Electrons In Jet Research Articles

Orbital alignment in atoms generated by photodetachment in a strong laser field

A pump-probe laser scheme is employed to investigate orbital alignment and its dynamics in the ground state of laser-generated neutral atoms. The alignment is initiated by electron photodetachment of an atomic negative ion in a strong laser pulse. The electron density distribution in the ground state of the residual atom is probed by means of strong-field ionization in a second laser pulse at a delayed time. The principle of the probe method relies on the fact that the portion of the electron density distribution oriented along the laser polarization axis constitutes the ionization yield in the high-energy jets of emitted electrons. A systematic study is carried out on C, Si, and Ge atoms, which possess two electrons in an open $p$ shell. A pronounced temporal modulation in the yield of high-energy electrons is observed for C and Si, revealing a periodic spatial rearrangement of the electron density distribution in these atoms. Its period is defined by the beat between the $J=1$ and $J=2$ spin-orbit components of the ground state.

Detailed elaboration and general model of the electron treatment of surfaces of charged plasmoids: From atomic nuclei to white dwarves, neutron stars, and galactic cores part III: Behavior, variation, and synergetism of positively charged cumulative-dissipative plasma structures (+CDS) under external actions

There has been performed an analysis of the 3D architecture of the accumulation and dissipation of energy-mass-momentum flows in plasma +CDS under the external action of a long-range electric field. The following cases are considered in this work: (1) the interaction between external electric fields and quasistationary positively charged plasmoids (plasma +CDS), in which some cumulative jets of high-energy electrons are formed due to the cumulation of electrons; (2) the clustering of single plasmoids into regular systems—dissipative “crystals”; and (3) the synergetic effects caused by the coalescence of +CDS.

Jets and photons.

This Letter applies the concept of "jets," as constructed from calorimeter cell four-vectors, to jets composed (primarily) of photons (or leptons). Thus jets become a superset of both traditional objects such as QCD jets, photons, and electrons, and more unconventional objects such as photon jets and electron jets, defined as collinear photons and electrons, respectively. Since standard objects such as single photons become a subset of jets in this approach, standard jet substructure techniques are incorporated into the photon finder toolbox. Using a (reasonably) realistic calorimeter model we demonstrate that, for a single photon identification efficiency of 80% or above, the use of jet substructure techniques reduces the number of QCD jets faking photons by factors of 2.5 to 4. Depending on the topology of the photon jets, the substructure variables reduce the number of photon jets faking single photons by factors of 10 to 10(3) at a single photon identification efficiency of 80%.

Cluster observations of kinetic structures and electron acceleration within a dynamic plasma bubble

Fast plasma flows are believed to play important roles in transporting mass, momentum, and energy in the magnetotail during active periods, such as the magnetospheric substorms. In this paper, we present Cluster observations of a plasma‐depleted flux tube, i.e., a plasma bubble associated with fast plasma flow before the onset of a substorm in the near‐Earth tail around X = −18 RE. The bubble is bounded by both sharp leading (∂bz/∂x < 0) and trailing (∂bz/∂x > 0) edges. The two edges are thin current layers (approximately ion inertial length) that carry not only intense perpendicular current but also field‐aligned current. The leading edge is a dipolarization front (DF) within a slow plasma flow, while the trailing edge is embedded in a super‐Alfvénic convective ion jet. The electron jet speed exceeds the ion flow speed thus producing a large tangential current at the trailing edge. The electron drift is primarily given by the E × B drift. Interestingly, the trailing edge moves faster than the leading edge, which causes shrinking of the bubble and local flux pileup inside the bubble. This resulted in a further intensification of Bz, or a secondary dipolarization. Both the leading and trailing edges are tangential discontinuities that confine the electrons inside the bubble. Strong electron acceleration occurred corresponding to the secondary dipolarization, with perpendicular fluxes dominating the field‐aligned fluxes. We suggest that betatron acceleration is responsible for the electron energization. Whistler waves and lower hybrid drift waves were identified inside the bubble. Their generation mechanisms and potential roles in electron dynamics are discussed.

Search for Long-Lived Particles and Lepton-Jets with the ATLAS detector

Many extensions of the Standard Model include neutral weakly-coupled particles that can be long- lived. These long-lived particles occur in many models, included gauge-mediated extensions of the Minimal Supersymmetric Model (MSSM), MSSM with R-parity violation, inelastic dark matter and the Hidden Valley scenario. Results are presented on the ATLAS searches at the LHC for possible rare Higgs boson decays to pair of neutral, long-lived hidden-sector particles that lead to final states containing collimated lepton jets or fermion anti-fermion pairs. No excess of events above the expected background has been observed on data collected in 2011 at a center of mass energy of 7 TeV and limits on the cross sections are set. of the leptons increases with d mass, but decreases with d. In this model, d = 0.0, 0.1, and 0.3, and d masses (m ) of 150, 300, and 500 MeV are used. For m = 150 MeV, the d is below the + threshold and can only de- cay to electrons. With m 300 MeV, the d decays to electron and muon pairs. Additionally, for m = 500 MeV, 20% of the decays produce pion pairs. This analysis con- siders LJs in three signatures: single muon-jets with four or more muons, pairs of muon-jets each with two or more muons, and pairs of electron-jets each with two or more electrons. Events containing electron-jets (EJs) were selected using single-electron triggers with an online pT threshold of 20 or 22 GeV. To ensure proper modelling of the trigger ac- ceptance, events were required to contain at least one re- constructed electron with pT > 35 GeV, above which the trigger e ciency is constant. The reconstructed electron was required to match an electron reconstructed above the pT threshold in the trigger system with a separation R less than 0.2. The EJ candidates were built from elec- tromagnetic (EM) clusters. At least two tracks from the primary vertex (PV) with pT > 10 GeV were required to have R < 0.1 of the cluster position in the second sam- pling layer of the calorimeter. Additional requirements were made on the number of hits along the track in the silicon pixel and microstrip detectors to suppress back- grounds from photon conversions. The analysis required two LJ candidates in each event, with one cluster match- ing the electron reconstructed in the trigger system. The invariant mass of the two highest-pT tracks associated with each EJ had to be less than 2 GeV. To reduce the back- ground coming from multi-jet events, the electron cluster concentration (R 2), defined as the ratio of total energy in 3 7 cells to the total energy in 7 7 cells in , in the second sampling layer of the EM calorimeter (ECAL) was used, together with the electron cluster lateral shower width and number of TRT high threshold hits. A scaled

Study of fast electron jet produced from interaction of intense laser beam with solid target at oblique incidence

Fast electrons generated along target normal direction from the interaction of intense ultrashort Ti:sapphire laser pulses (λ0 = 800 nm) with planar copper target at 45° incidence angle have been experimentally studied under different interaction conditions. Angular spread and energy spectrum of the fast electrons was measured for both p- and s-polarized laser irradiation at intensities in the range 4 × 1016 – 4 × 1017 W/cm2 (for a fixed pulse duration of 45 fs) and for pulse duration in the range 45 fs–1.2 ps (for a fixed laser fluence of 1.8 × 104 J/cm2). The fast electrons were observed consistently along the target normal direction over the entire range of interaction conditions in the form of a collimated jet, within a half cone angle of 20°. The fast electrons have continuous energy spectrum with effective temperature 290 keV and 160 keV, respectively, for p- and s-polarized 45 fs laser pulse irradiation at intensity 4 × 1017 W/cm2. Scaling laws for temperature of fast electrons with laser intensity and pulse duration were obtained. The experimental results have been explained on the basis of laser absorption and fast electron generation through the resonance absorption mechanism.

Plasmoid Ejection and Secondary Current Sheet Generation from Magnetic Reconnection in Laser-Plasma Interaction

Reconnection of the self-generated magnetic fields in laser-plasma interaction was first investigated experimentally by Nilson et al. [Phys. Rev. Lett. 97, 255001 (2006)] by shining two laser pulses a distance apart on a solid target layer. An elongated current sheet (CS) was observed in the plasma between the two laser spots. In order to more closely model magnetotail reconnection, here two side-by-side thin target layers, instead of a single one, are used. It is found that at one end of the elongated CS a fanlike electron outflow region including three well-collimated electron jets appears. The (>1 MeV) tail of the jet energy distribution exhibits a power-law scaling. The enhanced electron acceleration is attributed to the intense inductive electric field in the narrow electron dominated reconnection region, as well as additional acceleration as they are trapped inside the rapidly moving plasmoid formed in and ejected from the CS. The ejection also induces a secondary CS.

Numerical simulations of separatrix instabilities in collisionless magnetic reconnection

Electron scale dynamics of magnetic reconnection separatrix jets is studied in this paper. Instabilities developing in directions both parallel and perpendicular to the magnetic field are investigated. Implicit particle-in-cell simulations with realistic electron-to-ion mass ratio are complemented by a set of small scale high resolution runs having the separatrix force balance as the initial condition. A special numerical procedure is developed to introduce the force balance into the small scale runs. Simulations show the development of streaming instabilities and consequent formation of electron holes in the parallel direction. A new electron jet instability develops in the perpendicular direction. The instability is closely related to the electron MHD Kelvin-Helmholtz mode and is destabilized by a flow, perpendicular to magnetic field at the separatrix. Tearing instability of the separatrix electron jet is modulated strongly by the electron MHD Kelvin-Helmholtz mode.

Stimulated Raman scattering from ice-VIII by shock-induced compression in liquid water

Stimulated Raman scattering (SRS) from ice-VIII was investigated using shock-induced compression (SIC) generated by laser-induced breakdown in liquid water. Three backward SRS peaks of OH stretching vibrations and one backward SRS characteristic peak of lattice translation were observed. The SRS spectra indicated that the ice-VIII structure is formed by SIC, as the trajectory of the SIC passes through the stable pressure-temperature range of ice-VIII. The static electric field generated by electron jets protects proton-ordered structure. The laser-induced shock wave mechanism is also discussed.

Drifting localization of ionization runaway: Unraveling the nature of anomalous transport in high power impulse magnetron sputtering

The plasma over a magnetron’s erosion “racetrack” is not azimuthally uniform but concentrated in distinct dense ionization zones which move in the E×B direction with about 10% of the electron E×B/B2 drift velocity. The ionization zones are investigated with a gated camera working in concert with a streak camera for Al, Nb, Cu, and W targets in Ar or Kr background gas. It is found that each ionization zone has a high plasma density edge, which is the origin of a plasma-generating electron jet leaving the target zone. Each region of strong azimuthal plasma density gradient generates an azimuthal electric field, which promotes the escape of magnetized electrons and the formation of electron jets and plasma flares. The phenomena are proposed to be caused by an ionization instability where each dense plasma zone exhibits a high stopping power for drifting high energy electrons, thereby enhancing itself.

Satellite observations of plasma physics near the magnetic field reconnection X line

[1] Satellite observations near the X line are required to understand electromagnetic energy conversion and particle acceleration resulting from magnetic field reconnection. More than 900 orbits of Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft across the low-latitude dayside magnetopause, involving more than 4000 magnetopause crossings and 5000 h of data, were searched for examples of magnetic field reconnection within a few electron skin depths of the X line. Evidence that the X line was crossed in the best of these events comes from observations of DC electric and magnetic fields, electrostatic and electromagnetic lower hybrid waves, magnetosheath electrons flowing along the separatricies, and a super-Alfvenic electron jet flowing perpendicular to the magnetic field. A dispersion analysis identifies properties of the wave that are in agreement with the experiment. Neither these waves nor the DC electric field were sufficient to account for acceleration of the electron jet. The anomalous drag was not an important source of the observed DC electric field. The observed pressure gradient is a possible candidate for maintaining the electric field.

The inner structure of collisionless magnetic reconnection: The electron-frame dissipation measure and Hall fields

It was recently proposed that the electron-frame dissipation measure, the energy transfer from the electromagnetic field to plasmas in the electron’s rest frame, identifies the dissipation region of collisionless magnetic reconnection [Zenitani et al., Phys. Rev. Lett. 106, 195003 (2011)]. The measure is further applied to the electron-scale structures of antiparallel reconnection, by using two-dimensional particle-in-cell simulations. The size of the central dissipation region is controlled by the electron-ion mass ratio, suggesting that electron physics is essential. A narrow electron jet extends along the outflow direction until it reaches an electron shock. The jet region appears to be anti-dissipative. At the shock, electron heating is relevant to a magnetic cavity signature. The results are summarized to a unified picture of the single dissipation region in a Hall magnetic geometry.

Magnetic reconnection in the Jovian tail: X-line evolution and consequent plasma sheet structures

[1] Magnetic reconnection in planetary magnetospheres plays important roles in energy and mass transfer in the steady state, and also possibly in transient large-scale disturbances. In this paper we report observations of a reconnection event in the Jovian magnetotail by the Galileo spacecraft on 17 June 1997. In addition to the tailward retreat of a main X-line, signatures of recurrent X-line formations are found by close examination of energetic particle anisotropies. Furthermore, detailed analyses of multi-instrumental data for this period provide various spatiotemporal features in the plasma sheet. A significant density decrease was detected in the central plasma sheet, indicative of the transition to lobe (open field line) reconnection from plasma sheet (closed field line) reconnection. When Galileo vertically swept through the plasma sheet, a velocity layer structure was observed. We also analyze a strong southward magnetic field which is similar to dipolarization fronts observed in the terrestrial magnetotail: the ion flow (∼450 km s−1) was observed behind the magnetic front, whose thickness of 10000–20000 km was of the order of ion inertial length. The electron anisotropy in this period suggests an anomalously high-speed electron jet, implying ion-electron decoupling behind the magnetic front. Particle energization was also seen associated with these structures. These observations suggest that X-line evolution and consequent plasma sheet structures are similar to those in the terrestrial magnetosphere, whereas their generality in the Jovian magnetosphere and influence on the magnetospheric/ionospheric dynamics including transient auroral events need to be further investigated with more events.

Jet Deflection by Very Weak Guide Fields during Magnetic Reconnection

Previous 2D simulations of reconnection using a standard model of initially antiparallel magnetic fields have detected electron jets outflowing from the x point into the ion outflow exhausts. Associated with these jets are extended "outer electron diffusion regions." New PIC simulations with an ion to electron mass ratio as large as 1836 (an H(+) plasma) now show that the jets are strongly deflected and the outer electron diffusion region is broken up by a very weak out-of-plane magnetic guide field, even though the diffusion rate itself is unchanged. Jet outflow and deflection are interpreted in terms of electron dynamics and are compared to recent measurements of jets in the presence of a small guide field in Earth's magnetosheath.

Towards laboratory produced relativistic electron–positron pair plasmas

We review recent experimental results on the path to producing electron–positron pair plasmas using lasers. Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the past few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 10 16 cm −3 and 10 13 cm −3, respectively. With the increasing performance of high-energy ultra-short laser pulses, we expect that a high-density, up to 10 18 cm −3, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter.

Propagation of Jovian electron jets in heliospheric flux tube structures

We discuss the propagation of magnetic flux tubes of solar origin through the heliosphere up to the orbit of Jupiter and the possibility that Jovian electron jets result from the interaction of these flux tubes with the magnetosphere of Jupiter. In order to do so, we analyze Ulysses observations in the interplanetary medium along the spacecraft's highly inclined orbit between the orbits of Earth and Jupiter. We apply a method originally developed for the analysis of ACE measurements at 1 AU, in which it was shown that the distribution of the relative change in plasma quantities can actually be attributed to plasma turbulence on the one hand and the existence of individual flux tubes in the solar wind on the other hand. The application to Ulysses data shows that this typical behavior can be observed even up to the orbit of Jupiter. In a first step, we discuss possible consequences of the existence of these flux tubes at such large distances for the transport of charged particles through the inner heliosphere. In a second step, we analyze observations of so‐called Jovian electron jets with Ulysses and Pioneer 10 data with regard to changes in the magnetic field and interpret these as the result of the magnetic interaction of flux tubes with the Jovian magnetosphere.

Collimated proton beam generation from ultraintense laser-irradiated hole target

AbstractCollimated 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.

Fast electron energy deposition in a magnetized plasma: Kinetic theory and particle-in-cell simulation

The collisional dynamics of a relativistic electron jet in a magnetized plasma are investigated within the framework of kinetic theory. The relativistic Fokker–Planck equation describing slowing down, pitch angle scattering, and cyclotron rotation is derived and solved. Based on the solution of this Fokker–Planck equation, an analytical formula for the root mean square spot size transverse to the magnetic field is derived and this result predicts a reduction in radial transport. Some comparisons with particle-in-cell simulation are made and confirm striking agreement between the theory and the simulation. For fast electron with 1 MeV typical kinetic energy interacting with a solid density hydrogen plasma, the energy deposition density in the transverse direction increases by a factor 2 for magnetic field of the order of 1 T. Along the magnetic field, the energy deposition profile is unaltered compared with the field-free case.

Collimated hot electron jets generated from subwavelength grating targets irradiated by intense short-pulse laser

Hot electron emission from subwavelength grating targets irradiated by a 60 fs short-pulse laser was investigated at moderate intensities in excess of 1015 W/cm2. Collimated hot electron jets with a divergence angle as small as 5° were observed at the specular reflection direction when the laser beam was incident at the resonance angle for surface plasmon excitation. When the incident angle, which departs from the resonant angle, is increased, the collimated hot electron jet remains near the specular reflection direction, but its intensity attenuates gradually. At the same time, the number of the hot electrons with very large spreading angle emitting along the target normal direction increases with the incident angle.

Polarimetric detection of laser induced ultrashort magnetic pulses in overdense plasma

The interaction of intense (∼1016 W cm−2), subpicosecond pulses with solid targets can generate highly directional jets of hot electrons. These electrons can propagate in the solid along with the counterpropagating return shielding currents. The spontaneous magnetic field that is generated by these currents, captures in its time evolution, important information about the dynamics of the complex transport processes. By using a two pulse pump-probe polarimetric technique the temporal evolution of multimegagauss magnetic fields is measured for optically polished BK7 glass targets, each coated with a thin layer of either copper or silver. A simple model is then used for explaining the observations and for deducing quantitative information about the transport of hot electrons.