Résultats de recherche pour « Low-frequency radio emission »

Abstract The magnetized planets of the outer Solar System produce kilometric radio emissions at very low frequencies (MHz). They reveal the planetary magnetic dynamics and their interaction with the solar wind. Those radio emissions can also serve as a proxy for interplanetary space weather monitoring. Space‐borne radio interferometers will offer new capabilities for measuring planetary low‐frequency radio emissions as they are not limited by the Earth's ionospheric cutoff (MHz) and can provide spatially resolved observations. This study is conducted in the context of the NOIRE— Nanosatellites for a Radio Interferometric Observatory in Space —concept study. The observation of planetary radio emissions is part of its main scientific objectives and should be achievable with an array of 50 satellites. The instrument's sensitivity is studied with a detailed description of the noises and errors involved in the measurement process. We then detail the various planetary radio components that can be studied with the given instrument design and the constraints currently known at this stage of the project. We discuss how the design may be optimized to better suit these scientific objectives, and we discuss the data volumes involved. The results suggest that NOIRE is able to produce dynamic spectra for Jupiter and Saturn with temporal and spectral resolutions good enough for phenomenological studies and long‐term studies. They also suggest that Uranus' and Neptune's emissions may be detected, but with a low revisit rate ( point every 4 hr).

Abstract We demonstrate that a passive non-contact diagnostic technique, radio emission spectroscopy (RES), provides a sensitive monitor of currents in a low pressure radio frequency (RF) plasma. A near field magnetic loop antenna was used to capture RF emissions from the plasma without perturbing it. The analysis was implemented for a capacitively coupled RF plasma with an RF supply at a frequency of 13.56 MHz. Real-time measurements are captured in scenarios relevant to contemporary challenges faced during semiconductor fabrication (e.g. window coating and wall disturbance). Exploration of the technique for key equipment parameters including applied RF power, chamber pressure, RF bias frequencies and chamber wall cleanliness shows sensitive and repeatable function. In particular, the induced RES signal was found to vary sensitively to pressure changes and we were able to detect pressure and power variations as low as ~2.5 %/mtorr and ~3.5 %/watt, respectively, during the plasma processing during a trial generic plasma process. Finally, we explored the ability of RES to monitor the operation of a multiple frequency low-pressure RF plasma system (f1 = 2 MHz, f2 = 162 MHz) and intermixing products which suggests strongly that the plasma sheaths are the primary source of this non-linear diode mixing effect.

Abstract In this Letter we propose that coherent radio emission of the Crab pulsar, other young energetic pulsars, and millisecond pulsars is produced in the magnetospheric current sheet beyond the light cylinder. We carry out global and local 2D kinetic plasma simulations of reconnection to illustrate the coherent emission mechanism. Reconnection in the current sheet beyond the light cylinder proceeds in the very efficient plasmoid-dominated regime, where the current layer gets fragmented into a dynamic chain of plasmoids that undergo successive coalescence. Mergers of sufficiently large plasmoids produce secondary perpendicular current sheets, which are also plasmoid unstable. Collisions of plasmoids with each other and with the upstream magnetic field eject fast magnetosonic waves, which propagate upstream across the background field and successfully escape from the plasma as electromagnetic waves that fall in the radio band. This model successfully explains many important features of the observed radio emission from the Crab and other pulsars with high magnetic field at the light cylinder: phase coincidence with the high-energy emission, nanosecond duration (nanoshots), and extreme instantaneous brightness of individual pulses.