Hα Line Intensity Research Articles

Application of emission spectroscopy in plasma-assisted NH3/air combustion using nanosecond pulsed discharge

This work investigates the effects of atmospheric-pressure nanosecond (ns) pulsed plasma discharges on NH3/air flames using optical emission spectroscopy (OES). Firstly, spatially-resolved OES in the 200–800 nm range of NH3/air flames with and without discharges are presented to identify the plasma-induced excited species (such as N2* and H*). Then, time-resolved OES with ns timescale resolution are achieved to illustrate the discharge dynamics using a statistical imaging strategy, which is specifically designed to overcome the timing jitter of the discharge. From the time-resolved spectra of excited N2, the first and second emission events in NH3/air flames with a time interval of 80 ns are revealed, and each exhibits a profile with two exponential decays. Furthermore, spatial- and time-resolved rotational and vibrational temperatures are derived from the spectral fitting of N2(C→B) to quantify the thermal effects of ns plasmas, thus revealing the ultrafast and slow gas heating processes. In addition, the electron number density along the flame is obtained from the intense Hα line, which locally reaches up to 1 × 1017 cm−3. Besides, the spatial-resolved Hα line intensity suggests that the flame chemistry does not directly affect, but the discharge dominates the production of the atomic hydrogen. It provides insight into the kinetic effects of ns pulsed discharge on NH3 combustion enhancement.

LIBS plasma in atmospheric pressure argon, nitrogen and helium: Spatio-temporal distribution of plume emission and Hα linewidth

Laser Induced Breakdown Spectroscopy (LIBS) method is considered for assessing the retention of hydrogen isotopes in the ITER plasma-facing components during the maintenance breaks when the reactor is filled with near atmospheric pressure nitrogen or inert gas. At these conditions, the broadening of the spectral lines of hydrogen isotopes and the reduction of line intensities complicates the distinguishing of hydrogen isotopes. The aim of the present study was to investigate the effect of atmospheric pressure nitrogen, argon and helium ambient gas on the spatio-temporal distribution of the LIBS plasma plume emission and linewidths of Hα line, representing the hydrogen isotopes. Nd:YAG laser with 8 ns pulse width was used to ablate the molybdenum (Mo) target with hydrogen impurity. The development of the formed plasma plume was investigated by time and space-resolved emission spectra in the 20 nm range around the 656.28 nm Hα line. For all gases used in the experiments, the intensity and linewidth of Hα line decreased with the delay time between the laser pulse and the spectral registration. At the same linewidth values, the highest intensities were obtained in the helium atmosphere while the lowest intensity was obtained in nitrogen. According to spatially resolved spectral measurements, the Hα line was most intense near the Mo target while the Mo lines peaked farther away. In the case of the helium atmosphere, the plasma plume emission was observed at a longer distance from the target and it decayed faster than in argon and nitrogen atmospheres. According to these results, helium is the most beneficial ambient gas for hydrogen isotope detection by atmospheric pressure LIBS. The use of argon ambient gas may be required when LIBS is used for the simultaneous determination of fuel and He retention in the wall material.

Magnetic activity variability from Hα line intensive monitoring of two F-type stars with a hot Jupiter, τ Bootis A and υ Andromedae A

Abstract We report the results of intensive monitoring of the variability in the Hα line for two F-type stars, τ Boo and υ And, over the last four years 2019–2022, in order to investigate their stellar magnetic activity. The 4 yr Hα line intensity data taken with the 1.88 m reflector at the Okayama Branch Office, Subaru Telescope, shows the existence of a possible ∼123 d magnetic activity cycle for τ Boo. The result of the Hα variability as another tracer of the magnetic activity on the chromosphere is consistent with previous studies of the Ca ii H&K line and suggests that the magnetic activity cycle persists in τ Boo. For υ And, we suggest a quadratic long-term trend in the Hα variability. Meanwhile, the short-term monitoring shows no significant period corresponding to specific variations likely induced by their hot Jupiter in both cases (≈3.31 and 4.62 d, respectively). In this Hα observation, we could not find any signature of the star–planet magnetic interaction. It is speculated that the detected magnetic activity variability of the two F-type stars is related to the stellar intrinsic dynamo.

Laser induced breakdown spectroscopy for hydrogen detection in molybdenum at atmospheric pressure mixtures of argon and nitrogen

Present study investigated the effect of argon and nitrogen mixtures at atmospheric pressure on the hydrogen Hα line emission intensity during the Laser Induced Breakdown Spectroscopy (LIBS) measurements. LIBS is foreseen for the assessment of the fuel retention in ITER plasma facing components during the maintenance breaks when the reactor is filled with near atmospheric pressure nitrogen or dry air. The use of argon flow during LIBS measurements has shown to increase the LIBS signal at atmospheric conditions which aids the distinguishing of hydrogen isotopes. LIBS was used to ablate a small amount of molybdenum (Mo) target and the development of formed plasma plume was investigated by time-resolved emission spectra and photographs. Spectral measurements showed that the Hα line intensity and electron density decreased faster with the increased fraction of nitrogen in the background atmosphere. The electron temperature of created plasma was also lower in the nitrogen atmosphere. The spatial development of plasma plume was comparable in both argon and nitrogen atmospheres. According to these results, the reduction of Hα line intensity in the presence of nitrogen can be explained by higher fraction of energy consumption in dissociation and excitation processes of molecular gas and increased quenching of excited H states. Furthermore, the results demonstrate that a small amount of N2 impurities in Ar atmosphere does not have detrimental effect on LIBS measurements of hydrogen isotopes. Most of the local thermodynamic equilibrium (LTE) conditions required for the applicability of CF-LIBS were fulfilled in the time-window between 1-5 µs for Ar and 1-3 µs for N2 gas. One notable exception was the time-stability criterion for hydrogen atoms. The effect of this deviation from LTE on the applicability of CF-LIBS requires further studies.

Broadening and Redward Asymmetry of Hα Line Profiles Observed by LAMOST during a Stellar Flare on an M-type Star

Abstract Stellar flares are characterized by sudden enhancement of electromagnetic radiation in stellar atmospheres. So far, much of our understanding of stellar flares has come from photometric observations, from which plasma motions in flare regions could not be detected. From the spectroscopic data of LAMOST DR7, we have found one stellar flare that is characterized by an impulsive increase followed by a gradual decrease in the Hα line intensity on an M4-type star, and the total energy radiated through Hα is estimated to be of the order of 1033 erg. The Hα line appears to have a Voigt profile during the flare, which is likely caused by Stark pressure broadening due to the dramatic increase in electron density and/or opacity broadening due to the occurrence of strong nonthermal heating. Obvious enhancement has been identified in the red wing of the Hα line profile after the impulsive increase in the Hα line intensity. The red-wing enhancement corresponds to plasma moving away from the Earth at a velocity of 100–200 km s−1. According to our current knowledge of solar flares, this red-wing enhancement may originate from: (1) flare-driven coronal rain, (2) chromospheric condensation, or (3) a filament/prominence eruption either with nonradial backward propagation or with strong magnetic suppression. The total mass of the moving plasma is estimated to be of the order of 1015 kg.

X-Ray Spectral Shape Variation in Changing-look Seyfert Galaxy SDSS J155258+273728

Abstract We analyze the X-ray, optical, and mid-infrared data of a “changing-look” Seyfert galaxy SDSS J155258+273728 at z ≃ 0.086. Over a period of one decade (2009–2018), its broad Hα line intensity increased by a factor of ∼4. Meanwhile, the X-ray emission in 2014 as observed by Chandra was about five times brighter than that in 2010 by Suzaku, and the corresponding emissions in the V-band, mid-infrared W1 band brighten by ∼0.18, 0.32 mag, respectively. Moreover, the absorption in X-rays is moderate and stable, i.e., N H ∼ 10 21 cm − 2 , but the X-ray spectrum becomes harder in the 2014 Chandra bright state (i.e., photon index Γ = 1.52 − 0.06 + 0.06 ) than that of the 2010 Suzaku low state ( Γ = 2.03 − 0.21 + 0.22 ). With an Eddington ratio being lower than a few percent, the inner region of the accretion disk in SDSS J155258+273728 is likely a hot accretion flow. We then compile from literature the X-ray data of “changing-look” active galactic nuclei (AGNs), and find that they generally follow the well-established “V”-shaped correlation in AGNs, that is, above a critical turnover luminosity the X-ray spectra soften with the increasing luminosity, and below that luminosity the trend is reversed in the way of “harder when brighter.” This presents direct evidence that CL-AGNs have distinctive changes in not only the optical spectral type, but also the X-ray spectral shape. The similarity in the X-ray spectral evolution between CL-AGNs and black hole X-ray binaries indicates that the observed CL-AGNs phenomena may relate to the state transition in accretion physics.

Constraining Planetary Gas Accretion Rate from Hα Line Width and Intensity: Case of PDS 70 b and c

Abstract Recent observations of protoplanets embedded in circumstellar disks have shed light on the planet formation process. In particular, detection of hydrogen Balmer-line (Hα) emission gives direct constraints on late-stage accretion onto gas giants. Very recently Haffert et al. measured the spectral line widths, in addition to intensities, of emission from the two protoplanets orbiting PDS 70. Here, we study these protoplanets by applying radiation-hydrodynamic models of the shock-heated accretion flow onto protoplanets that Aoyama et al. have recently developed. As a result, we demonstrate that Hα line widths combined with intensities lead to narrowing down the possible ranges of the protoplanetary accretion rate and/or mass significantly. While the current spectral resolution is not high enough to derive a definite conclusion regarding their accretion process, high-resolution spectral imaging of growing protoplanets is highly promising.

Formation of Hydrogen Emission Lines in the Magnetospheres of Young Stars

The formation of hydrogen emission lines in the magnetospheres of young stars is considered. The magnetosphere is assumed to be formed by a dipolar magnetic field whose axis is aligned with the stellar rotation axis. The radiative transfer in spectral lines is considered in the Sobolev approximation by taking into account the nonlocal radiative coupling. The gas density and temperature distributions in the magnetosphere are taken to be the same as those in Hartmann et al. (1994). The results of our calculations of the Hα and Hβ line intensities and profiles are presented for the case of a slowly rotating star. We separately consider the magnetospheric models in which the infalling gas is heated by radiation from an accretion spot on the stellar surface and the case where the axis of the magnetosphere is tilted with respect to the stellar rotation axis. Rotational modulation of the spectral line profiles with the stellar rotation period is observed in the latter case.

Improving accuracy of Penning gauge spectroscopy for the determination of hydrogen isotope H/D ratios

Atomic spectral lines emitted from a Penning discharge are often used to quantify partial pressures and isotopes ratios in gases. To identify the potential of this method for thermal desorption studies, the hydrogen emission spectrum lines (Hα and Dα) were examined by an Alcatel Penning gauge. The hydrogen/deuterium pressures were measured by both a capacitive vacuum gauge and the Penning gauge. Different gas mixtures were produced by varying of hydrogen/deuterium flows. The Balmer-alpha lines intensities were recorded with help of a high etendue spectrometer coupled to the Penning gauge using relay optics together with fiber bundle and equipped with Peltier cooled CCD camera. Subsequent measurements using hydrogen and deuterium gases revealed for identical pressures in the range of 10−6–10−3mbar that the Hα line intensities are systematically higher the Dα line intensities by a factor of 1.28±0.01. This observation can be explained by the dissociative excitation of the molecular hydrogen by electron impact. In addition the Hα line intensity for the H2 gas having constant partial pressure is slightly increased with total gas mixture pressure. Taking into account of both effects essentially improves the accuracy of the determination of partial pressures and isotope H/D ratios.

High-rate growth of single crystal diamond in microwave plasma in CH4/H2 and CH4/H2/Ar gas mixtures in presence of intensive soot formation

The growth of single crystal diamond plates in a microwave plasma using H2-CH4 and H2-CH4-Ar gas mixtures in a broad range of methane concentration (2–15%) is studied. The growth rates up to 60μm/h in H2-CH4 mixtures and up to 105μm/h in Ar-H2-CH4 mixtures are achieved at high CH4 content, without adding nitrogen, still obtaining transparent crystals. The thermal conductivity k of the SCs in the temperature range of 220–420K is measured by a laser flash technique. High thermal conductivity k≈2300W/m⋅K at room temperature is found for the sample grown at low growth rate in H2-CH4, this value reducing to k≈2000W/mK for the material produced in high rate regime at 15% CH4. The spatial profiles of Hα and C2 line intensities in the plasma were determined with optical emission spectroscopy (OES). Soot formation at high CH4 contents is observed at the plasma border both for Ar-free and Ar-containing mixtures, the soot yield being roughly proportional to diamond growth rate. The soot temperature Ts, as measured with OES, is almost constant (3800±300K) in H2-CH4 mixtures over the all methane concentration range explored, while for Ar-containing plasma the Ts is even higher (4100–4200K) at [CH4]<10%, reducing, however, below 3800K in CH4-reach mixtures. Raman spectra of collected soot correspond to crystalline graphite with high density of defects. The estimated carbon conversion efficiency from CH4 precursor to the soot can exceed 10% and should be taken into account in overall carbon balance in the CVD process.

Connection between the appearance of γ-ray sources and Hα line impact linear polarization in the July 23, 2002 flare

During our spectropolarimetric observations of the 2B/4.8X flare on July 23, 2002, with the Large Solar Vacuum Telescope (LSVT), we detected impact linear polarization in the southern ribbon. The maximum polarization exceeded 10%. On the whole, the polarization was observed only for ~6 min out of almost 2 h of observations of this flare. At this time, the Hα line profiles had a deep central self-reversal. We have compared the LSVT observations with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) data, where the locations of γ-ray emission were obtained for the first time. A careful comparison has revealed that the effects in the Hα line were observed in a region <10″ located between two X-ray sources in the southern ribbon. According to the RHESSI data, a γ-ray source attributable to a beam of high-energy (~1 MeV) electrons was observed at the same place. The events in the corona and the upper chromosphere also coincide in time with the observed effects in the Hα line. The two X-ray sources are assumed to represent a common footpoint of the southern foot of the loop bifurcated due to the precipitation of high-energy electrons. It is suggested that the penetration of these electrons into the dense layers of the chromosphere could lead to impact polarization and a decrease of the Hα line intensity in the southern ribbon of the flare, in contrast to the northern ribbon where a typical hard X-ray source with an energy ~20–120 keV was observed; there were no self-reversal at the Hα line center and polarization.

Balmer Hα, Hβ and Hγ Spectral Lines Intensities in High-Power RF Hydrogen Plasmas

Hα (Balmer-alpha), Hβ (Balmer-beta) and Hγ (Balmer-gamma) spectral line intensities in atomic hydrogen plasma are investigated by using a high-power RF source. The intensities of the Hα, Hβ and Hγ spectral lines are detected by increasing the input power (0–6 kW) of ICPs (inductively coupled plasmas). With the increase of net input power, the intensity of Hα improves rapidly (0–2 kW), and then reaches its dynamic equilibrium; the intensities of Hβ can be divided into three processes: obvious increase (0–2 kW), rapid increase (2–4 kW), almost constant (4–6 kW); while the intensities of Hγ increase very slowly. The energy levels of the excited hydrogen atoms and the splitting energy levels produced by an obvious Stark effect play an important role in the results.

The broad line emission from the AGN 3C 390.3: complex broad-line region and perturbation in accretion disk

AbstractFrom 13-years of the spectral optical monitoring of a well-known broad-line radio galaxy 3C 390.3 we concluded that the geometry of the broad emission-line region is complex, while still the main part of the emission is coming from the accretion disk. Here we present part of the analysis of the broad Hα and Hβ emission lines, which are showing highly variable double-peaked profiles during the monitoring period (1995-2007), with the aim to probe the accretion disk properties. The disk-like geometry plays a dominant role, but the variability of Hα and Hβ line profiles and intensities shows a presence of an additional emission-line region, that has a different nature for different periods, e.g. in one period the observed variation can be well modeled if one assumes changes in position and size of the emitting disk along the accretion disk.

Studying instrumental linear polarization at the Large Solar Vacuum Telescope (LSVT)

Impact linear polarization in solar flares is studied with the Large Solar Vacuum Telescope (LSVT) using the spectral polarimetric method. This method makes it possible to minimize the effect of instrumental polarization with an error of up to 10−2 owing to the normalization of the spectral line intensity to the continuum spectrum intensity with negligible linear polarization. As a result, the Hα line intensity in two orthogonally polarized spectral stripes coincides in the absence of solar polarization. However, in the presence of linear polarization in a flare, the spectral polarimetric method does not rule out that the error can be present in determining the Stokes parameters Q and U because of their possible relative “leakage.” Linear instrumental polarization of LSVT has been performed using polaroid rotation before the major mirror. Twelve elements of a telescope matrix, characterizing linear polarization, have been determined. The usage of a matrix makes it possible to specify the observed Q and U values accurate to 10−3 of their magnitude.

Simulation of photosphere and chromosphere of two powerful solar flares (October 28, 2003 and September 1, 1990)

The spectra of two powerful flares with approximately the same intensities in the optical region but with different spectral features and power in other regions are studied. One of them is the unique flare which occurred on October 28, 2003, importance X17.2/4B, ranking third in magnitude among the recorded flares. Another occurred on September 1, 1990, 3B importance. The flares vary in the Balmer decrement. The flare of October 28, 2003, has a ratio of I(Hβ)/I(Hα) = 1.47. This is the largest value for solar flares ever observed. The flares also differ in magnitude of the D Na I lines emission: the emission of the flare of October 28, 2003, is substantially larger than that of the other flare. The chromosphere models of the flares are computed using the observed profiles of Balmer lines and D Na I lines. The satisfactory agreement of the calculated and observed profiles is obtained for the two-component models in which a hot component occupies 6% of the area. The hot component of the chromosphere model is characterized with the dense condensation available in the upper layers. For the flare of October 28, 2003, this condensation is located deeper and its substance concentration is greater than that for another flare. The Hα line intensity for the model hot component alone is approximately 30 and the continuous spectrum intensity is approximately 3% of the undisturbed level. The photosphere model is computed using the observed profiles of photosphere lines for the flare of October 28, 2003. It is found that very broad profiles of individual sigma-components of the Fe I λ 525.0 nm line may be only explained by the presence of magnetic fields having different directions. A great difference is detected between values of the magnetic field strength obtained in the splitting of sigma-components and those provided by simulation.

Neutral Transport Analysis in Plasma Edge Region of the GAMMA-10 Central-Cell

Based on the results of neutral transport simulation using cylindrical mesh-model, the effect of the plasma edge region was investigated in the GAMMA 10 central-cell. 3-dimensional geometry and neutral sources such as gas puffers, limiters, and neutral beam injection are precisely constructed in the mesh-model of the GAMMA 10 central-cell. From the neutral transport simulation in the case of each neutral source, 1/e decay lengths of Hα-line intensity (Hα decay length) along with z-axis were evaluated. It was found that Hα-line intensity calculated by the simulation of the gas puffer #3(GP#3) in mirror-throat region takes a broader profile than that of central-limiter and gas puffer #7(GP#7) around the central mid-plane region because the plasma density is low in mirror-throat and the neutral particles are given near the vacuum vessel, while the neutral particles in the central-limiter are given near the plasma core. The simulation results also revealed that the Hα-line intensity drastically decrease in the range with interior components. On the other hand, it was clarified that the Hα-line intensity in no interior component area takes a little reduction because of a large width in plasma edge region.

Study of impurity behaviour in ac plasma on the HT-7 tokamak

The 35-channel Hα (λ = 656.3 nm) line intensity and impurities behaviour of a 9-channel C III, 7-channel bremsstrahlung emission, single channel O II (λ = 441.5 nm) and O V (λ = 278.1 nm) diagnostics were investigated in ac discharges on the HT-7 tokamak. The data analysis identified that the intensity of multi-channel Hα emission and impurities emission of C III (λ = 464.7 nm), O II and O V for the negative current plasma are much lower than for the positive current plasma. Lower hybrid wave plays a different role for the co-driven and anti-driven directions during current transition in ac discharges. Therefore, the emission of C III, O II and Hα behaviours is very different when the current direction transits from positive to negative, and vice versa.

A new diagnostic of the plasma density profile near the edge transport barrier from measurements of the radial profile of the Hα line intensity

An edge transport barrier is now one of the most important subjects of controlled fusion research. The edge transport barrier is located in the plasma region where hydrogen atoms readily penetrate, so the intensity of the H(alpha) (D(alpha)) line is high enough. A new diagnostic method uses the well-known property of hydrogen atoms that the ratio of the ionization rate S(i) to the excitation rate S(v) for the H(alpha) line is nearly constant over a wide range of plasma temperatures and densities. An expression has been derived that relates the radial profiles of the plasma density and H(alpha) intensity. The use of charge coupled device detectors makes it possible to measure the radial profile of H(alpha) line intensity with a resolution approximately 0.1 cm; a high intensity of the H(alpha) line ensures a high time resolution approximately 1 ms. A high resolution is thus achieved for the density profile calculated from the H(alpha) intensity profile. The method was tested when studying the plasma density profile in the region of edge transport barrier in the L-2M stellarator. It has been shown that the density gradient varies during the barrier formation and that a fine structure of the density profile correlates with a character of the plasma transport near resonance magnetic flux surfaces.

Suppression and excitation of MHD activity with an electrically polarized electrode at the TCABR tokamak plasma edge

Two reproducible regimes of tokamak operation, with excitation or suppression of MHD activity can be obtained using a voltage-biased electrode inside the edge of the TCABR tokamak. The experiment was carried out adjusting the tokamak parameters to obtain two types of discharges: with strong or weak MHD activity, without biasing in both cases. The plasma current was adjusted to cover a range of safety factor from 2.9 up to 3.5, so that when biasing was applied the magnetic island (3,1) could interact with the edge barrier. The application of biasing in subsequent discharges of each type resulted in excitation or suppression of the MHD activity. The results show that the dominant modes are m = 2, n = 1 and m = 3, n = 1 for excitation and partial suppression, respectively. In both regimes a strong decrease in the radial electric field is detected with destruction of the transport barrier and of the improved confinement caused by different mechanisms. The measurements include temporal behaviour of edge transport, turbulence, poloidal electric and magnetic fields, edge density, radial electric fields and radial profile of Hα line intensity. The explanation of the excitation and suppression processes is discussed in the paper.

Investigation of Neutral Particles Using High Speed Camera and Monte-Carlo Simulation in the GAMMA 10 Central-Cell

Behavior of edge plasma and neutral particles are described based on visible measurement by using high-speed camera performed in the GAMMA 10 tandem mirror for the first time. In the central-cell midplane of GAMMA 10, two high-speed cameras (Ultima-SE, Photron Inc. and MEMRECAM fx-K4, NAC Inc.) were mounted and detailed time behavior of visible light emission from the plasma was investigated. In the standard plasma discharges heated by ion cyclotron range of frequency (ICRF) wave, a short gas puffing of hydrogen (3 ms) close to the central-cell midplane was carried out to illuminate the plasma periphery and the time evolution of visible light emission from the gas cloud was captured precisely. The time behavior of the emission cloud localized near the gas puff port was found to be similar to that of Hα line intensity measured nearby. The light emission on the central-cell limiter accompanied by central electron cyclotron heating (c-ECH) showed a rotation in the direction of the electron diamagnetic drift. the light emission also indicates another rotation mechanism, such as ExB drift at a plasma collapse. Fully three-dimensional neutral transport simulation using a Monte-Carlo code DEGAS is applied to gas puff imaging experiment and the simulation results qualitatively explained the experimental result.