223 research outputs found
Sealed operation, and circulation and purification of gas in the HARPO TPC
HARPO is a time projection chamber (TPC) demonstrator of a gamma-ray
telescope and polarimeter in the MeV-GeV range, for a future space mission. We
present the evolution of the TPC performance over a five month sealed-mode
operation, by the analysis of cosmic-ray data, followed by the fast and
complete recovery of the initial gas properties using a lightweight gas
circulation and purification system.Comment: Proceedings_MPGD2015, EPJ Web of Conference
Micromegas TPC studies at high magnetic fields using the charge dispersion signal
The International Linear Collider (ILC) Time Projection Chamber (TPC)
transverse space-point resolution goal is 100 microns for all tracks including
stiff 90 degree tracks with the full 2 meter drift. A Micro Pattern Gas
Detector (MPGD) readout TPC can achieve the target resolution with existing
techniques using 1 mm or narrower pads at the expense of increased detector
cost and complexity. The new MPGD readout technique of charge dispersion can
achieve good resolution without resorting to narrow pads. This has been
demonstrated previously for 2 mm x 6 mm pads with GEMs and Micromegas in cosmic
ray tests and in a KEK beam test in a 1 Tesla magnet. We have recently tested a
Micromegas-TPC using the charge dispersion readout concept in a high field
super-conducting magnet at DESY. The measured Micromegas gain was found to be
constant within 0.5% for magnetic fields up to 5 Tesla. With the strong
suppression of transverse diffusion at high magnetic fields, we measure a flat
50 micron resolution at 5 Tesla over the full 15 cm drift length of our
prototype TPC.Comment: 7 pages, 3 figure
New determinations of gamma-ray line intensities of the Ep = 550 keV and Ep = 1747 keV resonances of the 13-C(p,gamma)14-N reaction
Gamma-ray angular distributions for the resonances at Ep = 550 keV and 1747
keV of the radiative capture reaction 13-C(p,g)14-N have been measured, using
intense proton beams on isotopically pure 13-C targets. Relative intensities
for the strongest transitions were extracted with an accuracy of typically five
per cent, making these resonances new useful gamma-ray standards for efficiency
calibration in the energy range Egamma = 1.6 to 9 MeV.Comment: 17 pages, 6 figures, Nuclear Instruments and Methods, Sec. A,
accepte
Characterization of microbulk detectors in argon- and neon-based mixtures
A recent Micromegas manufacturing technique, so called Microbulk, has been
developed, improving the uniformity and stability of this kind of detectors.
Excellent energy resolutions have been obtained, reaching values as low as 11%
FWHM at 5.9 keV in Ar+5%iC4H10. This detector has other advantages like its
flexible structure, low material budget and high radio-purity. Two microbulk
detectors with gaps of 50 and 25 um have been characterized in argon- and
neon-based mixtures with ethane, isobutane and cyclohexane. The results will be
presented and discussed. The gain curves have been fitted to the Rose-Korff
gain model and dependences of the electron mean free path and the threshold
energy for ionization have been obtained. The possible relation between these
two parameters and the energy resolution will be also discussed.Comment: Submitted to the Journal of Instrumentatio
Measurement of 1.7 to 74 MeV polarised gamma rays with the HARPO TPC
Current {\gamma}-ray telescopes based on photon conversions to
electron-positron pairs, such as Fermi, use tungsten converters. They suffer of
limited angular resolution at low energies, and their sensitivity drops below 1
GeV. The low multiple scattering in a gaseous detector gives access to higher
angular resolution in the MeV-GeV range, and to the linear polarisation of the
photons through the azimuthal angle of the electron-positron pair.
HARPO is an R&D program to characterise the operation of a TPC (Time
Projection Chamber) as a high angular-resolution and sensitivity telescope and
polarimeter for {\gamma} rays from cosmic sources. It represents a first step
towards a future space instrument. A 30 cm cubic TPC demonstrator was built,
and filled with 2 bar argon-based gas. It was put in a polarised {\gamma}-ray
beam at the NewSUBARU accelerator in Japan in November 2014. Data were taken at
different photon energies from 1.7 MeV to 74 MeV, and with different
polarisation configurations. The electronics setup is described, with an
emphasis on the trigger system. The event reconstruction algorithm is quickly
described, and preliminary measurements of the polarisation of 11 MeVphotons
are shown.Comment: Proceedings VCI201
Simultaneous observations of the quasar 3C 273 with INTEGRAL, XMM-Newton and RXTE
INTEGRAL has observed the bright quasar 3C 273 on 3 epochs in January 2003 as
one of the first observations of the open programme. The observation on January
5 was simultaneous with RXTE and XMM-Newton observations. We present here a
first analysis of the continuum emission as observed by these 3 satellites in
the band from 3 keV to 500 keV. The continuum spectral energy distribution of
3C 273 was observed to be weak and steep in the high energies during this
campaign. We present the actual status of the cross calibrations between the
instruments on the three platforms using the calibrations available in June
2003.Comment: 4 figures, accepted for publication in A+A letter
Supercooled liquid water cloud observed, analysed, and modelled at the top of the planetary boundary layer above Dome C, Antarctica
Abstract. A comprehensive analysis of the water budget over the Dome C (Concordia,
Antarctica) station has been performed during the austral summer 2018–2019
as part of the Year of Polar Prediction (YOPP) international campaign. Thin
(∼100 m deep) supercooled liquid water (SLW) clouds have been
detected and analysed using remotely sensed observations at the station
(tropospheric depolarization lidar, the H2O Antarctica Microwave Stratospheric and Tropospheric
Radiometer (HAMSTRAD), net
surface radiation from the Baseline Surface Radiation Network (BSRN)), radiosondes, and satellite observations (CALIOP, Cloud-Aerosol LIdar with Orthogonal Polarization/CALIPSO, Cloud Aerosol Lidar and Infrared
Pathfinder Satellite Observations) combined with a specific
configuration of the numerical weather prediction model: ARPEGE-SH (Action
de Recherche Petite Echelle Grande Echelle – Southern Hemisphere). The
analysis shows that SLW clouds were present from November to March, with the
greatest frequency occurring in December and January when ∼50 % of the days in summer time exhibited SLW clouds for at least 1 h. Two case studies are used to illustrate this phenomenon. On 24 December 2018, the atmospheric planetary boundary layer (PBL) evolved
following a typical diurnal variation, which is to say with a warm and dry
mixing layer at local noon thicker than the cold and dry stable layer at
local midnight. Our study showed that the SLW clouds were observed at Dome C
within the entrainment and the capping inversion zones at the top of the
PBL. ARPEGE-SH was not able to correctly estimate the ratio between liquid
and solid water inside the clouds with the liquid water path (LWP) strongly
underestimated by a factor of 1000 compared to observations. The lack of
simulated SLW in the model impacted the net surface radiation that was 20–30 W m−2 higher in the BSRN observations than in the ARPEGE-SH
calculations, mainly attributable to the BSRN longwave downward surface
radiation being 50 W m−2 greater than that of ARPEGE-SH. The second
case study took place on 20 December 2018, when a warm and wet episode
impacted the PBL with no clear diurnal cycle of the PBL top. SLW cloud
appearance within the entrainment and capping inversion zones coincided with
the warm and wet event. The amount of liquid water measured by HAMSTRAD was
∼20 times greater in this perturbed PBL than in the typical
PBL. Since ARPEGE-SH was not able to accurately reproduce these SLW clouds,
the discrepancy between the observed and calculated net surface radiation
was even greater than in the typical PBL case, reaching +50 W m−2,
mainly attributable to the downwelling longwave surface radiation from BSRN
being 100 W m−2 greater than that of ARPEGE-SH. The model was then run
with a new partition function favouring liquid water for temperatures below
−20 down to −40 ∘C. In this test mode, ARPEGE-SH has
been able to generate SLW clouds with modelled LWP and net surface radiation
consistent with observations during the typical case, whereas, during the
perturbed case, the modelled LWP was 10 times less than the observations and
the modelled net surface radiation remained lower than the observations by
∼50 W m−2. Accurately modelling the presence of SLW
clouds appears crucial to correctly simulate the surface energy budget over
the Antarctic Plateau
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