35 research outputs found
Development of wavelength shifter coated reflectors for the ArDM argon dark matter detector
To optimise the design of the light readout in the ArDM 1-ton liquid argon dark matter detector, a range of reflector and WLS coating combinations were investigated in several small setups, where argon scintillation light was generated by radioactive sources in gas at normal temperature and pressure and shifted into the blue region by tetraphenyl butadiene (TPB). Various thicknesses of TPB were deposited by spraying and vacuum evaporation onto specular 3MTM-foil and diffuse Tetratex® (TTX) substrates. Light yields of each reflector and TPB coating combination were compared. Reflection coefficients of TPB coated reflectors were independently measured using a spectroradiometer in a wavelength range between 200 and 650 nm. WLS coating on the PMT window was also studied. These measurements were used to define the parameters of the light reflectors of the ArDM experiment. Fifteen large 120 × 25 cm2 TTX sheets were coated and assembled in the detector. Measurements in argon gas are reported providing good evidence of fulfilling the light collection requirements of the experiment
Recent updates on the ArDM project: A Liquid Argon TPC for Dark Matter Detection
ArDM is a new-generation WIMP detector which will measure simultaneously
light and charge from scintillation and ionization of liquid argon. Our goal is
to construct, characterize and operate a 1 ton liquid argon underground
detector. The project relies on the possibility to extract the electrons
produced by ionization from the liquid into the gas phase of the detector, to
amplify and read out with Large Electron Multipliers detectors. Argon VUV
scintillation light has to be converted with wavelength shifters such as
TetraPhenyl Butadiene in order to be detected by photomultipliers with bialkali
photocathodes. We describe the status of the LEM based charge readout and light
readout system R&D and the first light readout tests with warm and cold argon
gas in the full size detector.Comment: 10 pages, 9 figures, Talk given at the XIII International Conference
on Calorimetry in High Energy Physics (CALOR08), May 2008, Pavia, Ital
Luminescence quenching of the triplet excimer state by air traces in gaseous argon
While developing a liquid argon detector for dark matter searches we
investigate the influence of air contamination on the VUV scintillation yield
in gaseous argon at atmospheric pressure. We determine with a radioactive
alpha-source the photon yield for various partial air pressures and different
reflectors and wavelength shifters. We find for the fast scintillation
component a time constant tau1= 11.3 +- 2.8 ns, independent of gas purity.
However, the decay time of the slow component depends on gas purity and is a
good indicator for the total VUV light yield. This dependence is attributed to
impurities destroying the long-lived argon excimer states. The population ratio
between the slowly and the fast decaying excimer states is determined for
alpha-particles to be 5.5 +-0.6 in argon gas at 1100 mbar and room temperature.
The measured mean life of the slow component is tau2 = 3.140 +- 0.067 microsec
at a partial air pressure of 2 x 10-6 mbar.Comment: 7 pages submitted to NIM
First results on light readout from the 1-ton ArDM liquid argon detector for dark matter searches
ArDM-1t is the prototype for a next generation WIMP detector measuring both
the scintillation light and the ionization charge from nuclear recoils in a
1-ton liquid argon target. The goal is to reach a minimum recoil energy of
30\,keVr to detect recoiling nuclei. In this paper we describe the experimental
concept and present results on the light detection system, tested for the first
time in ArDM on the surface at CERN. With a preliminary and incomplete set of
PMTs, the light yield at zero electric field is found to be between 0.3-0.5
phe/keVee depending on the position within the detector volume, confirming our
expectations based on smaller detector setups.Comment: 14 pages, 10 figures, v2 accepted for publication in JINS
Argon Purification Studies and a Novel Liquid Argon Re-circulation System
Future giant liquid argon (LAr) time projection chambers (TPCs) require a
purity of better than 0.1 parts per billion (ppb) to allow the ionised
electrons to drift without significant capture by any electronegative
impurities. We present a comprehensive study of the effects of electronegative
impurity on gaseous and liquid argon scintillation light, an analysis of the
efficacy of various purification chemicals, as well as the Liverpool LAr setup,
which utilises a novel re-circulation purification system. Of the impurities
tested - Air, O_2, H_2O, N_2 and CO_2 in the range of between 0.01 ppm to 1000
ppm - H_2O was found to have the most profound effect on gaseous argon
scintillation light, and N_2 was found to have the least. Additionally, a
correlation between the slow component decay time and the total energy
deposited with 0.01 ppm - 100 ppm O_2 contamination levels in liquid argon has
been established. The superiority of molecular sieves over anhydrous complexes
at absorbing Ar gas, N_2 gas and H_2O vapour has been quantified using BET
isotherm analysis. The efficiency of Cu and P_2O5 at removing O_2 and H_2O
impurities from 1 bar N6 argon gas at both room temperature and -130 ^oC was
investigated and found to be high. A novel, highly scalable LAr re-circulation
system has been developed. The complete system, consisting of a motorised
bellows pump operating in liquid and a purification cartridge, were designed
and built in-house. The system was operated successfully over many days and
achieved a re-circulation rate of 27 litres/hour and high purity
First operation and drift field performance of a large area double phase LAr Electron Multiplier Time Projection Chamber with an immersed Greinacher high-voltage multiplier
We have operated a liquid-argon large-electron-multiplier time-projection
chamber (LAr LEM-TPC) with a large active area of 76 40 cm and a
drift length of 60 cm. This setup represents the largest chamber ever achieved
with this novel detector concept. The chamber is equipped with an immersed
built-in cryogenic Greinacher multi-stage high-voltage (HV) multiplier, which,
when subjected to an external AC HV of 1 kV, statically
charges up to a voltage a factor of 30 higher inside the LAr vessel,
creating a uniform drift field of 0.5 kV/cm over the full drift length.
This large LAr LEM-TPC was brought into successful operation in the
double-phase (liquid-vapor) operation mode and tested during a period of
1 month, recording impressive three-dimensional images of very
high-quality from cosmic particles traversing or interacting in the sensitive
volume. The double phase readout and HV systems achieved stable operation in
cryogenic conditions demonstrating their good characteristics, which
particularly suit applications for next-generation giant-scale LAr-TPCs.Comment: 26 pages, 19 figure
Probing the Local Velocity Distribution of WIMP Dark Matter with Directional Detectors
We explore the ability of directional nuclear-recoil detectors to constrain
the local velocity distribution of weakly interacting massive particle (WIMP)
dark matter by performing Bayesian parameter estimation on simulated
recoil-event data sets. We discuss in detail how directional information, when
combined with measurements of the recoil-energy spectrum, helps break
degeneracies in the velocity-distribution parameters. We also consider the
possibility that velocity structures such as cold tidal streams or a dark disk
may also be present in addition to the Galactic halo. Assuming a
carbon-tetrafluoride detector with a 30-kg-yr exposure, a 50-GeV WIMP mass, and
a WIMP-nucleon spin-dependent cross-section of 0.001 pb, we show that the
properties of a cold tidal stream may be well constrained. However, measurement
of the parameters of a dark-disk component with a low lag speed of ~50 km/s may
be challenging unless energy thresholds are improved.Comment: 38 pages, 15 figure
A prototype liquid Argon Time Projection Chamber for the study of UV laser multi-photonic ionization
This paper describes the design, realization and operation of a prototype
liquid Argon Time Projection Chamber (LAr TPC) detector dedicated to the
development of a novel online monitoring and calibration system exploiting UV
laser beams. In particular, the system is intended to measure the lifetime of
the primary ionization in LAr, in turn related to the LAr purity level. This
technique could be exploited by present and next generation large mass LAr TPCs
for which monitoring of the performance and calibration plays an important
role. Results from the first measurements are presented together with some
considerations and outlook.Comment: 26 pages, 27 figure
Towards a liquid Argon TPC without evacuation: filling of a 6 m^3 vessel with argon gas from air to ppm impurities concentration through flushing
In this paper we present a successful experimental test of filling a volume
of 6 m with argon gas, starting from normal ambient air and reducing the
impurities content down to few parts per million (ppm) oxygen equivalent. This
level of contamination was directly monitored measuring the slow component of
the scintillation light of the Ar gas, which is sensitive to {\it all} sources
of impurities affecting directly the argon scintillation.Comment: 9 pages, 6 figures, to appear in Proc. 1st International Workshop
towards the Giant Liquid Argon Charge Imaging Experiment (GLA2010), Tsukuba,
March 201