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
Direction along to the magnetic kick Direction orthogonal to the magnetic kick Simulated rate over the ToF wall Simulated rate on the TOF wall for Au-Au collisions at E=25 GeV/A 20 kHz/cm2 (rate capability of ordinary tRPCs is 0.3-1 kHz/cm2)
The behaviour of RPCs at high rates and the DC model (I) d (glass thickness) Φ (particle flux) g (gap thickness) ρ (resistivity) At high rates the average field in the gap Eo is modified (1) The assumption that the RPC performances 'just'depend on the average field in the gap is often referred as the DC model. (1) + For instance:
The behaviour of RPCs at high rate and the DC model (II)  H. Alvarez-Pol et al., NIM A, 535(2004)277,  V. Ammosov et al. NIM A, 576(2007)331,  R. Kotte et al. NIM A(2006)155,  L. Lopes et al., Nucl. Phys. B (Proc. Suppl.), 158(2006)66.
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 D. Gonzalez-Diaz et al., doi:10.1016/j.nima.2008.12.097 B. Bilki et al., arXiv:0901.4371
Rate capability in the transient situation (pulsed irradiation) Equilibration time: time needed for the field in the gap to fall by 1/e of the drop corresponding to the stationary value: D. Gonzalez-Diaz et al., Nucl. Phys. B (Proc. Suppl) 158(2006)111 B. Bilki et al., arXiv:0901.4371
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~1010Ωcm. • εr < 50. • Ebreakdown> 0.5 kV/2 mm.
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. Moya Adv. Mater. 2000, 12, No. 4 294 insulator metal percolation
Optical-microscope picture after homogenization 11% Mb 13% Mb 12% Mb 0. 5 mm
Samples after sintering D=2 cm
Relaxation curves I [A] time [s]
Electrical conductivity Ebreak>1 kV/2 mm High linearity and reproducibility
Electrical permittivity only few factors bigger than glass!
Summary of electrical properties two different sintering methods have been tried (SPS and HotPress)
Stability with transported charge over CBM life-time puzzling! we attribute this to the absence of pasivation of the sample surface. T variations 1 month of CBM operation at 50% duty cycle (HADES life-time!)
Conclusions • Five Mu/Mo samplescustomized 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
Deviations from the DC model. The stabilization time <Φ>=1200 Hz/cm2 measured rate in C@1GeV reactions (2003) at GSI-SIS (~8s time spill) DC limit <Φ>=580 Hz/cm2 DC limit by cutting the first 2 s of the spill the effect disappears.
Quantitative description of the stabilization time (II). The cell model cell model Equivalent circuit M. Abbrescia, NIM A 533(2004)7
Quantitative description of the stabilization time (III). Behaviour under X-ray irradiation
Deviations from the DC model.Thelocal fluctuations of the field Fit to the DC model Not fitted! (σT) response to secondary particles from C@1GeV reactions (2003) at GSI-SIS (~8s time spill)
Quantitative description of the local fluctuations of the field (I) An approximate analytical calculation based on the Campbel theorem and the exact M.C. one, differ slightly but show similar scaling properties Campbel theorem for shot-noise (Average number of shots contributing per cell of area A)
Quantitative description of the local fluctuations of the field (II) (all the N=4 gaps are assumed to equally contribute to the time resolution) A>0.3 mm2 D. Gonzalez-Diaz et al., Nucl. Phys. B (Proc. Suppl) 158(2006)111
The DC model and the case of warm glass(III) charge qp(x) rate Φ(x) T scan 1 2 1 2 3 3 4 4 HV scan T=210C 3 4 3 4 T=210C T=210C T=210C T=330C 3 3 T=330C fit: DC model fit: DC model
Quantitative description of the stabilization time (I) Measurement of the dielectric response function of float glass as the one used in HADES
Rate effects. Campbell theorem (analytical vs simulation) (1) Campbel theorem + Campbel theorem with average drop (2)
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 provides a better description of the data Drop at the end of the spill The result suggests a bias in the tRPC performances when extrapolating from short to long spills P. Colrain et al. NIM A, 456(2000)62