VGEM ( V )

350 400 450 500100

101

102

103

104

Kr(1.03atm)+Ar(0.1atm)ELKr= 3.3 kV/cm

Kr(1atm)ELKr= 2.7 kV/cm

Two-phase120K, 3GEMCurrent mode

Gai

n

∆ VGEM ( V )

- In gaseous state: successful operation in Kr+He and Kr+Ar mixtures

- In two-phase state: the basic idea is to suppress boiling and ion feedback.- However, in Kr+He cooling down to two-phase state was not possible- In Kr+Ar, cooling down to two-phase state was possible at only small (~0.1atm)Ar content- In Kr+Ar, secondary effects seems to be reduced, though the maximum gain did not increase.


Estimation of ionization coefficients in dense noble gases using GEMs with narrow holes

Parallel-plate approach:works well for hole diameter below40 µm:

1. Gain of 1GEM configuration:G = exp (a d ) .

2. Ionization (Townsend) coefficient:a / p = ln G / (p d ).

3. Electric field: computed value is taken in the center of the hole:

E = 80 kV/cm at ∆VGEM=500V.

See: Physics of multi-GEM structures, Buzulutskov, NIM A 494(2002)148.


100 101 10210-4

10-3

10-2

10-1

100

open: Hesolid: Kr

KrHe 1atm 3atm 5atm 7atm

10atm 15atm

curves: αL/p (p<0.1atm)points: αH/p (p>1atm)

Ioni

zatio

n co

effic

ient

(1/c

m/T

orr)

E / p (V/cm/Torr)

Ionization coefficients: high pressure versus low pressure

Using 1GEM (40/100µm) data

1. In He and Ne, ionization coefficients are considerably larger at high pressuresthan at low pressures.2. In He and Ne: strong violation of E/p scaling.3. In Ar, Kr and Xe: relatively good agreement between high and low pressure.

A + e → A+ + 2e Impact ionization: ~pA + e → A* + e ExcitationA + A* → A+

2 + e Associative ionization: ~p2

A* → A + hυ Deexcitation


100 101 10210-4

10-3

10-2

10-1

100

open: He, C=1.0atm-1

solid: Kr, C=0.05atm-1

Kr

He

1atm 3atm 5atm 7atm

10atm 15atm

curves: α L / p points: α H / p / (1+Cp)

Ioni

zatio

n co

effic

ient

(1/

cm/T

orr)

E / p (V/cm/Torr)

Ionization coefficients: accounting for associative ionization

)(]1[),(

~/

pEi

pEt

ia

ait

ppconstp

p

pαα

ααααα

⋅+≈

+=

pCppLH αα

≈+ )1(

Parameter C describes the contributionof associative ionization:

C~1.0 atm-1 for He and Ne;C<0.1 atm-1 for Ar, Kr and Xe.


Two-phase Kr: ionization coefficients

60 70 80 90 1000.1

1

gaseous: 295 K, 2.5 atm two-phase: 123 K, 1.32 atm two-phase: 118 K, 0.84 atm literature at p<0.1 atm

Kr

α /

N

( 10

-17 c

m2 )

E / N ( 10-17 V cm2 )

Important observations: - Scaling of ionization coefficients obtained at different pressures in two-phase mode- Larger ionization coefficients at lower T → modification of avalanche mechanism?


Gaseous mode:ion backdrift, ion feedback and photon feedback effects

- When C1 capacitor is off, the tail of anode pulse becomes substantially longer due to ion backdrift-induced signal: its width corresponds to ion drift time between GEMs- This would allow to estimate ion mobility at high densities and low T.

See: Further studies of cryogenic avalanche detectors based on GEMs, Bondar et al., Proceedings of Vienna Conf. on Instrum. 2004,NIM A (2004), in press.


He: signals induced by ions backdrifting in GEM3-GEM2 gap

T = 295 KN=7.5*1019 cm-3

Gain~30000Cu cathodeCapacitor in GEM3up is on

T = 295 KN=7.5*1019 cm-3

Gain~30000Cu cathodeCapacitor in GEM3up is off

Ion backdrift-induced signal


Ar and He: signals induced by ions backdrifting in GEM3-GEM2 gap

He, T = 295 K, N=7.5*1019 cm-3 , Gain~30000, Cu cathodeCapacitor in GEM3up is offEstimated reduced ion mobility: K0 = 16 cm2/V s(Compare to 10.4 and 16.7 cm2/V s for He + and He2

+ respectively)

Ar, T = 177 K, N=2.5*1019 cm-3 , Gain~30000, Cu cathodeCapacitor in GEM3up is offEstimated reduced ion mobility: K0 = 2.4 cm2/V s(Compare to 2.2 cm2/V s obtained from 1/T 1/2 dependence)

Ar, T = 295 K, N=2.5*1019 cm-3 , Gain~17000, Cu cathodeCapacitor in GEM3up is offEstimated reduced ion mobility: K0 = 1.7 cm2/V s(Compare to 1.50 and 1.86 cm2/V s for Ar + and Ar2

+ respectively)


He: photon feedback at high gains, at room T and with Cu cathode

Emission spectra of noble gases.

Quantum efficiency in VUV region.


He: photon feedback using Cu cathode

T = 124 KN=7.5*1019 cm-3


T = 295 KN=7.5*1019 cm-3

Gain~30000Cu cathode

Photon feedback-induced signal


Ar: photon feedback enhancement at low TT = 295 Kp = 1 atm , N=2.5*1019 cm-3

Gain~2000, V=2050 V Cu cathode

T = 170 Kp = 0.58 atm , N=2.5*1019 cm-3

Gain~6000, V=2050 VCu cathodePhoton feedback

240 260 280 300 320 340 360 380101

102

103

104

105

295 K

165 K

Ar3GEMρ = ρ(1atm,295K)

Gai

n

∆ VGEM ( V )


We have studied the performance of cryogenic avalanche detectors of ionizing radiation based on GEM multipliers and operated in gaseous and two-phase (liquid-gas) mode in pure He, Ar and Kr.

- It was shown that GEM structures could successfully operate at cryogenic T, down to 120 K, both in gaseous and two-phase modes.

- High gas gains, exceeding 104, were obtained at cryogenic T in gaseous mode, in all noble gases studied. Electron avalanching at cryogenic T, in the range of 120-300 K, has either weak, in He, or moderate, in Ar and Kr, temperature dependence.

- Stable avalanche mode of operation was observed in two-phase mode, in Kr at gains below 1000, indicating on possibility of long-term operation in avalanche mode in saturated vapor, using GEMs.

- In two-phase mode, signals induced by X-rays and gamma-quanta and beta-particles were successfully recorded, in current and pulse-counting mode, respectively.

Conclusions


Physics of electron avalanching at low T:- Ionization coefficients at low T- Associative ionization at low T- Avalanching in saturated vapor- Electron and ion mobility at low T

Physics of two-phase media:- Electron emission from liquid (solid) into gas phase- Ion transport through phase interface- Charging-up effects at phase interface

Physics of ion clusters at low T:- Ion clustering- Mobility of ion clusters

Outlook: physics of CAD


- Two-phase cryogenic particle and X-ray detectors: in He and Ne, for solar neutrino, and in Kr and Xe, for dark matter and PET/SPECT.

- High-pressure X-ray detectors in Xe and Kr, for mammography and radiography.

- Neutron detectors in compressed He3, He acting as both a detection and amplification medium.

- Sealed detectors.

Outlook: possible applications

cryogenic avalanche detectors based on gas electron ...ju/paper/talk/alexei-bnl.pdf · 2004nov 17...

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