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Development of customized ceramic-metal composites. L. A. Diaz, J. A. Garzon, D. Gonzalez-Diaz, F. Guitian, L. Lopes, G. Mata, M. Morales , C. Pecharroman. 1. Considerations on high rates. Direction along to the magnetic kick. Direction orthogonal to the magnetic kick. - PowerPoint PPT Presentation
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L. A. Diaz, J. A. Garzon, D. Gonzalez-Diaz, F. Guitian, L. Lopes, G. Mata, M. Morales, C. Pecharroman
1. Considerations on high rates
Simulated rate over the ToF wall
20 kHz/cm2
Direction orthogonal to the magnetic kick
Direction along to the magnetic kick
Simulated rate on the TOF wall for Au-Au collisions at E=25 GeV/A
(rate capability of ordinary tRPCs is 0.3-1 kHz/cm2)
The behaviour of RPCs at high rates and the DC model (I)
qdg
ERIg
EE oogap 11
The assumption that the RPC performances 'just' depend on the average field in the gap is often referred as the DC model.
)( gapEqq
(1)
(1) + )( dEE gapgap
d (glass thickness)Φ (particle flux)g (gap thickness)ρ (resistivity)
At high rates the average field in the gap Eo is modified
)1(
)(
dag
EEdaEE tho
ogap
thgap EEaq For instance:
)( gapT E
)( gapE
)( dT
)( d
[1] H. Alvarez-Pol et al., NIM A, 535(2004)277, [2] V. Ammosov et al. NIM A, 576(2007)331, [3] R. Kotte et al. NIM A(2006)155, [4] L. Lopes et al., Nucl. Phys. B (Proc. Suppl.), 158(2006)66.
)(0
1 refgap EEe
)(
)'( 0
gapT ES
nK
The behaviour of RPCs at high rate and the DC model (II)
Rate capability in the DC situation
rate capability = particle flux for a 5% efficiency drop
Rate capability in the transient situation (pulsed irradiation)
D. Gonzalez-Diaz et al., Nucl. Phys. B (Proc. Suppl) 158(2006)111
B. Bilki et al., arXiv:0901.4371
D. Gonzalez-Diaz et al., doi:10.1016/j.nima.2008.12.097
)1ln(
d
dV
dq
ddVdq
teq
Rate capability in the transient situation (pulsed irradiation)
D. Gonzalez-Diaz et al., Nucl. Phys. B (Proc. Suppl) 158(2006)111
Equilibration time:time needed for the fieldin the gap to fall by 1/e of the drop corresponding to the stationary value:
ddVdq
teq
B. Bilki et al., arXiv:0901.4371
2. Ceramic-metal composites
Ceramic-metal composites. what is it?
• Active field in material research.
• The high di-similarity of both materials allows to obtain an
optimum
combination of their properties.
• Main difficulty: an adequate procedure to obtain an homogenous
mixture with small grain sizes.We have chosen mullite-molybdenum composites because they were expected to exhibit:
• Electronic conductivity.• ρ~1010 Ωcm.• εr < 50.• Ebreakdown> 0.5 kV/2 mm.
Molybdenum
• Atomic number 42
• Density 10.22 g/cm3
• High melting temperature 2623 °C
• Lowest linear thermal expansion coefficient of the engineering metals
4.8 x 10-6 / K at 25°C
• High thermal conductivity 138 W/m K at 20°C
• Crystal structureBody centered cubicLattice constant a = 3.1470 Å
Molybdenite
Mullite
a bit of explanation of this!
Al2O3+SiO2
Electrical behaviour of ceramic-metal composites
'Experimental Evidence of a Giant Capacitance in Insulator-Conductor Composites at the Percolation Threshold'
Carlos Pecharroman and Jose S. MoyaAdv. Mater. 2000, 12, No. 4 294
insulator metal
qco
pccer
ff
ff
)(
)(
percolation
Optical-microscope picture after homogenization
11% Mb
12% Mb
13% Mb
0. 5 mm
Samples after sintering
D=2 cm
Relaxation curves
time [s]
I [A
]
Electrical conductivity
High linearity and reproducibility
Ebreak>1 kV/2 mm
Electrical permittivity
only few factors bigger than glass!
Summary of electrical properties
f(Mo) ρ[GΩ cm] εr(100 Hz) εr(1 MHz)
SPS
11% 23.3 39 32
12% 22.8 46 38
13% 10.5 145 100
HotPress
11% 19.8 25 -
13% 6.08 55 -
two different sintering methods have been tried (SPS and HotPress)
Stability with transported charge over CBM life-time
22 /2)/5.1(205.05/ cmCgappCkHz/cmyAQ
)/20/(8 2cmmCG
1 month of CBM operation at 50% duty cycle (HADES life-time!)
puzzling!
we attribute this to the absence of pasivation of the sample surface.T variations
Conclusions
•Five Mu/Mo samples customized for standing comfortably the highest CBM-TOF rates have been produced.
•Stability of the electrical properties within 25% was observed for 1 CBM month-equivalent. The observed decrease is likely to be produced through electrode-sample reaction due to the absence of sample pasivation. This is being studied under controlled conditions.
•The degree of reproducibility of the samples is very high, with 11%- and 12%-Mo samples produced both in SPS or HotPress.
•We considered the samples promising for RPC stable operation at high rates so several 1 and 4-gap RPCs with area ~3 cm2 will be produced and its rate capability evaluated in a realistic situation.
with a bit of luck...
rate capability = particle flux for a 5% efficiency drop
we are there!
rate capability = particle flux for a 5% efficiency drop
appendix
Deviations from the DC model. The stabilization time
<Φ>=1200 Hz/cm2
<Φ>=580 Hz/cm2
by cutting the first 2 s of the spill the effect disappears.
measured rate in C@1GeV reactions (2003) at GSI-SIS (~8s time spill)DC limit
DC limit
cell model
Equivalent circuit
M. Abbrescia, NIM A 533(2004)7
Quantitative description of the stabilization time (II). The cell model
Quantitative description of the stabilization time (III). Behaviour under X-ray irradiation
Fit to the DC model Not fitted! (σT)
Deviations from the DC model. The local fluctuations of the field
response to secondary particles from C@1GeV reactions (2003) at GSI-SIS (~8s time spill)
An approximate analytical calculation based on the Campbel theorem and the exact M.C. one, differ slightly but show similar scaling properties
N
qrms
EE
rmsq
gapo
Egap
2
1 2
2
AN (Average number of shots contributing per cell of area A)
2
22
2
222 1
2 q
rmsq
Ag
drms q
Egap
Campbel theorem for shot-noise
Quantitative description of the local fluctuations of the field (I)
222
2
22
gap
EgapoT E
rms
dE
dS
S
E
N
t
S
Krms gap
(all the N=4 gaps are assumed to equally contribute to the time resolution)
Quantitative description of the local fluctuations of the field (II)
A>0.3 mm2
D. Gonzalez-Diaz et al., Nucl. Phys. B (Proc. Suppl) 158(2006)111
T scan
HV scan
rate Φ(x) charge qp(x)
1 2
3 4
1 2
3
4
3 4
3
T=210C
T=210C
T=330C
3 4
3
T=210C
T=210C
T=330C
The DC model and the case of warm glass (III)
fit: DC model fit: DC model
Quantitative description of the stabilization time (I)
21 /2
/1
tt eAeAI
Measurement of the dielectric response function of float glass as the one used in HADES
Rate effects. Campbell theorem (analytical vs simulation)
2
22
222 1
2 q
rmsq
A
drms q
gVgap
Campbel theorem
+ )( thgap VVaq Campbel theorem with average drop (2)
(1)
Rate effects. Stabilization time (comparison with data)
The value of Vgap(t) from M.C. and the parameterization of to can be used for describing to as a function of the time within the spill
)(3
1DCrr provides a better
description of the data
The result suggests a bias in the tRPC performances when extrapolating from short to long spills
Drop at the end of the spill
P. Colrain et al. NIM A, 456(2000)62