Propagation Of Relativistic Electron Beam Research Articles

Branching of High-Current Relativistic Electron Beam in Porous Materials.

Propagation of high-current relativistic electron beam (REB) in plasma is relevant to many high-energy astrophysical phenomena as well as applications based on high-intensity lasers and charged-particle beams. Here, we report a new regime of beam-plasma interaction arising from REB propagation in medium with fine structures. In this regime, the REB cascades into thin branches with local density a hundred times the initial value and deposits its energy 2 orders of magnitude more efficiently than that in homogeneous plasma, where REB branching does not occur, of similar average density. Such beam branching can be attributed to successive weak scatterings of the beam electrons by the unevenly distributed magnetic fields induced by the local return currents in the skeletons of the porous medium. Results from a model for the excitation conditions and location of the first branching point with respect to the medium and beam parameters agree well with that from pore-resolved particle-in-cell simulations.

Direct comparison of analytically derived “Fedosov” solution with experimental measurements and numerical simulations of relativistic thin annular electron beam generation and propagation in magnetically insulated coaxial diode of SINUS-6 high-current electron-beam accelerator

The analytically derived solution for a thin annular electron-beam generation in a magnetically insulated coaxial diode (MICD), also known as “Fedosov solution,” is validated by direct experimental measurements of current–voltage (I–V) characteristics of MICD driven by the high-current electron-beam accelerator SINUS-6 and numerical particle-in-cell (PIC) simulations of a thin annular electron-beam generation and propagation in computer model of MICD of corresponding geometry and initial/boundary conditions. The experimental measurements of I–V characteristics of MICD are performed by monitoring and analyzing a voltage applied to MICD and an electron-beam current generated by an explosive-emission cathode of MICD. Numerical simulations of MICD operation are performed using ICEPIC code. The comparisons of analytically derived “Fedosov” solution with experimentally measured I–V characteristics of MICD as well as with results of ICEPIC simulations of a three-dimensional computer model of MICD operation are analyzed, and a conclusion is made that all three measures are pretty much consistent with each other. The appliance of the analysis is purposed now in using SINUS-6 accelerator for designing, prototyping, and studying different variants of O-type slow-wave high-power microwave/millimeter-wavelength vacuum electronic devices.

Experimental research on a gigawatt-class Ku-band coaxial transit-time oscillator with low guiding magnetic field

A Ku-band relativistic transit-time oscillator with a three-cavity extractor and a distance-tunable reflector was proposed in our previous work [Ling et al., Phys. Plasmas 24(1), 013103 (2017)]. Recently, a new experiment was carried out on this device with an intense relativistic electron beam generator that produces electron beams with a duration of 55 ns and voltage of 0.4–1 MV. In preliminary experiments, mode competition was found with three main frequencies of which the reasons are analyzed theoretically and experimentally. The results show that plasmas generated from the collector's surface are most likely to cause this problem. To solve this problem, the collector structure is extended axially. With an input voltage of 600 kV and a current of 11.7 kA, a microwave output power 1.9 GW with pulse width 26 ns and frequency 12.42 GHz is obtained under a 0.7 T guiding magnetic field. These experimental results effectively confirm the potential of high power capacity of this proposed Ku band transit-time oscillator.

Recording of Superenergetic Electrons and Ions in the High-Current Pulsed Relativistic Electron Beam Generator

Recording of Superenergetic Electrons and Ions in the High-Current Pulsed Relativistic Electron Beam Generator

Axial effect analysis of relativistic electron beam propagation in vacuum

In geostationary orbits and other quasi-vacuum environments, relativistic electron beams are affected by the initial emittance and space charge effects during the propagation process, resulting in beam quality degradation. Furthermore, axial energy distribution change in the beam and the axial transient electromagnetic effect caused by current changes in the head and tail regions of the beam also cause the beam to expand and affect its quality. In this study, the particle-in-cell method was used to construct a long-range propagation model of a relativistic electron beam in a vacuum environment. By calculating and simulating the axial energy distribution of the beam and the changes in the transient electromagnetic field, the axial effect during the propagation process was analyzed, and the parameter change law of the effective propagation of the beam was explored. This provided a theoretical reference for a more accurate assessment of the beam quality during propagation.

Modeling and Simulation of Relativistic Multiple Electron Beam Generation With Different Energies From a Single-Cathode Potential for High-Power Microwave Sources

The traveling wave tube (TWT) has been a reliable conventional vacuum electron device (CVED) since the 1940s. Researchers, beginning in the late 1980s, extended the TWT to the relativistic electron beam regime to generate 100- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{s}\cdot $ </tex-math></inline-formula> MW power in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band. Since the mid-1990s, there has been little advancement in the field. Recently, the linear theory of a multistream TWT was published, which showed superexponential amplification properties. This article describes a novel technique for producing multiple electron beams with an energy difference of about 6%–27% with comparable currents from a single cathode at a single potential for a multistream TWT. We present a new model of two nested cathodes where two annular electron beams are generated and propagated in a smooth cylindrical pipe that emerged into a strong magnetic field. The two nested cathodes are magnetically insulated coaxial diodes (MICDs). The simulation results are obtained using the MAGIC particle-in-cell (PIC) code for the experimental vacuum diode geometry of the SINUS-6 high-current electron beam accelerator at The University of New Mexico. Results are obtained, which are then: 1) compared with earlier experimental results for a single beam; 2) study the current–voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> ) characteristics of two electron beams powered by a single cathode at a single potential immersed in a strong magnetic field; and 3) show 6%–27% energy differences with comparable currents between two beams. This technique is viable for pulsed power-driven, relativistic electron beams for a relativistic multistream TWT.

Pulsed laser-plasma gamma radiation source for radiography

We have performed experiments on the generation of relativistic electron beams in helium gas jets (electron density ∼1020 cm−3) using a femtosecond Ti : sapphire laser. Electron beams with a total charge of 0.2−0.5 nC, a maximum electron energy of up to 60 MeV, and a divergence of up to 300 mrad are recorded. The generated electron beams are converted into bremsstrahlung X-rays using a Ta plate 2 mm thick. The average dose of bremsstrahlung radiation in the air at a distance of 1 m from the source was 5.4 ±1.7 mrad per pulse. The emitting region size measured by the blurriness of the X-ray image is about 650 μm (FWHM).

Acceleration of electrons in hollow glass capillaries under the action of intense picosecond laser pulses

The generation of relativistic electron beams in hollow glass capillaries is investigated using a picosecond laser system. A plasma is formed in a capillary due to the ablation of its inner walls by a specially formed pre-pulse. Electron beams with an opening angle of ∼40 mrad, exponential energy spectrum with maximum energy about 20 MeV, and a total charge of ∼0.2 nC are experimentally detected.

HIGH-CURRENT RELATIVISTIC ELECTRON BEAM FOCUSING IN PLASMA

The analysis of the envelope equation for high-current relativistic electron beam propagation in plasma in an external uniform magnetic field is presented. The envelope equation is obtained in a Hamiltonian form with an effective potential, which depends from electron beam and plasma parameters, and external magnetic field. Hamiltonian aproach allows fully analyze the behavior of the beam envelope as a function of the beam current, beam energy, plasma density and conductivity, as well as on the external magnetic field and the initial beam angular momentum.

Methods of Laser Shadow Photography with Recording by Streak Camera to Study Plasma Dynamics in the Diode of a Relativistic Electron Beam Generator

Methods of Laser Shadow Photography with Recording by Streak Camera to Study Plasma Dynamics in the Diode of a Relativistic Electron Beam Generator

Laser-assisted propagation of a relativistic electron bunch in air

This paper assesses the feasibility of using kilo-joule class laser systems to pre-ionise an air column enhancing the propagation of relativistic electron beams. In a vacuum a charged beam will always diverge. In a plasma it may focus depending on the degree of beam charge and current neutralisation. Beams diverge due to scattering, but this paper highlights a parameter regime where plasma focusing in a pre-formed plasma may allow propagation of ∼10 GeV electron beams over a distance ∼10 m. Central to this theory is the degree to which the background plasma acts to charge or current neutralise the electron beam. These effects are quantified in a reduced 2D model using relativistic kinetic plasma simulations. These demonstrate that charge neutralisation is sufficiently high, and current neutralisation sufficiently low, that the proposed scheme is viable. The key problem identified in this paper is the difficulty in forming a suitable ionised channel. The primary laser energy loss mechanism for the parameters chosen is through inverse bremsstrahlung, not air ionisation, and possible ways to mitigate these losses are discussed.

The Evolution of Beam Spot in the Geomagnetic Field During Long-Range Propagation of Relativistic Electron Beam

Research on the location and shape of a beam spot at a target altitude can lay the foundation for understanding and diagnosing the long-range propagation of relativistic electron beams. Only a few studies have focused on this approach. In this study, a terrestrial atmosphere with a 3-D geomagnetic field was constructed in accordance with the International Geomagnetic Reference Field model and a relevant atmosphere model. Monte Carlo simulations were applied to the long-range propagation of relativistic (1–10 MeV) electron beams in the altitude range of 200–300 km. The results showed that when beams with various parameters were emitted in one location, the centers of the beam spots were distributed in concentric circles with different radii. The direction of the geomagnetic field determined the locations of the circle centers, whereas the beam energy and pitch angle determined the radii. When the initial gyrophase changed, the center of the beam spot rotated through the same angle. The beam spot was distributed as a partial ring with a width mainly related to the initial beam radius when the energy spread was relatively small. If the energy spread exceeded the limit, the beam spot was ring-shaped; the ring width was determined by both the initial beam radius and the energy spread.

Fast electron transport dynamics and energy deposition in magnetized, imploded cylindrical plasma.

Inertial confinement fusion approaches involve the creation of high-energy-density states through compression. High gain scenarios may be enabled by the beneficial heating from fast electrons produced with an intense laser and by energy containment with a high-strength magnetic field. Here, we report experimental measurements from a configuration integrating a magnetized, imploded cylindrical plasma and intense laser-driven electrons as well as multi-stage simulations that show fast electrons transport pathways at different times during the implosion and quantify their energy deposition contribution. The experiment consisted of a CH foam cylinder, inside an external coaxial magnetic field of 5 T, that was imploded using 36 OMEGA laser beams. Two-dimensional (2D) hydrodynamic modelling predicts the CH density reaches , the temperature reaches 920 eV and the external B-field is amplified at maximum compression to 580 T. At pre-determined times during the compression, the intense OMEGA EP laser irradiated one end of the cylinder to accelerate relativistic electrons into the dense imploded plasma providing additional heating. The relativistic electron beam generation was simulated using a 2D particle-in-cell (PIC) code. Finally, three-dimensional hybrid-PIC simulations calculated the electron propagation and energy deposition inside the target and revealed the roles the compressed and self-generated B-fields play in transport. During a time window before the maximum compression time, the self-generated B-field on the compression front confines the injected electrons inside the target, increasing the temperature through Joule heating. For a stronger B-field seed of 20 T, the electrons are predicted to be guided into the compressed target and provide additional collisional heating.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

Performance of an impedance-variable pulsed high-power electron-beam accelerator based on energy efficient transmission.

Versatile high-power pulsed electron-beam accelerators that meet the requirements of pulsed high-power specifications are needed for appropriate applications in medical industry, defense, and other industries. The pulsed electron beam accelerator comprising a Marx generator and Blumlein pulse forming line (PFL) is designed to accelerate the electron beams at the level of 1 MeV when electrostatically discharging. The performance specifications of Marx generators consisting of a 100 kV DC power supply, R-L-C circuit, and high voltage switch are at a maximum 800 kV. At this time, by using the capacitance mismatching principle between the Marx generator and the Blumlein PFL under the law of preserving the amount of charge, it is possible to generate a high voltage in the form of a square pulse up to about 1.1 MV, as much as 1.37 times the charged voltage of the Marx generator. As a result, energy transmission from the Marx generator with a high efficiency of about 85% to the Blumlein PFL is possible. The aim of this study is that the pulsed high-power electron-beam accelerator can be used to change the diode impedance, and the energy of the accelerated electron beam reaches a level of 1 MeV with the square pulse width of about 100 ns at the flat-top in the range of relativistic electron beam generation. Performance tests were securely carried out by installing a dummy load based on CuSO4 solution varying the diode impedance to deter damage to the circuit by preventing reflected waves from being generated in the load.

Influence of Geomagnetic Field on the Long-Range Propagation of Relativistic Electron Beam in the Atmosphere

It is known that Earth’s atmosphere and geomagnetic field affect the propagation of an artificial electron beam; many previous studies have neglected the effect of their variation on the propagation dynamics. In this article, parameters in envelope equations were modified according to the International Geomagnetic Reference Field (IGRF) model and MSIS-90 atmosphere model; then, the model was constructed to study the propagation of artificial electron beam in the atmosphere. Calculation of the beam’s energy loss and radial expansion in propagation showed that the variation of geomagnetic field intensity can be the main reason for the radial pinch in the altitudes above 150 km, and the ambient particle density plays a dominant role in the beam’s radial expansion in altitudes below 150 km. The Monte Carlo model was used to simulate the interactions of a relativistic (1 MeV) electron beam with the atmosphere in the altitude range 100–150 km. Energy deposition density demonstrates that the geomagnetic field can limit the radial expansion of the beam. The relativistic electron beam was emitted horizontally in the atmosphere. The geomagnetic field can limit the beam’s radial expansion and cause the beam to propagate along the field line, irrespective of the direction in which the beam is emitted.

Direct laser acceleration of electrons in a high-Z gas target and the effect of threshold plasma density on electron beam generation

An experimental study of laser driven electron acceleration in N2 and N2-He mixed gas-jet targets using laser pulses with durations of ∼60–70 fs is presented. Generation of relativistic electron beams with quasi-thermal spectra was observed at a threshold plasma density of ∼1.6 × 1018 cm−3 in the case of pure N2. The threshold density was found to increase with increasing doping concentrations of He. At an optimum fraction of 50% of He in N2, generation of quasi-monoenergetic electron beams was observed at a comparatively higher threshold density of ∼2 × 1018 cm−3, with an average peak energy of ∼168 MeV, average energy spread of ∼21%, and average total beam charge of ∼220 pC. The electron acceleration could be attributed to direct laser acceleration as well as the hybrid mechanism. The observation of an optimum fraction of He in N2 (in turn threshold plasma density) for comparatively better quality electron beam generation can be understood in terms of the plasma density dependent variation in the dephasing rate of electrons with respect to the transverse oscillating laser field. Results are also supported by 2D particle-in-cell simulations performed using the code EPOCH.

Experiments on Ion Acceleration in the Diode of the KALMAR REB Generator

Experiments on ion acceleration in the ambipolar field were carried out at the Kalmar relativistic electron beam generator with a pulsed voltage of ~250 kV, current of ~40 kA, and pulse duration of ~150 ns. Previously developed methods were used to measure the ion fluxes and determine some other properties of the generated ion beams. It was found that aluminum ions (the heaviest particles present in the thin anode film) acquired the maximum energy of 6.1 MeV, while the maximum proton energy was ~800 keV. The energy of ions propagating at an angle of 20° relative to the accelerator axis was approximately 15% lower than the energy of ions propagating along the axis. The total energy of accelerated ions varied from 0.07 to 0.35 J, while the angular divergence of the electron beams was 1.2°–2.2°.

Ultrafast Relativistic Electron Nanoprobes

One of the frontiers in electron scattering is to couple ultrafast temporal resolution with highly localized probes to investigate the role of microstructure on material properties. Here, taking advantage of the high average brightness of our electron source, we demonstrate the generation of ultrafast relativistic electron beams with picometer-scale emittance and their ability to probe nanoscale features on materials with complex microstructures. The electron beam is tightly focused at the sample plane by a custom in-vacuum lens system, and its evolution around the waist is accurately reconstructed. We then use the focused beam to characterize a Ti-6 wt% Al polycrystalline sample by correlating the diffraction and imaging modality, showcasing the capability to locate grain boundaries and map adjacent crystallographic domains with sub-micron precision. This work provides a paradigm for ultrafast electron instrumentation, enabling characterization techniques such as relativistic ultrafast electron nano-diffraction and ultrafast scanning transmission electron microscopy.

RS-20MR High-Current Relativistic Electron Beam Generator Based on a Plasma Opening Switch and Its Applications

A modified scheme of the RS-20MR generator is presented that can be used not only as a source of high-power pulsed hard X-ray emission (the dose power per 1-L volume in atmospheric air exceeds 1010 rad/s) but also as a tool to study various processes occurring under the interaction of high-current electron beams with materials: excitation and propagation of shock waves, destruction of solids, etc. Due to specific properties of the sharpening system, the diode voltage pulse has a relatively steep front, which ensures the dominance electrons with energies of about 1 MeV in the beam. For electron beams with currents of I = 20–100 kA and particle energies of E ≥ 0.5 MeV, isochoric energy release can be achieved in the volume of the irradiated sample. This can lead to substantial changes in the formation mechanism of a shock wave and the character of damage it causes. The results of the first experiments of this kind are reported.

Magnetized fast isochoric laser heating for efficient creation of ultra-high-energy-density states

Fast isochoric heating of a pre-compressed plasma core with a high-intensity short-pulse laser is an attractive and alternative approach to create ultra-high-energy-density states like those found in inertial confinement fusion (ICF) ignition sparks. Laser-produced relativistic electron beam (REB) deposits a part of kinetic energy in the core, and then the heated region becomes the hot spark to trigger the ignition. However, due to the inherent large angular spread of the produced REB, only a small portion of the REB collides with the core. Here, we demonstrate a factor-of-two enhancement of laser-to-core energy coupling with the magnetized fast isochoric heating. The method employs a magnetic field of hundreds of Tesla that is applied to the transport region from the REB generation zone to the core which results in guiding the REB along the magnetic field lines to the core. This scheme may provide more efficient energy coupling compared to the conventional ICF scheme.