Electron Beam Injection Research Articles

A novel design of the electrostatic storage ring using quadrupole deflector

A novel electrostatic storage ring (ESR) design was created using an electrostatic quadrupole deflector (EQD) and quadrupole doublet lens (QDL). EQD was used to turn the electron beam 90 degrees in order to create an innovative ESR design. The impact of EQD designs on ESR performance was investigated, and the results showed that the performance of ESR was directly affected by the EQD design. The calculations showed that increasing the EQD diameter by 20% led to an enhancement in the electron beam dimensions by 88% for ∆x and 44% for ∆y for the initial angle of the electron beam α = 0.2°. Also, the design achieved its goal of keeping kinetic energy constant, where for an initial kinetic energy of 1000 eV, the difference between the energy of the injected electron beam and the emerging electron beam from the ESR is approximately 1–5 eV, i.e., despite changing the diameter of the EQD, the dimensions of the electron beam improve and the kinetic energy remains constant.

Quasi-regular formation of rogue waves in gyrotrons due to periodic injection of electron beams

We theoretically study specific non-stationary dynamics of gyrotrons generation in conditions of significant excess of the operating current over the starting value. In this case, gyrotrons with continuous electron beams unpredictably emit “giant” ultrashort radiation spikes, which can be interpreted as microwave rogue waves. Within the frame of the average approach and direct 3D particle-in-cell simulations, we demonstrate that the occurrence of gyrotron rogue waves can be regularized by periodic injection of an electron beam. More regular formation of rogue waves would enhance interest in the implementation of such systems for possible applications.

Mechanism of Beam-Plasma Discharge Development in the Gas Dynamic Trap

The work studies how a plasma discharge in the Gas Dynamic Trap (GDT) is ignited in a volume significantly exceeding the volume of the injected electron beam. This property of a beam-plasma discharge makes it attractive to use relatively low-power electron beams to create starting plasma in open traps with parameters sufficient for its further effective heating by the neutral injection. Despite the fact that effective ionization of plasma far beyond the electron beam in open traps has been observed experimentally for more than 60 years, the detailed mechanism of this phenomenon is still not clear. Particularly many questions arise in regimes that are implemented in such large fusion facilities as GDT, where the relaxation length of the beam turns out to be significantly less than the length of the trap, and the turbulence excited by the beam is localized near the entrance magnetic mirror. Based on recent experiments [E.I. Soldatkina et al. Nucl. Fusion 62, 066034 (2022)], we have proposed a scenario for the development of a discharge in GDT, according to which a compact region of intense plasma turbulence first rapidly expands radially, ionizing the gas outside the beam tube in the vicinity of a magnetic mirror, and then a slower ionization process begins in the rest trap volume both due to the tail of suprathermal particles that are formed in the turbulence zone, and due to thermal electrons that receive energy from the pumping region via the longitudinal electron thermal conductivity. To assess how well this scenario explains the experimentally observed dynamics of plasma density growth in different parts of the facility, we carry out particle-in-cell simulations of the radial expansion of the turbulence zone and propose a simplified model of impact ionization in the entire volume of the trap by both thermal and suprathermal electrons.

Excitation of Terahertz Spoof Surface Plasmons on a Roofed Metallic Grating by an Electron Beam.

In this paper, both fundamental SSP modes on a roofed metallic grating and its effective excitation of the bounded SSP mode by an injected electron beam on the structure are numerically examined and investigated in the THz regime. Apart from the bounded SSP mode on the metallic grating with open space, the introduced roofed metallic grating can generate a closed waveguide mode that occupies the dispersion region outside the light line. The closed waveguide mode shifts gradually to a higher frequency band with a decreased gap size, while the bounded SSP mode line becomes lower. The effective excitation of the bounded SSP mode on this roofed metallic grating is also implemented and studied by using a particle-in-cell simulation studio. The output SSP power spectrums with various gap sizes by the same electron beam on this roofed metallic grating are obtained and analyzed. The simulation results reveal that the generated SSP spectra show a slight red shift with a decreased gap size. This work on the excitation of the SSP mode using an electron beam can benefit the development of high-power compact THz radiation sources by utilizing the strong near-field confinement of SSPs on metallic gratings.

Electronic excitation of high-order spoof surface plasmons on metallic grating at terahertz frequencies

High-order spoof surface plasmon (SSP) mode on corrugated metallic surfaces can find many interesting applications, such as in imaging, sensing, transmission and enhanced radiation source, etc. In this paper, an efficient excitation method of the high-order SSP mode by using an injected electron beam on the uniform rectangular metallic grating is proposed and investigated numerically. Based on the matched wave momentum between the SSP mode and the electron beam, both the fundamental and high-order SSP modes can be excited on the structure by using a single injected electron beam. Numerical simulation results indicate that the maximum electric field intensity of the generated high-order SSP mode is about two orders higher than that of the fundamental SSP mode. In addition, the peak power of the excited high-order SSP mode is almost two times that of the fundamental SSP mode power by the same energy electron beam, which demonstrates the obvious advantage of the high-order SSP electronic excitation approach compared to the previous fundamental SSP mode excitation on the structure. The central working frequency of high-order SSP power spectrum is about three times that of the fundamental SSP power spectrum. Moreover, the influences of the injected electron beam energy on the excited SSP power spectrum are analyzed specifically. It is shown that the generated SSP power spectrum demonstrates a blue shift with the decreased working voltage of the electron beam simultaneously, with its peak power increasing. However, the working bandwidth is narrowed with decreased beam voltage, which further reveals its working mechanism of presented electronic excitation of the SSP mode. The presented studies provide a new method to excite a high-order SSP mode on the metallic grating, which can find some potential applications in high-sensitivity sensing, deep sub-wavelength waveguide, and many others in terahertz spectra.

Numerical characterization of dual-frequency capacitively coupled plasmas modulated by electron beam injection

The modulated approach of electron beam (EB) injection can achieve favorable parameters for capacitive coupled plasmas (CCP). In this work, a one-dimensional particle-in-cell/Monte Carlo collision (PIC/MCC) model is used to simulate the stable dual-frequency CCP with EB injection. First, when the parameters of EB are kept constant at 0.01 A and 30 eV, the results demonstrate significant enhancements in electron density, self-bias voltage, and ion flux. Furthermore, the electron energy probability function (EEPF) appears to have a transition from a typical bi-Maxwellian distribution to a Maxwellian distribution, and the dominant heating mode shifts from the α-mode to the α-γ-mode. Secondly, when the EB current and energy are all changed, the basic parameters of DF-CCP can be achieved by different modulations. Furthermore, we also discuss the transition of the electron heating mode as the current increases from 0.001 A to 1 A and the energy increases from 10 eV to 490 eV. In particular, we conduct a comparative study among different cases of EB injection. According to these results, the modulation capability of EB injection in DF-CCP is thoroughly investigated, which can greatly benefit atom-scale etching in practical applications.

Spiral copropagation of two relativistic intense laser beams in a plasma channel.

The copropagation of two relativistic intense laser beams with orthogonal polarization in a parabolic plasma channel is studied analytically and numerically. A set of coupled equationsfor the evolution of the laser spot sizes and transverse centroids are derived by use of the variational approach. It is shown that the centroids of the two beams can spiral and oscillate around each other along the channel axis, where the characteristic frequency is determined both by the laser and plasma parameters. The results are verified by direct numerical solution of the relativistic nonlinear Schrödinger equationsfor the laser envelopes as well as three-dimensional particle-in-cell simulations. In the case with two ultrashort laser pulses when laser wakefields are excited, it is shown that the two wake bubbles driven by the laser pulses can spiral and oscillate around each other in a way similar to the two pulses. This can be well controlled by adjusting the incidence angle and separation distance between the two laser pulses. Preliminary studies show that externally injected electron beams can follow the trajectories of the oscillating bubbles. Our studies suggest a new way to control the coupling of two intense lasers in plasma for various applications, such as electron acceleration and radiation generation.

Effect of sharp vacuum–plasma boundary on the electron injection and acceleration in a few-cycle laser driven wakefield

The electron injection and acceleration driven by a few-cycle laser with a sharp vacuum–plasma boundary have been investigated through three-dimensional (3D) particle-in-cell simulations. It is found that an isotropic boundary impact injection (BII) first occurs at the vacuum–plasma boundary, and then carrier-envelope-phase (CEP) shift causes the transverse oscillation of the plasma bubble, resulting in a periodic electron self-injection (SI) in the laser polarization direction. It shows that the electron charge of the BII only accounts for a small part of the total charge, and the CEP can effectively tune the quality of the injected electron beam. The dependences of laser intensity and electron density on the total charge and the ratio of BII charge to the total charge are studied. The results are beneficial to electron acceleration and its applications, such as betatron radiation source.

Observation of Monoenergetic Electrons from Two-Pulse Ionization Injection in Quasilinear Laser Wakefields

The generation of low emittance electron beams from laser-driven wakefields is crucial for the development of compact x-ray sources. Here, we show new results for the injection and acceleration of quasimonoenergetic electron beams in low amplitude wakefields experimentally and using simulations. This is achieved by using two laser pulses decoupling the wakefield generation from the electron trapping via ionization injection. The injection duration, which affects the beam charge and energy spread, is found to be tunable by adjusting the relative pulse delay. By changing the polarization of the injector pulse, reducing the ionization volume, the electron spectra of the accelerated electron bunches are improved.

Control of electron beam current, charge, and energy spread using density downramp injection in laser wakefield accelerators

Density downramp injection has been demonstrated to be an elegant and efficient approach for generating high-quality electron beams in laser wakefield accelerators. Recent studies have demonstrated the possibilities of generating electron beams with charges ranging from tens to hundreds of picocoulombs while maintaining good beam quality. However, the plasma and laser parameters in these studies have been limited to specific ranges or attention has been focused on separate physical processes such as beam loading, which affects the uniformity of the accelerating field and thus the energy spread of the trapped electrons, the repulsive force from the rear spike of the bubble, which reduces the transverse momentum p⊥ of the trapped electrons and results in small beam emittance, and the laser evolution when traveling in the plasma. In this work, we present a comprehensive numerical study of downramp injection in the laser wakefield, and we demonstrate that the current profile of the injected electron beam is directly correlated with the density transition parameters, which further affects the beam charge and energy evolution. By fine-tuning the plasma density parameters, electron beams with high charge (up to several hundreds of picocoulombs) and low energy spread (around 1% FWHM) can be obtained. All these results are supported by large-scale quasi-three-dimensional particle-in-cell simulations. We anticipate that the electron beams with tunable beam properties generated using this approach will be suitable for a wide range of applications.

Study of character of modulation instability in cyclotron resonance interaction of an electromagnetic wave with a counterpropagating rectilinear electron beam

In this paper, the interaction of a monochromatic electromagnetic wave with a counterpropagating electron beam moving in an axial magnetic field is considered. The purpose of this study is to investigate the conditions for occurrence of modulation instability (MI) in such a system and to determine at which parameters of the incident wave the MI is absolute or convective. Methods. Theoretical analysis of the MI character is carried out by studying the asymptotic form of unstable perturbations using the saddle-point analysis. The analytical results are verified by numerical simulations. Results. Theoretically, the boundary of change in the character of MI on the plane of input signal parameters (amplitude and detuning of the frequency from the cyclotron resonance) is determined. Numerical simulations confirm that as the signal frequency increases, the regime of self-modulation, which corresponds to the absolute MI, is replaced by the stationary single-frequency transmission corresponding to the convective MI. The numerical results coincide with the analytical ones for the system, which is matched at the end. The matching is implemented by smooth increasing of the guiding magnetic field in the region of electron beam injection. Conclusion. Determining the analytical conditions for the implementation of the absolute MI is of practical interest, since the emerging self-modulation can lead to the generation of trains of pulses with the spectrum in the form of frequency combs.

Morphology Features of Ferroelectric Submicron Domains Written by E-Beam under a Metal Film in LiNbO3

The practical significance of ferroelectric domains and various domain boundaries has been growing steadily in recent years. In this work, various domain structures were written with an electron beam through a thin aluminum film on a −Z cut of bulk lithium niobate. The use of relatively low accelerating voltages (5 and 10 kV) and the grounding of the surface metallization made it possible to write periodic structures (1D and 2D) on large areas with domain sizes ≤1 μm. Selective domain etching and AFM in contact mode were used to observe various domain shapes obtained in the experiments. An unusual feature of the submicron-sized domains was needle-like vertices. Importantly, the vertices of the domains were deepened relative to the irradiated surface. It was found that the size and proximity of the irradiated regions to each other in the patterns used can significantly change the upper part of the domains. The experimental data were analyzed and discussed taking into account the computer simulation of the spatial field distribution of injected electron beam charges. The obtained results contribute to the development of controlled writing of submicron-sized domain structures using an electron beam.

Injection of electron beams into two laser wakefields and generation of electron rings.

Mutual injection of electron beams into two laser plasma wakefields was observed experimentally when driving laser pulses interfered in plasma at a small crossing angle and were slightly relatively delayed, approximately by one pulse duration. Particle-in-cell simulations revealed that the mutual injection was sensitive to the spatial overlap of the laser pulses, which therefore could be used to control the mutual injection. The dual synchronized, femtosecond electron beams are potentially useful for pump-probe experiments in ultrafast science. In addition, out-of-axis ring-shaped electron beams were detected in both experiments and simulations.

Tracking a Beam of Electrons from the Low Solar Corona into Interplanetary Space with the Low Frequency Array, Parker Solar Probe, and 1 au Spacecraft

Type III radio bursts are the result of plasma emission from mildly relativistic electron beams propagating from the low solar corona into the heliosphere where they can eventually be detected in situ if they align with the location of a heliospheric spacecraft. Here we observe a type III radio burst from 0.1 to 16 MHz using the Parker Solar Probe (PSP) FIELDS Radio Frequency Spectrometer (RFS) and from 20 to 80 MHz using the Low Frequency Array (LOFAR). This event was not associated with any detectable flare activity but was part of an ongoing type III and noise storm that occurred during PSP encounter 2. A deprojection of the LOFAR radio sources into 3D space shows that the type III radio burst sources were located on open magnetic field from 1.6 to 3 R ⊙ and originated from a near-equatorial active region around longitude E48°. Combining PSP/RFS observations with WIND/WAVES and Solar Terrestrial Relations Observatory (STEREO) WAVES, we reconstruct the type III radio source trajectory in the heliosphere interior to PSP’s position, assuming ecliptic confinement. An energetic electron enhancement is subsequently detected in situ at the STEREO A spacecraft at compatible times, although the onset and duration suggests the individual burst contributes a subset of the enhancement. This work shows relatively small-scale flux emergence in the corona can cause the injection of electron beams from the low corona into the heliosphere, without needing a strong solar flare. The complementary nature of combined ground and space-based radio observations, especially in the era of PSP, is also clearly highlighted by this study.

Orbital angular momentum-resolved convergent-beam electron diffraction by the post-selected injection of electron beam.

Recent advances in the production of electron vortex beams carrying orbital angular momentum (OAM) offer unique opportunities to explore materials at the nanoscale level. We present a novel method for observing convergent-beam electron diffraction (CBED) patterns by using an electron vortex beam. In a transmission electron microscope, a series of electron vortex beams generated by a forked grating mask located above the specimen illuminate the specimen, and CBED patterns are imaged onto the observation plane of the microscope, selecting one of the electron vortex beams using an aperture located beneath the specimen. We demonstrate that the post-selection method yields the same OAM-resolved CBED patterns as when a single convergent electron beam is injected. The formation mechanism of the post-selected CBED is also discussed. This post-selection method is general and can be applied to electron energy-loss spectroscopy to probe multipole excitations using electron vortex beams.

Plasma generation in a long, narrow, metal tube by electron beam injection

We present results of experimental studies of plasma generation in a long, narrow metal tube by electron beam injection into the tube and simultaneous application of a negative potential to the tube. We show that the threshold electron beam current for plasma initiation increases with decreasing pressure, decreasing tube diameter, and increasingly negative tube potential.

Computational study of microdischarges driven by electron beam injection with particle-in-cell/Monte Carlo collision simulations

Microdischarges (MDs) have attracted increasing attention recently due to their widespread applications. The electron beam injection as an external source can affect the formation and characteristics of microdischarges. Aimed at exploring the kinetic properties of the atmospheric-pressure microdischarges purely driven by electron beam injection without external voltage, the one-dimensional implicit particle-in-cell/Monte Carlo collision model is developed. The monoenergetic electron beam is injected from the left electrode with a current of 0.001–0.05 A and an emission energy of 20–80 eV. It is found that similar to voltage and current-driven MDs, electron beam driven MDs can sustain steady glow discharge with high density (1021–1022m−3) but has much lower plasma potential (∼0.15−0.30 V) and electron temperature (<1 eV) due to the absence of an external field. The electron energy distribution function is composed of a low-energy group with two-temperature distribution and a high-energy group with a discrete distribution. In addition, the injected electron beam current and energy can influence the plasma properties significantly, such as plasma density, electron temperature, plasma potential, etc. The characteristics of ion bombardment can also be modulated by the beam energy and current, resulting in achievement of low energy and high flux. By enlarging the gap between the electrodes, the parameter difference on both sides can be realized.

Design and research of a novel structure for extended interaction oscillators

To improve the bandwidth and output of an extended interaction oscillator (EIO), this article proposes a new structure and tests its S parameters. Through simulation analysis and theoretical calculations, it is verified that the structure cannot only increase the bandwidth of the device but also suppress the influence of weak-coupling characteristics of the grating and increases the power capacity of the device. The optimized structure was analyzed by particle-in-cell simulations. The results show that the X-EIO structure has a wide electrical tuning range of 800 MHz under the condition that the effective output is not less than 150 W. The dual-coupling hole of this structure cannot only obtain the same frequency and the same power output synchronously but also has higher efficiency and greater power than the traditional single-hole output. With oxygen-free copper as the background material, at 20.8 kV, 1 A electron beam injection, both coupling holes can obtain a power of more than 2.6 kW, and the highest output efficiency reaches 12.67%. The slow-wave structure has been assembled and tested, and the distribution result of its S parameter is similar to the simulation result, which can achieve broadband adjustable output.

Overview of coordinated spherical tokamak research in Japan

Spherical tokamak (ST) research in Japan has produced many innovative results: (i) plasma start-up to I p > 70 kA was achieved by electron cyclotron wave (ECW) with N ∥ = 0.75, while electron heating to T e > 500 eV was achieved with N ∥ = 0.26 on QUEST. (ii) The radiofrequency (RF)-induced transport model was combined with the x-ray emission model, and extended magnetohydrodynamics equilibrium with kinetic electrons was developed to interpret fast-electron-dominated lower hybrid wave sustained plasmas on TST-2. (iii) Density as high as 30 times the cutoff density was achieved by electron Berstein wave current drive combined with electron beam injection on LATE. (iv) Multiple plasmoids formed by tearing instability in the elongated current sheet were observed, and flux closure and ion heating by plasmoid-mediated fast magnetic reconnection were observed on HIST. (v) Optimization of ECW-assisted inductive start-up with a vertical field with positive decay index was performed on TST-2. (vi) Stabilization of the vertical displacement event by a set of upper and lower helical field coils was demonstrated on TOKASTAR-2. (vii) A 6 h discharge was achieved by cool-down of the center stack cover on QUEST, where the plasma duration limit was consistent with the wall saturation time estimated by modeling. (viii) Extension of ion heating by plasma merging was achieved on TS-3U, TS-4U, UTST, MAST, and ST40.

Uluslararası Doğrusal Çarpıştırıcı Operasyonu için Gamma Işını Serbest Elektron Lazeri Salındırıcı Tasarımının Kısa Bir Gözden Geçirilmesi

In this paper, we make a review of the International Linear Collider design with regard to its positron source. The properties of the intense gamma ray undulator radiation of the dedicated free electron laser is reviewed. We review the discussions about the proposed undulator parameters to obtain an efficient operation of the positron source. The proposals and experimental results about the optimization of the positron beam yield, undulator properties, the injected electron beam energy, polarisation qualities of the produced gamma rays and the positron beam, are discussed. Alternative ideas and suggestions about the use of excess gamma rays in other nuclear energy experiments or the use of positrons in the undulator instead of electrons are also mentioned.