Beam Density Research Articles

Simulation Design of an Electron Gun for Microchannel Plate Scrubbing

The microchannel plate (MCP) is susceptible to the adsorption of substantial amounts of gas during its fabrication process. To mitigate this, a uniform electron source is essential for effective electron scrubbing and gas removal. Thermionic emission, a method of electron generation, can be employed to create the electron source. In this study, a flat spiral filament was designed and simulated using the CST Studio Suite electron simulation software to assess the cleaning performance of the electron gun. The impact of variations in electron gun parameters on the uniformity of the electron beam and current density was systematically analysed. The simulation results show that, with filament, grid, focusing sleeve, and anode voltages set to 200 V, 500 V, 250 V, and 300 V, respectively, a uniform electron beam with a diameter exceeding 30 mm can be achieved. In order to obtain the current density (5~50 nA/mm2) required for the MCP, the temperature of the filament should be 1800–2000 K through theoretical calculation. These findings offer valuable insights for designing a more efficient electron gun for MCP scrubbing.

Preliminary neutronics optimization on the concept of multi-beam accelerator driven system

A new subcritical reactor concept is proposed as one accelerator beam splitting into multiple beams to drive the subcritical reactor in this work, which is so called Multi-Beam Accelerator Driven System (MB-ADS). The spallation target is designed as a target assembly to the fuel assembly. The high current proton beam is divided into multiple parts and injected into different targets scattered among the core to improve the beam efficiency and flatten the spatial power distribution of the core. Based on different MB-ADS schemes, neutronics were conducted on the effects of splitting beam number, target assembly arrangements, fuel zoning, and neutron data libraries. The results show that a reasonable multi-beam scheme can significantly improve the efficiency of the proton beam and flatten the power distribution of the reactor compared to the one target ADS scheme. With the improved beam efficiency, the beam density on the target window is greatly reduced.

Beam-driven electron-acoustic waves in auroral region of magnetosphere with superthermal trapped electrons

The propagation characteristics of nonlinear electron-acoustic (EA) waves are studied in a four-component magneto-plasma, containing inertial cold electrons, warm drifting beam electrons, trapped superthermal hot electrons, and static ions. A linear dispersion relation for EA waves is derived to analyze the impact of electron superthermality on the ω−k relation. For nonlinear analysis, a reductive perturbation formalism is adopted to solve the set of model equations in the form of a trapped Zakharov–Kuznetsov (tZK) equation. The latter is analyzed to determine the solitary structures in terms of phase portraits and exact soliton solutions showing the impact of electron trapping efficiency (γ), hot electron superthermality (κ), drifting speed, temperature and density of beam electrons, and temperature and density of cold electrons, using typical parameters from the short-duration burst of broad-band electrostatic noise emissions observed by the Viking spacecraft in the auroral region. The solitary structures propagate as positive potential pulses and become modified with superthermal trapped electrons, leading to hole (hump) in cold (hot) electron density excitations. The electric field structures of the EA waves are found to be in exact agreement with the observed solitary structures in the auroral region. It is observed that electric field strength associated with these waves decreases as the magnetic field increases. The present model can be used to understand the transport of energy and momentum between plasma particles and to comprehend magnetic reconnection region in magnetopause, where two-temperature electrons and large-amplitude parallel electrostatic waves have been reported by magnetopause multiscale observations.

Design and 3D printing of pelvis phantoms for cementoplasty.

Percutaneous image-guided cementoplasty is a medical procedure for strengthening bones structurally altered by disease, such as osteolytic metastasis. This procedure involves injecting biocompatible liquid bone cement, through one or more trocars into the damaged bone. Within a few minutes the bone cement hardens and restores the rigidity of the bony structure. The introduction of this technique in the case of large cancellous bones, such as the pelvis, raises some practical issues such as: how to manage the flow of cement with variable viscosity over time and how to inject a large amount of cement under fluoroscopy to effectively restore the patient's ability to bear weight? As a means of training for young practitioners to ensure maximal filling of a metastatic bone area, we have designed and manufactured a pelvic phantom capable of replicating cement diffusion in healthy and metastatic bone under fluoroscopic and computed tomographyguidance. The preliminary stage of the study consisted of an analysis of various lattice structures, with the objective of reproducing the haptic feedback experienced during the needle insertion and diffusion of cement within the trabecular bone. Cementoplasty tests were conducted by an experienced radiologist under fluoroscopy and CT guidance to evaluate the performance of the lattice structure. The initial analysis provided the groundwork for the design of the phantom pelvis, which was then evaluated against a patient case. The phantom was divided into two distinct components: a disposable sectionwith lattice structure, intended for the injection of cement, and a reusable part representing the pelvic bones. Two additive manufacturing methods were selected for the production of the phantom: Stereolithography (SLA) for the lattice structure and Fused Deposition Modeling (FDM) for the pelvic bones. The disposable component was composed of different lattice structures, selected to best match the anatomic conditions of both healthy and diseased areas visible on the patient images. Subsequently, the performance of the phantom was validated against patient images through a cementoplastytest. A total of 12 distinct lattice structures were subjected to three tests of cementoplasty. Stochastic lattices with 500 microns beam thickness and densities varying from 15% to 5% demonstrated the most effective replication of the needle haptic feedback, as well as the diffusion of the cement into healthy and osteolytic cancellous bone. These structures were then implanted in the phantom and validated against one patientcase. A methodology to design and manufacture a phantom dedicated to cementoplasty from patient images is proposed. Initially, a series of lattice structures, exhibiting diverse structure types, thicknesses, and densities, were evaluated to assess their capacity to accurately reproduce the haptic feedback of the needle and the diffusion of cement in the trabecular bone. Subsequent to the outcomes of these investigations, several structures were selected for the development of a phantom capable of accurately replicating a cementoplasty procedure under fluoroscopy and CT guidance. This phantom will enable the training of future practitioners on the procedure of cementoplasty in thepelvis.

Self-dual electromagnetic fields

Self-dual electromagnetic fields are shown to be maximally chiral. Monochromatic self-dual beams have electric and magnetic fields that are eigenstates of curl. The chiral density and chiral current of self-dual monochromatic beams are proportional to the energy and momentum densities. Their energy and momentum densities do not oscillate in time. Self-dual pulses based on an oscillatory solution of the wave equation lack the oscillations of non-self-dual pulses based on the same wave function. All of these properties could be significant in physical applications, but few self-dual fields seem to have been studied experimentally.

Abnormal magnetic field topology in the beam-plasma instability driven by ion dynamics

We report on abnormal topological structures in the particles and electromagnetic field distributions induced by current filamentation instability, with emphasis on the effects of plasma ions. In the plasma filament (PF) situation, the transverse magnetic field reaches its maximum at the edge of the plasma filaments, in contrast to the case of beam filament (BF, i.e., the magnetic field reaches the maximum at the edge of the beam filaments). An analytical model is proposed to estimate the response time of the beam electrons and plasma ions, which is essential to determine the criterion of PF occurrence. With increase in beam energy and density, and decrease in plasma ion mass, the transition from BF to PF can be observed. The results are also confirmed by detailed electromagnetic particle-in-cell simulations. Moreover, the influence of PF on the synchrotron photon emission power is also discussed.

Propagation dynamics of dust acoustic modes in collisional multicomponent plasmas

A comprehensive understanding of the physics underlying the dust-based processes and the ability to control the evolution of structures are essential in the field of plasma physics. This knowledge provides the foundation for numerous advanced scientific applications including the study of celestial objects and the synthesis of nanostructures. In this research, we consider the linear propagation of dust acoustic (DA) and dust ion acoustic (DIA) modes in a collisional plasma in the presence of an electron beam. The obtained dispersion relation demonstrates that the collision parameter and the electron beam density have significant contributions to the mode dynamics. The interactions of cold charged particles with neutrals result in a damping effect in the mode dynamics, which subsequently leads to a typical cutoff in the propagation of dust acoustic modes. Furthermore, the electron beam density can control the damping rate at different conditions. An increase in the electron beam density results in an acceleration of the DA mode damping, while the effect on the DIA mode is the opposite. The influence of the electron beam on the dynamics of the modes is more pronounced in the presence of strong collisions. Our analysis also shows that the propagation dynamics of each mode is strongly related to the wave vector. The damping rate is more pronounced in small wave vectors. Numerical analysis indicates that mode propagation can be controlled by the collision parameters and electron beam density. Furthermore, as a general trend, increasing the wave vector causes a shift in the cutoff toward higher collisions.

Non-Fourier thermal spike effect on nanocrystalline Cu phase engineering

The thermal spike effect dominates rapid heating and quenching at the nanoscale in ion beam assisted materials surface phase engineering. This phenomenon often leads to the formation of metastable nanocrystalline phases in the resulting micro-/nanostructures. However, such a non-equilibrium process cannot be accurately described by the conventional Fourier thermal spike model. In this study, a non-Fourier model is proposed to elucidate the dynamics of heat diffusion in sub-keV Cu ion beam sputter deposition. The effects of beam density and energy on the non-equilibrium thermal and stress fields are quantitatively investigated. The influence of high stress field on nanocrystalline Cu phase content is also studied. It is found that the energetic Cu ion beams produce a rapidly oscillating stress field with a maximum of ∼ 10 GPa within 50 ps, which significantly constrains the growth of nanocrystalline Cu phase at a threshold of ∼ 4 GPa. This understanding provides new insights into the formation of metastable nanocrystalline phases in the fabrication and modification of surface micro-/nanostructures using ion beam assisted techniques.

Twisted complex-variable-function Gaussian model beams with special correlations

Abstract We introduce a new class of twisted complex-variable-function Gaussian model (TCVFGM) beams and provide the propagating cross-spectral density (CSD) of optical beams with various correlations. Sufficient conditions are provided to guarantee that the CSD function is physically genuine. We designed an experimental setup to synthesize TCVFGM beams endowed with various correlations using complex transmittance screens. The experimental results of a sinc-correlated TCVFGM source are presented, indicating that the spectral density is present as an array and rotates during propagation. These findings may be useful in beam shaping and particle manipulation.

Growth of stimulated Raman instability by a density-modulated electron beam in laser-plasma interactions

A way to enhance the growth of stimulated Raman instability in laser-plasma interactions was investigated. This relies on the application of density modulation of a co-propagating electron beam in plasmas. In the stimulated Raman scattering process, an electromagnetic pump wave decays into a low-frequency wave and a scattered electromagnetic sideband wave. In this process, the pump wave produces an oscillatory velocity associated with the plasma electrons and the beam electrons. These oscillatory velocities combine with the existing low-frequency mode, producing ponderomotive force that drives high-frequency sideband waves. The sidebands couple to the pump wave, driving the beam-mode. A modulation of the electron beam density enhances the growth rate of the instability. The theoretical calculations show about 40% enhancements in growth of Raman instability at resonance (where the electron beam density modulation parameter approaches to unity) for the plasma density of the order of 1018 cm−3.

Spin angular momentum and optical chirality of Poincaré vector vortex beams

Abstract The optical chirality and spin angular momentum of structured scalar vortex beams has been intensively studied in recent years. The pseudoscalar topological charge ℓ of these beams is responsible for their unique properties. Constructed from a superposition of scalar vortex beams with topological charges ℓ A and ℓ B , cylindrical vector vortex beams are higher-order Poincaré modes which possess a spatially inhomogeneous polarization distribution. Here we highlight the highly tailorable and exotic spatial distributions of the optical spin and chirality densities of these higher-order structured beams under both paraxial (weak focusing) and non-paraxial (tight focusing) conditions. Our analytical theory can yield the spin angular momentum and optical chirality of each point on any higher-order or hybrid-order Poincaré sphere. It is shown that the tunable Pancharatnam topological charge ℓ P = ( ℓ A + ℓ B ) / 2 and polarization index m = ( ℓ B − ℓ A ) / 2 of the vector vortex beam plays a decisive role in customizing their spin and chirality spatial distributions. We also provide the correct analytical equations to describe a focused, non-paraxial scalar Bessel beam.

State primary standard for units of absorbed dose and absorbed dose rate of photon, electron, proton radiation and in carbon ion beams, quantity, fuence, fux density and energy of particles in proton beams and heavy charged particles GET 38-2024

The problem of ensuring the accuracy and traceability of the measurement results of the absorbed dose in carbon ion beams, as well as the measurement results of the amount, fluence, flux density and energy of particles in proton and heavy charged particles beams is considered. Until now, in practice, these values have been measured only by indirect methods. The lack of approved measuring instruments for the quantities under consideration and the metrological traceability of measurement results of these quantities to standards did not allow achieving consistency of measurement methods used in practice and confirming the reliability of the results obtained. To solve this problem, three measuring complexes have been developed and created, which are included in the State Primary Standard of units of absorbed dose and absorbed dose rate of photon, electron, proton radiation and in carbon ion beams, quantity, fluence, flux density and energy of particles in proton and heavy charged particles beams GET 38-2024. The measuring complex for reproducing the unit of absorbed dose in carbon ion beams consists of an adiabatic calorimeter, a thermostating system, a data collection and processing system and a vacuum pumping station. To reproduce the unit of energy of protons and heavy charged particles, a complex has been implemented, which includes a total absorption calorimeter, a data collection and processing system, a vacuum pumping station and a particle count determination system based on the use of a Faraday cup. To reproduce the units of fluence and particle flux density in proton and heavy charged particles beams, a measuring complex has been created containing a Faraday cup, a set of collimators and a low current meter. The schemes, the principles and the results of studies of the metrological characteristics of the developed measuring complexes are described. The results are relevant for the field of radiation therapy and radiation resistance tests of the electronic component base used in the space industry.

Effect of Nonuniform Plasma on Grid Erosion of the Water Ion Thruster

Miniature water ion thrusters provide CubeSats with orbit transfer capability and enable missions that require high ΔV. Erosion on the grids is critical for the thruster’s lifetime and propellant utilization efficiency. It was shown numerically that the nonuniformity of the plasma in the discharge chamber causes inhomogeneous erosion of the grid. However, deviation from experiments was still a problem. In this study, we evaluate the performance and the change in the grid erosion of the miniature water ion thruster during 1000 h of operation. The propellant utilization efficiency decreases from 16% to 12% due to grid erosion. The contamination effect of the antenna and magnets on the performance of the thruster was less than that due to the change of grid geometry. In terms of grid erosion, in the center and the periphery of the grid where the ion beam density is low, the direct impingement of the ion beam is dominant, and the diameter of the accelerator grid eroded from 0.31 to 0.52 mm. On the other hand, in the middle part of the grid, where the ion beam is dense, charge exchange ions dominate the erosion, and the diameter was eroded from 0.31 to 0.39–0.45 mm in hexagonal.

Determining the carbon detection limit with magnetic sector dynamic secondary ion mass spectrometry (SIMS)

Dynamic SIMS is often used to evaluate the concentration of impurities in solids because of its high sensitivity, depth profiling capabilities, good depth resolution, and high throughput. Continuous ion beam sputtering with a high-density primary beam provides high sensitivity and reduces the background contribution from residual gases within the analytical chamber. Dynamic SIMS experiments performed with several magnetic sector instruments using various sputtering rate conditions demonstrated a slow decrease of the carbon detection limit with the increase of sputtering rate (SR), when it was varied by changing the sputtering beam density. The dependence data, within the scatter limits, can be fit by a power function of SR with the exponent of about −1/2. The observed detection-limit-dependence curve is common for magnetic sector SIMS instruments, owing to contamination and the design of the analytical chamber. The depth resolution of light-element SIMS analysis (except for oxygen) performed using Cs+ sputtering is limited and cannot be improved by reducing the impact energy of the sputtering beam. A segregation-type depth profile with a long trailing edge was observed in the B, C, and N depth profiles when Cs+ sputtering was employed under ultra-high vacuum conditions. This effect is plausibly associated with preferential sputtering owing to the difference in the surface binding energy, along with the large difference in the mass of the interacting atoms within the collision cascade during sputtering. The depth resolution improved with surface oxidation when Cs + sputtering was combined with backfilling of the analytical chamber using O2. The analytical chamber backfilled with oxygen can be sufficiently replaced with a very low-impact energy-focused oxygen beam, enabling simultaneous oxygen and cesium co-sputtering SIMS analysis. The practical feasibility of using a co-sputtering with focused Cs+ and O2+ sputtering beams to achieve a high depth-resolution for carbon analysis under ultrahigh vacuum conditions was demonstrated.

Comparative analysis of microwave radiation generated by the interaction between electron beam and plasma under different methods

This article presents a physical model that describes the interaction between surface electron beams and plasma. The dispersion relations for beam plasma interactions were derived using perturbation method and field matching methods. The study investigates how different parameters affect radiation frequency and bandwidth. The results indicate that as electron beam velocity increases, the associated kinetic energy also rises, leading to an increase in both the maximum radiation frequency and bandwidth at high frequencies. Conversely, the radiation bandwidth at low frequencies decreases. Similarly, a higher plasma density results in a greater maximum radiation frequency, but the high-frequency bandwidth decreases, while the low-frequency bandwidth increases. Additionally, when the electron density and electron velocity of the electron beam remain constant, increasing the plasma density can increase the microwave radiation frequency However, there exists a plasma density threshold, beyond which high-frequency electromagnetic waves are no longer radiated.

Preparation of magnetic films using the laser induced forward transfer technique

In the study, laser induced forward transfer (LIFT) of magnetic materials such as α-Fe and Nd–Fe–B was performed to directly deposit on a substrate using a YAG laser. Usage of an optical shatter and Galvano scanner enabled us to obtain LIFT-made films with a dotted pattern. The effects of conditions of laser irradiation on the deposited films were investigated. There was a threshold energy density for obtaining α-Fe dot patterns with LIFT. Energy density of a laser beam enabled a larger size of deposited dot patterns under the same laser spot size. In LIFT-prepared α-Fe films, atmosphere during the deposition did not strongly affect the crystalline structure. On the other hand, the deterioration of coercivity and squareness in LIFT-made Nd–Fe–B films was observed under a low vacuum atmosphere of 10 Pa compared with those of LIFT-made ones in a high vacuum of 10−4 Pa. It was also confirmed that Nd–Fe–B films with a coercivity of 290 kA m−1 on paper could be deposited via the LIFT technique.

Spoke-Type Structures in an Ion Diode with Magnetic Insulation of Electrons

The article presents the results concerning the cross-sectional energy density distribution of a pulsed ion beam for two types of diodes with electron open drift: with external magnetic insulation (250 kV, 80 ns, 0.6 T) and with self-magnetic insulation of electrons (250–300 kV, 120 ns, 0.8 T). Anode plasma is formed using a breakdown along the surface of the anode dielectric coating (single-pulse mode) or explosive electron emission (with double opposite-polarity pulses). It was found that, when the energy density of the ion beam exceeds ≈0.4 J/cm2, periodic spoke-type structures with a step of 3–6 cm in the beam cross section are formed. The processes of formation of such a structure—nonuniform density of anode plasma and self-organization of anode and/or cathode plasma in crossed electric and magnetic fields—are analyzed. It is shown that the formation of local plasma regions in the anode–cathode gap of an ion diode can cause the formation of a periodic structure of the cross-sectional energy density distribution.

Multi-Fresnel-Lens Pumping Approach for Simultaneous Emission of Seven TEM00-Mode Beams with 3.73% Conversion Efficiency

TEM00-mode operation is a requirement in many laser-based applications due to the small divergence and high-power density of the emitted laser beam. A solar laser scheme was designed and numerically studied with the goal of increasing the solar-to-laser power conversion efficiency in the TEM00-mode operation. The collection and primary concentration of sunlight was performed via twelve sets of folding mirrors and Fresnel lenses, toward a laser head composed of a fused silica torus volume and seven Ce:Nd:YAG rods, in a side-pump configuration. With this scheme, TEM00-mode laser power totaling 212.39 W could potentially be produced from seven beams, with six of them being 32.60 W each and with Mx2 = 1.00, My2 = 1.01 quality factors. Notably, 35.40 W/m2 collection efficiency and, most importantly, 3.73% solar-to-laser power conversion efficiency were numerically achieved. The latter efficiency value represents a 1.81-time improvement over the experimental record, established with a prototype that had a single Ce:Nd:YAG rod in an end-side pump configuration.

Enhanced energy deposition of laser-produced proton beams in high-density plasmas due to beam density self-steepening

The energy deposition of laser-accelerated proton beams in solid-density plasmas with different ion charge numbers is studied with detailed one-dimensional particle-in-cell simulations. In the plasma with a high ion charge number, in which the plasma collision frequency approaches electron oscillation frequency, the beam protons are strongly decelerated by the electric field induced by the plasma return current. The energy deposition is further enhanced as the beam travel distance increases due to beam density self-steeping, which is also confirmed by multi-dimensional particle-in-cell simulation. A simple analytical model is proposed to estimate the characteristic travel distance for significant density self-steeping, showing agreement with the simulation results. While in the plasma with a low ion charge number, in which the plasma collision frequency is much smaller than the electron oscillation frequency, the proton beam is modulated significantly by the excited two-stream instability.

On the modulated fifth order dressed electron acoustic electrostatic and energy features in auroral plasma

In this work, the higher order electrostatic and solitonic EA energy plasma in auroral plasma has been investigated. The perturbed KdV form has been solved. The modulated soliton speed, energy of the cold beam electrons, and the associated higher fifth order electrostatic field have been mathematically derived. The effect of perturbed beam density as well as beam temperature parameters on the dressed electrostatic and energy properties has been discussed. The auroral plasma results in this work may be important in space applications.