Plasma Region Research Articles

Enhanced confinement induced by pellet injection in the stellarator TJ-II

Enhanced confinement is observed in neutral beam injector (NBI)-heated hydrogen discharges made in the stellarator TJ-II after the injection of a single cryogenic fuel pellet into the plasma core. In addition to the expected increase in electron density, ne, in the core after pellet injection (PI), the plasma diamagnetic energy content is seen to rise, with respect to similar discharges without PI, by up to 40%. Furthermore, the energy confinement time, τEdiag, as determined using a diamagnetic loop, is enhanced when compared to predictions obtained using the International Stellarator Scaling law [H. Yamada et al., Nucl. Fusion 45, 1684 (2005)] and the triple product, ne · Ti · τEdiag, exhibits a clear bifurcation point toward an improved confinement branch as compared to the branch product predicted by this scaling law. In general, once such a pellet-induced enhanced confinement (PiEC) phase has been established, it is characterized by steepened radial density gradients, by more negative plasma potential in the core, more negative radial electric fields, Er, across a broad plasma region, as well as by reductions in density and plasma potential fluctuations in the density gradient region. In addition, experimental observations show increased peaking of core radiation losses, this pointing to edge/core plasma decoupling. In parallel, neoclassical simulations of reference and PiEC plasmas predict increased particle and energy confinement times during a PiEC phase together with a more negative Er profile. Qualitative rather than quantitative agreement with experimental parameters is found, indicating that turbulence seems to play a significant role here. In summary, single cryogenic pellet injection facilitates the achievement of an enhanced operational regime that was previously not observed in NBI-heated discharges of the TJ-II.

Investigating the Impact of Vertically Extended Coronae on X-Ray Reverberation Mapping

Accreting black holes commonly exhibit hard X-ray emission, originating from a region of hot plasma near the central engine referred to as the corona. The origin and geometry of the corona are poorly understood, and models invoking either inflowing or outflowing material (or both) can successfully explain only parts of the observed phenomenology. In particular, recent works indicate that the time-averaged and variability property might originate in different regions of the corona. In this paper we present a model designed to move beyond the lamppost paradigm, with the goal of accounting for the vertical extent of the corona. In particular, we highlight the impact of including self-consistently a second lamppost, mimicking, for example, an extended jet base. We fully include the effect that the second source has on the time-dependent disk ionization, reflection spectrum, and reverberation lags. We also present an application of this new model to NICER observations of the X-ray binary MAXI J1820+070 near its hard-to-soft state transition. We demonstrate that in these observations, a vertically extended corona can capture both spectral and timing properties, while a single-lamppost model can not. In this scenario, the illumination responsible for the time-averaged spectrum originates close to the black hole, while the variability is likely associated with the ballistic jet.

Scalable non-thermal plasma trielectrode reactor: A theoretical and experimental study on carbon monoxide removal in a nitrogen atmosphere

Non-thermal plasma technology has a great interest for very diverse environmental applications. In this work a trielectrode non-thermal plasma reactor was studied for carbon monoxide (CO) removal, in a nitrogen (N2) atmosphere, both experimentally and theoretically. The reactor combines a dielectric barrier discharge (DBD) with a remote third electrode, DC-biased, to extend the DBD generated plasma region with long streamers permeating its cross section. Also, a theoretical model to predict reactor efficiency, considering possible chemical reactions involved in CO degradation was applied. A good correspondence between experimental and theoretical efficiency values was found. It was concluded that the most relevant reaction was the isocyanate (NCO) radical production. The byproducts of NCO degradation, nitrogen monoxide (NO) and nitrogen dioxide (NO2), were experimentally detected.

Plasma knots

We present a Lagrangian method for the computation of ideal plasma knots and links. It is based on a variational principle for stable equilibria of an ideal plasma in the case of a free boundary subjected to external magnetic or plasma pressure forces. For this purpose, we introduce a structure preserving discretization of plasma based on decompositions of Riemannian manifolds representing pressure confined plasma regions in magnetohydrostatic equilibrium. Moreover, we show that, by the virtue of an analogy, the method can be used for the approximation of steady Euler-flows of arbitrarily complex topology.

Numerical investigation of the entropy generation analysis for radiative MHD power-law fluid flow of blood through a curved artery with Hall effect

In the last few decades, mortality rate due to blood vessel diseases has hiked rapidly and it is almost one-third of total mortalities. Identifying the vascular geometry and hemodynamic blood flow inside the artery is essential for preventing vascular disease progression. By motivating vascular diseases effects on the human body, a mathematical model has been developed to discuss the blood flow phenomena and entropy estimation in the stenosed curved artery in the presence of a magnetic field and the Hall effect. The patient-specific condition of elliptic shape stenosis has been considered at the arterial wall. Blood is considered in the artery as two-phases; core and plasma region. Power-law fluid has been considered for core region fluid, while, Newtonian fluid is considered in the plasma region. The non-dimensional governing equations have been discretized using the second-order central difference method. Then, Stone's strongly implicit scheme is used in the ‘MATLAB’ software to solve a system of nonlinear partial differential equations (PDEs). A computing error tolerance of has been set for each iteration step throughout the computing process. The influence of various parameters such Hall parameter (m), Brinkman number (Br), flow behavior index (q), Radiation parameter (N), magnetic field (M), arterial curvature, etc., have been discussed graphically. The present study concludes that the heat transfer rate enhances with the increase in the Hall parameter values while wall shear stress reduces with it. In addition, the chances of stenosis deposition rise for highly curvature arteries, and also blood produces more entropy with the increase in viscous heating and thermal radiation intensity. Results from the current computational study will aid clinical researchers in making more accurate predictions about the prevalence of vascular diseases.

Laser energy partitioning in nanosecond pulsed laser-induced air breakdown: effect of incident laser energy.

Air breakdown is generated by a 1064nm nanosecond pulsed laser beam, and laser energy deposited in the breakdown (E d), transmitted through the plasma region (E t) and carried away by the shock wave (E s) is estimated for the incident laser energy (E i) range of 60-273mJ. The E d is approximately 85% of E i at 60mJ, rapidly increasing to 92% at 102mJ. The shock wave front velocity and radius are measured as a function of E i and propagation distance. The shock wave velocity nicely follows the v∝E i0.3 trend predicted by the laser-supported detonation wave model. The Sedov-Taylor theory is used to estimate E s, which rapidly increases with E i, but E i to E s conversion linearly decreases from 83% to 48%. At lower values of E i, most of the laser energy is carried away by the shock wave, whereas the laser energy used in plasma heating or released in the form of electromagnetic and thermal radiation becomes important at higher laser energies. This implies that laser energy partitioning is highly dependent on the value of incident laser energy. These findings provide important insights into the fundamental physics of air breakdown and will be useful in a variety of applications such as laser-induced breakdown spectroscopy, laser ignition, and laser propulsion.

The Spatiotemporal Dynamics of Electron Plasma in Femtosecond Laser Double Pulses Induced Damage in Fused Silica

In this study, we employed the fs time-resolved shadowgraphy method to investigate the impact of the first pump pulse (DP1) on the transient temporal and spatial evolution of electron plasma induced by femtosecond (fs) laser double pulses (DPs) in fused silica. It was observed that the DP1-induced phase transition acted as a waveguide, confining the propagation of the second pump pulse (DP2) light inside the material and resulting in a decrease in the diameter of the DP2-induced electron plasma region. Moreover, the DP2-induced maximum peak electron density was higher than that induced by a single pulse (SP) at the same pulse energy, which may be explained by the DP1-induced highly absorbing semi-metallic state of warm dense glass in fused silica. Importantly, as the energy of DP1 increased, the mean diameter of the DP2-induced electron plasma region further decreased, and the maximum peak electron density increased. Compared with SPs, DPs more easily produced damage in fused silica. In addition, the mean diameter of the DP2-induced electron plasma region and the maximum peak electron density remained almost unchanged when the pulses’ time separation (ts) was changed from 1 to 50 ps, mainly due to the long relaxation time of the phase transition caused by DP1.

2.5D magnetohydrodynamic models of circumstellar discs around FS CMa post-mergers – I. Non-stationary accretion stage

ABSTRACT We investigate the dynamic evolution of the gaseous regions around FS CMa post-mergers. Owing to the slow rotation of the central B-type star, the dynamics is driven mainly by the magnetic field of the central star. Recent observations have allowed us to set realistic initial conditions, such as the magnetic field value ($B_\star \approx 6\times 10^{3}\, \mathrm{G}$), the mass of the central star ($M_\star =6\, \mathrm{M}_\odot$), and the initial disc density $\rho _{d0}\in [10^{-13}\, \mathrm{g\, cm^{-3}},10^{-11}\, \mathrm{g \, cm^{-3}}]$. We use the pluto code to perform 2.5D magnetohydrodynamic simulations of thin and thick disc models. Especially relevant for the interpretation of the observed properties of FS CMa post-mergers are the results for low-density discs, in which we find a jet emerging from the inner edge of the disc, as well as the formation of the so-called ‘hot plasmoid’ in the coronal region. Jets are probably detected as discrete absorption components in the resonance lines of FS CMa stars. Moreover, the magnetic field configuration in the low-density plasma region favours the appearance of magnetocentrifugal winds from the disc. The currents towards the star created by the magnetic field may explain accidentally observed material infall. The disc structure is significantly changed owing to the presence of the magnetic field. The magnetic field is also responsible for the formation of a hot corona, as observed in several FS CMa stars through the Raman lines. Our results are valid for all magnetic stars surrounded by a low-density plasma, that is, by some stars showing the B[e] phenomenon.

Alzheimer's Disease and Age-Related Changes in the Cu Isotopic Composition of Blood Plasma and Brain Tissues of the APPNL-G-F Murine Model Revealed by Multi-Collector ICP-Mass Spectrometry.

Alzheimer's' disease (AD) is characterized by the formation of β-amyloid (Aβ) plaques and neurofibrillary tangles of tau protein in the brain. Aβ plaques are formed by the cleavage of the β-amyloid precursor protein (APP). In addition to protein aggregations, the metabolism of the essential mineral element Cu is also altered during the pathogenesis of AD. The concentration and the natural isotopic composition of Cu were investigated in blood plasma and multiple brain regions (brain stem, cerebellum, cortex, and hippocampus) of young (3-4 weeks) and aged (27-30 weeks) APPNL-G-F knock-in mice and wild-type controls to assess potential alterations associated with ageing and AD. Tandem inductively coupled plasma-mass spectrometry (ICP-MS/MS) was used for elemental analysis and multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) for high-precision isotopic analysis. The blood plasma Cu concentration was significantly altered in response to both age- and AD-related effects, whereas the blood plasma Cu isotope ratio was only affected by the development of AD. Changes in the Cu isotopic signature of the cerebellum were significantly correlated with the changes observed in blood plasma. The brain stem showed a significant increase in Cu concentration for both young and aged AD transgenic mice compared with healthy controls, whereas the Cu isotopic signature became lighter as a result of age-related changes. In this work, ICP-MS/MS and MC-ICP-MS provided relevant and complementary information on the potential role of Cu in ageing and AD.

Plasma-catalytic synthesis of ammonia over Ru/BaTiO3-based bimetallic catalysts: Synergistic effect from dual-metal active sites

Plasma-catalytic synthesis of ammonia (NH3) was carried out using BaTiO3 supported Ru-M bimetallic catalysts (Ru-M/BaTiO3, M = Fe, Co and Ni) in a dielectric barrier discharge (DBD) reactor. The NH3 synthesis performance followed the order of Ru-Ni/BaTiO3 > Ru/BaTiO3 > Ru-Co/BaTiO3 > Ru-Fe/BaTiO3, with the highest NH3 concentration (3895 ppm) and energy yield (0.39 g kWh−1) achieved over Ru-Ni/BaTiO3 at 25 W and 10 W, respectively. To gain insights into the physio-chemical properties of the Ru-M/BaTiO3 catalysts, comprehensive catalyst characterizations were performed, including X-ray diffraction, N2 physisorption measurements, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), and temperature-programmed desorption of CO2 and N2 (CO2 and N2-TPD). The results indicated that the loading of Ni enhanced the basicity and N2 adsorption capacity of the catalyst, as well as the density of oxygen vacancy (OV) on the BaTiO3 surface, which facilitated the adsorption and activation of N2 on catalyst surface. These effects led to the enhanced NH3 synthesis, as excited N2 could be adsorbed on Ru-Ni/BaTiO3 from plasma region and stepwise hydrogenated to form NHx species and ultimately NH3.

Gyrokinetic simulation of electromagnetic instabilities in the high β p scenario on EAST

High poloidal beta scenarios with favorable plasma performance () have be achieved on Experimental Advanced Superconducting Tokamak (EAST) since the 2018 international atomic energy agency (IAEA). Linear electromagnetic gyrokinetic simulations using gyrokinetic toroidal code (GTC) code are performed based on the experimental data of a typical high discharge on EAST. In the core region of plasma, an electromagnetic instability with similar dependence and mode structure with kinetic ballooning mode (KBM) but exhibits positive or nearly zero frequency is observed. This instability is referred as unconventional KBM (UKBM). Simulation results demonstrate that UKBM occurs in low ion–electron temperature ratio conditions and UKBM will transit to KBM when ion–electron temperature is high. Further investigation shows the driven mechanism of UKBM differs at different electron beta region. When the electron beta exceeds the threshold of electrostatic instability to UKBM, UKBM is driven by electron pressure gradient. When electron beta is close to the beta threshold of UKBM, the main driven mechanism is . Reversed magnetic shear is found to have a significant stabilize effect on UKBM.

Experimental study of the motion of a shock wave in the plasma of a pulsed volume discharge in air

The motion of quasi-plane shock waves with Mach numbers = 2.20–3.50 in the plasma of a nanosecond combined volume discharge in air at an initial pressure of 10–100 Torr has been experimentally studied on the basis of high-speed shadow registration of the flow field. The dynamics of shock–wave configurations after the discharge at various stages of an unsteady supersonic flow, which is formed after the diffraction of a plane shock wave by a rectangular obstacle, is studied. An increase in the velocity of the shock wave front over a time interval of up to 15 𝜇s in a plasma region of 9–40 mm long and its dependence on the plasma parameters is found. An analysis of relaxation processes in plasma showed that the acceleration of the shock wave front can be caused by air heating due to the quenching of electronically excited nitrogen molecules, in which the internal energy is converted into thermal energy at times up to 30 𝜇s.

How well can VMEC predict the initial saturation of external kink modes in near circular tokamaks and l = 2 stellarators?

The equilibrium code, VMEC, is used to study external kinks in low β tokamaks and l = 2 stellarators. The applicability of the code when modeling nonlinear MHD effects is explored in an attempt to understand and predict how the initial saturation of the MHD mode depends on the external rotational transform. It is shown that helicity preserving, free boundary VMEC computations do not converge to a single perturbed solution with increasing spectral resolution. Additional constraints are applied to narrow down the numerical resolution parameters appropriate for physical scans. The dependence of the modeled (4, 1) kink mode on the external rotational transform and field periodicity is then studied. While saturated states can be identified which decrease in amplitude with increasing external rotational transform, alternative bifurcated states are found, which contradict this trend. As a result, it was not possible to use VMEC alone to identify the physical dependency of the nonlinear mode amplitude on the magnetic geometry. Nevertheless, the accuracy of VMEC solutions is demonstrated by showing that the expected toroidal mode coupling is captured in the magnetic energy spectrum for stellarator cases. Comparing with the initial value code, JOREK, the predicted redistribution of poloidal magnetic energy from the vacuum to plasma region in VMEC is shown to be physical. This work is a first step toward using VMEC to study MHD modes in stellarator geometry.

A new J.E probe for measurement of spatial profiles of power absorption in RF produced plasma.

This paper reports an indigenously developed probe for the measurement of spatial profiles of the absorbed/generated RF power density Pabs (W/m3) in RF discharges. The technique utilizes a calibrated current (J) probe based on the Rogowski coil principle and an electric field (E) probe based on capacitive coupling, both integrated into a single probe called the J.E probe. Various aspects of the probe, such as its design, fabrication, calibration, and limitations, were resolved before it was used for obtaining axial profiles of RF power absorption/generation. Also presented are the first experimental results for the absorbed power density profiles at the fundamental (13.56MHz) and harmonic (27.12MHz) along the length of a capacitively coupled discharge. The axial scans between the powered and grounded electrode were taken at different argon gas pressures (10-800mTorr) at a fixed RF power of 10W. Detailed analysis of the results shows that even for systems with large electrode gaps, i.e., plasmas with long bulk plasma regions, practically all the fundamental power is absorbed in a narrow edge region near the powered electrode, irrespective of the pressure. Absorption is high near the RF electrode since the RF fields peak in this region. Another important conclusion is that stochastic absorption of the fundamental and harmonic generation proceeds fairly efficiently in the vicinity of the powered electrode even at high pressures. It may be mentioned that the probe technique introduced here is the first of its kind, and although there is considerable scope for miniaturization, it has, nonetheless, provided some key insights into the nature of RF power absorption in capacitive discharges.

Development of vertical edge Thomson scattering diagnostic on HL-2M Tokamak

A vertical edge Thomson scattering diagnostic system on HL-2 M Tokamak has been developed recently. A Nd: YAG laser (1064 nm, 0.6–2.0 J, 30 Hz, 15 ns) is used as the probe beam. The laser beam propagates vertically through the plasma region and the scattered light is observed horizontally. The combination of a half-wave plate and a polarized beam splitter is used for stray light suppression. A group of in-vacuum collection lens is designed to image the 400 mm scattered region onto the rectangular fiber arrays. The laser beam waist and vertical spatial resolution are 2 mm and 10 mm, respectively. Scattered light is imaged on the 2.20 × 2.86 mm (10 × 13) fiber optic bundle. The development of collection optics with a special designed safety shutter ensures a reliable scattered signal, where the solid angle at central field of view (FOV) is 0.018 sr. A compact polychromator is developed to measure the scattered light. Relative calibration of the filter response (1060 nm, 1052 nm, 1029 nm and 982 nm) and absolute calibration by nitrogen Raman scattering have been completed. In the 2022 plasma campaign of HL-2M, the scattering signal is measured at E0 = 1.2 J, confirming the capability of the system for pedestal measurement in the future H-mode campaign.

Quantitation of Brain and Blood Glutathione and Iron in Healthy Age Groups Using Biophysical and In Vivo MR Spectroscopy: Potential Clinical Application.

The antioxidant glutathione (GSH) and pro-oxidant iron levels play a balancing role in the modulation of oxidative stress (OS). There is a significant depletion of GSH in the left hippocampus (LH) in patients with Alzheimer's disease (AD) with concomitant elevation of iron level. However, the correlation of GSH and iron distribution patterns between the brain and the peripheral system (blood) is not yet known. We measured GSH and magnetic susceptibility (e.g., iron) in the LH region along with GSH in plasma and iron in serum across four age groups consisting of healthy volunteers (age range 18-72 y, n = 70). We report non-variability of the mean GSH in the plasma and LH region across mentioned age groups. The mean iron level in the LH region does not change, but the iron level in the serum in the 51-72 y age group increases non-significantly. Regression analysis of our data indicated that GSH and iron levels (both in blood and in brain) are not related to age. This research pave the way for the identification of a risk/susceptibility biomarker for AD and Parkinson's disease from the evaluation of GSH (in plasma) and iron (in serum) levels concomitantly.

Non-uniform splines for semi-Lagrangian kinetic simulations of the plasma sheath

Numerical methods based on non-uniform splines of varying degrees are used to run kinetic semi-Lagrangian simulations of the plasma sheath. The sheath describes a region of plasma in contact with a wall, acting as a heat, momentum, and particle bath. The latter regulates the current loss and consequently the electric field. At micro scale it then influences the development of plasma turbulence and at a larger scale plasma rotation. However this region is particularly difficult to simulate, due to its kinetic nature and the presence of steep gradients requiring fine numerical resolution. In this work, a new well-conditioned method for determining the coefficients for Schoenberg's “best” quadrature is presented, providing improved precision compared to a naive approach based on b-spline derivatives (4 extra significant figures of precision are obtained for coefficients of the fifth order scheme). The construction of a simulation grid from Greville abcissae of judiciously chosen non-uniform knots is shown to reduce the memory requirements by 89% for the simulation presented. Cubic splines are found to provide a good compromise between fast convergence and controlled oscillations preserving positivity. Despite the reduction in performance associated with using non-uniform spline schemes, effective parallelisation through the use of GPUs leads to non-uniform simulations running 5.5 times faster than uniform simulations providing equivalent results.

Characteristics of the flame flashback in a dual-mode scramjet combustor by the gliding arc plasma

A multi-channel gliding arc (MCGA) plasma with an average power of 6000 W is utilized to control the flame flashback in a dual-mode scramjet combustor with a cavity flameholder. Optical measurements, including synchronous high-speed CH* emissions and high-speed schlieren, simultaneous high-speed camera with the oblique view and high-speed CH* emission, accompanied by the three-dimensional RANS simulation, were employed to characterize the flame flashback with or without the MCGA plasma. The results show that a typical flame flashback cycle can be observed with a period of ∼2 ms in the combustor. The back pressure reduced by the dynamic heat release of the reaction zone is not sufficient to form the steady thermal choking in the mainstream in the absence of the MCGA, which results in the oblique shocks and bow shocks appearing in dual-mode scramjet combustion. When the plasma is added, the flame is strengthened near the plasma region, and the combustion oscillation is suppressed significantly. The re-ignition and attachment characteristics of the MCGA plasma provide the new flame kernels to the mainstream flame, and the leading edge of the mainstream flame follows the MCGA plasma. Due to the relatively stable heat release near the fuel jet assisted by the plasma, the thermal choking is stable presented in the combustor with bow shocks by higher back pressure, indicating that the combustion oscillation is suppressed by the MCGA plasma in the dual-mode scramjet combustor.

Study of Atmospheric Pressure Plasma Temperature Based on Silicon Carbide Etching.

In order to further understand the excitation process of inductively coupled plasma (ICP) and improve the etching efficiency of silicon carbide (SiC), the effect of temperature and atmospheric pressure on plasma etching of silicon carbide was investigated. Based on the infrared temperature measurement method, the temperature of the plasma reaction region was measured. The single factor method was used to study the effect of the working gas flow rate and the RF power on the plasma region temperature. Fixed-point processing of SiC wafers analyzes the effect of plasma region temperature on the etching rate. The experimental results showed that the plasma temperature increased with increasing Ar gas until it reached the maximum value at 15 slm and decreased with increasing flow rate; the plasma temperature increased with a CF4 flow rate from 0 to 45 sccm until the temperature stabilized when the flow rate reached 45 sccm. The higher the RF power, the higher the plasma region's temperature. The higher the plasma region temperature, the faster the etching rate and the more pronounced the effect on the non-linear effect of the removal function. Therefore, it can be determined that for ICP processing-based chemical reactions, the increase in plasma reaction region temperature leads to a faster SiC etching rate. By processing the dwell time in sections, the nonlinear effect caused by the heat accumulation on the component surface is effectively improved.

CO2 conversion in a microwave plasma torch: 2D vs 1D approaches

In the present study, we computationally investigate the splitting of CO2 to carbon monoxide and oxygen in an atmospheric pressure microwave (MW) plasma torch. We demonstrate different stages of CO2 conversion while using 2D and 1D models. For both models, we use identical sets of chemical reactions, cross sections, power profiles and dimensions of the plasma region. Based on the real MW plasma torch device, we first constructed two-dimensional geometry and obtained results using the 2D model. Then, the 1D plug-flow model was employed. With 1D model we expected to obtain the results close to those we already had from the 2D approach. However, we revealed that the gas temperature and plasma species behaviour in 1D model was quite different from those obtained with the 2D code. We revisited the 2D results and found that the reverse (upstream) gas flow near the central electrode was responsible for the observed discrepancies. In 2D model, the residence time of a certain portion of gas was much longer. When the flow rate in 1D model was adjusted, the reasonable agreement between both models was achieved.