Subauroral proton arcs are a type of terrestrial auroral phenomena, which are often detached equatorially from the auroral oval. This work presents evolution of a subauroral proton arc using observations of the Special Sensor Ultraviolet Spectrographic Imager and Special Sensor J (SSJ) on board Defense Meteorological Satellite Program (DMSP) spacecraft. The arc was observed in the afternoon sector and was located within 60°–70° geomagnetic latitude during the recovery phase of a moderate magnetic storm with the minimum SYM‐H index of −55 nT. Particle measurements from DMSP F17/SSJ indicate that the arc was detached from the normal oval and produced by energetic ring current ions with energies above 10 keV. These energetic ions were likely scattered into the magnetic loss cone by electromagnetic ion cyclotron waves in the frequency range between 0.1 and 0.5 Hz, as confirmed by Pc1 waves derived from the observations of a ground station. Continuous auroral observations directly show that the subauroral proton arc was detached from the oval during evolution. Following a northward interplanetary magnetic field turning, the auroral oval moved toward higher latitudes. We propose that the equatorward edge of the auroral oval is less influenced by the convection electric field, and thus moves more slowly than the poleward edge. This mechanism is proposed for producing a separation between the equatorward and poleward parts of the auroral oval, with the former evolving into the subauroral proton arc.
Collimated proton beams from laser interaction with a slab having a hole on its backside are investigated using particle-in-cell simulation. The hot target electrons driven by the laser expand rapidly into the hole. However, at the hole's corners the electrons are strongly compressed and an intense electron jet is emitted from each corner, tightly followed by the ions. The plasma jets focus and collimate along the axis of the hole and can propagate without divergence within the hole. The effect of the hole diameter on the collimated proton beam is considered.
An electron injection regime in laser wake-field acceleration, namely electron bow-wave injection, is investigated by two- and three-dimensional particle-in-cell simulation as well as analytical model. In this regime electrons in the intense electron bow wave behind the first bubble catch up with the bubble tail and are trapped by the bubble finally, resulting in considerable enhancement of the total trapped electron number. For example, with the increase of the laser intensity from 2 × 10(19) to 1 × 10(20) W/cm(2), the electron trapping changes from normal self-injection to bow-wave injection and the trapped electron number is enhanced by two orders of magnitude. An analytical model is proposed to explain the numerical observation.
A relatively simple interfering-pulses-assisted laser wakefield acceleration (IPA-LWFA) scheme is proposed for enhancing the charge of the LWFA electron bunch. Prior to the short intense pump pulse, two long lowintensity auxiliary laser pulses first interact in the plasma and excite a slow electron plasma wave at the beat frequency. The weak but finite-amplitude plasma wave energizes the affected electrons and acts like a slow-moving grating. Particle-in-cell simulations show that electron trapping in the wakefield of the pump laser pulse, which arrives at a later time, can be significantly enhanced. The charge of the IPA-LWFA electron bunch depends mainly on the intensity of the auxiliary pulses and the time delay of the pump laser.
Generation and propagation of attosecond electron bunches along a cone-and-channel target are investigated by particle-in-cell simulation. The target electrons are pulled out by the oscillating electric field of an intense laser pulse irradiating a cone target and accelerated forward along the cone walls. It is shown that the energetic electrons can be further guided and confined by a channel attached to the cone tip. The propagation of these electrons along the channel induces a strong quasistatic magnetic field as well as a sheath electric field since a part of the energetic electrons expands into the surrounding vacuum. The electromagnetic field in turn confines the surface currents. With the cone-and-channel target the energetic electrons can be much better collimated and propagate much farther than that from the classical cone target.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.