Spectroscopic data and Stark broadening of Cu I and Ag I spectral lines: Selection and analysis

Optical emission and linear laser absorption spectroscopy techniques were used in investigation of plasma with copper and silver admixture. The method of selection of spectral lines and spectroscopic data with the aim of diagnostics of multicomponent air plasma with two metal vapors admixture was developed. Energy level populations behavior on the Boltzmann plot were used for Cu I and Ag I spectroscopic data selection. In this way the selection of spectroscopic data for some of Cu I and Ag I lines was realized. Stark broadening parameters of Cu I and Ag I were examined. Experimentally obtained temperature and electron density radial distributions were used in the calculation of plasma composition in the assumption of local thermodynamic equilibrium. Linear laser absorption spectroscopy was used to examine the state of plasma.     

Differential emission measure distributions in X-ray solar flares

X-ray spectrometer RESIK has observed spectra in the four wavelength bands from 3.3 Å to 6.1 Å. This spectral range contains many emission lines of H- and He-like ions for Si, S, Ar and K. These lines are formed in plasma of coronal temperatures (T > 3 MK). Analysis of their intensities allows studying differential emission measure distributions (DEM) in temperature range roughly between 3 MK and 30 MK. The aim of present study was to check whether any relationship exists between the character of DEM distribution, the event phase and the X-ray flare class. To do this we have calculated and analyzed the DEM distributions for a set of flares belonging to different GOES classes from the range B5.6–X1. The DEM distributions have been calculated using “Withbroe–Sylwester” multiplicative, maximum likelihood iterative algorithm. As the input data we have used absolute fluxes observed by RESIK in several spectral bands (lines + continuum). Respective emission functions have been calculated using the CHIANTI v. 5.2 atomic data package.     

The chromosphere-corona transition zone above an active region

Intensities and profiles of ion emission lines between 1170 A and 1700 A from an active region on the Sun are measured from spectra obtained with the Naval Research Laboratory's High Resolution Telescope and Spectrograph - HRTS. The measurements provide simultaneous determination of line intensities, wavelength shifts and Doppler widths at 50 separate positions in the active region, with spatial resolution of 1 arc second and spectral resolution 0.07 A. Fine structure variation of intensities and gas flow velocities in the temperature range 20,000–200,000 K are determined. The density sensitive line pair I(1486 N IV)/I(1548 C IV) has been used to measure electron pressures. Derived emission measures imply filling factors of 0.05–0.1 to balance the divergence of conductive flux width radiative losses above 60,000 K.     

Time resolved study of laser triggered electric discharge spark in atmosphere: Machine learning approach

In this paper we analyze the possibilities of using machine learning algorithms for analysis of optical spectra of electric discharge spark in atmosphere. Breakdown in air can be initiated by intense laser pulse, making plasma which has a significant electrical conductivity. The formed plasma can be further maintained by electric current obtained from capacitor discharge. In such a case the capacitor voltage can be much lower than the striking voltage (the voltage needed to initiate the electric breakdown in air). Present setup has timing precision and low jitter of fast laser and arbitrary high energies corresponding to capacitance and voltage to which the capacitor is charged. We have used a streak camera equipped with a spectrograph to analyze optical emission of plasma obtained in this way. Q-switched Nd:Yag laser was used to achieve the initial breakdown in air. Machine learning methods were used in order to classify optical spectra of plasmas with different electron temperatures obtained with different excitation energies. We have shown that, instead of using the usual way of identifying the spectral peaks and calculating their intensity ratio, it is possible to train the computer software to recognize the spectra corresponding to different electron temperatures. Principal component analysis was used to reduce the dimensionality of problem. We present possibilities of plasma electron temperature estimation based on several clustering algorithms.     

Electron acceleration and parallel electric fields due to kinetic Alfvén waves in plasma with similar thermal and Alfvén speeds

We investigate electron acceleration due to shear Alfvén waves in a collissionless plasma for plasma parameters typical of 4–5R_E radial distance from the Earth along auroral field lines. Recent observational work has motivated this study, which explores the plasma regime where the thermal velocity of the electrons is similar to the Alfvén speed of the plasma, encouraging Landau resonance for electrons in the wave fields. We use a self-consistent kinetic simulation model to follow the evolution of the electrons as they interact with a short-duration wave pulse, which allows us to determine the parallel electric field of the shear Alfvén wave due to both electron inertia and electron pressure effects. The simulation demonstrates that electrons can be accelerated to keV energies in a modest amplitude sub-second period wave. We compare the parallel electric field obtained from the simulation with those provided by fluid approximations.     

Rocket observations of propagating waves in the night time equatorial F-region over Brazil

A Brazilian SONDA III rocket carrying plasma diagnostic experiments was launched from the Brazilian rocket launching stations in Alcântara (2.31°S, 44.4°W Geog. Lat.) to measure the height profiles of electron density, electron temperature and the ambient electric field. High frequency capacitance probe was used to measure the height profile of the electron density and the Langmuir probe was used to measure the electron density and the spatial structures of plasma irregularities. An electric field double probe was used to measure the electric field fluctuations associated with the F-region plasma irregularities. Spectral analysis of the fluctuations in electron density and electric field indicated the presence of propagating waves in the night time F-region over a large height range. The electron temperatures estimated from the LP data showed abnormally high values in the base of the F-region during the upleg of the rocket and practically normal values in the same height region during the downleg. A brief study of the characteristic features of the spectra of electron density and electric field fluctuations and the associated electron temperature variations are presented and discussed here.     

Global characteristics of ionospheric electric fields and disturbances during the first hours of magnetic storms

The ionospheric plasma density can be significantly disturbed during magnetic storms. In the conventional scenario of ionospheric storms, the negative storm phases with plasma density decreases are caused by neutral composition changes, and the positive storm phases with plasma density increases are often related to atmospheric gravity waves. However, recent studies show that the global redistribution of the ionospheric plasma is dominated primarily by electric fields during the first hours of magnetic storms. In this paper, we present the measurements of ionospheric disturbances by the DMSP satellites and GPS network during the magnetic storm on 6 April 2000. The DMSP measurements include the F region ion velocity and density at the altitude of ∼840 km, and the GPS receiver network provides total electron content (TEC) measurements. The storm-time ionospheric disturbances show the following characteristics. The plasma density is deeply depleted in a latitudinal range of ∼20° over the equatorial region in the evening sector, and the depletions represent plasma bubbles. The ionospheric plasma density at middle latitudes (20°–40° magnetic latitudes) is significantly increased. The dayside TEC is increased simultaneously over a large latitudinal range. An enhanced TEC band forms in the afternoon sector, goes through the cusp region, and enters the polar cap. All the observed ionospheric disturbances occur within 1–5 h from the storm sudden commencement. The observations suggest that penetration electric fields play a major role in the rapid generation of equatorial plasma bubbles and the simultaneous increases of the dayside TEC within the first 2 h during the storm main phase. The ionospheric disturbances at later times may be caused by the combination of penetration electric fields and neutral wind dynamo process.     

Electron density inversed by plasma lines induced by suprathermal electron in the ionospheric modification experiment

Incoherent scatter radar (ISR) is the most powerful ground-based measurement facility to study the ionosphere. The plasma lines are not routinely detected by the incoherent scatter radar due to the low intensity, which falls below the measured spectral noise level of the incoherent scatter radar. The plasma lines are occasionally enhanced by suprathermal electrons through the Landau damping process and detectable to the incoherent scatter radar. In this study, by using the European Incoherent Scatter Association (EISCAT) UHF incoherent scatter radar, the experiment observation presents that the enhanced plasma lines were observed. These plasma lines were considered as manifest of the suprathermal electrons generated by the high-frequency heating wave during the ionospheric modification. The electron density profile is also obtained from the enhanced plasma lines. This study can be a promising technique for obtaining the accurate electron density during ionospheric modification experiment.     

Study of UV Ne II line shapes in the cathode sheath of an abnormal glow discharge

We report results of an experimental and theoretical study of complex UV line shapes of Ne II 369.421 nm, Ne II 370.962 nm, Ne II 371.308 nm, and.Ne II 372.711 nm lines in the cathode sheath (CS) region of an abnormal DC glow discharge in pure neon. Two sets of experimental profiles and electric field distributions, one for discharge with tungsten and the other with titanium cathode, were obtained by means of the optical emission spectroscopy (OES) and theoretically studied by the iterative CS kinetic model. It is shown that our theoretical model enables the determination of the most important CS parameters (e.g. the thickness of the CS region, and the theoretical distributions of electric field and gas temperature) and thereupon based accurate theoretical predictions of the experimentally observed profiles of the studied lines.     

On high-altitude electric fields in the auroral downward current region and their coupling to ionospheric electric fields

The downward field-aligned current region plays an active role in magnetosphere–ionosphere coupling processes associated with aurora. A quasi-static electric field structure with a downward parallel electric field forms at altitudes between 800 km and 5000 km, accelerating ionospheric electrons upward, away from the auroral ionosphere. Other phenomena including energetic ion conics, electron solitary waves, low-frequency wave activity, and plasma density cavities occur in this region, which also acts as a source region for VLF saucers. Results are presented from high-altitude Cluster observations with particular emphasis on the characteristics and dynamics of quasi-static electric field structures. These, extending up to altitudes of at least 4–5 Earth radii, appear commonly as monopolar or bipolar electric fields. The former occur at sharp boundaries, such as the polar cap boundary whereas the bipolar fields occur at softer boundaries within the plasma sheet. The temporal evolution of quasi-static electric field structures, as captured by the pearls-on-a-string configuration of the Cluster spacecraft, indicates that the formation of electric field structures and of ionospheric plasma density cavities are closely coupled processes. A related feature of the downward current is a broadening of the current sheet with time, possibly related to the depletion process. Preliminary studies of the coupling of electric fields in the downward current region, show that small-scale structures are typically decoupled from the ionosphere, similar to what has been found for the upward current region. However, exceptions are also found where small-scale electric fields couple perfectly between the ionosphere and Cluster altitudes. Recent FAST results indicate that the degree of coupling differs between sheet-like and curved structures, and that it is typically partial. The electric field coupling further depends on the current–voltage relationship, which is highly non-linear in the downward current region, and still unrevealed, as to its specific form.     

Estimation of plasma density from wave data of cold electron plasma

Based on the dispersion relation of electron plasma, one can expect, that the waves excited in the frequency band (f_p, f_u=sqrt(f_p^*f_p+f_c^*f_c)) should persist in experimental spectra. For wave data from a spacecraft immersed in a cold plasma such an assumption may be misleading. In measurements performed on board the INTERCOSMOS-19, ACTIVE, APEX satellites and VC36.064CE rocket the most prominent spectral structure is centered around frequency f_r fulfilling the relation f_crp and corresponds to resonant detection of Bernstein waves excited in the surrounding plasma by spacecraft systems. Input network mismatch at frequencies around fu significantly depresses natural plasma noise as well as that excited by the spacecraft. Plasma emissions in the band (f_p, f_u) are prominent if the electromagnetic excitation is preferential (topside sounders) or if the excitation introduces nonequilibrium components into the plasma e.g. particle beams or clouds. Experimental examples are presented and parameters of cold plasma spectra useful for electron density estimation are discussed. The application to other spacecraft-cold plasma configurations is suggested.     

等离子体密度对栅极系统束流影响分析

针对现有离子推力器栅极系统束流引出分析中未考虑放电室等离子体密度均匀性影响的不足,基于数值方法对该问题进行了研究。采用单元内粒子 （Particle In Cell,PIC） 方法对栅极系统束流引出进行了数值模拟。PIC方法中电场求解采用有限差分方法,离子加速方法采用跳蛙格式。以国产20cm Xe离子推力器作为算例,计算得到了栅极中心和边缘孔引出束流离子和电场的分布。结果显示栅极中心孔相对边缘孔束流聚焦性好,束流发散角小,但中心孔轴线的鞍点电势较边缘孔高24.8V。因此,放电室等离子体密度分布对束流引出具有重要影响,电子返流现象最先出现在栅极中心位置。     

Acceleration of charged particles by fluctuating and steady electric fields in a X-type magnetic field

Release of stored magnetic energy via particle acceleration is a characteristic feature of astrophysical plasmas. Magnetic reconnection is one of the mechanisms for releasing energy from magnetized plasmas. Collisionless magnetic reconnection could provide both the energy release mechanism and the particle accelerator in space plasmas. Here we studied particle acceleration when fluctuating (in-time) electric fields are superposed on an static X-type magnetic field in collisionless hot solar plasma. This system is chosen to mimic the reconnective dissipation of a linear MHD disturbance. Our results are compared to particle acceleration from constant electric field superposed on an X-type magnetic field. The constant electric field configuration represents the effects of steady state magnetic reconnection. Time evolution of ion and electron distributions are obtained by numerically integrating particle trajectories. The frequencies of the electric field represent a turbulent range of waves. Depending on the frequency and amplitude of the electric field, electrons and ions are accelerated to different degrees and have energy distributions of bimodal form consisting of a lower energy part and a high energy tail. For frequencies (ω in dimensioless units) in the range 0.5 ? ω ? 1.0 a substantial fraction (20%–30%) of the proton distribution is accelerated to gamma-ray producing energies. For frequencies in the range 1 ? ω ? 100.0 the bulk of the electron distribution is accelerated to hard X-ray producing energies. The acceleration mechanism is important for solar flares and solar noise storms but it could be applicable to all collisionless astrophysical plasmas.     

太阳帆板驱动机构内带电效应试验

太阳帆板驱动机构（Solar Array Drive Assembly,SADA）是长寿命、大功率航天器能源系统的关键部件.在空间高能电子环境下,SADA内部会发生静电放电甚至诱发二次放电,导致航天器丧失能源.利用双束加速器建立试验平台,对SADA进行内带电效应试验.试验中高能电子束的电子能量为2MeV,束流密度为5pA·cm-2,模拟SADA工作电压为50~150V,工作电流为0.5~1.5A.试验样品充电电位在辐照5h后达到平衡,形成的电场约为5×106V·m-1.相同工作电流下的放电次数随工作电压增大而明显增加,说明工作电压形成的电场与高能电子沉积形成的电场叠加会增加SADA发生放电的风险.依据试验结果,提出SADA抗内带电设计方案:一是降低SADA介质盘的体电阻率;二是改进导电环结构体的结构设计,降低导电环间电压在介质盘上形成的电场.      

霍尔推力器分割高偏压电极等离子体放电特性

霍尔推力器通道等离子体与壁面有很强的相互作用,为了降低壁面腐蚀,提高在轨寿命, 针对推力器全通道放电过程建立二维物理模型,采用粒子模拟方法（Particle In Cell）,数值研究了电离区壁面分割高于阳极偏压的低发射石墨电极对推力器放电特性的影响,讨论了放电通道电势、离子数密度、电子温度、电离速率及比冲的变化规律。结果表明：在电离区不同位置分割高偏压电极对等离子体放电特性影响明显,电极位置在电离区前端时,电极偏压高于阳极电压60V时通道内放电等离子体参数几乎不变。而电极位置在电离区末端,电极偏压高于阳极电压18V时就会导致加速区轴向扩张,离子聚焦效果强,电子温度显著升高,电子与壁面相互作用减弱,羽流发散角减小。由此推力器比冲提升约12%,寿命延长,性能提高。     

瞬态空气等离子体场的全息术研究

采用双波长双脉冲激光全息术,对有激波存在下的空气放电现象进行了研究。建立了双波长电弧折射率场方程,推导出冲击波区的压强同折射率之间的关系式,得出电弧场的压强分布.曲线及等离子体区的温度分布和电子、离子、原子、分子等粒子的数密度分布。     

High-resolution, coupled thermosphere–ionosphere models for space weather applications

Current first-principles global models of the coupled thermosphere–ionosphere (T–I) system use grids that are too coarse to simulate the mesoscale and small-scale structures that occur in this complex system. These small-scale and mesoscale structures have a great effect on global-scale neutral and plasma distributions and have important consequences for daily space weather. In this paper, we present a new first-principles, high-resolution, T–I nested grid (TING) polar cap model that incorporates multiple nesting levels and two-way interaction. The TING model simulation of the electron densities and temperatures demonstrates the importance of high spatial resolution. It is found that both the mid-latitude electron density trough and its associated dawn electron temperature peak are more pronounced and structured in the nested grid than in the coarse grid. Using the TING model to simulate ionospheric F₂ region electron density variations with geomagnetic activity and universal time (UT) is also discussed.     

Modelling the plasmasphere for the international reference ionosphere

The paper discusses how profiles of electron and/or ion distributions that are produced by two different computer models can be smoothly coupled together. The first of these models is the empirical International Reference Ionosphere which produces a vertical profile of ionospheric parameters up to an altitude of 1000 km. The second is a physically-based, diffusive equilibrium model of the plasmasphere based upon the theoretical work of Angerami and Thomas /1/, in which plasma is constrained to move parallel to the Earth's magnetic field lines. Some problems associated with this work are considered, as are some initial results.     

Observations of electron density in the solar corona during sunspot minimum and global electric currents around the sun

The observed difference in electron density between the equatorial plane and the polar direction is compared for three empirical distributions: the Allen distribution, the Saito distribution, and the Saito-Munro-Jackson distribution. It is shown that from 1.5R_o to 5R_o the observed difference in electron density is sufficient to result in a global azimuthal electric current flow around the sun. The dependence of the calculated current density on the radial distance and solar latitude is discussed.     

Response of the ionosphere to super geomagnetic storms: Observations and modeling

The relative importance of the main drivers of positive ionospheric storms at low-mid latitudes is studied using observations and modeling for the first time. In response to a rare super double geomagnetic storm during 07–11 November 2004, the low-mid latitude (17°–48°N geomag. lat.) ionosphere produced positive ionospheric storms in peak electron density (NmF2) in Japan longitudes (≈125°–145°E) on the day of main phase (MP1) onset (06:30 LT) and negative ionospheric storms in American longitudes (≈65°–120°W) on the following day of MP1 onset (13:00–16:00 LT). The relative effects of the main drivers of the positive ionospheric storms (penetrating daytime eastward electric field, and direct and indirect effects of equatorward neutral wind) are studied using the Sheffield University Plasmasphere Ionosphere Model (SUPIM). The model results show that the penetrating daytime (morning–noon) eastward electric field shifts the equatorial ionisation anomaly crests in NmF2 and TEC (total electron content) to higher than normal latitudes and reduces their values at latitudes at and within the anomaly crests while the direct effects of the equatorward wind (that reduce poleward plasma flow and raise the ionosphere to high altitudes of reduced chemical loss) combined with daytime production of ionisation increase NmF2 and TEC at latitudes poleward of the equatorial region; the later effects can be major causes of positive ionospheric storms at mid latitudes. The downwelling (indirect) effect of the wind increases NmF2 and TEC at low latitudes while its upwelling (indirect) effect reduces NmF2 and TEC at mid latitudes. The net effect of all main drivers is positive ionospheric storms at low-mid latitudes in Japan longitude, which qualitatively agrees with the observations.