Beam Plasma Research Articles

Experimental study of a neutralizer-free gridded ion thruster using radio-frequency self-bias effect

An experimental study on the quasi-neutral beam extracted by a neutralizer-free gridded ion thruster prototype was presented. The prototype was designed using an inductively coupled plasma source terminated by a double-grid accelerator. The beam characteristics were compared when the accelerator was radio-frequency (RF) biased and direct-current (DC) biased. An RF power supply was applied to the screen grid via a blocking capacitor for the RF acceleration, and a DC power supply was directly connected to the screen grid for the DC acceleration. Argon was used as the propellant gas. Furthermore, the characteristics of the plasma beam, such as the floating potential, the spatial distribution of ion flux, and the ion energy distribution function (IEDF) were measured by a four-grid retarding field energy analyzer. The floating potential results showed that the beam space charge is compensated in the case of RF acceleration without a neutralizer, which is similar to the case of classical DC acceleration with a neutralizer. The ion flux of RF acceleration is 1.17 times higher than that of DC acceleration under the same DC component voltage between the double-grid. Moreover, there are significant differences in the beam IEDFs for RF and DC acceleration. The IEDF of RF acceleration has a widened and multi-peaked profile, and the main peak moves toward the high-energy region with increasing the DC self-bias voltage. In addition, by comparing the IEDFs with RF acceleration frequencies of 3.9 and 7.8 MHz, it is found that the IEDF has a more centered main peak and a narrower energy spread at a higher frequency.

Second-harmonic generation of intense Laguerre Gaussian Beam in collisional plasma: Effect of nonlinear absorption

Second-harmonic generation of intense Laguerre Gaussian Beam in collisional plasma: Effect of nonlinear absorption

Influence Of Critical Beam Power On Propagation Dynamics Of q-Gaussian Laser Beams In Isotropic Collisional Plasma

In current work, the beam-width parameter (BWP) equation is reduced to two variables such as q and critical beam power (p 0) which govern the propagation dynamics and intervals of critical beam power p 0 of a q-Gaussian laser beam have been investigated. The non-linear dependence of dielectric function in collisional plasma used herein is primarily because of heterogeneous heating of carriers along the wavefront of the laser beam. The influence of intervals of p 0 is further used to explore propagation dynamics of q-Gaussian laser beam in isotropic, homogeneous and collisional plasma has been studied. The Akhmanov’s parabolic equation approach under WKB (Wentzel-Kramers-Brillouin) and paraxial approximations are used in current work. The results have been found reasonably interesting which are revealed graphically and discussed.

Dynamics of Hermite–Gaussian laser beam in plasma and terahertz generation

In the present work, the dynamical study of a Hermite–Gaussian (HG) laser beam propagating through plasma with relativistic nonlinearity has been carried out. Furthermore, the dependency of THz generation on the HG laser dynamics has also been investigated. Self-focusing of laser beam inside plasma is achieved due to the modification in electron’s rest mass due to their motion at relativistic velocities. The coupled differential equations obtained using the method of moment determines the variation in spot size of laser beam and have been solved numerically. The laser beam propagating through plasma excites the plasma wave and the nonlinear coupling of HG beam and plasma wave generates THz radiation. It has been observed that THz generation strongly depends upon the variation of spot size, TEM modes, plasma density and intensity of laser beam. Furthermore, the self-trapping of HG laser beam has also been studied.

Improvement in the performance of focusing plasma desorption ionization by altering its counter electrode.

Plasma-based ionization sources play a vital role in rapidly analyzing diverse compounds without extensive sample pretreatment. In contrast to other sources, DC voltage-based ionizations are more advantageous due to their high analytical sensitivity and good tandem with commercially available mass spectrometers without extra power supplies. However, their performance is at the risk of high current DC voltage and helium flow rate, which poses significant challenges to practical operation and increased expense. In this work, we propose a novel focusing plasma desorption ionization (FPDI) in which a visible plasma beam is favorably generated between a conducting wire in a polymeric tube and a counter electrode composed of metal mesh and filter paper drilled with holes. A systematic investigation has been conducted on the influences of the geometry of drilled holes in filter paper, applied DC voltage, helium flow rate, and filter paper size. The optimized system is used to analyze various pesticides in fluid foodstuffs. Compared to metal mesh and conducting paper as the counter electrode for FPDI-MS, combining metal mesh and filter paper drilled holes improved the analysis sensitivity by a factor of more than five. By applying the developed protocol for determining pesticides in complex matrixes such as orange juice and milk, a limit of detection as low as 1.3-3.0ng mL-1 could be achieved. A novel FPDI-MS technique has been developed by combining metal mesh and filter paper drilled with holes as the counter electrode and sample carrier. The corresponding improvement in analysis sensitivity facilitates the future expansion of FPDI-MS applications into different pesticides and other compounds in complex matrixes.

Localization of a Gaussian laser beam in thermal quantum plasma with density ramp

Localization of a Gaussian laser beam in thermal quantum plasma with density ramp

Формирование плазмы в атмосфере азота импульсным электронным пучком вблизи диэлектрической мишени при форвакуумных давлениях

Features of the processes of beam plasma formation near a dielectric (aluminum oxide ceramic) target being irradiated by an intense pulsed electron beam in the forevacuum pressure range (4–15 Pa) have been investigated. It has been established that the density of the beam plasma near the irradiated dielectric target is higher than in the case of "free" propagation of the electron beam. The observed increase in plasma density depends on the emission current (electron beam current), gas pressure, and accelerating voltage. The influence of the dielectric target on the beam plasma density is due to emission of electrons from the target surface and the uncompensated negative potential on the target surface, which determines the energy of emitted electrons. An increase in gas pressure leads to a smaller increase in the beam plasma density due to a decrease in the absolute value of the negative potential. Varying the electron beam current and accelerating voltage provide to control the beam plasma density.

Stimulated Brillouin Scattering of Elliptical q-Gaussian Laser Beams in Plasmas with Axial Density Ramp: Effect of Self-Focusing

Stimulated Brillouin Scattering of Elliptical q-Gaussian Laser Beams in Plasmas with Axial Density Ramp: Effect of Self-Focusing

Inverse Faraday effect of weakly relativistic full Poincaré beams in plasma

The inverse Faraday effect (IFE), which usually refers to the phenomenon in which a quasi-static axial magnetic field is self-generated when a circularly polarized beam propagates in a plasma, has rarely been studied for lasers with unconventional polarization states. In this paper, IFE is reconsidered for weakly relativistic full Poincaré beams, which can contain all possible laser polarization states. Starting from cold electron fluid equations and the conservation of generalized vorticity, a self-consistent theoretical model combining the nonlinear azimuthal current and diamagnetic current is presented. The theoretical results show that when such a laser propagates in a plasma, an azimuthally varying quasi-static axial magnetic field can be generated, which is quite different from the circularly polarized case. These results are qualitatively and quantitatively verified by three-dimensional particle-in-cell simulations. Our work extends the theoretical understanding of the IFE and provides a new degree of freedom in the design of magnetized plasma devices.

Механизм протекания тока в композитной алюмохромной керамике при ее электронно-лучевом спекании в форвакууме

It is shown that during electron beam sintering in the forevacuum pressure region of powder components of composite Al2O3-Cr ceramics, the magnitude of the current flowing through the sample depends both on the percentage of chromium and on the heating temperature of the sample. When a certain temperature is reached, the process of current flow is influenced by thermoelectric emission from the sample surface. Along with the ions from the beam plasma, a noticeable thermoelectric emission current contributes to the process of neutralizing the charging of the ceramic surface with an electron beam and reduces the absolute value of the negative potential of the sample surface. This ultimately contributes to an increase in the efficiency of energy transfer from the electron beam to the sample.

Contribution of thermal dissociation during steel nitriding in electron beam plasma

We report the results of measurements of mass-to-charge ion composition of the beam plasma generated by a forevacuum plasma-cathode electron source in a nitrogen atmosphere during electron beam interaction with the surface of a steel sample. It has been found that as the sample surface temperature increases from 540 ℃ to 930 ℃, the fraction of atomic nitrogen ions in the spectrum increases by 4-10%. This increase in atomic nitrogen occurs at the backdrop of decreasing number of molecular nitrogen monoxide ions and is associated with thermal dissociation of its molecules.

Ionization mechanism of beam plasma generated by an electron beam in medium vacuum

We present the results of the measurements of the ionic composition of plasma generated by an accelerated electron beam at medium vacuum (fore-vacuum) pressures. Calculations of the contribution of plasma electrons and beam electrons to the mechanism of ionization are presented. Comparison of the calculated with the experimental data led us to the conclusion about the dominating contribution of beam electrons and to the ionization process. Keywords: beam plasma, fore-vacuum, electron beam, plasma-cathode electron source.

The mechanism of current flow in composite alumochromiun ceramics during its electron beam sintering in a forevacuum

It is shown that during electron beam sintering in the forevacuum pressure region of powder components of composite Al2O3-Cr ceramics, the magnitude of the current flowing through the sample depends both on the percentage of chromium and on the heating temperature of the sample. When a certain temperature is reached, the process of current flow is influenced by thermoelectric emission from the sample surface. Along with the ions from the beam plasma, a noticeable thermoelectric emission current contributes to the process of neutralizing the charging of the ceramic surface with an electron beam and reduces the absolute value of the negative potential of the sample surface. This ultimately contributes to an increase in the efficiency of energy transfer from the electron beam to the sample. Keywords: Electron beam irradiation of oxide ceramics, electrical conductivity, alumina ceramics, chromium, composite, electron beam, forevacuum.

Механизм ионизации пучковой плазмы, генерируемой электронным пучком в среднем вакууме

We present the results of the measurements of the ionic composition of plasma generated by an accelerated electron beam at medium vacuum (fore-vacuum) pressures. Calculations of the contribution of plasma electrons and beam electrons to the mechanism of ionization are presented. Comparison of the calculated with the experimental data led us to the conclusion about the dominating contribution of beam electrons and to the ionization process.

Physical analysis and numerical simulations of ultra wideband plasma relativistic microwave noise amplifier

The physical mechanism and output properties of the plasma relativistic microwave noise amplifier (PRNA) are studied numerically by using the all electromagnetic particle-in-cell (PIC) code. Firstly, the dispersion relation between the operating mode and the slow space charge wave of relativistic electron beam without coupling is simulated and analyzed. Simulation results show that both the plasma density <i>n</i><sub>p</sub> and radial thickness Δ<i>r</i><sub>p</sub> affect the dispersion characteristics markedly and their increasing can lead the frequency at the beam-wave resonant point to be enhanced. The beam voltage and current also affect the resonant frequency, but the effect is relatively slight. Secondly, variation of the linear growth rate and the bandwidth are then evaluated by using the linear theory. Calculations show that the PRNA has the virtue of wideband output. Its bandwidth can reach a GHz level. By adjusting the plasma parameters <i>n</i><sub>p</sub> and Δ<i>r</i><sub>p</sub>, the relativistic electron beam voltage and current, the operating frequency can be tuned over a wide frequency range. Therefore the PRNA also has virtue of fine frequency tunability. Based on the above calculation results, the whole PIC simulations of the PRNA are then carried out to verify the virtues of wideband microwave output and frequency tunability. The basic features of the field distributions of the operating in the evolution process and out coupling process are given. The bunching process and the energy release process of relativistic electron beam are also plotted. Simulations show that with a plasma density of 1.4×10<sup>19</sup> /m<sup>3</sup>, beam voltage and current of 500 kV and 2 kA and applied magnetic field of 2.0 T, 200 MW output microwave with efficiency about 20% can be obtained. The frequency ranges from about 7.0 to 9.0 GHz, the band width reaches 2 GHz. And the output mode is the TEM mode of the coaxial waveguide. Both <i>n</i><sub>p</sub> and Δ<i>r</i><sub>p</sub> affect the dispersion relations markedly and the output frequency increases clearly with <i>n</i><sub>p</sub> and Δ<i>r</i><sub>p</sub> increasing. The influence of beam voltage and current on the output frequency are both relatively small and the gap distance between the plasma and electron beam has little effect on the output frequency. The research results will provide useful reference for further designing the PRNA.

Effect of cyclic thermal load on beryllium

The paper presents data on the behavior of TGP-56 beryllium after exposure to an electron beam and hydrogen plasma. The experiments were conducted with different numbers of pulses at surface temperatures of ∼ 360 °C, ∼800 °C, and ∼ 1200 °C. The temperature mode is determined by the operating conditions of the first wall coating at a standard thermal load. To assess the changes in beryllium after testing, microanalysis, X-ray diffraction analysis, and microhardness measurements were performed. It has been found that the beryllium coating is resistant to normal International Thermonuclear Experimental Reactor (ITER) operation modes, but at temperatures above 800 °C, critical damage to the material is possible over the time of operation of the thermonuclear facility.

Photons’ Scattering in Relativistic Plasma with Velocity Shear: Generation of High Energy Power-law Spectra

A high energy power law is a common feature in the spectra of many astrophysical objects. We show that the photons in an unmagnetized relativistic plasma composed of electrons and protons with a variable Lorentz factor (or a velocity shear) go through repeated scattering with electrons to gain energy. The escaped population of photons naturally produces a power-law-shaped spectrum making it a photon’s analog to the conventional Fermi acceleration mechanism for charged particles. Thus, this mechanism provides a natural alternative to current explanations of high energy power-law spectra via synchrotron or thermal Comptonization. The model is applicable to any relativistic plasma beam with an arbitrary Lorentz factor profile. We implement the theory to the gamma-ray burst prompt phase and show that the obtained range of the photon indices is compatible with the observed values and the results of Monte Carlo simulations that we carry out independently. Therefore, the observed high energy spectral indices provide a unique indicator of the jet structure.

Influence of helium plasma on the structural state of the surface carbide layer of tungsten

<abstract> <p>This paper presents the results of the experimental studies of the helium plasma interaction with a surface carbide layer of tungsten. The experiments were carried out on a plasma beam installation (PBI) at a constant energy of incoming ions of 2 keV and at a surface temperature of the tungsten carbide layer of ~905 and ~1750 ℃. The local parameters (T<sub>e</sub>, n<sub>0</sub>) of the helium plasma were evaluated using the probe method and spectrometric analysis of the plasma composition. The helium plasma irradiated two types of the carbide layer on the tungsten surface, WC and W<sub>2</sub>C. The mechanisms of changing the tungsten surface morphology in the result of the plasma irradiation have been described. The study of the surface structure of the tungsten samples with a carbide layer of two types (WC, W<sub>2</sub>C) after the exposure to the helium plasma has revealed two different types of the formation of helium bubbles and changes in the surface morphology. The physical mechanism of the formation of helium bubbles consists in the capture of helium atoms by the thermal vacancies generated at high temperature by the material surface. However, with a significant increase in temperature to 1750 ℃, the formation of the bubbles was no longer observed and the sample surface had a developed coral-like structure with crystallographically oriented grains.</p> </abstract>

Two-dimensional numerical study of effect of magnetic field on evolution of laser-driven jets

Astrophysical jets are highly collimated supersonic plasma beams distributed across various astrophysical backgrounds. The triggering mechanism, collimation transmission, and stability of jets have always been a research hotspot of astrophysics. In recent years, observations and laboratory research have found that the magnetic field plays a crucial role in jet collimation, transmission, and acceleration. In this work, the two-dimensional numerical simulation of the jet in front of the CH plane target driven by an intense laser is carried out by using the open-source MHD FLASH simulation program. We systematically investigate the dynamic behaviors of jet evolution caused by the Biermann self-generated magnetic field, the external magnetic field with different directions and initial strengths and compare them with each other. Simulation results show that the Biermann self-generated magnetic field does not affect the jet interface dynamics. The external magnetic field has a redirecting effect on the plasma outflow. The external magnetic field, which is parallel to the direction of the plasma outflow center in front of the target, is conducive to the generation and collimation of the jet. The evolution of the jet goes through three stages: antimagnetic ellipsoid cavity, conical nozzle, and collimated jet. Its formation process and evolution process result from competition among plasma thermal, magnetic, and ram pressure. In terms of force, plasma thermal pressure gradient and magnetic pressure forces play a decisive role in the jet evolution process. The presence of magnetic pressure significantly limits the radial expansion of the jet to achieve axial collimation transmission. The length-diameter ratio of the jet is positively correlated with the initial axial applied magnetic field intensity. In addition, we observe in the simulation that there are many node-like structures in the jet evolution zone, similar to the jet node in YSO. The results provide a reference for future experimental research related to jets and contribute to a more in-depth understanding of the evolution of celestial jets.

Combined Surface Heating by Laser Beam and Subsonic Nitrogen Plasma Jet

The paper describes new combined heating capability of the IPMech RAS inductively coupled plasma facility VGU-4. A 200 W ytterbium laser was added to the facility as a source of radiative heating. The cylindrical specimen made of the Buran orbital vehicle’s heat-shielding tile material with a black low catalytic coating was exposed to subsonic pure nitrogen plasma jet and laser radiation. The specimen surface temperature reached 1325 ∘C during combined radiative and convective heating. The maximum heat flux obtained in the combined mode for a laser incident power of 47 W and a VGU-4 HF-generator anode power of 22 kW was 32.1 W/cm2. The convective heat flux from the nitrogen plasma jet at the same anode power was 12.6 W/cm2. Adding a laser to an existing inductively coupled plasma facility gives the future opportunity to better simulate entry into the atmospheres of Mars, Venus, the outer planets and their moons.