Gossip ageing studies
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Transcript of 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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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
Micro pattern gas detectors (RD51) workshop. Nikhef, April 16 - 18, 2008
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