Intense Line Radiation Research Articles

Hall MHD Simulations of MARFE movements in limiter and divertor configurations

Abstract MARFE movements in limiter and divertor configurations are studied using impurity Hall MHD code CLT. We simulate the MARFE movement experiment on J-TEXT and validated the simulation by comparing the line-averaged density and line radiation intensity between the simulation and the experiment. It is found that impurity radiation cooling enhances the Hall effect, leading to the MARFE movement. Impurity radiation cooling causes the locally enhanced distribution of the current density. When the enhanced current approaches close to the q=2 resonant surface, the tearing mode is excited. We also simulated MARFE movement in a lower divertor configuration with the X-point. The results show that the impurity radiation cooling at the X-point generates a clockwise poloidal velocity flow towards the high-field side. This velocity is mainly driven by the impurity radiation cooling while the Hall effect can be ignorable. When the temperature cooling is strong, this poloidal velocity is significant enough to drive MARFE towards the high-field side. Otherwise, MARFE remains located at the X-point.

In-situ measurement of temperature and potassium concentration during the combustion of biomass pellets based on the emission spectrum

Here, a calibration method using the K concentration, temperature and the characteristic spectral line radiation intensity in flame is described. In addition, a radiation function model between these three variables, Iλ766T,CK=0.821·Ib(λ766,T)·CK, was established. A Y-type optical fiber was used to connect the spectral signals from the same direction to two spectrometers. The continuous spectra in the 500–800 nm band were used for multi-spectral temperature measurements. The combination of the measured temperature and the K characteristic spectral line radiation intensity at 766 nm was used for measurements of K concentration. The temperature and equivalent ratio of the heating atmosphere were 1300 K (±20 K) and 0.786, respectively. Compared with rice straw pellet, pine wood pellet had a lower K concentration and higher combustion temperature during the entire combustion process. The peak K release concentrations of the pine wood pellet and the rice straw pellet during the volatile combustion stage were 2.09 ppm and 10.03 ppm, respectively, and the peak flame temperatures were 1774 K and 1756 K, respectively. In the char combustion stage, the peak K release concentrations were 27.83 ppm and 110.43 ppm, respectively, and the peak surface temperatures were 1287 K and 1143 K, respectively. The established function model for measuring K concentration is also applicable to the combustion diagnosis of other K-rich fuels.

Influence of atomic physics on EDGE2D-EIRENE simulations of JET divertor detachment with carbon and beryllium/tungsten plasma-facing components

The EDGE2D-EIRENE code is applied for simulation of divertor detachment during matched density ramp experiments in high triangularity, L-mode plasmas in both JET-Carbon (JET-C) and JET-ITER-Like Wall (JET-ILW). The code runs without drifts and includes either C or Be as impurity, but not W, assuming that the W targets have been coated with Be via main chamber migration. The simulations reproduce reasonably well the observed particle flux detachment as density is raised in both JET-C and JET-ILW experiments and can better match the experimental in-out divertor target power asymmetry if the heat flux entering the outer divertor is artificially set at around 2–3 times that entering the inner divertor. A careful comparison between different sets of atomic physics processes used in EIRENE shows that the detachment modelled by EDGE2D-EIRENE relies only on an increase of the particle sinks and not on a decrease of the ionization source. For the rollover and the beginning of the partially detached phase, the particle losses by perpendicular transport and the molecular activated recombination processes are mainly involved. For a deeper detachment with significant target ion flux reduction, volume recombination appears to be the main contributor. The elastic molecule-ion collisions are also important to provide good neutral confinement in the divertor and thus stabilize the simulations at low electron temperature (Te), when the sink terms are strong. Comparison between EDGE2D-EIRENE and SOLPS4.3 simulations of the density ramp in C shows similar detachment trends, but the importance of the elastic ion-molecule collisions is reduced in SOLPS4.3. Both codes suggest that any process capable of increasing the neutral confinement in the divertor should help to improve the modelling of the detachment. A further outcome of this work has been to demonstrate that key JET divertor diagnostic signals—Langmuir probe Te and bolometric tomographic reconstructions—are running beyond the limit of validity in high recycling and detached conditions and cannot be reliably used for code validation. The simulations do, however, reproduce the trend of the evolution of the line integrated bolometer chord measurements. The comparison between the code results and high-n Balmer line radiation intensity profiles confirms that a strong volume recombination is present during the experimental detachment and may play a role in this process, as suggested by the code.

High-Pressure Microdischarges: Sources of Ultraviolet Radiation

Spatially confined plasmas with dimensions in the submillimeter range have been found to be stable at atmospheric pressure. These microplasmas are nonequilibrium plasmas with an electron energy distribution which contains a significant fraction of high energy electrons. This favors, in combination with the high gas density, the formation of excimers. The possibility for operating these discharges in parallel, or expanding the nonequilibrium plasma two-dimensionally on a flat cathode allows for extended area light-sources, including excimer lamps. The spectral range of these lamps reaches from the visible into the vacuum ultraviolet, down to wavelengths of 75 nm for helium excimer radiation. Highest efficiencies of 6-9% were obtained for xenon excimers when the discharge was operated dc, and 20% when operated in a nanosecond pulsed mode. Besides excimer radiation, microdischarges have also been shown to emit intense line radiation in the vacuum ultraviolet when noble gases with small admixtures of hydrogen and oxygen were used. In this paper, we discuss basic properties of several types of high-pressure microplasmas, focusing on their dc and pulsed dc operation, followed by an overview of the experimental and modeling results relevant for their use as ultraviolet light sources. The prospect of developing microplasma lamps by forming arrays of microdischarges and possibly excimer lasers by operating microdischarges in series is briefly discussed.

Development of a soft X-ray pulse height analyzer on the J-TEXT tokamak

A soft X-ray pulse height analyzer has been designed and installed on the J-TEXT tokamak for measuring the electron temperature and possibly for monitoring the impurity content and concentration. A multi-channel analyzer, a set of amplifiers, and three silicon drift detectors constitute the detection system. An off-line analysis code was developed to analyze the raw data recorded by the system. The system can measure a minimum electron temperature of 400eV, and its routine operation provides electron temperature measurements at three different positions with a temporal resolution of 60ms and channel separation of 18cm. Line radiation from some moderate and high Z impurities are observable by the system. The results show that the intensity of line radiation from heavy impurity ions is inversely proportional to the plasma density under similar discharge conditions.

A New Method of Measuring the Magnetic Field in Hot Plasmas Using Helium Neutral Beam Injection

A new method is proposed to measure the magnetic field direction in hot plasmas using helium (He) neutral beam injection. The injected He beam is ionized by collisions with field electrons, and the ionized He beam atoms emit line radiation during their gyromotion with their rotational axis in the direction of the magnetic field. The direction of that axis can be determined locally from the Doppler width of the line radiation in the region along the beam path. The current intensity and energy of the injected He beam necessary to obtain reasonable intensity of line radiation from He+ ions are estimated. This estimation includes the effect of ionization from the metastable state of the He beam atoms and takes the 468.6 nm line radiation from He+ ions as an example. It is shown that the radiation intensity and line broadening width obtained using a He neutral beam with energy of 1 keV and current of 10 mA - 100 mA are sufficient for spectral measurement in typical reversed field pinches. It is also shown that the beam with energy of 10 keV and current of 0.1 - 1 A is sufficient in medium sized tokamaks.

The simulation of the processes of formation and decay of neutral particles in DC discharge plasma in an argon-oxygen mixture

Results are given of calculations of concentrations of fundamental neutral particles in the positive column of a dc discharge in an argon-oxygen mixture. The calculations are based on simultaneous solution of Boltzmann equation, vibrational kinetic equations for the ground state of O2 molecule, and chemical kinetic equations for the ground and excited states of O2 molecules and Ar and O atoms with the experimentally determined value of reduced intensity of electric field E/N. The results are compared with measured values of radiation intensities of lines of 811.5 nm (Ar) and 845 nm (OI) and of atmospheric band O2(b 1Σ g + → X 3Σ g − , 0-0).

Line radiation effects in laboratory and astrophysical plasmas

Theoretical enhancement of line radiation above the optically thin limit has been previously noted to occur in solar and stellar coronal plasmas, but presented without clear physical explanation. Here, we give an analysis of the angular dependence of these radiative transfer effects, which explain the previously calculated but poorly understood line radiation intensity enhancements. There are two important ramifications of this analysis: firstly, it provides a reason for the indeterminate status of opacity in relation to the coronal lines of distant stellar sources—hence potentially solving an important problem in astrophysics; secondly, it provides the opportunity to derive geometric information from the spectrum of a spatially unresolvable stellar object. We discuss the potential for observation of such opacity enhancement effects in laser plasmas, and present a feasibility study for experiments of this type.

Investigation of the parameters of a nonstationary arc spot on a copper cathode by the thermospectroscopic method. II. Dynamics of movement of the spot

Indirect data on the features of the dynamics of a cathode spot in different erosion regimes have been obtained by investigation of the fluctuations of the intensity of radiation from the arc of the 5218 A CuI copper spectral line modulated by the rotational frequency in a magnetic field. It has been revealed that the velocity of the cathode spot in the regime of intense radiation of this line in macroerosion is always lower than that in the regime of weak radiation in microerosion, whereas the variance of its distribution is, conversely, higher. A hypothesis for the relationship between the line-radiation intensity and the occurrence of a cathode copper-vapor jet affecting the mobility and dynamics of the spot and, in terms of them, the erosion has been proposed.

Enhancement of Optically Thick to Thin Line Intensities in Solar and Stellar Coronal Plasmas through Radiative Transfer Effects: An Angularly Resolved Study

An analysis of radiative transfer effects present in the Fe XV ion stage of solar and stellar coronal plasmas provides a general explanation of line radiation intensity enhancement above the optically thin limit. Full linearization radiation transfer is compared with the escape factor method and found to be in good agreement at the lower column densities. An angular study of the enhancement shows that symmetry factors are of great importance. This gives a possible reason for the indeterminate status of opacity in relation to coronal lines of distant stellar sources, where only emission integrated across the whole surface is detected.

A capillary discharge plasma source of intense VUV radiation

The results of investigation of a capillary discharge plasma, used as a source of intense VUV radiation and soft X-rays, are presented. The plasma was generated during the discharge of low-inductance condensers in a gas-filled ceramic capillary. Intense line radiation was observed in a broad spectral range (30-400 Å) in various gases (CO2, Ne, Ar, Kr, Xe). The absolute radiation yield for the xenon discharge was ~5 mJ (2π sr)-1 pulse-1 within a spectral band of width 9 Å at 135 Å. Such a radiation source can be used for various practical applications, such as EUV projection lithography, microscopy of biological objects in a 'water window', reflectometry, etc.

Plasma Spectroscopy at the Gol-3 Facility

A set of diagnostics for plasma spectroscopy was developed for multimiror trap GOL-3. It includes survey spectrometer with spatial resolution and the high spectral resolution complex for line shape analysis. The systems allow recording waveforms of plasma radiation with spectral resolution of 0.01 nm and measure spatial distribution of line radiation intensity (simultaneously in π and σ components).Analysis of radiation spectra was used for investigation of impurities structure and dynamics. Precise measurements of spectral line shape were used for finding the electron density and ion temperature from a line broadening. Description of the equipment and experimental technique as well the recent results are presented in the paper.

Comparative study of x-ray sources characterizing x-ray instrumentation

A study of x-ray sources for the purpose of characterizing x-ray instrumentation is presented. Specifically, in the soft x-ray wavelength region, we compare a proton-induced x-ray emission (PIXE) source to a conventional electron-beam x-ray source, and to a radioactive α fluorescence x-ray source. We find that PIXE has intense line radiation with respect to background continuum [C. K. Li et al., Rev. Sci. Instrum. 63, 4843 (1992)]. This desirable feature, as well as others, will make PIXE potentially a useful tool for characterizing x-ray detectors, optics, and filter.

Fluorescence in Mg IX emission at 48.340 Å from Mg pinch plasmas photopumped by Al XromanI line radiation at 48.338.

Resonant photopumping of Be-like Mg ix ions by Li-like Al xi line radiation has been studied in pulsed-power-driven plasmas as a possible approach to achieve laser action in the extreme-ultraviolet wavelength region. An Al x-pinch or z-pinch plasma imploded by a 0.5-TW pulsed power generator produced intense line radiation at 48.338 \AA{}. A separate Mg z-pinch plasma, driven by the same pulsed power generator, was created in parallel with 1 cm separating the two plasmas. Evidence for fluorescence (resonant scattering) was the appearance of 48.340-\AA{} resonance line emission from the 4p level of Mg ix ions due to photopumping by the Al xi line radiation at 48.338 \AA{}. Fluorescence may also have been observed on the Mg viii line at 52.395 \AA{}, photopumped by Al xi line radiation at 52.446 \AA{}. Both Al and Mg plasmas were characterized in the experiments. Improvements to the pump geometry required to achieve gain on the Mg ix line at 228 \AA{} are also discussed.

Electron density profile determination by means of laser blow-off injected neutral beam

This paper is devoted to the experimental and theoretical studies of the determination of the electron density profiles by means of laser blow-off neutrals. For the determination of the density profile the time and spatial distributions of the spectral line radiation intensity of the injected neutrals are used. The method is compared to other previously proposed methods and the advantages and disadvantages of the different methods are discussed. The result of the comparison is that our method gives the most reliable result with the highest temporal resolution for the density profile of the edge plasma. The only disadvantage is the need of careful calibration of the sensitivity of the spatial channels. The advantage is the ability of the method as a standard diagnostic.

A simple method for determination of electron density profiles in the plasma boundary layer

Abstract A novel method based on the injection of sodium atoms by the laser blow-off technique is proposed to determine the electron density profile in the plasma boundary at a given moment of the injection. For this purpose the radial and temporal distributions of the light intensity of line radiation of the injected neutrals have been measured. A simple model is presented to simulate the penetration of injected atoms into the edge plasma of the MT-IM tokamak. The model calculates the light intensity of line radiation of the neutrals. The calculated and measured radial profiles of the light intensity are compared at a given moment and an iterative process is given to obtain the electron density profile.

Description of neutral gas in a divertor under conditions of strong interaction with plasma

A model for hydrogen neutral gas description in a tokamak divertor is proposed. The model includes hydrodynamic equations for cold neutrals and a kinetic equation for the hot atoms entering the gas from the plasma layer. The results of the gas parameter calculation are presented for the experimental conditions prevailing in the DITE tokamak. An explanation is given for the experimental observation that the D α line radiation intensity increases more slowly than the gas pressure. The gas target efficiency in a reactor scale divertor is calculated.

Temporal evolution of the decaying spheromak in the CTCC-I experiment

In the CTCC-I spheromak experiment, after low-Z impurities have been suppressed by titanium coating on the inner surface of the flux conserver, MHD activity increases to the point that instabilities are present in every discharge at some time during the decay process. Most of the instabilities occur intermittently, as evidenced by the O V line radiation intensity which rises gradually and then drops abruptly. In some experiments, a conducting pole is inserted along the symmetry axis to increase the magnetic shear of the configuration. This conducting pole effectively suppresses a destructive instability, but other MHD instabilities are still present. Magnetic field measurements indicate that the occurrence of the instability is correlated with a relaxation process during which the peaked current profile at the magnetic axis is flattened by the MHD instability. An estimate of the energy loss during the subsequent relaxation process is given.

6209. A high-current hollow cathode as a source of intense line radiation in the VUV

In the present work samples of W and graphite were exposed in the C2H2 plasma for modelling the co-deposition process in a tokomak divertor. The energy of C2H2 ions, bombarding the surface was 300 eV. This means that the H+-ion energy was lower than the threshold energy for W and C sputtering. Carbon co-deposited layers with globular structure similar to that obtained in tokamaks on W and C were produced. The structure of co-deposited films on W varied from uniformly smooth under low irradiation doses (⩽1×1023 m−2) to a globular one under high doses (1024 m−2). Films with a globular structure appear on graphite already at a dose of 2×1023 m−2. The globular film production occurs by the appearance of separate small globules and by a gradual increase in their density and size. The film density is equal to 0.52 and 0.79 of that for crystalline graphite for the homogeneous structure and for the globular one, respectively. The integral H content in the co-deposited films is reduced with an increase in the globular structure fraction on the W surface from 7.2×1021 to 3.2×1021 m−2 for a dose increase from 1×1023 to 1×1024 m−2. Under simultaneous irradiation of W and C by C2H2 ions mixed (W+C) layers, 500 nm thick, were produced on W and C surfaces. The integral hydrogen content in the (W+C) film on graphite is 2.3 times higher than the H content in the mixed layer on W.

A high-current hollow cathode as a source of intense line radiation in the VUV

The VUV line emission of a high-current DC hollow cathode was investigated in the wavelength region 10 nm to 100 nm. Spectra of quadruply ionised atoms could be observed. The radiance in the Al IV lines at 13 nm and 16 nm and in the He II Lyman-series was determined by a comparison with the spectral concentration of radiant intensity of the synchrotron radiation emitted by the electron storage ring BESSY. The authors found the radiance of the lines to be reproducible within +or-25%.