Source Of Relativistic Electrons Research Articles

Unveiling Energetic Particle Dynamics in the Near‐Earth Environment From CubeSat Missions

AbstractThe discovery of the Van Allen radiation belts marked a prominent milestone in space physics. Recent advances, through the measurements of two CubeSat missions, have shed new light on the dynamics of energetic particles in the near‐Earth environment. Measurements from CSSWE, a student‐led mission, revealed that the decay of low‐energy neutrons, associated with cosmic rays impacting the atmosphere, is the primary source of relativistic electrons at the inner edge of the inner belt (Li et al., Nature, 2017, https://doi.org/10.1038/nature2464). Recently CIRBE captured striking details of energetic electron dynamics (Li et al., GRL, 2024, https://doi.org/10.1029/2023gl107521), further demonstrating high‐quality science achievable with CubeSat missions.

Three-stage laser wakefield accelerator scheme for sub-Joule few-cycle laser pulses

Laser-driven electron acceleration in underdense plasma is a promising route towards the realization of reliable sources of relativistic electrons in the 0.1–1 GeV energy range. Generation of such electron bunches at high repetition rates is hindered by the limited energy per pulse, which inevitably results in very short pulse duration and tight focusing. Compressing the laser energy in time and space allows scientists to use higher plasma density to drive wakefieds, which in turn results in enhanced diffraction and dispersion of the broadband laser pulse. These features make difficult to control the acceleration in the plasma wave and to improve the beam quality. Here we propose a mm-long three-stage acceleration scheme, which allows for tunable injection and optimal acceleration of high-quality electron bunches. The full interaction length is modeled by 3D particle-in-cell simulations.

Single-shot electron radiography using a laser–plasma accelerator

Contact and projection electron radiography of static targets was demonstrated using a laser–plasma accelerator driven by a kilojoule, picosecond-class laser as a source of relativistic electrons with an average energy of 20 MeV. Objects with areal densities as high as 7.7 g/cm2 were probed in materials ranging from plastic to tungsten, and radiographs with resolution as good as 90 μm were produced. The effects of electric fields produced by the laser ablation of the radiography objects were observed and are well described by an analytic expression relating imaging magnification change to electric-field strength.

Sub-kpc radio jets in the brightest central galaxy of the cool-core galaxy cluster RXJ1720.1+2638

ABSTRACT The cool-core galaxy cluster RXJ1720.1+2638 hosts extended radio emission near the cluster core, known as a minihalo. The origin of this emission is still debated and one piece of the puzzle has been the question of whether the supermassive black hole in the brightest central galaxy is actively powering jets. Here, we present high-resolution e-MERLIN observations clearly indicating the presence of sub-kpc jets; this may have implications for the proposed origin of the minihalo emission, providing an ongoing source of relativistic electrons rather than a single burst sometime in the past, as previously assumed in simulations attempting to reproduce observational characteristics of minihalo-hosting systems.

Polymer-Gel Radiation Dosimetry of Laser-Based Relativistic Electron Sources for Biomedical Applications: First Qualitative Results and Experimental Challenges

The generation of laser based relativistic electron sources involves impressive basic science as well as innovative applications. This study reports first novel qualitative results on polymer-gel radiation dosimetry of ultrafast laser-based relativistic electron beams. The fabricated polymer-gels are irradiated by the ultra-high dose rate (FLASH) laser-generated electron beams and then are analysed using magnetic resonance imaging. The reading of the irradiated dosimeters is performed using a clinical 1.5 T Magnetic Resonance Imaging system. Three-dimensional colour parametric T2 maps are then constructed from the original PD-T2 weighted images obtained from the clinical MRI scanner. For comparison, the gels are also irradiated with standard electron beams of various energies utilizing a radiotherapy clinical linear accelerator system. For the calibration measurements of the gel dosimetry method, special calibrated dosimetric films are also implemented. The preliminary results demonstrate the potential of polymer gel dosimetry for 3D-dose-distribution of FLASH type irradiation of laser generated electron beams. Furthermore, they illustrate potential issues related to the polymer gel based dosimetry in challenging irradiation arrangements, such as the oxygen sensitivity and necessity for oxygen impermeable container material.

Improving a high-power laser-based relativistic electron source: the role of laser pulse contrast and gas jet density profile

A relativistic electron source based on high power laser interaction with gas jet targets has been developed at the Institute of Plasma Physics and Lasers of the Hellenic Mediterranean University. Initial measurements were conducted using the ‘Zeus’ 45 TW laser with peak intensities in the range of 1018–1019 W cm−2 interacting with a He pulsed gas jet having a 0.8 mm diameter nozzle. A significant improvement of the electron signal was measured after using an absorber to improve the laser pulse contrast from 10−10 to 10−11. A high stability quasi-mono-energetic electron beam of about 50 MeV was achieved and measured using a magnetic spectrometer for pulsed gas jet backing pressure of 12 bar. Supplementary studies using a 3 mm diameter nozzle for backing pressures in the range of 35–40 bar showed electron beam production with energies spread in the range from 50 to 150 MeV. The pulsed jet density profile was determined using interferometric techniques. Particle-in-cell simulations, at the above experimentally determined conditions, support our experimental findings.

Can Earth's Magnetotail Plasma Sheet Produce a Source of Relativistic Electrons for the Radiation Belts?

AbstractSimultaneous observations from Van Allen Probes in Earth's outer radiation belt (∼4–6 RE) and Magnetospheric Multiscale (MMS) in the magnetotail plasma sheet at >20 RE geocentric distance are used to compare relative levels of relativistic electron phase space density (PSD) for constant values of the first adiabatic invariant, M. We present new evidence from two events showing: (a) at times, there is sufficient PSD in the central plasma sheet to provide a source of >1 MeV electrons into the outer belt; (b) the most intense levels of relativistic electrons are not accelerated in the solar wind or transported from the inner magnetosphere and thus must be accelerated rapidly (within ∼minutes or less) and efficiently across a broad region of the magnetotail itself; and (c) the highest intensity relativistic electrons observed by MMS were confined within only the central plasma sheet. The answer to the title question here is: yes, it can, however whether Earth's plasma sheet actually does provide a source of several 100s keV to >1 MeV electrons to the outer belt and how often it does so remain important outstanding questions.

Small accelerators and their applications in the CANAM research infrastructure at the NPI CAS

The Nuclear Physics Institute (NPI) of the Czech Academy of Sciences (CAS) operates, among other facilities, a Tandetron linear accelerator, TR-24 and U-120M cyclotrons, and an MT25 microtron. A new accelerator mass spectrometry (AMS) instrument, MILEA, has recently been acquired. Except for the MT25, all facilities are synergic parts of the Centre of Accelerators and Nuclear Analytical Methods Research Infrastructure (CANAM RI) ( http://canam.ujf.cas.cz ). This paper demonstrates the instrumental, scientific and application capabilities of the devices for many fundamental nuclear physics experiments and a wide spectrum of applications. The Tandetron Laboratory has a full arsenal of ion-beam analytical methods, ion-beam nano- and microstructuring techniques, as well as tools for the doping and synthesis of new progressive materials using energetic ion beams. It uniquely utilises ion beams for 3D elemental mapping; it studies internal morphology using ion-microprobe methods applicable in many scientific branches. The TR-24 and U-120M cyclotrons provide the primary beams of accelerated ions as well as the generated secondary fast neutrons, including the necessary instrumentation and the target technology, and enable fundamental experiments in nuclear physics, astrophysics, dosimetry, etc. The microtron MT25 is a source of relativistic electrons (the primary electron beam), the secondary photon beam (bremsstrahlung) and neutrons from photonuclear reactions which are used, e.g. for analysis and preservation of cultural heritage. The MILEA AMS system offers a highly sensitive isotopic ratio measurement of very long-lived radionuclides at levels up to 10–15.

Design of a THz-driven compact relativistic electron source

A THz-pulse-driven compact, < 150 mm in total length, two-stage electron accelerator setup was designed. It uses 2 × 2 pairs of nearly counter-propagating focused THz pulses. The effects of the initial bunch charge and the propagation direction of the THz pulses on the energy of the accelerated electrons were investigated by numerical simulations. Generation of 8 fC electron bunches with up to 340 keV energy; only 2.0% energy spread and compressed on-target duration of 200 fs is predicted using single-cycle low-frequency THz pulses with less than 4.5 mJ total energy.

Ultimate energy recovery from spent relativistic electron beam in energy recovery linear accelerators

Energy recovery linear accelerators (ERLs) rely upon single-axis superconducting radio frequency (SRF) cavities to be an efficient source of relativistic electrons for high energy and nuclear physics. SRF cavities are also considered relevant for next-generation photon factories and radio-isotope production facilities. The ultimate energy recovery capability for the accelerator would be the ability to operate with a sufficiently spent beam and decrease the energy of the beam before the beam dump to a value lower than the beam injection energy. This is especially important for high current accelerators, where the beam injection energy could be as high as several MeV, and systems where partial beam loss can be expected. The efficient operation of energy recovery in linear accelerators is adversely affected by the typical degradation of the beam quality and current loss. This hinders the application of the ERLs in research and industry, and enabling the use of spent (partially lost current), degraded beams should broaden their application. We suggest that the use of the asymmetric operating mode observed in the dual-axis asymmetric cavities will enable such ultimate capabilities. We discuss the advantages of the application of fields of different amplitude along the cavity accelerating and decelerating axes and demonstrate that the fields can be tuned separately in each axis of the dual-axis cavity. The design of such a cavity and ways to optimize the energy recovery of a spent electron beam by tuning the dual-axis asymmetric SRF cavity are discussed.

Non-thermal emission from cosmic rays accelerated in H II regions

Context.Radio observations at metre-centimetre wavelengths shed light on the nature of the emission of H IIregions. Usually this category of objects is dominated by thermal radiation produced by ionised hydrogen, namely protons and electrons. However, a number of observational studies have revealed the existence of H IIregions with a mixture of thermal and non-thermal radiation. The latter represents a clue as to the presence of relativistic electrons. However, neither the interstellar cosmic-ray electron flux nor the flux of secondary electrons, produced by primary cosmic rays through ionisation processes, is high enough to explain the observed flux densities.Aims.We investigate the possibility of accelerating local thermal electrons up to relativistic energies in H IIregion shocks.Methods.We assumed that relativistic electrons can be accelerated through the first-order Fermi acceleration mechanism and we estimated the emerging electron fluxes, the corresponding flux densities, and the spectral indexes.Results.We find flux densities of the same order of magnitude of those observed. In particular, we applied our model to the “deep south” (DS) region of Sagittarius B2 and we succeeded in reproducing the observed flux densities with an accuracy of less than 20% as well as the spectral indexes. The model also gives constraints on magnetic field strength (0.3–4 mG), density (1–9 × 104cm−3), and flow velocity in the shock reference frame (33–50 km s−1) expected in DS.Conclusions.We suggest a mechanism able to accelerate thermal electrons inside H IIregions through the first-order Fermi acceleration. The existence of a local source of relativistic electrons can explain the origin of both the observed non-thermal emission and the corresponding spectral indexes.

Modeling the Quasi‐Trapped Electron Fluxes From Cosmic Ray Albedo Neutron Decay (CRAND)

AbstractRecently, cosmic ray albedo neutron decay (CRAND) has been identified as the main source of relativistic electrons measured at the inner edge of inner radiation belt. Here we introduce a drift‐source model that includes azimuthal drift and a CRAND electron source to simulate the quasi‐trapped electron distribution measured by the DEMETER satellite during 20–30 April 2010. The simulated longitude distribution of quasi‐trapped electron fluxes at the inner edge of inner radiation belt successfully reproduces the DEMETER observations, confirming CRAND as the main source for these electrons. Furthermore, a comparison of the energy spectrum and the L distribution of the quasi‐trapped relativistic electrons between simulations and observations further suggests that CRAND is likely the dominant source for 300–700‐keV quasi‐trapped electrons at L &lt; 2 and L ≈ 3.

Terahertz-driven wakefield electron acceleration

A relativistic electron source is proposed, driven by the wakefield of an intense terahertz (THz) pulse in low-density gas plasma. In contrast to the optical and near-infrared regimes, the low (3.5 THz) frequency and the long (λT = 85.6 μm) wavelength of the THz pulse offers distinct advantages, such as the -scaling of the electron ponderomotive energy. Two-dimension-in-space and three-dimension-in-velocity particle-in-cell simulation results show that relativistic electrons of ∼1 MeV energy and high charge can be generated by an intense THz pulse at kilohertz repetition rate from a gas plasma target. These results may lead to a new regime of applications, such as ultrafast electron diffraction or high-repetition-rate gamma ray sources for materials characterization or medical radiography, which would benefit from lower energy (1–10 MeV) but higher repetition rate (∼1 kHz) sources of relativistic electrons.

High-charge relativistic electron bunches from a kHz laser-plasma accelerator

We report on electron wakefield acceleration in the resonant bubble regime with few-millijoule near-single-cycle laser pulses at a kilohertz repetition rate. Using very tight focusing of the laser pulse in conjunction with microscale supersonic gas jets, we demonstrate a stable relativistic electron source with a high charge per pulse up to 24 pC/shot. The corresponding average current is 24 nA, making this kilohertz electron source useful for various applications.

Silicon nanowire based high brightness, pulsed relativistic electron source

We demonstrate that silicon nanowire arrays efficiently emit relativistic electron pulses under irradiation by a high-intensity, femtosecond, and near-infrared laser (∼1018 W/cm2, 25 fs, 800 nm). The nanowire array yields fluxes and charge per bunch that are 40 times higher than those emitted by an optically flat surface, in the energy range of 0.2–0.5 MeV. The flux and charge yields for the nanowires are observed to be directional in nature unlike that for planar silicon. Particle-in-cell simulations establish that such large emission is caused by the enhancement of the local electric fields around a nanowire, which consequently leads to an enhanced absorption of laser energy. We show that the high-intensity contrast (ratio of picosecond pedestal to femtosecond peak) of the laser pulse (10−9) is crucial to this large yield. We extend the notion of surface local-field enhancement, normally invoked in low-order nonlinear optical processes like second harmonic generation, optical limiting, etc., to ultrahigh laser intensities. These electron pulses, expectedly femtosecond in duration, have potential application in imaging, material modification, ultrafast dynamics, terahertz generation, and fast ion sources.

Relativistic electron beams driven by kHz single-cycle light pulses

Laser-plasma acceleration is an emerging technique for accelerating electrons to high energies over very short distances. The accelerated electron bunches have femtosecond duration, making them particularly relevant for applications such as ultrafast imaging or femtosecond X-ray generation. Current laser-plasma accelerators are typically driven by Joule-class laser systems that have two main drawbacks: their relatively large scale and their low repetition-rate, with a few shots per second at best. The accelerated electron beams have energies ranging from 100 MeV to multi-GeV, however a MeV electron source would be more suited to many societal and scientific applications. Here, we demonstrate a compact and reliable laser-plasma accelerator producing high-quality few-MeV electron beams at kilohertz repetition rate. This breakthrough was made possible by using near-single-cycle light pulses, which lowered the required laser energy for driving the accelerator by three orders of magnitude, thus enabling high repetition-rate operation and dramatic downsizing of the laser system. The measured electron bunches are collimated, with an energy distribution that peaks at 5 MeV and contains up to 1 pC of charge. Numerical simulations reproduce all experimental features and indicate that the electron bunches are only $\sim 1$ fs long. We anticipate that the advent of these kHz femtosecond relativistic electron sources will pave the way to wide-impact applications, such as ultrafast electron diffraction in materials with an unprecedented sub-10 fs resolution.

Simple scalings for various regimes of electron acceleration in surface plasma waves

Different electron acceleration regimes in the evanescent field of a surface plasma wave are studied by considering the interaction of a test electron with the high-frequency electromagnetic field of a surface wave. The non-relativistic and relativistic limits are investigated. Simple scalings are found demonstrating the possibility to achieve an efficient conversion of the surface wave field energy into electron kinetic energy. This mechanism of electron acceleration can provide a high-frequency pulsed source of relativistic electrons with a well defined energy. In the relativistic limit, the most energetic electrons are obtained in the so-called electromagnetic regime for surface waves. In this regime, the particles are accelerated to velocities larger than the wave phase velocity, mainly in the direction parallel to the plasma-vacuum interface.

Mapping atomic motions with ultrabright electrons: towards fundamental limits in space-time resolution.

The long held objective of directly observing atomic motions during the defining moments of chemistry has been achieved based on ultrabright electron sources that have given rise to a new field of atomically resolved structural dynamics. This class of experiments requires not only simultaneous sub-atomic spatial resolution with temporal resolution on the 100 femtosecond time scale but also has brightness requirements approaching single shot atomic resolution conditions. The brightness condition is in recognition that chemistry leads generally to irreversible changes in structure during the experimental conditions and that the nanoscale thin samples needed for electron structural probes pose upper limits to the available sample or "film" for atomic movies. Even in the case of reversible systems, the degree of excitation and thermal effects require the brightest sources possible for a given space-time resolution to observe the structural changes above background. Further progress in the field, particularly to the study of biological systems and solution reaction chemistry, requires increased brightness and spatial coherence, as well as an ability to tune the electron scattering cross-section to meet sample constraints. The electron bunch density or intensity depends directly on the magnitude of the extraction field for photoemitted electron sources and electron energy distribution in the transverse and longitudinal planes of electron propagation. This work examines the fundamental limits to optimizing these parameters based on relativistic electron sources using re-bunching cavity concepts that are now capable of achieving 10 femtosecond time scale resolution to capture the fastest nuclear motions. This analysis is given for both diffraction and real space imaging of structural dynamics in which there are several orders of magnitude higher space-time resolution with diffraction methods. The first experimental results from the Relativistic Electron Gun for Atomic Exploration (REGAE) are given that show the significantly reduced multiple electron scattering problem in this regime, which opens up micron scale systems, notably solution phase chemistry, to atomically resolved structural dynamics.

The contribution of millisecond pulsars to the Galactic cosmic-ray lepton spectrum

Pulsars are believed to be sources of relativistic electrons and positrons. The abundance of detections of γ-ray millisecond pulsars by Fermi Large Area Telescope coupled with their light curve characteristics that imply copious pair production in their magnetospheres, motivated us to investigate this old pulsar population as a source of Galactic electrons and positrons and their contribution to the enhancement in cosmic-ray positron flux at GeV energies. We use a population synthesis code to predict the source properties (number, position, and power) of the present-day Galactic millisecond pulsars, taking into account the latest Fermi and radio observations to calibrate the model output. Next, we simulate pair cascade spectra from these pulsars using a model that invokes an offset-dipole magnetic field. We assume free escape of the pairs from the pulsar environment. We then compute the cumulative spectrum of transported electrons and positrons at Earth, following their diffusion and energy losses as they propagate through the Galaxy. Our results indicate that the predicted particle flux increases for non-zero offsets of the magnetic polar caps. Comparing our predicted local interstellar spectrum and positron fraction to measurements by AMS-02, PAMELA, and Fermi, we find that millisecond pulsars are only modest contributors at a few tens of GeV, after which this leptonic spectral component cuts off. The positron fraction is therefore only slightly enhanced above 10GeV relative to a background flux model. This implies that alternative sources such as young, nearby pulsars and supernova remnants should contribute additional primary positrons within the astrophysical scenario.

Simulation of the acceleration of relativistic electrons in the inner magnetosphere using RCM-VERB coupled codes

[1] Radiation belt dynamics have been modeled by the modified Fokker-Planck diffusion equation with sources from the low-energy plasma sheet population and losses to the atmosphere and magnetopause. We perform a coupled simulation of the Rice Convection Model (RCM) and Versatile Electron Radiation Belt (VERB) code. The RCM models magnetospheric convection and provides a low-energy electron seed population for the VERB diffusion code simulations of the Earth's radiation belts. VERB simulations are driven by the realistic time-dependent electron seed population and by the Kp index, which is used to specify rates of diffusion by ultralow frequency (ULF) and very low frequency wave activity and, therefore, diffusion processes. Radial diffusion is produced by ULF waves, while pitch angle and energy diffusion are produced by chorus waves outside the plasmasphere and by hiss waves inside the plasmasphere. The results of the simulation indicate that storm time enhanced magnetospheric convection combined with radial diffusion can bring electrons with tens of keV energy close to the Earth and can affect electron fluxes at 3–4 RE. These electrons can be further accelerated locally by chorus waves to MeV energies. Furthermore, outward radial diffusion smooths out the peak of the high-energy fluxes and produces MeV electron enhancement around geosynchronous orbit (6–7 RE) despite the absence of local electron acceleration in that region. Our coupled simulations indicate that local acceleration in the inner magnetosphere may be a dominant source of relativistic electrons that reach geosynchronous orbit.