D2 Emission Research Articles

Experimental investigation of the Cs behavior in the cesiated H- ion source during high power long beam operation.

The behavior of the Cesium (Cs) in Cs-seeded negative ion sources has been investigated experimentally under the beam accelerations of up to 0.5 MeV. The pulse length was extended to 100 s to catch the precise variations in the Cs D2 emission, discharge power, negative ion current, and temperatures in the ion source. The variations of the negative ions were estimated by the beam current and the heat loads in the accelerator. This experiment shows that the buildup of temperature in the chamber walls lead to the evaporation of deposited Cs to enter the plasma region and influenced H- ion production. The H- ion beams were stably sustained by reducing the temperature rise of the chamber wall below 50 °C. A stable long pulse beam could be achieved through the temperature control of the surfaces inside the source chamber walls.

Observation of deuterium molecule emission spectra under an active feedback control of H-mod plasma divertor detachment experiment on the EAST tokamak**Project supported by the National Natural Science Foundation of China (Grant No. 11805234).

Based on neon gas puffing, an active feedback control of H-mod plasma divertor detachment experiment was successfully operated on the EAST tokamak. During the feedback control discharge, the plasma was detached by puffing neon gas and the strike point splitting phenomenon on divertor target was also clearly observed by divertor probes diagnostic. In boundary region, many neutral particle processes (atom and molecule) were happened and accompanied by their emission spectra under the detachment discharge. By studying these emission spectra, it is helpful for us to understand the role of atoms and molecules in boundary recycling, which is important for studying the physical mechanism of divertor detachment. For the Fulcher-α system (, D2 emission spectra in the range from 601 nm to 606 nm were observed, identified and fitted in the detachment experiment for the first time on the EAST, and the spectra in the Q(0–0) band ( in the Q branch of the Fulcher-α system were used for detailed analysis to acquire the boundary region temperature Te (below 5 eV), which could not be provided very well by other diagnostics on the EAST. An electronic version deuterium molecular spectral line database was established to identify the spectral lines and a multi-peak fitting program was developed to fit and analyze the observed spectra.

Imaging divertor strike point splitting in RMP ELM suppression experiments in the DIII-D tokamak

Fast visible imaging of the lower divertor from above is used to study the structure and dynamics of lobes induced by resonant magnetic perturbations (RMPs) in Edge-Localized Mode (ELM) suppression experiments in DIII-D. The best compromise between the amount of light and sharp imaging was obtained using emission at 601 nm from Fulcher band molecular deuterium. Multiple spatially resolved peaks in the D2 emission, taken as a proxy for the particle flux, are readily resolved during RMPs, in contrast to the heat flux measured by infrared cameras, which shows little spatial structure in ITER-like conditions. The 25 mm objective lens provides high spatial resolution (2-4 mm/pixel) from the centerpost to the outer shelf over 40° toroidally that overlaps the field of view of the IRTV that measures the divertor heat flux, allowing direct comparison in non-axisymmetric discharges. The image is coupled to a Phantom 7.3 camera using a Schott wound fiber bundle, providing high temporal resolution that allows the lobe dynamics to be resolved between ELMs and across ELM suppression onset. These measurements are used to study the heat and particle flux in 3D magnetic fields and to validate models for the plasma response to RMPs.

Evidence for two distinct defect related luminescence features in monolayer MoS2

Apart from the defect related emission peak which lies ∼100 meV below the A exciton/trion peak and is labeled D1 here, this study shows that there is another distinct feature D2 lying ∼200 meV below A in the photoluminescence spectrum of the exfoliated monolayer MoS2 on SiO2/Si substrates. The D2 feature is explicitly resolved at low temperature only in few samples. Both D1 and D2 do not show circular polarization anisotropy for 633 nm excitation. Both decay with the increase in temperature in a seemingly activated manner with similar activation energy of ∼50 meV, but D1 decays earlier and therefore D2 dominates at high temperature in all samples. Annealing in vacuum increases both D1 and D2 emission intensities while annealing under sulfur vapour decreases them. Comparison with reported theoretical studies on defects in monolayer MoS2 suggests that these two emissions possibly involve excitons bound to single and double sulphur vacancies, the latter binding excitons more strongly.

Satellite line mapping in Eu3+–Ce3+ and Pr3+–Ce3+ codoped Y2SiO5

In this work we perform a high-resolution spectroscopic investigation of Eu3+–Ce3+ and Pr3+–Ce3+ codoped Y2SiO5 crystals. Satellite line spectra were recorded at low temperatures around the Eu3+:7F0→5D0 and the Pr3+:3H4→1D2 transitions. It is observed that the incorporation of Ce3+ as a codopant notably changes the Eu3+ and Pr3+ satellite line patterns. Satellite lines measured in singly doped Eu3+:Y2SiO5 were found at the same spectral positions in Eu3+–Ce3+ codoped crystals. These coincident lines were concluded to be due to pairs of Eu3+ ions. Extra satellite lines appeared in the codoped crystals, which were assigned to Ce3+ related structures such as Ce3+–Eu3+ pairs. The analysis of the Pr3+ satellite line spectra presents further challenges. Satellite lines associated to Pr3+ pairs show weaker intensity, presumably due to the efficient quenching of the Pr3+1D2 emission through cross-relaxation paths (1D2→1G4; 3H4→3F4). The investigation of the Eu3+ and Pr3+ satellite line patterns in Y2SiO5 is particularly interesting for their exploitation in rare-earth based quantum computation schemes.

Study of physical and chemical assisted physical sputtering of beryllium in the JET ITER-like wall

The effective sputtering yield of Be was determined in situ by emission spectroscopy of low ionizing Be as function of the deuteron impact energy (Ein = 25–175 eV) and Be surface temperature (Tsurf = 200 °C–520 °C) in limiter discharges carried out in the JET tokamak. Be self sputtering dominates the erosion at high impact energies (Ein > 150 eV) and causes far beyond 1. drops to low values, below 4.5%, at the accessible lowest impact energy (Ein ≃ 25 eV) achievable in limiter configuration. At medium impact energies, Ein = 75 eV, two contributors to the measured of 9% were identified: two third of the eroded Be originates from bare physical sputtering and one third from chemical assisted physical sputtering . The later mechanism has been clearly identified by the appearance of BeD A–X emission and quantified in cause of a temperature dependence at which the BeD practically vanishes at highest observed Be limiter temperatures. The recorded Tsurf dependence, obtained in a series of 34 identical discharges with ratch-up of Tsurf by plasma impact and inertial cooling after the discharge, revealed that the reduction of BeD is correlated with an increase of D2 emission. The release mechanism of deuterium in the Be interaction layer is exchanged under otherwise constant recycling flux conditions at the limiter.The reduction of with Tsurf is also correlated to the reduction of the Be content in the core plasma providing information on the total source strength and Be screening. The chemical assisted physical sputtering, always present at the nominal limiter pre-heating temperature of Tsurf = 200 °C, is associated with an additional sputtering channel with respect to ordinary physical sputtering which is surface temperature independent. These JET experiments in limiter configuration are used to benchmark the ERO code and verify ITER first wall erosion prediction. The ERO code overestimates the observed Be sputtering in JET by a factor of about 2.5 which can be transferred to ITER predictions and prolong the expected lifetime of first wall elements.

High‐resolution spectroscopy of the lunar sodium exosphere

AbstractWe have applied high‐resolution Fabry‐Perot spectroscopy to the study of the lunar sodium exosphere for the study of exospheric effective temperature and velocity variations. Observing from the National Solar Observatory McMath‐Pierce Telescope, we used a dual‐etalon Fabry‐Perot spectrometer with a resolving power of 180,000 to measure line widths and Doppler shifts of the sodium D2 (5889.95 Å) emission line. Our field of view was 360 km, and measurements were made in equatorial and polar regions from 500 km to 3500 km off the limb. Data were obtained from full moon to 3 days following full moon (waning phase) in March 2009. Measured Doppler line widths within 1100 km of the sunlit east and south lunar limbs for observations between 5 and 40° lunar phase imply effective temperatures ranging between 3260 ± 190 and 1000 ± 135 K. Preliminary line center analysis indicates velocity displacements between different locations off the lunar limb ranging between 100 and 600 m/s from the lunar rest velocity with a precision of ±20 to ±50 m/s depending on brightness. Based on the success of these exploratory observations, an extensive program has been initiated that is expected to constrain lunar atmospheric and surface‐process modeling and help quantify source and escape mechanisms.

Short‐term variations of Mercury's Na exosphere observed with very high spectral resolution

Short time variations of Mercury's exosphere cannot be tracked easily from ground based observatories because of the difficulty of distinguishing them from Earth atmospheric effects. On July 13th 2008, using THEMIS solar telescope, we were able to simultaneously measure brightness, Doppler shift and width of the exospheric sodium D2 emission line during half a day with a resolving power of ∼370,000. Mercury's exosphere displayed an emission brightness peak in the Northern hemisphere which vanished in few hours and a more persistent Southern Hemispheric peak. The bulk Doppler shift of the exosphere suggests a period of strong escape from Mercury. The global changes of the Doppler shift and of the Doppler width suggest that a cloud of sodium atoms ejected before or at the beginning of our sequence of observations passed through THEMIS field of view moving anti‐sunward. A preferentially southern ejection of sodium atoms leading to the observed persistent southern emission peak is consistent with the orientation of the Interplanetary Magnetic Field during that period.

Comet McNaught C/2006 P1: observation of the sodium emission by the solar telescope THEMIS

Comet McNaught C/2006 P1 was the brightest comet of the last forty years when reaching its perihelion at an heliocentric distance of 0.17 AU. Two days before this perihelion, at an heliocentric distance of 0.2 AU, Themis, a French-Italian solar telescope in the Canary Islands, Spain, observed the Comet sodium emission of McNaught. The measured maximum sodium brightness of the D2 emission line peaked at 900 Mega-Rayleigh. The spatial distribution of the sodium emission with respect to the nucleus of the comet is in agreement with previous observations. It displays a clear sunward-tailward asymmetry that suggests a dichotomy of the sodium sources between a source close to the nucleus and an extended source most probably corresponding to the dust tail. The spatial distribution along the slit of the width and speed of the Doppler Na distribution also suggests such a dichotomy. The sodium ejection rate inferred from this observation agrees with the value of the ejection rate extrapolated from comet Hale-Bopp, taking into account the heliocentric distance of comet McNaught and its significantly larger dust release. If we suppose a similar concentration of sodium atoms in both comets, this observation suggests that the sodium ejection rate from comets McNaught and Hale-Bopp is proportional to the solar flux. Therefore the most probable ejection mechanisms are photo-sputtering, solar wind sputtering, or cometary ion sputtering, and not thermal desorption.

Attempt to identify a source mechanism of Mercury’s sodium exosphere by a spectrometer using Fabry–Perot etalon

The Mercury’s Sodium Atmosphere Spectral Imager (MSASI) on BepiColombo (BC) will address a range of fundamental scientific questions pertaining to Mercury’s exosphere. The measurements will provide new information on regolith–exosphere–magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral range around sodium D2 emission (589 nm). A tandem Fabry–Perot etalon is used to achieve a compact design. We presents a design of the spectral analyzer using Fabry–Perot interferometer. We conclude that: (1) The MSASI optical design is practical and can be implemented without new or critical technology developments; (2) The thermally-tuned etalon design is based on concepts, designs and materials that have good space heritage.

Observation of Mercury's sodium exosphere by MSASI in the BepiColombo mission

The Mercury's sodium atmosphere spectral imager (MSASI) on BepiColombo (BC) will address a range of fundamental scientific questions pertaining to Mercury's exosphere. The measurements will provide new information on regolith–exosphere–magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral range around sodium D2 emission (589 nm). A tandem Fabry–Perot etalon is used to achieve a compact design. A one-degree-of-freedom scanning mirror is employed to obtain full-disk images of the planet. This paper presents an overview of the MSASI and the design of its spectral analyzer, which uses a Fabry–Perot interferometer. We conclude that: (1) The MSASI optical design is practical and can be implemented without new or critical technology developments. (2) The thermally tuned etalon design is based on concepts, designs and materials that have good space heritage. (3) The MSASI instrument achieves a high SNR ( > 10 ) in the range of 2k–10 MRayleigh.

Spectroscopic measurement of atomic and molecular deuterium fluxes in the DIII-D plasma edge

Molecular deuterium fluxes into the edge of deuterium-fuelled L-mode discharges are measured using passive visible spectroscopy of D2 emission lines. Comparison with the atomic deuterium influx measured using Dα emission suggests that a significant fraction of the plasma edge fuelling from the walls is in the form of D2. Molecular deuterium flux is observed in both the divertor and main chamber regions but is roughly a factor 100 smaller near the inner main chamber wall and roughly a factor 1000 smaller near the outer main chamber wall, when compared with the divertor region. Very high levels of molecular D2 excitation are measured, with ground state D2 rotational population temperatures Trot up to 10 000 K and vibrational population temperatures Tvib up to 30 000 K. Comparisons between rotational population temperatures and the local electron density suggest that Trot can be used as a reasonably good indicator of electron density in the D2 line emission region. In recombining, detached divertor operation, estimates of the enhanced volume recombination rate due to the presence of vibrationally-excited D2 suggest that the effect of molecular-assisted volume recombination could be comparable in magnitude to that of normal D+ volume recombination (EIR).

Spin-exchange optical pumping of high-density xenon-129

Gas mixtures with high xenon densities are explored for continuous flow spin-exchange optical pumping. It is shown that the Xe-NMR129 signal increases significantly with increasing xenon partial pressures up to about 200 kPa, despite a decreasing spin-polarization. Comparison of the rubidium infrared D2 emission with the xenon polarization demonstrates that radiation quenching by molecular nitrogen is of no substantial benefit for the pumping process at xenon pressures above 100 kPa. This reflects a diminished importance of spin-depolarization by radiation trapping due to the increased significance of spin-relaxation by rubidium-xenon collisions at high xenon densities. A quantitative expression for this effect is provided.

Characteristics of Chlorine and Carbon Flow in Two Municipal Waste Incinerators in Taiwan

Characteristics of chlorine and carbon flow at two municipal solid waste incinerators (MWIs) equipped with different air pollution control devices in Taiwan are investigated based on sampling/analysis and system operating data. The distributions of chlorine and carbon at various locations were evaluated based on the mass concentrations and emission rates. The removal efficiencies of HCl are 88.3 and 94.1% at MWI-A and MWI-B, respectively. Approximately 60% of the chlorinated compounds (expressed as chlorine) from municipal solid waste (MSW) at both MWIs exists in particulate form after incineration and is captured by the baghouse or electrostatic precipitator. The rest, 30‰ of the chlorine, is removed with bottom ash and wet scrubbing liquid or cyclone ash discharge at both MWIs. The results indicate that approximately 98% of the carbonaceous compounds contained in MSW is converted to CO\d2 and emitted from the stack at both MWIs due to good incineration efficiency. CO\d2 emission factors are 845 and 816 kg/ton waste for MWI-A and MWI-B, respectively. The mass percentages of chlorine and carbon in the municipal solid waste are then back-computed. The chlorine contents are 0.53 and 0.72% whereas the carbon contents of MSW are back-calculated as 23.5 and 22.7% for MWI-A and MWI-B, respectively.

The sodium tail of Mercury

Abstract— Mercury is difficult to observe because it is so close to the Sun. However, when the angle of the ecliptic is near maximum in the northern hemisphere, and Mercury is near its greatest eastern elongation, it can be seen against the western sky for about a half hour after sunset. During these times, we were able to map sodium D2 emission streaming from the planet, forming a long comet‐like tail. On 2001 May 26 (U.T.) we mapped the tail downstream to a distance of ˜40 000 km. Sodium velocities in the tail increased to ˜11 km s−1 at 40 000 km as the result of radiation pressure acceleration. On 2000 June 5 (U.T.) we mapped the cross‐sectional extent of the tail at a distance of ˜17 500 km downstream. At this distance, the half‐power full‐width of the emission was ˜20 000 km. We estimated the transverse velocity of sodium in the tail to range from 2 to 4 km s−1. The velocities we observed imply source velocities from the planet surface of the order of 5 km s−1, or 4 eV. Particle sputtering is a likely candidate for production of sodium atoms at these velocities. The total flux of sodium in the tail was ˜1 times 1023 atoms s−1, which corresponds to 1 to 10% of the estimated total production rate of sodium on the planet.

Triplet states of rubidium dimers on helium nanodroplets

Rubidium dimers in their 1 3Σu+ states are formed through collisions of Rb atoms that have been deposited on the surface of helium nanodroplets. Visible absorption spectra between 550 and 690 nm were probed by laser induced fluorescence and emission spectra measured for selected excitation wavelengths. A system absorbing around 595 nm with its emission to the ground state centered at 604 nm is identified as the Rb2 2 3Πg–1 3Σu+ transition. A broad unstructured band is measured near 667 nm. Following its excitation, two fluorescence channels are detected, one representing the 1 1Πu–1 1Σg+ (Rb2 B–X) transition and the other leading to atomic Rb D1 and D2 emission. Various explanations of this observation are discussed, each of which requires the presence of a third rubidium atom on the droplet. All spectra have been modeled using energy potentials from previous theoretical work and the results are compared. Relaxation after laser excitation experiences various bottlenecks, which show up in the vibrational emission intensities and may be interpreted in terms of intramolecular interactions.

Sodium D2 line profiles: clues to the temperature structure of Mercury’s exosphere

The velocity distribution of atoms in an exosphere can be used to constrain source and loss processes. The velocity distribution itself can be constrained by observing the line profile of an atmospheric emission line. The only atomic species known to exist in the Hermean exosphere that has a strong enough resonance transition in the visible spectrum that its line profile can be observed from the ground with existing instruments is sodium. Line profiles of the sodium D2 emission (5889 A) were obtained at two facilities. On 29 and 30 May 1997, we obtained line profiles with the 107 inch telescope at The McDonald Observatory at coude focus. On 6 January 1998, we obtained line profiles at the Anglo–Australian telescope. The line profiles show that the sodium in Mercury’s atmosphere is at least 700 K hotter than the surface temperature throughout the atmosphere. This implies that the interaction of the Na atoms with the surface is governed by energetic processes.

Observations of Sodium in the Lunar Atmosphere during International Lunar Atmosphere Week, 1995

We report results of a part of an organized effort of five observing groups to simultaneously observe sodium in the lunar atmosphere. International Lunar Atmosphere Week spanned the week of September 15–22, 1995. Of the seven nights, we experienced four nights with good viewing conditions. We used the Mt. Lemmon Lunar Coronagraph (MLLC) and DARRK spectrograph. Both are especially designed for lunar atmospheric measurements from the surface extending to an altitude of approximately 1 lunar radius or ∼1700 km (860 km geopotential height). Emission rates for Na were compatible with those previously reported for relatively large phase angles (96° to 129°) with the average total of D2 and D1 emission rate ∼6.9 kRayleigh. A thermal component was observed only on the night of September 17, when the solar zenith angle at the limb was only 6°. We observed a factor of ∼2 greater column abundances over the north pole than over the sunlit equatorial limb on September 18 while on September 19, the equatorial bright limb column abundance was a factor of ∼5 higher than the north polar. Apparent geopotential scale heights varied from 279 to 435 km, indicating an extended atmosphere. If the scale heights are represented by a temperature, values are 985 to 1470 K. The data set appears to support the idea that the dominant source during this period was meteoritic impact volatilization.

Doppler-free high resolution laser spectroscopy of the Cs2 D 1Σ+u state and the predissociation

A Doppler-free polarization spectrum of the D 1Σ+u(v′,J′)–X 1Σ+g(v″,J″) transition has been observed, and the molecular constants of the D 1Σ+u state were determined. A remarkable variation of the vibrational spacing ΔGv with v′, and large deviations of ΔGv from the fitted ΔGv curve for v′≳35 were analyzed. The potential curve of the perturbing state, which was identified as the bound (2)3Πu state, was estimated. By using an experimental setup where a collimated cesium beam is crossed at right angles by the laser beam, we measured the excitation spectra by monitoring separately the molecular fluorescence and the D2 or D1 atomic emission. We found that a predissociation of the D 1Σ+u state occurred for v′≳20, and the probability of predissociation increased with v′. The measured v′ and J′ dependence of the linewidth Γ showed a significant increase for v′≳25. The predissociation of the D 1Σ+u state is caused by a combination of spin–orbit interaction between the D 1Σ+u(v′J′) and (2)3Π0u(e vJ′) levels, and the L-uncoupling interaction between the bound (2)3Π0u(e vJ′) and dissociative c 3Σ+u(N = J′J′) levels.

Electronic behaviour of decorated stacking faults in silicon

Oxygen-induced stacking faults have been generated at a concentration of about 10 7 cm −2 in n-type silicon. The photoluminescence, electron capture and electron emission from clean stacking faults and from faults decorated with gold and platinum have been investigated. In contrast to previously published work on extended defects in plastically deformed silicon we observe a simple photoluminescence spectrum dominated by the D1 line with a weak D2 emission; other D lines are absent. Using deep level transient spectroscopy we observed electron traps with an activation energy of 415 meV which vary linearly in concentration with the stacking fault density. This activation energy increases when either gold or platinum is diffused into the sample, tending to move the state towards midgap where it acts as a powerful generation centre. The capture properties of the stacking-fault-related deep state are also modified by decoration. The behaviour is almost point defect like for “clean” stacking faults but capture tends towards the previously reported logarithmic behaviour in the decorated case.