Decrease In Plasma Temperature Research Articles

Unraveling the Trigger Mechanism of Explosive Reconnection in Partially Ionized Solar Plasma

Plasmoid instability usually accounts for the onset of fast reconnection events observed in astrophysical plasmas. However, the measured reconnection rate from observations can be one order of magnitude higher than that derived from magnetohydrodynamic (MHD) simulations. In this study, we present the results of magnetic reconnection in the partially ionized low solar atmosphere based on 2.5D MHD simulations. The whole reconnection process covers two different fast reconnection phases. In the first phase, the slow Sweet–Parker reconnection transits to the plasmoid-mediated reconnection, and the reconnection rate reaches about 0.02. In the second phase, a faster explosive reconnection appears, with the reconnection rate reaching above 0.06. At the same time, a sharp decrease in plasma temperature and density at the principle X-point is observed, which is associated with the strong radiative cooling, the ejection of hot plasma from the local reconnection region, or the motion of the principle X-point from a hot and dense region to a cool and less dense region along the narrow current sheet. This causes gas pressure depletion and increases magnetic diffusion at the main X-point, resulting in the local Petschek-like reconnection and a violent and rapid increase in the reconnection rate. This study for the first time reveals a common phenomenon where the plasmoid-dominated reconnection transits to an explosive faster reconnection with a rate approaching the order of 0.1 in partially ionized plasma in the MHD scale.

Correlation between impurity radiation rollover and divertor detachment with boundary impurity seeding in HL-2A

Divertor detachment has significant potential for reducing the divertor target thermal load, and impurity seeding is the primary method for achieving divertor detachment. In this study, different impurity seeding scenarios (N, Ne, and Ar) at the boundary region of HL-2A were simulated using the SOLPS-ITER code. Density scans revealed that when the divertor target electron temperature dropped below 5 eV, a rollover in impurity radiation from the core edge regions of Ar, N, and Ne occurred, and the radiation from impurities in the divertor started to increase concurrently, indicating a correlation between impurity radiation rollover and divertor detachment. Impurity radiation rollover is discovered to be primarily related to impurity transport, which is governed by thermal and friction forces.Prior to divertor detachment, the dominance of thermal forces over friction forces causes impurity ions to transport upstream. However, after detachment, friction forces dominate the impurity ions transport to the divertor region. After analyzing the density and velocity of impurity ions in different charge states, it was found that the core radiation rollover after detachment is mainly caused by high charge state impurity ions. Furthermore, the ability of the divertor to achieve particle flow rollover primarily depends on whether the decrease in plasma pressure ( P t ) exceeds the decrease in plasma temperature ( T t 1 / 2 ).

Formation of fast-ignition hotspots and propagartion of burning waves in pre-compressed isochoric plasmas

The formation and evolution of hotspots is important for achieving ignition and high energy gain in inertial fusion process. However, most of relevant studies are carried out on pre-compressed plasmas with an isobaric configuration, the evolution of the hotspot in a plasma with an isochoric configuration is rarely studied. In this paper, a semi-analytical model is developed to describe the evolution of the hotspot boundary and propagation of fusion burning waves for a high-density pre-compressed plasma with an isochoric configuration in the double-cone ignition scheme. For the shock wave, the strong shock wave approximation and the quasi-isobaric approximation are reasonable. The quasi-isobaric approximation shows that as the plasma density behind the shock wave increases, the plasma temperature decreases. Because of these, the range of <inline-formula><tex-math id="M4">\begin{document}$ {\mathrm{\alpha }} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231474_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231474_M4.png"/></alternatives></inline-formula>-particles decreases rapidly behind the shock wave, forming an <inline-formula><tex-math id="M5">\begin{document}$ {\mathrm{\alpha }} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231474_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231474_M5.png"/></alternatives></inline-formula>-particle absorption peak. Therefore, considering that the hotspot is the main region where <inline-formula><tex-math id="M6">\begin{document}$ {\mathrm{\alpha }} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231474_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231474_M6.png"/></alternatives></inline-formula>-particles are produced and deposited, the position of the shock peak can be used to identify the boundary of the hotspot in a high-density plasma with an isochoric configuration. It also shows that a “self-regulating burning process” exists in the burning process of the isochoric hotspot, most of <inline-formula><tex-math id="M7">\begin{document}$ {\mathrm{\alpha }} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231474_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231474_M7.png"/></alternatives></inline-formula>-particles are deposited in the stable region and behind the shock, and finally, transport through the shock peak and heat the cold fuel, resulting in the temperature rising. In the high-density hotspots of plasma with an isochoric configuration, the deposition of α-particles behaves as an obvious non-uniform distribution effect. By analyzing the non-uniform deposition of α-particles, the deposition rate of α-particles at the edge of spherical uniform hotspot is calculated, then the temperature and density evolution of the isochoric hotspot can be well described. The model can be used to estimate the Lawson parameter of the hotspots at the end of the early stage of ignition. It is found that a lower fast electron energy is more beneficial to ignition and high gain operation of fusion plasma. It is also shown that the high density of the hotspots in the isochoric plasma will lead to a higher fusion burning rate, which can offset the negative influence of the shock wave and even achieve higher energy gain. The semi-analytical model is verified by the hydrodynamic simulations of O-SUKI-N.

Continuation of investigation of effect of O2 in plasma gas on parameters of nitrogen microwave-induced plasma optical emission spectrometry

We studied the effect of O2 content in the range up to 80% in plasma gas on the plasma characteristics, the analyte signal and the intensity of the molecular species in the nitrogen microwave-induced plasma (MIP). The plasma temperature decrease from 3.9·103 to 3.3·103 K with increasing O2 content. Mg (II)/Mg (I) intensity ratio decrease from 1.02 to 0.18, the electron density decrease from 6.6·1012 to 4·1011 cm−3. The intensity of N2 (1+ system), N2 (2+ system), N2+, NH, NO, and OH intensities increases to a certain content, and then decrease (NH) or remain constant (OH) when O2 is added. The effect of O2 content on the intensity of several atomic and ionic emission lines (covering Esum values from 1.6 to 14.7 eV) of 22 elements has been studied. The line intensity was suppressed over the entire energy range. It was shown that the O2 addition increased the limit of detection (LOD) by 1.2–4 for lines with Esum of 1.5–4 eV and by 50–60 times for lines with Esum of 4–15 eV.

Study on the characteristics of different species in the vacuum arc devices with deuteride cathode

To study the physical mechanism of the separation between heavy and light species in the vacuum arc devices with deuteride cathodes, a three-fluid model based on magnetohydrodynamic (MHD) theory is established. In the model, different kinds of species are considered to be different kinds of fluids, and their physical parameters are calculated separately. Moreover, the distribution of arc current is calculated by the generalized Ohm's law, and the ionization and recombination of species are taken into account. In the paper, the two cases where the cathode is Zr or ZrD0.67 are simulated, respectively. The results show that in the case of ZrD0.67 cathode, the separation of light and heavy species is remarkable. Because of D's lighter mass and lower mass-to-charge ratio, the distribution of it is more uniform. In addition, the differences between species also lead to large differences in other physical characteristics, such as ion velocity, ion temperature, and so on. Notably, the desorption and ionization of deuterium lead to a decrease in plasma temperature. The self-generated magnetic field of the arc has an inhibitory effect on the expansion of each species, and it is more obvious for ions with lower mass-to-charge ratio. The simulation results are consistent with the experimental results. The theoretical analysis can provide theoretical guidance for the improvement of vacuum arc devices with composite or gas-saturated cathodes.

Studying the Effect of Delay Time on Intensity of Laser Induced Breakdown Spectroscopy Technique Using Mas Cement Sample

Cement is a soft bond material that hardens and acquires its mechanical properties in the presence of water; it is an industrial product that has many uses, including its use in construction, roads, bridges, and others. It is important in our life to know its components. In this study, a laser-induced breakdown spectrometer was used to detect the elements present in a sample of Sudanese mas cement. In this technique, a high-energy laser is applied to the surface of the sample, ionizing the atoms of the material and then evaporating it, and then producing hot plasma on the surface of the sample, and this plasma is analyzed with a spectrometer, and thus the components of the sample can be known. The laser source used in this study is (Nd: YAG). Delay times are one of the factors affecting the intensity of the libs signal, To determine the relationship between laser delay times and LIBS signal intensity, a mas cement sample was irradiated with 32mj laser pulse energy and (200, 300, 400, 500, 600, 700, 800, 1000, 2000) nanoseconds delay times. We observed a decrease in the LIBS signal with increasing laser delay times. For quantitative analysis, the plasma temperature and electron density at (300, 500 and 700) laser delay times at 32mj laser pulse energy were calculated using standard equations and well-resolved spectral lines for Ca in the region of (422.67, 430.25 and 430.774) nm. It has been observed that when the delay time increases, the plasma temperature decreases and the electron density decrease. It was found that the density of electrons is directly proportional to the temperature of the plasma.

Spatial characterization of ns-laser induced Tungsten plasma in air using laser induced breakdown spectroscopy

The laser induced plasma (LIP) of tungsten is studied using space-resolved laser induced breakdown spectroscopy (SR-LIBS). In the present work a Q-switched Nd:YAG laser working at wavelength of 532 nm having maximum energy of 600 mJ and pulse duration of 7 ns with repetition rate of 1 Hz is used to generate the plasma onto the target sample surface. The LIP is generated at four different incident laser energy of 25, 50, 75 and 100 mJ. The spectra recorded from the different location of the LIP is analyzed to get the spatial distribution of plasma emission intensity of atomic and ionic transitions, plasma temperature and electron density. The plasma temperature is determined using the Boltzmann plot from the WI lines and that of the electron density estimated using Stark broadened profile of WI transition at 430.2 nm. The intensity of atomic lines as well as plasma parameters attain the maximum value at a distance ranging from 1.6 mm to 2.0 mm away from the target surface for the incident laser energy of 25 mJ and 50–100 mJ, respectively. The thermal conduction towards the solid target and radiative cooling of the plasma and conversion of thermal energy into kinetic energy is responsible for the decrease in plasma temperature towards the plasma edge away from the target surface whereas the direct ejection of low velocity neutrals around the target surface is responsible for lower temperature. Both these plasma parameters are also studied at incident laser energy of 25, 50, 75 and 100 mJ. The validity of the local thermodynamic equilibrium (LTE) is studied by Mc-Whirter criteria and diffusion length is estimated at different location of the plasma to understand the effect of inhomogeneous nature of LIP on the validity of LTE. The branching ratio method is employed to study optical thin condition of the LIP at different axial location as function of energy. From this an optimized spatial window is identified for the LIBS studies.

Comparison of a collisional-radiative fluid model of H2 in UEDGE to the kinetic neutral code EIRENE

• H 2 density agreement of the UEDGE fluid model and EIRENE within 20% is achievable. • Vibrational H 2 populations become significant for T e < 6 eV at n e = 1 x 10 18 m −3 . • Atom-molecule equipartition becomes significant in UEDGE at n e = 1 x 10 19 m −3 . A fluid collisional-radiative model for H 2 has been implemented in the edge-fluid code UEDGE and compared to the kinetic neutral code EIRENE on a simple, 2D, orthogonal domain with a constant, static plasma distribution. The novel CRUMPET Python tool was used to implement dissociation and energy rate coefficients that consider molecular-assisted processes, binding energy, and radiation due to molecular processes into the UEDGE fluid molecular model. The agreement between the fluid and kinetic molecular models was found to be within 20% when corresponding rates were used in UEDGE and EIRENE for a domain with absorbing boundaries. When wall recycling was considered, EIRENE predicted up to a factor of 2.2 higher molecular densities than UEDGE at T < 5 eV. The difference is due to the absence of radial gradients driving diffusive wall fluxes and, thus, recycling in UEDGE and molecular self-scattering in EIRENE, and is likely dependent on plasma profiles and domain geometry. Comparison of the molecular energy sources in EIRENE and UEDGE suggest the constant elastic scattering rate coefficient used in UEDGE needs to be updated to a temperature-dependent coefficient and that atom-molecule equipartition should be considered in the EIRENE model for background plasma density in excess of 1 × 10 19 m - 3 . Finally, collisional-radiative CRUMPET simulations indicate that the vibrational molecular populations become comparable to the ground-state molecular population when the plasma temperature decrease below 6 eV and, thus, require time-dependent evaluation.

Thermodynamics of the Magnetotail Current Sheet Thinning

AbstractSubstorm growth phase in the magnetotail is characterized by formation of a thin current sheet (CS) becomes unstable due to external or internal drivers. Such instability results in magnetic field line reconnection, the substorm onset. The CS thinning, as a key process of substorm dynamics, has been included into many global and local simulations of the magnetotail magnetic reconnection. However, recent observations indicate that the evolution of plasma characteristics and magnetic field configuration during the CS thinning can differ from predictions of the classical adiabatic scenario. In this study, we combine two most extensive datasets of the CS evolution, as observed by Cluster and THEMIS missions for 2001–2009 and 2015, respectively. We show that for a wide range of downtail distances and dawn‐dusk direction there are quite similar quantitative characteristics of the thinning: the magnetic field line stretching (north‐south magnetic field decrease), the intensification of the current density, and the evolution of plasma temperatures and densities. We confirm that the process cannot be directly associated with increase of the lobe magnetic pressure. Using advantages of multispacecraft measurements and CS flapping motion, we demonstrate that the thinning is usually result in the equatorial density increase and plasma temperature decrease. We discuss the revealed evolution features in the context of the thermodynamical CS characteristics for contemporary thinning models.

Simulation of supersonic molecular beam injection fueling into H-mode plasmas on EAST using BOUT++

Transport dynamic 2D simulations for supersonic molecular beam injection (SMBI) fueling into H-mode deuterium plasmas on the Experimental Advanced Superconducting Tokamak (EAST) is first simulated using a seven-field two-fluid model in the BOUT++ framework. The SMB is assumed to be injected into plasma from the midplane at the low field side with a fixed width and constant molecular flux. The different densities and injection velocities of SMBI are investigated within the upper single-null geometry of EAST. The simulations indicate that the SMBI has a self-shielding effect on molecules' inward transport into the plasma, and the deposition of SMBI leads to a large increase in plasma density and decrease in plasma temperature. There is a velocity threshold for SMB penetrating the pedestal and depositing at the top of density pedestal. However, the deposition point would be back toward the plasma boundary after SMB arriving at the deepest penetration position. Comparing the different molecular injection velocities and densities, the outcomes demonstrate that the depth of deposition is closely related to the injection velocity rather than the molecular density. The simulated results show good agreement with the EAST experiments by comparing the electron density profiles obtained by simulation and experiment, respectively. These results will be helpful for guiding future experiments, as well as the design of the SMBI system.

Investigation on Insulation Performance of Thermally Aged Natural Ester Oil Impregnated Pressboard

An attempt is made to understand the effect of thermal ageing on natural ester oil impregnated pressboard material. Surface discharge inception voltage of natural ester oil impregnated pressboard material is reduced drastically under AC, harmonic AC voltages and with DC voltages with high ripple content. Phase-resolved partial discharge studies show an increase in the number of discharges for natural ester oil impregnated pressboard (OIP) aged at higher temperature, under AC and harmonic AC voltages with different total harmonic distortions. Surface potential measurement study complies with results obtained by surface discharge inception voltage. It indicates the presence of high-density charge traps evolved as a function of ageing time and temperature. Laser-induced breakdown spectroscopy analysis is carried out to understand the characteristic variation with thermally aged OIP material. A decrease in plasma temperature is observed for sample aged at higher temperature. Differential scanning calorimetric studies indicate reduction in peak temperature with thermally aged specimens. Ageing observed to affect mechanical strength of the cellulosic material, as indicated by tensile test. Dielectric response spectroscopy study indicates that with an increase in thermal ageing, the permittivity, tan(δ), DC conductivity and relaxation time have increased. A reduction in activation energy of the aged material is observed, which indicates the status of the OIP material.

2-D Numerical Investigation of the Formation of Z-Pinch-Driven Dynamic Hohlraum at 8-MA Current Level

The newly developed code MULTI2D-Z is applied to simulate the formation process of a dynamic hohlraum driven by tungsten wire-array Z-pinch at 8-MA current level. In the initial phase, the foam is expanding due to the radiation heating from the imploding wire-array plasma. At the same time, this causes a compression-wave spreading inward in the foam, and in turn a challenge for the safety of capsule embedded in the center of the foam in the inertial confinement fusion ignition experiment. There is instability development during the collision of the expanding foam plasma and the imploding wire-array plasma. However, fortunately, this instability was then spontaneously restrained due to the subsequent snow-plow implosion. The formed wall-like high-Z plasma (shock wave), in which the radiation mean free path is about 10 $\mu \text{m}$ , compresses the foam, and plays a well role in trapping the radiation in the foam. When the foam has been compressed a little and the high-Z plasma temperature decreases, the dynamic hohlraum begins to form. While the thermal radiation wave in the foam is spreading toward the center axis, the radiation temperature profile becomes comparatively uniform, and almost equates to the plasma (matter) temperature except at the place of the shock wave. The radiation temperature in the hohlraum is above 100 eV. The simulated results also suggested that the radiation energy loss to the electrodes would be one of the main reasons for the nonuniformity in the radiation field and implosion instability development during hohlraum formation.

The study of thermal description for non-thermal plasma needle system

Cold plasma is a relatively low temperature gas, so this feature enables us to use cold plasma to treat thermally sensitive materials including polymers and biologic tissues. In this research, the non-thermal plasma system is designed with diameter (3 mm, 10 mm) Argon at atmospheric pressure as well as to be suitable for use in medical and biotechnological applications.The thermal description of this system was studied and we observed the effect of the diameter of the plasma needle on the plasma, when the plasma needle slot is increased the plasma temperature decrease, as well as the effect of the voltages applied to the temperature of the plasma, where the temperature increasing with increasing the applied voltage . Results showed that the plasma temperature would be low, which enables the use of this system in many medical aspects.

Design-Oriented Modelling of Different Quenching Solutions in Induction Plasma Synthesis of Copper Nanoparticles

The aim of this paper is to compare the effects of different mechanisms underlying the synthesis of copper nanoparticles using an atmospheric pressure radio-frequency induction thermal plasma. A design oriented modelling approach was used to parametrically investigate trends and impact of different parameters on the synthesis process through a thermo-fluid dynamic model coupled with electromagnetic field equations for describing the plasma behaviour and a moment method for describing nanoparticles nucleation, growth and transport. The effect of radiative losses from Cu vapour on the precursor evaporation efficiency is highlighted, with occurrence of loading effect even with low precursor feed rate due to the decrease in plasma temperature. A method to model nanoparticle deposition on a porous wall is proposed, in which a sticking coefficient is employed to model particle sticking on the porous wall used to carry a quench gas flow into the chamber. Two different reaction chamber designs combined with different quench gas injection strategies (injection through a porous wall for “active” quenching; injection of a shroud gas for “passive” quenching) are analysed in terms of process yield and size distribution of the synthetized nanoparticles. Conclusion can be drawn on the characteristics of each quenching strategy in terms of throughput and mean diameter of the synthesized nanoparticles.

A novel flexible field-aligned coordinate system for tokamak edge plasma simulation

Tokamak plasmas are confined by a magnetic field that limits the particle and heat transport perpendicular to the field. Parallel to the field the ionised particles can move freely, so to obtain confinement the field lines are “closed” (i.e. form closed surfaces of constant poloidal flux) in the core of a tokamak. Towards, the edge, however, the field lines intersect physical surfaces, leading to interaction between neutral and ionised particles, and the potential melting of the material surface. Simulation of this interaction is important for predicting the performance and lifetime of future tokamak devices such as ITER. Field-aligned coordinates are commonly used in the simulation of tokamak plasmas due to the geometry and magnetic topology of the system. However, these coordinates are limited in the geometry they allow in the poloidal plane due to orthogonality requirements. A novel 3D coordinate system is proposed herein that relaxes this constraint so that any arbitrary, smoothly varying geometry can be matched in the poloidal plane while maintaining a field-aligned coordinate. This system is implemented in BOUT++ and tested for accuracy using the method of manufactured solutions. A MAST edge cross-section is simulated using a fluid plasma model and the results show expected behaviour for density, temperature, and velocity. Finally, simulations of an isolated divertor leg are conducted with and without neutrals to demonstrate the ion-neutral interaction near the divertor plate and the corresponding beneficial decrease in plasma temperature.

Synthesis of (B-C-N) Nanomaterials by Arc Discharge Using Heterogeneous Anodes

In spite of the current prevalence of the CVD-based processes, the electric arc remains an interesting process for the synthesis of carbon nanoforms, thanks to its versatility, robustness and easiness. It also allows performing in-situ substitution of carbon atoms by hetero-elements in the graphene lattice. Our work aims to establish a correlation between the plasma properties, type and chemical composition (and the substitution rate) of the obtained single-wall carbon nanotubes. The plasma was characterized by optical emission spectroscopy and the products were analyzed by high resolution transmission electron microscopy and core level Electron Energy-Loss Spectroscopy (EELS). Results show that a high boron content leads to a plasma temperature decrease and hinders the formation of nanotubes. This effect can be compensated by increasing the arc current and/or yttrium content. The optimal conditions for the synthesis of boron- and/or nitrogen-substituted nanotubes correspond to a high axial plasma temperature associated to a strong radial gradient. EELS analysis confirmed that the boron incorporates into the graphenic lattice.

2D simulations of transport dynamics during tokamak fuelling by supersonic molecular beam injection

Time-dependent transport of both plasma and neutrals is simulated during supersonic molecular beam injection (SMBI) yielding the evolution of edge plasma and neutral profiles. The SMBI model is included as a module, called trans-neut, within the original BOUT++ boundary plasma turbulence code. Results of calculations are reported for the realistic divertor geometry of the HL-2A tokamak. The model can also be used to study the effect of gas puffing. A seven-field fluid model couples plasma density, heat, and momentum transport equations together with neutral density and momentum transport equations for both molecules and atoms. Collisional interactions between molecules, atoms, and plasma include dissociation, ionization, recombination and charge-exchange effects. Sheath boundary conditions and particle recycling are applied at both the wall and the divertor plates. A localized boundary condition of constant molecular flux (product of density times speed) is applied at the outermost flux surface to model the SMBI. Steady state profiles with and without particle recycling are achieved before SMBI. During SMBI, the simulation shows that neutrals can penetrate several centimetres inside the last closed (magnetic) flux surface (LCFS). Along the SMBI path, plasma density increases while plasma temperature decreases. The molecule penetration depth depends on both the SMBI flux and the initial plasma density and temperature along its path. As the local plasma density increases substantially, molecule and atom penetration depths decrease due to their higher dissociation and ionization rates if the electron temperature does not drop too low. Dynamic poloidal spreading of the enhanced plasma density region is observed due to rapid ion flow along the magnetic field (parallel) driven by a parallel pressure asymmetry during SMBI. Profile relaxation in the radial and poloidal directions is simulated after SMBI termination, showing that the plasma returns to pre-SMBI conditions on a time scale of 60 ms.

Effect of Analyte Concentration on the Laser-Induced Plasma Temperature and Electron Density in Liquid Matrix

ABSTRACT In the present work, we report spectroscopic studies of laser-induced plasmas produced by focusing the second harmonic (532 nm) of a Nd:YAG laser onto the laminar flow of a liquid containing chromium. The plasma temperature is determined from the coupled Saha–Boltzmann plot and the electron density is evaluated from the Stark broadening of an ionic line of chromium [Cr(II)] at 267.7 nm. Our results reveal a decrease in plasma temperature with an increase in Cr concentration up to a certain concentration level; after that, it becomes approximately constant, while the electron density increases with an increase in analyte (Cr) concentration in liquid matrix.

IMPACT OF TEMPERATURE-DEPENDENT RESISTIVITY AND THERMAL CONDUCTION ON PLASMOID INSTABILITIES IN CURRENT SHEETS IN THE SOLAR CORONA

In this paper we investigate, by means of two-dimensional magnetohydrodynamic simulations, the impact of temperature-dependent resistivity and thermal conduction on the development of plasmoid instabilities in reconnecting current sheets in the solar corona. We find that the plasma temperature in the current sheet region increases with time and it becomes greater than that in the inflow region. As secondary magnetic islands appear, the highest temperature is not always found at the reconnection $X$-points, but also inside the secondary islands. One of the effects of anisotropic thermal conduction is to decrease the temperature of the reconnecting $X-$points and transfer the heat into the $O-$points, the plasmoids, where it gets trapped. In the cases with temperature-dependent magnetic diffusivity, $\eta \sim T^{-3/2}$, the decrease in plasma temperature at the $X-$points leads to: (i) increase in the magnetic diffusivity until the characteristic time for magnetic diffusion becomes comparable to that of thermal conduction; (ii) increase in the reconnection rate; and, (iii) more efficient conversion of magnetic energy into thermal energy and kinetic energy of bulk motions. These results provide further explanation of the rapid release of magnetic energy into heat and kinetic energy seen during flares and coronal mass ejections. In this work, we demonstrate that the consideration of anisotropic thermal conduction and Spitzer-type, temperature-dependent magnetic diffusivity, as in the real solar corona, are crucially important for explaining the occurrence of fast reconnection during solar eruptions.

Spatial diagnostics of the laser induced lithium fluoride plasma

We present spatial characteristics of the lithium fluoride plasma generated by the fundamental and second harmonic of a Nd:YAG laser. The plume emission has been recorded spatially using five spectrometers covering the spectral region from 200 nm to 720 nm. The electron density is measured from the Stark broadened line profile of the line at 610.37 nm, whereas the plasma temperature has been determined using the Boltzmann plot method including all the observed spectral lines of lithium. Both the plasma parameters; electron density and plasma temperature decrease with the increase of the distance from the target surface. The thermal conduction towards the target, the radiative cooling of the plasma, and the conversion of thermal energy into kinetic energy are the main mechanisms responsible for the spatially decrease of the plasma parameters.