Gossip ageing studies

Gossip ageing studies

Fred Hartjes

NIKHEF

Ageing gaseous detectors Ageing dummy Gossip using 90Sr source Ageing SiProt using 90Sr source Ageing induced by UV light

Micro pattern gas detectors (RD51) workshopNikhef, April 16 - 18, 2008

Fred Hartjes 2

Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008

Gaseous detector ageing No ageing of the ionising medium

Gas permanently renewed Ageing of electrode material, support structure or services

In most cases not the first concern

Ageing of gaseous detectors normally from a remainder on the anode deposited by the hot avalanche Homogeneous soft insulating layer Crumbly layer Spikes …………

Leading to Decay of gas gain Broadening of the charge signal distribution HV instability

Ageing by remainder on the anode directly linked to ionisation in the chamber gas => ageing studies of gaseous detectors may be exclusively done by inducing

ionisation

Fred Hartjes 3


Dependence on electrode geometry

Crucial is the field strength in the vicinity of the anode

High field => high avalanche temperature Production of radicals Dissociating organic molecules => deposit on the anode

Electrical field near anode for different detector technologies MSGC: very high Wire chamber: moderate Micromegas/InGrid: comparatively low GEM: high at edges of the hole

Additional effect: magnitude anode surface MSGC: very small (edge of anode strip) Wire chamber: quite small Micromegas/InGrid: large GEM: avalanche not in vicinity of anode

Field strength (E) along the central drift path (X) to the anodefor three different electrode geometries

X (m)

0 20 40 60 80 100E

(kV

/mm

)0

10

20

30

40

Wire chamber

MSGC

Micromegas/InGrid

Fred Hartjes 4


Nature of the deposits

No single compound in the gas is known to cause (deposit) ageing

Si-oil from bubbler has NOT been identified as ageing causing compound

Hydrocarbons are more prone causing ageing than CO2, CF4

Deposits often contain Si and/or C

One of the ageing mechanisms: in hydrocarbons (from fossile oil), a C may be

replaced by Si:

SiH4, CSiH6, C2SiH8

Not exclusively by the avalanche

ionising radiation may create radicals as well in the gas and at the detector walls

Fred Hartjes 5


Possible ionisation sources for ageing studies

PS beam at CERN Best radiation test Mip ionisation profile (24 GeV/c p) Average rate 3 - 9 GHz/cm2

but current during spill order of magnitude higher (> 50 GHz/cm2) Can Gossip handle this??

Running a testbeam experiment is time and money consuming Tight time schedules

Powerful (5 GBq) 90Sr source at Nikhef Up to ~ 1.5 GHz/cm2 continuously Rate still OK for Gossip Mip ionisation profile (1 – 2 MeV/c e-) simulating b-layer environment Always available Not ultimate radiation test

UV light source at Nikhef (Harry van der Graaf) Continuous operation Easy in use (no personal danger) Different ionisation profile

individual photoelectrons mainly liberated from metal surfaces

Reference: pixel b-layer at SLHC rate up to 0.4 GHz/cm2

dose up to 1016 cm-2

mostly hadrons: p, in GeV range (mips) (MeV - GeV range) n (MeV range)

Fred Hartjes 6


Irradiation facility with 5 GBq source

Remote controlled irradiation stage Sample can be moved in and out by

pneumatic piston => separating induced signal from

background signal

Ageing sample

source

Fred Hartjes 7


90Sr source at Nikhef

5GBq 90Sr 1 – 2 Mev e- simulating mips

Rate calibrated with ionisation chamber

Distance sample to source 4.7 mm => 1.33 GHz/cm2 (sphere) 1.25 GHz/cm2 (parallel surface)

=> 1.15*1014 mips/cm2/day in bulk material

SLHC aim: 1016 mips/cm2 for the ATLAS b-layer

Fred Hartjes 8


GOSSIP: Gas On Slimmed SIlicon Pixels

InGrid

Drift gap: 1.2 mmGas filledMax drift time: 25 ns

MIP

CMOS pixel chip‘slimmed’ to 30 μm

Cathode foil

What is Gossip? Gaseous pixel detector Slimmed silicon pixel chip Short drift distance

1.2 mm => high rate capabilities

(GHz/cm2 region) Good position resolution

expected (low diffusion) => suited for SLHC b-layer Aim for G = 1000

Thickness gas layer marginal

=> limited by efficiency requirements

Gossip prototype

Fred Hartjes 9


Dummy detector for GOSSIP ageing studies

Dummy glass ROC Circular pads on 60 µm pitch Drift volume 13 x 13 mm, 1.24 +/- 0.01 mm high Centre signal electrode: 2 x 2 mm structure of 1089

pads (red) => Final detection volume is a block of 2 x 2 x 1.2 mm

Gas gain by Micromegas Closed gas volume of 210 µl Gas flow ~ 0.5 l/h

=> more than 2000 volume exchanges/hour

1.2

Cathode foil Micromegas Gas tube

Dummy ROC

16

Icentre electrode

Iguard electrode

Fred Hartjes 10


Source geometry during irradiation

Distance centre source to centre drift volume 4.7 mm Homogeneous irradiation of centre electrode

4.7drift cathode

Micromegas

Dummy ROC

2.0

centre electrode

Guard electrode

Ø5.01.0 5 GBq 90Sr source

1.2

Dimensions uniformly scaled

Fred Hartjes 11


Rate dependence

Gas gain of Gossip 23

Vgrid (-V)

500 520 540 560 580 600 620 640

I anod

e (n

A)

20

30

40

50

60

70

8090

200

10

100

G = 1000

Fit: y = 0.0047e0.0161

Ar/iC4H10 30/70

mip rate 1.15 GHz/cm2

27-11-07

Gas: Ar/iC4H10 70/30

Rate 1.33 GHz/cm2 Rate dependence

investigated by gain curve

No sign of saturation until gain = 900

Fred Hartjes 12


Ageing method Two gas mixtures tested so far

Gossip21: He/iC4H10 78/22

Gossip23: Ar/iC4H10 70/30

Data taking every 2s Background current periodically measured

for reference 20 s per 4 hour Part of the raw data

t (s)

0.0 2.0e+4 4.0e+4 6.0e+4 8.0e+4 1.0e+5 1.2e+5 1.4e+5 1.6e+5

I cen

tre

(nA

)

-400

-300

-200

-100

0

I guar

d (

nA)

-1500

-1000

-500

0

500

1000

1500

Raw data (detail)

t (s)

1.151e+5 1.152e+5 1.152e+5 1.153e+5 1.153e+5

I cent

re (

nA)

-400

-300

-200

-100

0

I guar

d (n

A)

-1500

-1000

-500

0

500

1000

1500

Icentre

Iguard

Centre current

Guard current

Fred Hartjes 13


Gossip21: He/iC4H10 78/22

Sept 07gain = 1100He/iC4H10 78/22

Gossip ageing using mips from 90Sr source

Time (days)

0 5 10 15 20 25 30 35

I cent

re (

nA)

0

25

50

75

G = 1000 G = 1000

Fluence (mips/cm2)

0 1e+15 2e+15 3e+15 4e+15

No sign of decay of gas gain

Instabilities partly caused by

variations in temperature and pressure?

But measurement had to be terminated because of increased sensitivity for HV trips

Tripping induced by radiation

Vgrid = -418 VVcathode = -627 V

Fred Hartjes 14


Gossip23: Ar/iC4H10 78/22

More fluctuation but no significant indication for decay of gas gain

Trip (Iguard > 2 µA) at about once a week

Again measurement had to be terminated after 22 days because of increased sensitivity for tripping

Gossip 23Nov 28Ar/iC4H10 70/30

Particle flux: 1.6 GHz

Gossip ageing using mips from 90Sr source

Time (days)

0 5 10 15 20 25

I cen

tre (

nA)

0

100

200

G = 1000 G = 1000

Fluence (mips/cm2)

0 1e+15 2e+15 3e+15

switch fromVgrid = -635 to -640 V

Vgrid = -635 VVcathode = -889 V

Fred Hartjes 15


Linear fitI = I0 + a.ta = -0.5932=> a/I2 = 0.0183

av current = 5.9 A=> total charge deposited = 5.9*3600*24*4 = 2.55 Csurface 0.49 cm2

=> 5.2 C/cm2

assume: drift distance 1 mm Ar/CH4 having 9e-/mm=> 1 mip = 9*1000*1.6*10-19

= 1.44 10-15Cdeposited charge corresponds to3.6 1015 mips/cm2

X ray irradiation at PANalytical (detail)

Time

14-M

ay-0

5

16-M

ay-0

5

18-M

ay-0

5

I cath

(A

)

0

2

4

6

8

Icath

1/x fit

3.6x1015 mips/cm2@ gain = 1000

Comparison to earlier measurement 8.04 keV X-rays at

Panalytical Here 40% reduction in gain

but no tripping problems Using X rays instead of

MIPs? Anode: solid aluminium plate

instead of small pads glass ROC?

Gas: Ar/CH4 90/10 vs Ar or He / iC4H10 mixtures?

At Panalytical ~ 5x higher charge rate?

Much lower gas refreshment rate

Other reasons???

Fred Hartjes 16


Examining Gossip21 after irradiation

Field foil removed Coloured spot on top of Micromegas

near one of the gas pipes Probably inlet

When removing Micromegas no other pollutions/damages found Dummy ROC and Micromegas were

still clean

=> no visual cause for HV tripping traced

Fred Hartjes 17


SiProt ageing test SiProt: amorphous silicon layer to protect the ROC against discharges

Dummy glass ROC fully covered with 20 µm SiProt layer

Guard electrode set on +5V Measuring leakage current on centre

electrode => bulk resistance SiProt layer

measured parallel across 8 mm length

Icentre electrode

Iguard electrode

Bias current from voltage across a SiProt layer

Vbias (V)

0 20 40 60 80 100 120 140

I bias

(nA

)

0

20

40

60

80

voltage set between centre electrode and guard electrode of the SiProt1 glass ageing substrate28-2-2008

SiProt IV curve

Measured resistance 2 – 10 G=> bulk resistance ~ 0.5 – 2.5 109 cm2.6 - 13 1011 between two pads(just OK for b-layer SLHC)

Fred Hartjes 18


SiProt ageing

t (days)

0 5 10 15 20 25 30

I cent

re (

nA)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

tem

pera

ture

(o C

)

0

5

10

15

20

25

dose (1015 cm-2)0 1 2 3 4

Sample: SiProt1 glass aging substratecovered with 20 m SiProtGuard electrode set at + 5VCurrent measured at centre electrode

8-4-2008

+5V on guard electrodeinterrupted for 5h

pedestal current

induced current

temperature

SiProt current at 5V during mip irradiation

SiProt conductivity shows unstable behaviour Variations within factor ~2

from average Induced current not

exceptionally high Not much effect expected at

SLHC rate (0.4 instead of 1.15 GHz)

Also long term effects Increase of current over a

period of several days

But no significant effects on the operation and protection of the ROC expected

Until 4 x 1015 mips/cm2 no ageing observed

Fred Hartjes 19


Ageing test chamber with ionisation by UV light Initiated by Harry van der

Graaf Long, thin chambers from

clean materials SS glass ceramics No plastics, epoxies

Closed loop gas system Gas gain by InGrid

structure Inserting suspicious

material in test container Possible purification of the

gas by avalanches Downstream chambers

have less ageing (LHC-b experience)

Still in development

Test container

Quartz window

Fred Hartjes 20


Conclusions

For the Gossip prototypes we do not see the common ageing behaviour of gaseous detectors No significant decrease of gas gain even at a high dose But for iC4H10 mixtures deterioration of HV stability

Not in agreement with earlier X-ray CH4 test for unknown reasons

Will continue tests with other quenchers CO2

DME CH4

Verification required with other kinds of irradiation (hadrons, , n)

SiProt ageing looks promising No significant effect observed until 4 *1015 cm-2

Protection and ROC operation remain intact To be repeated with neutrons

UV light ageing Convenient experimenting Easy way tracing ageing compounds

Documents

Gossip ageing studies