127 research outputs found
Efficient ion blocking in gaseous detectors and its application to gas-avalanche photomultipliers sensitive in the visible-light range
A novel concept for ion blocking in gas-avalanche detectors was developed,
comprising cascaded micro-hole electron multipliers with patterned electrodes
for ion defocusing. This leads to ion blocking at the 10^{-4} level, in DC
mode, in operation conditions adequate for TPCs and for gaseous
photomultipliers. The concept was validated in a cascaded visible-sensitive gas
avalanche photomultiplier operating at atmospheric pressure of Ar/CH_{4} (95/5)
with a bi-alkali photocathode. While in previous works high gain, in excess of
10^{5}, was reached only in a pulse-gated cascaded-GEM gaseous photomultiplier,
the present device yielded, for the first time, similar gain in DC mode. We
describe shortly the physical processes involved in the charge transport within
gaseous photomultipliers and the ion blocking method. We present results of ion
backflow fraction and of electron multiplication in cascaded
patterned-electrode gaseous photomultiplier with K-Cs-Sb, Na-K-Sb and Cs-Sb
visible-sensitive photocathodes, operated in DC mode.Comment: Proceeding paper to 10-th International Conference On Instrumentation
For Colliding Beam Physics, Budker Institute of Nuclear Physics, Novosibirsk,
Russia, February 28 - March 5, 2008, Submitted to NIMA, 5 pages, 7 figure
Further progress in ion back-flow reduction with patterned gaseous hole-multipliers
A new idea on electrostatic deviation and capture of back-drifting
avalanche-ions in cascaded gaseous hole-multipliers is presented. It involves a
flipped reversed-bias Micro-Hole & Strip Plate (F-R-MHSP) element, the strips
of which are facing the drift region of the multiplier. The ions, originating
from successive multiplication stages, are efficiently deviated and captured by
such electrode. Experimental results are provided comparing the ion-blocking
capability of the F-R-MHSP to that of the reversed-bias Micro-Hole & Strip
Plate (R-MHSP) and the Gas Electron Multiplier (GEM). Best ion-blocking results
in cascaded hole-multipliers were reached with a detector having the F-R-MHSP
as the first multiplication element. A three-element F-R-MHSP/GEM/MHSP cascaded
multiplier operated in atmospheric-pressure Ar/CH4 (95/5), at total gain of
~10^{5}, yielded ion back-flow fractions of 3*10^{-4} and 1.5*10^{-4}, at drift
fields of 0.5 and 0.2 kV/cm, respectively. We describe the F-R-MHSP concept and
the relevance of the obtained ion back-flow fractions to various applications;
further ideas are also discussed.Comment: 17 pages, 11 figures, published in JINS
Cryogenic Gaseous Photomultiplier for position reconstruction of liquid argon scintillation light
Presented here are first tests of a Gaseous Photomultiplier based on a cascade of Thick GEM structures intended for gamma-ray position reconstruction in liquid argon. The detector has a MgF2 window, transparent to VUV light, and a CsI photocathode deposited on the first THGEM . A gain of 8⋅ 105 per photoelectron and ~ 100% photoelectron collection efficiency are measured at stable operation settings. The excellent position resolution capabilities of the detector (better than 100 μm) at 100 kHz readout rate, is demonstrated at room temperature. Structural integrity tests of the detector and seals are successfully performed at cryogenic temperatures by immersing the detector in liquid Nitrogen, laying a good foundation for future operation tests in noble liquids
High-gain DC-mode operated Gaseous Photomultipliers for the visible spectral range
We shortly describe recent progress in photon detectors combining bi-alkali
photocathodes and cascaded patterned gas-avalanche electron multipliers. It
permitted the development and the first feasibility demonstration of high-gain
gaseous photomultipliers sensitive in the visible spectral range, operated in
DC mode with single-photon sensitivity.Comment: Proceedings to the 5th International Conference on New Developments
In Photodetection 2008, Aix-les-Bains, France, June 15-20, 2008, submitted to
NIM
MHSP in reversed-biased operation mode for ion blocking in gas-avalanche multipliers
We present recent results on the operation of gas-avalanche detectors
comprising a cascade of gas electron multipliers (GEMs) and Micro-Hole and
Strip Plates (MHSPs) multiplier operated in reversed-bias (R-MHSP) mode. The
operation mechanism of the R-MHSP is explained and its potential contribution
to ion-backflow (IBF) reduction is demonstrated. IBF values of 4E-3 were
obtained in cascaded R-MHSP and GEM multipliers at gains of about 1E+4, though
at the expense of reduced effective gain in the first R- MHSP multiplier in the
cascade.Comment: 23 pages, 8 figure
Ion-induced effects in GEM & GEM/MHSP gaseous photomultipliers for the UV and the visible spectral range
We report on the progress in the study of cascaded GEM and GEM/MHSP gas
avalanche photomultipliers operating at atmospheric pressure, with CsI and
bialkali photocathodes. They have single-photon sensitivity, ns time resolution
and good localization properties. We summarize operational aspects and results,
with the highlight of a high-gain stable gated operation of a visible-light
device. Of particular importance are the results of a recent ion-backflow
reduction study in different cascaded multipliers, affecting the detector's
stability and the photocathode's liftime. We report on the significant progress
in ion-blocking and provide first results on bialkali-photocathode aging under
gas multiplication.Comment: 6 pages, 8 figure
A simulation toolkit for electroluminescence assessment in rare event experiments
A good understanding of electroluminescence is a prerequisite when optimising
double-phase noble gas detectors for Dark Matter searches and high-pressure
xenon TPCs for neutrinoless double beta decay detection.
A simulation toolkit for calculating the emission of light through electron
impact on neon, argon, krypton and xenon has been developed using the Magboltz
and Garfield programs. Calculated excitation and electroluminescence
efficiencies, electroluminescence yield and associated statistical fluctuations
are presented as a function of electric field. Good agreement with experiment
and with Monte Carlo simulations has been obtained
CsI-THGEM gaseous photomultipliers for RICH and noble-liquid detectors
The properties of UV-photon imaging detectors consisting of CsI-coated THGEM
electron multipliers are summarized. New results related to detection of
Cherenkov light (RICH) and scintillation photons in noble liquid are presented.Comment: 5 Pages, 10 Figures; Presented at the 7th International Workshop on
Ring Imaging Cherenkov Detectors (RICH 2010) RICH2010 - Cassis, Provence,
France, 3-7 May 201
Evaluation of turbulent dissipation rate retrievals from Doppler Cloud Radar
Turbulent dissipation rate retrievals from cloud radar Doppler velocity measurements are evaluated using independent, in situ observations in Arctic stratocumulus clouds. In situ validation data sets of dissipation rate are derived using sonic anemometer measurements from a tethered balloon and high frequency pressure variation observations from a research aircraft, both flown in proximity to stationary, ground-based radars. Modest biases are found among the data sets in particularly low- or high-turbulence regimes, but in general the radar-retrieved values correspond well with the in situ measurements. Root mean square differences are typically a factor of 4-6 relative to any given magnitude of dissipation rate. These differences are no larger than those found when comparing dissipation rates computed from tetheredballoon and meteorological tower-mounted sonic anemometer measurements made at spatial distances of a few hundred meters. Temporal lag analyses suggest that approximately half of the observed differences are due to spatial sampling considerations, such that the anticipated radar-based retrieval uncertainty is on the order of a factor of 2-3. Moreover, radar retrievals are clearly able to capture the vertical dissipation rate structure observed by the in situ sensors, while offering substantially more information on the time variability of turbulence profiles. Together these evaluations indicate that radar-based retrievals can, at a minimum, be used to determine the vertical structure of turbulence in Arctic stratocumulus clouds
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