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R&D on Hadron Blind detector, recent results 27.11.2002 - 15.01.2003. Issues addressed: - gain limits in CF 4 with heavily ionizing particles - operation with reflective CsI photo-cathode, gain and
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27.11.2002 - 15.01.2003
- gain limits in CF4 with heavily ionizing particles
- operation with reflective CsI photo-cathode, gain and
ion back-flow, optimization of the powering scheme
- measurement of stability (first attempts)
of the mesh for the
measurement of signal
as a function of drift field
R = 10MW
of the G1 top for the measurement
of ion back-flow
Set-up for the study of operation
with CsI photo-cathode
Set-up for the study of gain limits
Current to the PCB as a function of Vgem.
GEM1 with respect to the mesh.
Final procedure to determine current at gain=1: apply Vmesh = 1kV, wait 20 min, read current to the mesh.
Factor 2 discrepancy is not understood yet
of electrons collection efficiency.
History of the 2nd run with CsI photo-cathode. Each point is the measurement
of extraction to the mesh (current at gain=1). Medium-term stability
measurements were performed during day 3 (4 mC/cm2), day 4 (3 mC/cm2),
day 5 (2 mC/cm2).
Upper limit of the total charge in 10 years of PHENIX
operation estimeted to 1 mC/cm2
Stability measurements. UV intensity corresponds to ~108 photons/cm2/s.
In the 1st and 2nd runs UV and HV were applied simultaneously, in the 3d
run UV was applied 2h later than HV.
of accumulated charge
- Triple-GEM provides stable operation in CF4 at gain 104
in short term (hours - days);
- Strong non-linearity is observed when total avalanche charge
exceeds ~3*106 electrons;
- Discharges in the presence of HIPs occur in CF4 at gain of ~106(small GEM,
no defects). In case of large GEM discharge threshold is determined by the
GEM quality rather than avalanche charge or voltage.
- Triple-GEM with CsI reflective photo-cathode shows stable performance
at gain of 104in short term (hours to days);
- Ion back-flow can be optimized down to the level of 0.7, it does not depend
on gas and electric fields inside GEMs package;
- No deterioration of CsI observed after delivering charge up to 9mC/cm2