Plasma Electron Density Research Articles

Scattering of X-ray Ultrashort Laser Pulses on Bound Electrons in Dense Plasma

We considered the resonance scattering of ultrashort laser pulses (USLP) on the bound electrons of hydrogen-like ions in a dense plasma. A process description was proposed in terms of full scattering probability during the time of pulse action. Dense plasma’s effect was demonstrated at the resonance scattering cross-section spectrum, and the probability dependence on USLP carrier frequency and duration was obtained for the cases of isolated ions and ions in a dense plasma.

Electron acceleration by wakefield generated by the propagation of chirped laser pulse in plasma

A study of generation of wakefield and particle acceleration via propagation of linearly polarised, chirped, Gaussian laser pulse in preformed plasma channel is presented. Perturbation technique is used to separate slow and fast varying plasma electron velocities and density. Considering the laser pulse length and amplitude to be evolving along the propagation distance, nonlinear fluid equations are used to derive longitudinal electric wakefields at varying propagation distances for chirped as well as unchirped pulses. It has been seen that longitudinal wakefield amplitude generated by positively (negatively) chirped laser pulses is higher (lower) than the amplitude obtained by unchirped laser pulses. The wakefield amplitudes are optimized with respect to the propagation distance. Further, trapping and acceleration of electrons by the generated wakes, is analysed. Comparing the energy of an accelerated test electron using chirped and unchirped laser pulses, it is shown that positively chirped laser pulses are capable of accelerating test electron to maximum energy using minimum injection energy. Hence, highest energy gain can be obtained by propagation of positively chirped laser pulse in plasma.

Digital holographic measurement of electron temperature and density of laser-produced plasmas with an ultrashort laserpulse.

Holography, which can provide the information of phase as well as amplitude of a laser probe, could be a powerful method to diagnose the electron density and temperature of a plasma simultaneously. In this paper, digital holography with an ultrashort laser pulse is applied to diagnose laser-produced aluminum plasmas. Detailed analyses show that the reconstruction of the wave amplitude could be profoundly affected by the difference between the phase and group velocity of the ultrashort laser pulse in the plasma, which makes it a challenge to accurately reconstruct the amplitude in the case when ultrashort laser pulses are utilized for high-temporal resolution of holography.

X-ray transmission effects in a high-density dynamic-dusty plasma environment

X-ray communication (XCOM), which employs modulated X-ray photons as the carrier for signal transmission, is a promising wireless optical technology for space applications, particularly during spacecraft blackout re-entry. Currently, several challenges related to XCOM require solutions, including incomplete transmission attenuation models and a lack of experimental verification of the dynamic-dusty communication effects. This study improved the XCOM transmission characteristics in high-density dynamic-dusty plasma based on a collision model. A dynamic-dusty plasma XCOM was built to verify a modulated X-ray tube and an alkali-metal plasma source. The results show that with an increase in photon energy and flow, the X-ray carrier achieves a higher transmission speed, which is sharper than that of photon energy under the influence of flow. When the average electron density of the dusty plasma is 1012–1013 cm−2, the plasma flow speed is 550–650 m/s, the macro temperature exceeds 1500 K, and the communication demonstration system achieves a stable data rate of 50 kbps at a bit error (BER) of 1.7 × 10−5 with a carrier amplitude and frequency of approximately 20 kV and 4.8 Mcps, respectively. This experiment yielded theoretical and actual values for the development of XCOM technology in space applications during re-entry blackouts.

Numerical Simulations of Plasmas Generated by Air Explosion

The explosion process of explosives is very complex, often accompanied by phenomena such as luminescence, heat, and electromagnetic radiation. Many studies have shown that the electromagnetic radiation of explosive explosions is related to plasma generated by explosion. In this paper, through the thermal equilibrium ionization model, the plasma model of explosive explosion is established, the calculation formula of plasma state parameters is obtained, and the plasma dynamics program is written. The numerical simulation analysis of the air explosion conditions is carried out by using the plasma dynamics program, and the relationship between the electron density and conductivity of the air explosion plasma and the mass of explosive and distance are summarized.

Scale-invariant resonance characteristics in magnetized capacitive radio frequency plasmas

Resonance mechanisms have been found to be essential for the generation of high-density rf plasmas at low pressures, in which electrons can be continuously accelerated through multiple interactions with the oscillating rf sheaths. In this work, we report the scale-invariant resonance mechanisms, such as bounce resonance heating and plasma series resonance, in low-pressure capacitive rf plasmas in the presence of an external magnetic field. The generation conditions for the resonance mechanisms are determined via fully kinetic simulations. It is found that the resonance dynamical properties of single-frequency plasmas (e.g., a double-peak electron density vs magnetic field curve) can be exactly replicated at different scales when three combined control parameters, i.e., the reduced gap distance pd (pressure × distance), reduced driving frequency f/p (frequency divided by pressure), and reduced magnetic field B/p (magnetic field divided by pressure), are kept constant. The similarity relations for the electron density and electron power absorption in magnetized rf plasmas are numerically confirmed. Furthermore, the similarity and scale-invariant resonance characteristics are elucidated through the scaling of the Boltzmann equation with collisional terms for weakly ionized rf plasmas with a magnetic field, which is proven to be theoretically exact.

The computation of interstellar extinction in photoionized nebulae

Context. The proper plasma analysis practice (PPAP) method has been proposed to analyze spectroscopic data of ionized nebulae. The method is based on a coherent and simultaneous determination of the reddening correction and physical conditions in nebulae. The PPAP method’s creators reanalyzed the results of nine of the brightest planetary nebulae in M31. They claim that, if standard values of the physical conditions are used to compute the extinction instead of their proposed method, extinction correction is underestimated by more than 50%, and hence, ionic and elemental abundance determinations, especially the N/O ratio, are incorrect. Aims. The discrepancies between the two methods are investigated. Methods. Several tests were performed to assess the accuracy of the non-PPAP results when determining: (i) the interstellar extinction coefficient, (ii) the plasma electron temperature and density, and (iii) the ionic abundances, in particular of singly ionized nitrogen. In the last case, the ionic N+/H+ abundance was recalculated using both Hα and Hβ as the reference H I emissivity. Results. The analysis shows that the errors introduced by adopting standard values of the plasma conditions are small, within the uncertainties. On the other hand, the interstellar extinction determined using the PPAP method (uncritically making use of all available Paschen and Balmer lines, without considering observational, random and/or systematic effects) is found to be overestimated for five of the nine nebulae considered. This has consequences for the subsequent analysis of the physical and chemical properties of the nebulae and their progenitors. The python notebook used to generate all the results presented in this Letter is publicly available at a GitHub repository. Conclusions. The initial, non-PPAP results and conclusions are proven valid. Although the PPAP method is, in principle, a recommended practice, we insist that it is equally important to critically assess which H I lines are included in the determination of the interstellar extinction coefficient, and to make sure that physical results are obtained for the non-de-reddened line ratios.

Collimation and energy enhancement in laser driven MeV protons

Enhancing the energy and controlling the divergence of proton beam have been crucial tasks since the development of laser-based ion accelerators. In this study, we employ 2D particle-in-cell EPOCH simulation to investigate a method to control the divergence and enhance the energy of MeV proton beam produced from the interaction of high intensity laser with a gold target. The energy and divergence of proton beam for the conventional laser-foil target configuration are compared with our proposed three laser-three target configuration. In the single laser-single target configuration, a high intensity laser irradiates a gold foil target resulting in proton acceleration from the plasma. In contrast, in the three laser-three target configuration, the generated proton beam is allowed to traverse through the configuration of two parallel Al plates irradiated with high intensity lasers. The new configuration provides the proton energy enhancements of 40% and more collimated beam compared to the single laser-foil target setup. This collimation and energy increase are due to the vertical and horizontal components of the electric field generated by the hot electron plasma of Al plates. The proton energy and divergence can also be tuned by varying the plasma electron density of the Al plasma. Also, the control of proton beam collimation is explored by varying target parameters as well, and it is observed that the separation between the Al plates and length of the Al plates plays major role in controlling the divergence of the beam. This study will have a significant impact in the ongoing laser fusion program, fast ignition, and laser ion therapy.

Nonlinear Equilibrium Structure of Super Thin Current Sheets: Influence of Quasi‐Adiabatic Electron Population

AbstractRecent MMS observations confirmed the existence of the quasi‐stationary electron‐scale super‐thin current sheets (STCSs) with a half‐thickness of few electron gyroradii. STCSs contain the electron population consisting of magnetized and demagnetized particles. To study the role of the demagnetized electrons, we developed a self‐consistent combined model of a STCS in which the dynamics of a part of the electron population is described by the quasi‐adiabatic approximation, while the motion of the other part is described by the guiding center approximation. Demagnetized ion population can be described in a frame of quasi‐adiabatic approach. In the presented model we introduced the weight coefficient of the demagnetized electron plasma density χ depending on the magnetic field normal component Bn/B0 and compared the characteristic profiles of two STCSs differing by the presence (χ ≠ 0) and absence (χ = 0) of demagnetized electrons. It is shown that the presence of demagnetized electrons makes the current density profile of STCS significantly more intense and narrower. The thickness and intensity of STCS depend on the anisotropy coefficient of magnetized electrons and the incoming drift velocity of demagnetized electrons. The maximum current density continuously increases with the growth of the demagnetized electron population and is controlled by the ratio of the thermal to the incoming drift electron velocities. Thus intense current sheets can be formed even in the absence of strong electron anisotropy, which is confirmed by MMS observations.

ATHMON HB: Athletenmonitoring im Handball – Schritt für Schritt zur Best Practice

In this article, the propagation of electromagnetic waves in a multi-layered cylindrical photonic crystal is considered. We have arranged the plasma and dielectric layers alternatively in two ways of sharply square and semi-sinusoidal refractive index variations that are not studied so far. In our investigations, we have used transfer matrix programming in MATLAB software. We have chosen the cylindrical photonic crystals because they have been studied less than the conventional planar ones. The cylindrical photonic crystals have potential applications in optical communications, optoelectronics, etc. Our numerical results show that the shape of the layers (i.e., sharp or gradual variation of the refractive index in the photonic crystal) has a major impact on the reflection pattern. In the current study, the effect of the increasing starting radius of the photonic crystal, plasma electron density, and the number of layers have been investigated. It was seen that by increasing the dielectric refractive index, the optical gaps do not show a well-defined change.

Investigating with rectangular and semi-sinusoidal variation of the refractive index

In this article, the propagation of electromagnetic waves in a multi-layered cylindrical photonic crystal is considered. We have arranged the plasma and dielectric layers alternatively in two ways of sharply square and semi-sinusoidal refractive index variations that are not studied so far. In our investigations, we have used transfer matrix programming in MATLAB software. We have chosen the cylindrical photonic crystals because they have been studied less than the conventional planar ones. The cylindrical photonic crystals have potential applications in optical communications, optoelectronics, etc. Our numerical results show that the shape of the layers (i.e., sharp or gradual variation of the refractive index in the photonic crystal) has a major impact on the reflection pattern. In the current study, the effect of the increasing starting radius of the photonic crystal, plasma electron density, and the number of layers have been investigated. It was seen that by increasing the dielectric refractive index, the optical gaps do not show a well-defined change.

Spatial, spectral, and temporal properties of laser-induced plasma in air near an aqueous solution and comparison with ambient air

Laser-induced breakdown and subsequent plasma are produced in ambient air in the proximity of an aqueous surface using a Nd:YAG Q-switched laser at 1064 nm with a pulse width of 9 ns and a delivered focused input energy of 170 mJ. The distance between the focal point of a 10 cm convex lens and the aqueous surface is 4 mm with laser propagation perpendicular to the surface. Using an intensified CCD camera attached to a 1-m spectrometer, spatial and wavelength-resolved plasma emission data are obtained for delay times after breakdown ranging from 50 ns to 10 μs with a gate window typically 5 ns. Plasma electron density is determined by applying Lorentzian fitting and FWHM extraction to three Stark-broadened spectral lines: N II 3P-3Do multiplet (593.85 nm), Hα (656.27 nm), and the Na D doublet (589.00 and 589.59 nm). One-dimensional spatially resolved measurements of the total emission intensity and electron density are obtained by binning the camera image along the laser axis in intervals of 250 μm and are reported as a function of time from 50 ns to 10 μs. Two plasmas are ignited from a single laser pulse; one from laser breakdown at the water surface and the other a few nanoseconds later from laser-induced air breakdown at the focal point of 4 mm above the water surface. Comparisons between the evolution of the air plasma near and far from the water surface are presented along with data for the water surface plasma itself.

Development of diagnostics of electron density and temperature for atmospheric-pressure helium plasma based on optical emission spectroscopy analysis and a collisional-radiative model

An algorithm for diagnosing the electron density and temperature of helium plasma at atmospheric pressure has been developed based on a revised helium collisional-radiative (CR) model. Atomic collision processes are included, and part of the atomic data of electron collision processes in the conventional CR model has been updated to expand its valid pressure. The algorithm uses eight emission lines in the visible-wavelength range as inputs to determine the electron density, electron temperature, and number density of the two metastable states by fitting the number density of the states corresponding to the emission lines. The algorithm has a considerably small theoretical error. In the microwave-discharged low-pressure helium plasma experiment, the results obtained with the algorithm agreed well with the results obtained with the probe method. The electron density and temperature of the atmospheric-pressure helium plasma obtained with the algorithm agreed well with the results of the continuum spectrum analysis.

Investigating of plasma diagnostics by utilizing spectroscopic measurements of Balmer emission

Plasma technology offers revolutionary potential for particle accelerators by enabling the acceleration of electron beams to ultra-relativistic velocities in a small-scale dimension. The compact nature of plasma-based accelerators permits the creation of accelerating gradients on the GV scale. Plasma acceleration structures are created by utilizing either ultra-short laser pulses (Laser Wakefield Acceleration, LWFA) or energetic particle beams (Particle Wakefield Acceleration, PWFA), which need to be tailored to the plasma parameters. However, both methods face the challenge of limited acceleration length, which is currently only a few centimeters. To overcome this challenge, one approach is to generate plasma within a capillary tube, which can extend the acceleration length up to approximately forty centimeters or more. Consequently, it is crucial to characterize the produced plasma in terms of density and geometric structure. Optical emission spectroscopy (EOS) methods can be employed to measure and characterize the plasma electron density by analyzing the emitted plasma light. This paper presents measurements of the plasma electron density distribution for a hydrogen-filled capillary tube using both Balmer alpha (Hα) and Balmer beta (Hβ) lines. Comparing the intensities of Hα and Hβ emissions enables more precise measurements of the plasma electron density and provides additional information about other plasma properties.

Estimation of the Electron Density in the Near 3–4 RE Magnetosphere Based on the Measurement of the Interball-2 Satellite Potential

A new method is proposed for determining the electron density in rarefied plasma, based on simultaneous measurements of the Interball-2 satellite potential using IESP-2 (electric field instrument) and KM-7 (electron temperature sensor) probe devices. This makes it possible to estimate the photoelectron current density based on a procedure proposed earlier by the authors of this study. The electron concentration was determined only for the positive potential of the spacecraft. The balance equations for the satellite and the probe between the currents of the surrounding plasma electrons and photoelectrons emitted by the illuminated surface were compiled. In the magnetosphere, to bring the probe potential to the potential of the surrounding plasma, a bias current is directed into the probe, which was taken into account in the current balance equation for the probe. The electron energy used in the calculations was kTe = 1 eV. We analyzed data from ~350 orbits in the auroral region of the magnetosphere at altitudes of 2–3 RE from October 1996 to March 1998 during the period of low solar activity at the beginning of the 23rd cycle. Examples of the calculated electron density are given, which is in the range of 1–30 cm–3.

Phase jump detection and correction based on the support vector machine

In general, interferometers are used to perform electron density measurements in magnetically confined plasma, where the electron density is dependent on the refractive index of the plasma. Measurements can be made through comparisons of the phase shift variation between the probe and reference laser beam. The plasma electron density should vary continuously during discharge; however, the fringe jump is a step-like change of the apparent electron density caused by a sudden jump of the measured phase shift. The appearance of fringe jump will degrade the interferometric measurements accuracy. This study attempted to solve the fringe jump problem on the polarimeter-interferometer (POINT) diagnostics system of the Experiment Advanced Superconducting Tokamak (EAST) by proposing a support vector machine model for electron density fringe jump detection and correction. The established model can efficiently classify the fringe jump data from the raw measurement data in a manner robust to noise and interference, and subsequently correct the jump. This model greatly improves the correction efficiency and precision of electron density data from the POINT system, and is expected to be embedded into the plasma control system to perform more accurate real-time electron density feedback control. Moreover, the algorithm is not limited to specific fusion devices or interferometer diagnostics, and is applicable to other interferometric measurement systems.

Factors influencing the electromagnetic transmission of mercury vapor discharge plasma tube arrays

Low-pressure Mercury vapor discharge plasma tubes were used to form arrays to control electromagnetic transmission. The internal and external factors influencing a discharge tube array were adjusted to expand the electromagnetic wave manipulation ability. The plasma electron density (n e) is the key parameter for electromagnetic wave manipulation. Microwave transmission was used to diagnose n e under different working conditions. Simulations and electromagnetic transmission measurements were used to investigate the behavior of the effect of internal and external factors on electromagnetic transmission. Simulation results indicated that increasing n e increased the attenuation, widened the attenuation bandwidth, and shifted the attenuation band to higher fRequencies. The experimental results showed that increasing the discharge power significantly increased n e and widened the strong attenuation frequency band. n e first increased and then decreased when the gas pressure was increased. The tube diameter affected both n e and the plasma layer thickness, and the attenuation band of the plasma tube array moved to a low frequency with an increase in tube diameter. The primary and secondary order of the influence of external factors other than power on the attenuation bandwidth obtained via an orthogonal experiment is as follows: gas composition > tube diameter > pressure. The maximum attenuation bandwidth for 10 dB attenuation was 9.85 GHz. The results show that the attenuation control ability of the plasma tube array can be significantly improved by adjusting the external factors of the plasma tube.

Soliton trains induced by femtosecond laser filamentations in transparent materials with saturable nonlinearity

Femtosecond laser inscriptions in optical media current offer the most reliable optical technology for processing of transparent materials, among which is the laser micromachining technology. In this process, the nonlinearity of the transparent medium can be either intrinsic or induced by multiphoton ionization processes. In this work, a generic model is proposed to describe the dynamics of femtosecond laser inscription in transparent materials characterized by a saturable nonlinearity. The model takes into account multiphoton ionization processes that can induce an electron plasma of inhomogeneous density and electron diffusions. The mathematical model is represented by a one-dimensional complex Ginzburg–Landau equation with a generalized saturable nonlinearity term in addition to the residual nonlinearity related to multiphoton ionization processes, coupled to a rate equation for time evolution of the electron plasma density. Dynamical properties of the model are investigated focusing on the nonlinear regime, where the model equations are transformed into a set of coupled first-order nonlinear ordinary differential equations, which are solved numerically with the help of a sixth-order Runge–Kutta algorithm with a fixed time step. Simulations reveal that upon propagation, spatiotemporal profiles of the optical field and of the plasma density are periodic pulse trains, the repetition rates and amplitudes of which are increased with an increase of both the multiphoton ionization order and the saturable nonlinearity. When electron diffusions are taken into account, the system dynamics remains qualitatively unchanged; however, the electron plasma density gets strongly depleted, leaving almost unchanged the amplitude of pulses composing the femtosecond laser soliton crystals.

Study on Characteristics of Special ICP-Heated Wind Tunnel by Improved HCN Laser Interferometer

The results of the experimental investigation of a plasma jet created by a large-volume, high-enthalpy plasma wind tunnel are presented. The plasma wind tunnel generates an electric field by applying a time-varying power with a frequency of 440 kHz, which excites the plasma and ejects it from the nozzle due to the pressure difference. This article uses high-voltage probes, cameras, and laser interferometers to understand the properties of plasma wind tunnels. In order to diagnose the electron density at different positions of the plasma jet, a laser interferometer is improved in this article. The waveform of the power supply, the length of the plasma jet, and the brightness and electron density of the plasma jet were obtained during the experiment. The results show that the electron density increases by about an order of magnitude when the supply voltage rises from 8 to 12 kV. As the distance increases by 150 mm, the plasma electron density decreases by a factor of 1.5 or 2, but the electron density increases with the increase of pressure. Finally, the electron density distribution characteristics can be explained by the simulation results.

Model-based electron density estimation using multiple diagnostics on TCV

Estimation of the dynamic evolution of the electron plasma density during a tokamak discharge is crucial since it directly affects the plasma performance, confinement and stability. Therefore it needs to be monitored and controlled. Knowledge of the density profile can also be used to control in a more direct way the desired aspects of the plasma density, for example choosing to control the core, volume averaged or edge density, replacing control methods that rely e.g. on a single line-averaged electron density from a specific interferometer chord. The reconstruction of the density profile can be performed with the RAPDENS code, employing the Extended Kalman Filter (EKF) technique. The code collects the electron plasma density measurements from the available real-time diagnostics and uses them to constrain the solution of a predictive model that describes the 1D particle transport equation for the electron plasma density.Following recent improvements to the code for use on ASDEX-Upgrade, we report on the application of this method for the reconstruction of density profiles in the TCV tokamak using low-frequency Thomson Scattering measurements and high-frequency interferometer measurements simultaneously, both of which are available in real-time. We show how to treat the time-varying relation between the measurements and the density profile due to the evolving equilibrium. Additionally, we show a method to compensate for offsets in interferometer measurements in real-time using Thomson Scattering information.