MARTA: A high-energy cosmic-ray detector concept with high-accuracy muon measurement

A new concept for the direct measurement of muons in air showers is presented. The concept is based on resistive plate chambers (RPCs), which can directly measure muons with very good space and time resolution. The muon detector is shielded by placing it under another detector able to absorb and measure the electromagnetic component of the showers such as a water-Cherenkov detector, commonly used in air shower arrays. The combination of the two detectors in a single, compact detector unit provides a unique measurement that opens rich possibilities in the study of air showers.Comment: 11 page

Nonstationarity of a two-dimensional perpendicular shock: Competing mechanisms

International audienceTwo-dimensional particle-in-cell (PIC) simulations are used for analyzing in detail different nonstationary behaviors of a perpendicular supercritical shock. A recent study by Hellinger et al. (2007) has shown that the front of a supercritical shock can be dominated by the emission of large-amplitude whistler waves. These waves inhibit the self-reformation driven by the reflected ions; then, the shock front appears almost “quasi-stationary.” The present study stresses new complementary results. First, for a fixed βi value, the whistler waves emission (WWE) persists for high MA above a critical Mach number (i.e., MA ≥ MAWWE). The quasi-stationarity is only apparent and disappears when considering the full 3-D field profiles. Second, for lower MA, the self-reformation is retrieved and becomes dominant as the amplitude of the whistler waves becomes negligible. Third, there exists a transition regime in MA within which both processes compete each other. Fourth, these results are observed for a strictly perpendicular shock only as B0 is within the simulation plane. When B0 is out of the simulation plane, no whistler waves emission is evidenced and only self-reformation is recovered. Fifth, the occurrence and disappearance of the nonlinear whistler waves are well recovered in both 2-D PIC and 2-D hybrid simulations. The impacts on the results of the mass ratio (2-D PIC simulations), of the resistivity and spatial resolution (2-D hybrid simulations), and of the size of the simulation box along the shock front are analyzed in detail

Cluster PEACE observations of electrons of spacecraft origin

Abstract. The two PEACE (Plasma Electron And Current Experiment) sensors on board each Cluster spacecraft sample the electron velocity distribution across the full 4π solid angle and the energy range 0.7 eV to 26 keV with a time resolution of 4 s. We present high energy and angular resolution 3D observations of electrons of spacecraft origin in the various environments encountered by the Cluster constellation, including a lunar eclipse interval where the spacecraft potential was reduced but remained positive, and periods of AS-POC (Active Spacecraft POtential Control) operation which reduced the spacecraft potential. We demonstrate how the spacecraft potential may be found from a gradient change in the PEACE low energy spectrum, and show how the observed spacecraft electrons are confined by the spacecraft potential. We identify an intense component of the spacecraft electrons with energies equivalent to the spacecraft potential, the arrival direction of which is seen to change when ASPOC is switched on. Another spacecraft electron component, observed in the sunward direction, is reduced in the eclipse but unaffected by ASPOC, and we believe this component is produced in the analyser by solar UV. We find that PEACE anodes with a look direction along the spacecraft surfaces are more susceptible to spacecraft electron contamination than those which look perpendicular to the surface, which justifies the decision to mount PEACE with its field-of-view radially outward rather than tangentially. Key words. Magnetosheric physics (general or miscellaneous) Space plasma physics (spacecraft sheaths, wakes, charging)

Nonlinear mirror mode dynamics: Simulations and modeling

Journal of Geophysical Research (Space Physics), 113, p. 08219, http://dx.doi.org./10.1029/2007ja012898International audienc

Whistler waves observations upstream the bowshock during 31 March 2001 bow shock crossings: Cluster II observations

International audienc

Mirror structures above and below the linear instability threshold: Cluster observations, fluid model and hybrid simulations

International audienceUsing 5 years of Cluster data, we present a detailed statistical analysis of magnetic fluctuations associated with mirror structures in the magnetosheath. We especially focus on the shape of these fluctuations which, in addition to quasi-sinusoidal forms, also display deep holes and high peaks. The occurrence frequency and the most probable location of the various types of structures is discussed, together with their relation to local plasma parameters. While these properties have previously been correlated to the ? of the plasma, we emphasize here the influence of the distance to the linear mirror instability threshold. This enables us to interpret the observations of mirror structures in a stable plasma in terms of bistability and subcritical bifurcation. The data analysis is supplemented by the prediction of a quasi-static anisotropic MHD model and hybrid numerical simulations in an expanding box aimed at mimicking the magnetosheath plasma. This leads us to suggest a scenario for the formation and evolution of mirror structures

Whistler waves observations upstream the bowshock during 31 March 2001 bow shock crossings: Cluster II observations

International audienc

Whistler waves observations upstream the bowshock during 31 March 2001 bow shock crossings: Cluster II observations

International audienc