The origins of mysterious γ ray and radio flashes recently detected by satellite‐based instruments passing over thunderstorms are examined in the context of upward propagating discharges initiated by ...runaway air breakdown. Preliminary calculations normalized by the recent optical measurements of so‐called sprites indicate that the runaway mechanism may well be the source of these emissions. If this is true, then upward discharges represent the first known manifestation of a fundamental, new process in plasma physics.
Operation of a resistive Micromegas in air Procureur, S.; Attié, D.; Aune, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2012, Volume:
688
Journal Article
Peer reviewed
The recent developments on resistive Micromegas have enhanced the performance of this detector, and in particular have offered the possibility to reach higher amplification gains in stable operation. ...In this paper, the detection capabilities of a resistive Micromegas in air have been investigated. A clear Fe55 spectrum has been obtained, as well as MIP signals using cosmic rays. In the latter case, the detection efficiency reaches 42%, and could probably be further improved. The stable operation of a gaseous detector in air, i.e. without bottles, pipes or safety systems, can lead to many new applications or simplifications of existing setups.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
63.
Carbon wire chamber at sub-atmospheric pressure Charles, G.; Audouin, L.; Bettane, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2017, Volume:
855
Journal Article
Peer reviewed
Present in many experiments, wire and drift chambers have been used in a large variety of shapes and configurations during the last decades. Nevertheless, their readout elements has not evolved much: ...tungsten, sometimes gold-plated or aluminum, wires. By taking advantage of the developments in the manufacture of conducting carbon fiber, we could obtain interesting improvements for wire detectors. In this article, we present recent tests and simulations using carbon fibers to readout signal in place of traditional tungsten wires. Unlike metallic wires, their low weight guaranties a reduced quantity of material in the active area.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In the past two decades, deeply virtual Compton scattering of electrons has been successfully used to advance our knowledge of the partonic structure of the free proton and investigate correlations ...between the transverse position and the longitudinal momentum of quarks inside the nucleon. Meanwhile, the structure of bound nucleons in nuclei has been studied in inclusive deep-inelastic lepton scattering experiments off nuclear targets, showing a significant difference in longitudinal momentum distribution of quarks inside the bound nucleon, known as the EMC effect. In this Letter, we report the first beam spin asymmetry (BSA) measurement of exclusive deeply virtual Compton scattering off a proton bound in He-4. The data used here were accumulated using a 6 GeV longitudinally polarized electron beam incident on a pressurized He-4 gaseous target placed within the CLAS spectrometer in Hall-B at the Thomas Jefferson National Accelerator Facility. The azimuthal angle (phi) dependence of the BSA was studied in a wide range of virtual photon and scattered proton kinematics. The Q(2), x(B), and t dependencies of the BSA on the bound proton are compared with those on the free proton. In the whole kinematical region of our measurements, the BSA on the bound proton is smaller by 20% to 40%, indicating possible medium modification of its partonic structure.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
In the past two decades, deeply virtual Compton scattering of electrons has been successfully used to advance our knowledge of the partonic structure of the free proton and investigate correla- tions ...between the transverse position and the longitudinal momentum of quarks inside the nucleon. Meanwhile, the structure of bound nucleons in nuclei has been studied in inclusive deep-inelastic lepton scattering experiments off nuclear targets, showing a significant difference in longitudinal momentum distribution of quarks inside the bound nucleon, known as the EMC effect. In this work, we report the first beam spin asymmetry (BSA) measurement of exclusive deeply virtual Compton scattering (DVCS) off a proton bound in 4He. The data used here were accumulated using a 6 GeV longitudinally polarized electron beam incident on a pressurized 4He gaseous target placed within the CLAS spectrometer in Hall-B at the Thomas Jefferson National Accelerator Facility. The azimuthal angle ($φ$) dependence of the BSA was studied in a wide range of virtual photon and scattered proton kinematics. The $Q^2$, $x_B$, and t dependencies of the BSA on the bound proton are compared with those on the free proton. In the whole kinematical region of our measurements, the BSA on the bound proton is smaller by 20% to 40%, indicating possible medium modification of its partonic structure.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
In the past two decades, deeply virtual Compton scattering of electrons has been successfully used to advance our knowledge of the partonic structure of the free proton and investigate correlations ...between the transverse position and the longitudinal momentum of quarks inside the nucleon. Meanwhile, the structure of bound nucleons in nuclei has been studied in inclusive deep-inelastic lepton scattering experiments off nuclear targets, showing a significant difference in longitudinal momentum distribution of quarks inside the bound nucleon, known as the EMC effect. In this Letter, we report the first beam spin asymmetry (BSA) measurement of exclusive deeply virtual Compton scattering off a proton bound in He-4. The data used here were accumulated using a 6 GeV longitudinally polarized electron beam incident on a pressurized He-4 gaseous target placed within the CLAS spectrometer in Hall-B at the Thomas Jefferson National Accelerator Facility. The azimuthal angle (phi) dependence of the BSA was studied in a wide range of virtual photon and scattered proton kinematics. The Q(2), x(B), and t dependencies of the BSA on the bound proton are compared with those on the free proton. In the whole kinematical region of our measurements, the BSA on the bound proton is smaller by 20% to 40%, indicating possible medium modification of its partonic structure.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
Positron beams, both polarized and unpolarized, are identified as essential ingredients for the experimental programs at the next generation of lepton accelerators. In the context of the hadronic ...physics program at Jefferson Lab (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of nucleons and nuclei, in both the elastic and deep-inelastic regimes. For instance, elastic scattering of polarized and unpolarized electrons and positrons from the nucleon enables a model independent determination of its electromagnetic form factors. Also, the deeply-virtual scattering of polarized and unpolarized electrons and positrons allows unambiguous separation of the different contributions to the cross section of the lepto-production of photons and of lepton-pairs, enabling an accurate determination of the nucleons and nuclei generalized parton distributions, and providing an access to the gravitational form factors. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model of particle physics through the search of a dark photon, the precise measurement of electroweak couplings, and the investigation of charged lepton flavor violation. This document discusses the perspectives of an experimental program with high duty-cycle positron beams at JLab.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The basic mechanisms that govern the generation of an electromagnetic pulse (EMP) following a nuclear detonation in the atmosphere, including heights of burst (HOB) relevant to surface bursts (0 km), ...near surface bursts (0-2 km), air bursts (2-20 km) and high-altitude bursts (> 20 km), are reviewed. Previous computational codes developed to treat the source region and predict the EMP are discussed. A new 2-D hydrodynamic code (HYDROFLASH) that solves the fluid equations for electron and ion transport in the atmosphere and the coupled Maxwell equations using algorithms extracted from the Conservation Law (CLAW) package for solving multi-dimensional hyperbolic equations with finite volume techniques has been formulated. Simulations include the ground, atmospheric gradient, and an azimuthal applied magnetic field as a first approximation to the geomagnetic field. HYDROFLASH takes advantage of multiprocessor systems by using domain decomposition together with the Message Passing Interface (MPI) protocol for parallel processing. A detailed description of the model is presented along with computational results for a generic 10 kiloton (kT) burst detonated at 0 and 10 km altitude.
Detailed 2D hydrodynamic and quasi-electrostatic simulations of high-altitude discharges driven by runaway air breakdown are presented for four cases, corresponding to sprites initiated by positive ...cloud-to-ground lightning strikes in which 200 C of charge is neutralized at an altitude of 11.5 km in 10, 7, 5 and 3 ms. We find that the computed optical emissions agree well with low-light level camera images of sprites, both in terms of the overall intensity and spatial distribution of the emissions. Our results show the presence of blue emissions extending down to 40 km (blue tendrils) and red sprite tops extending from 50 to 77 km. Simulated spectra show that N
2 1st positive emissions dominate in the wavelength range from 550 to 850 nm, in good agreement with observations. Strong radio pulses with durations of ∼300
μs and peak electric field amplitudes ranging from 20 to 75 V/m at an altitude of 80 km and an approximate distance from the discharge of 50 km were computed. The magnitude and duration of these pulses is sufficient to cause breakdown and heating of the lower ionosphere (80–95 km) and leads us to suggest that sprites may also launch the EMP responsible for the production of elves. The computed values for the
γ-ray fluxes are in agreement with observations of
γ-ray bursts of atmospheric origin and the peak secondary electron densities which we obtain are in good agreement with recent measurements of HF echoes at mesospheric heights and associated with lightning.
Full text
Available for:
IJS, IMTLJ, KILJ, KISLJ, NUK, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
PDF
