Deuterium Flux Research Articles

Molecular dynamics simulation of the formation, growth and bursting of bubbles in tungsten exposed to high fluxes of low energy deuterium

Molecular dynamics simulations are carried out to investigate the formation, growth and bursting of bubbles in tungsten exposed to the irradiation of an extremely high deuterium flux. It is found that the bubbles form in the region near the location of the implanted ion distribution peaks, and that the effect of the substrate temperature on the bubble formation depth is negligible; it is also found that the percentage of deuterium that is found in D2 molecules increases as the bubble grows, and that the evolution of the bubble’s internal pressure is strongly associated with the properties of its surrounding structure. The simulations display the development of a dome-shaped structure at the tungsten surface during the bubble growth. The merging of two deuterium bubbles is also observed. The present simulations also show that the bubble bursts by generating a partially opened lid, which has already been observed in previous independent experiments.

Deuterium gas-driven permeation and subsequent retention in rolled tungsten foils

Experiments concerning deuterium gas-driven permeation through rolled tungsten foils in the temperature range of 850–950K and subsequent deuterium retention have been performed. The steady state permeation flux of deuterium is proportional to the square root of the driving pressure. The permeability of deuterium is in an order of 10−14molm−1s−1Pa−1/2 in this temperature range and the activation energy for permeation is 1.21eV. Measurements of diffusivity are significantly affected by the driving pressure, which can be well explained by a saturable-trap model. Thermal desorption spectra of samples feature a single deuterium release peak at about 873K. TMAP 4 modeling of this peak gives a detrapping energy of 1.70eV, which fits the dissociation enthalpy of deuterium desorbing from the inner wall of vacancy clusters or pores in tungsten.

Thermally Activated D2 Emission upon Decomposition of Thin Deuterofullerene Films on Au(111)

We have studied the formation and thermal properties of thin, deuterofullerene-containing films on Au(111) under ultrahigh vacuum conditions. The films were prepared in situ by exposure of predeposited C60 layers to a flux of atomic deuterium. With increasing deuterium dose, a D + C60 → C60Dx reaction front propagates through the fullerene film toward the gold surface. Heating the resulting deuterofullerene-containing films to >600 K leads to desorption of predominantly C60 and C60Dx. Interestingly, some D2 is also evolved while a significant fraction of the carbon initially deposited is left on the surface as nondesorbable residue. This is in contrast to analogous deuterofullerene-containing films prepared on graphite, which sublime completely but do not measurably evolve D2, suggesting that the gold surface can act as a catalyst for D2 formation. To explore this further, we have systematically studied (i) the thermal properties of C60/Au(111) reference films, (ii) the reaction of C60/Au(111) films with D atoms, and (iii) the heating-induced degradation of deuterofullerene-containing films on Au(111). In particular, we have recorded temperature-resolved mass spectra of the desorbing species (sublimation maps) as well as performed ultraviolet photoionization spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning tunneling microscopy measurements of the surfaces at various stages of study. We infer that heating deuterofullerene-containing films generates mobile deuterium atoms which can recombine to form molecular deuterium either at the gold surface or on fullerene oligomers in direct contact with it.

Visualization of deuterium flux and grain boundary diffusion in duplex stainless steel and Fe–30 % Ni alloy, using secondary ion mass spectrometry equipped with a Ga focused ion beam

Time of flight secondary ion mass spectrometry (TOF-SIMS) equipped with a high spatial resolution Ga focused ion beam (Ga-FIB) was applied to understand hydrogen diffusion and desorption behavior in duplex stainless steel and Fe–30 % Ni alloys. Deuterium was used as a tracer of hydrogen. Results showed that the secondary ion intensity from body-centered cubic (bcc) and face-centered cubic (fcc) Fe represents the flux of deuterium from the surface and the concentration of deuterium, respectively. The deuterium-depleted zone can be visualized from the interface between bcc and fcc phase to fcc Fe on the surface. Furthermore, direct visualization of the grain boundary diffusion of deuterium is also possible in fcc Fe–30 % Ni alloys, using Ga-FIB-TOF-SIMS.

Investigating permeation and transport of H isotopes in tungsten by first-principles

We have investigated permeation and transport of hydrogen (H) isotopes in tungsten (W) single crystal employing first-principles calculations in junction with Fick’ law. Permeability was approximately evaluated according to the solubility and diffusion coefficient of H. The solubility for H in bulk W from present calculation is consistent with the experimental results measured by Frauenfelder. The permeation fluxes of H isotopes are examined at the different thickness of W wall. The permeation fluxes of deuterium with the W thickness of 21μm at the temperature of 770K and with the W thickness of 50μm at the temperature of 893K were 0.68×1013 atom/m2s and 0.34×1014 atom/m2s, respectively. The dissociation coefficients of H isotopes are also evaluated. We believe that the present first-principles combined with Fick’ law method can be also generalized to investigate permeation and transport of H isotopes in most metals since such H isotopes behaviors in most metals are similar to those of H isotopes in W.

Hydrogen retention in tungsten materials studied by Laser Induced Desorption

Development of methods to characterise the first wall in ITER and future fusion devices without removal of wall tiles is important to support safety assessments for tritium retention and dust production and to understand plasma wall processes in general. Laser based techniques are presently under investigation to provide these requirements, among which Laser Induced Desorption Spectroscopy (LIDS) is proposed to measure the deuterium and tritium load of the plasma facing surfaces by thermal desorption and spectroscopic detection of the desorbed fuel in the edge of the fusion plasma. The method relies on its capability to desorb the hydrogen isotopes in a laser heated spot. The application of LID on bulk tungsten targets exposed to a wide range of deuterium fluxes, fluences and impact energies under different surface temperatures is investigated in this paper. The results are compared with Thermal Desorption Spectrometry (TDS), Nuclear Reaction Analysis (NRA) and a diffusion model.

Effect of surface oxide layer on deuterium permeation behaviors through a type 316 stainless steel

Abstract Effect of surface oxide layer on the hydrogen isotope permeation was studied. Iron oxide was uniformly formed in the oxide layer, although chromium was limited at the interface between the oxide layer and bulk SS-316. The permeation behavior of deuterium for oxidized SS-316 was compared with that for unoxidized SS-316 at temperature range of 333–673 K. The deuterium permeability for the oxidized SS-316 was reduced 1/10–1/20 times as high as that for unoxidized one. However, the activation energy of deuterium permeation as gas form for oxidized SS-316 was almost the same as that for unoxidized SS-316 and was 0.64 eV, which was almost consistent with the sum of activation energies for diffusion and solubility. This fact indicates that the deuterium permeation is diffusion limited. The permeability of deuterium as water form was almost constant even if heating temperature is high, showing that the deuterium was permeated through bulk SS-316 and react with oxygen at the oxide layer as water desorption, which is controlled by the permeation flux of deuterium and oxygen concentration on the surface of oxide layer in downstream side.

Linear microstability analysis of a low-Z impurity doped tokamak plasma

Improved electron and deuterium energy and particle confinement in the presence of low-Z impurities have been observed in many tokamaks under various experimental conditions. Peaked electron density profiles have been obtained in the Frascati Tokamak Upgrade (FTU) ohmic plasmas where a high concentration of lithium has been detected following the installation of a Liquid Lithium Limiter (LLL). This paper presents the results of a gyrokinetic study on the effects of lithium and other low-Z impurities on the linear stability of deuterium and electron temperature driven modes and their associated fluxes for plasma parameters such as those found in the core of LLL-FTU plasmas.Simulations show that a lithium concentration in excess of nLi/ne = 15%, as estimated in the initial phase of a reference FTU discharge, is found to have a strong stabilizing effect on the TEM and high-frequency ETG modes. A significant stabilization of the electron driven modes can still be observed when the lithium concentration is reduced to 3%.In the presence of a significant impurity concentration (nLi/ne = 3–15%) the long wavelength ITG modes drive an inward electron and deuterium flux and outward lithium flux. This process may lead eventually to an increased electron and deuterium density peaking and a reduced Zeff (lithium density below nLi/ne = 1%).

Compilation of erosion yields of metal-doped carbon materials by deuterium impact from ion beam and low temperature plasma

The erosion yield by deuterium impact was determined for various doped carbon-based materials. Ion beam bombardment with 30 and 200eV at elevated temperatures (600–850K) and low temperature plasma exposure with 30eV ion energy (∼7×1020ions/m2s) and about 170 times higher thermal atomic deuterium flux at 300K and 630K were performed. The total yield of fine-grain graphites doped with 4at.% Ti and Zr is reduced by a factor of 4 for 30 and 200eVD impact at elevated temperatures at D fluences above 1024m−2 compared to undoped graphite. Extensive carbide particle loss can be excluded up to fluences of ∼1025m−2.

The ion-driven permeation experiment PERMEX

A new installation PERMEX for the investigation of ion-driven permeation through metals was designed and built. A metal membrane under investigation separates two high-vacuum chambers. In the implantation chamber, the membrane surface is irradiated with a monoenergetic deuterium ion beam with an incident energy in the interval of 100-3000 eV/D. The ion flux at the surface is in a range of 10(13)-2 x 10(14) D/cm2 s, the membrane temperature can be varied in the interval of 290-1050 K. The permeating deuterium flux from the outlet membrane surface to the volume of the second chamber (registration chamber) is measured by a quadrupole mass-analyzer. The outlet surface of the membrane can be cleaned by an argon ion beam. To approve the correct work of the setup a number of experiments were performed with Ni membranes. First results of experiments with tungsten membranes are presented.

Calculation of deuterium retention, re-emission and reflection from a tungsten material under D + ions irradiation with ACAT-DIFFUSE code

We calculated, with a dynamic Monte Carlo code ACAT-DIFFUSE, fluxes of thermal D 2 re-emission, reflection and segregated self-sputtering of D from a D + implanted wrought tungsten material during a time sequence of l00 eV D + implantation, post-implanted isothermal out-gassing and thermal desorption spectroscopy. The obtained result was in good agreement with an existing experiment if two different trap sites with de-trapping energy of 0.85 eV and 2.2 eV and density fraction of 0.05 D/W and 0.01 D/W were assumed to exist. The re-emission, reflection and self-sputtering fluxes in the implantation period were shown to be almost comparable. The integrated deuterium flux released in the same period was estimated. The amount of deuterium retained at 300 K was nearly six times higher than that at 473 K, which reflects the result that mobile atoms and atoms trapped in 0.85 eV trap existed abundantly at 300 K but scarcely at 473 K.

Effect of carbon on accumulation of deuterium in beryllium irradiated with stationary plasma

Beryllium targets placed in the PLAST beam-plasma discharge facility were irradiated with a flux of stationary deuterium (D) plasma with a deuterium ion energy of 200 eV and plasma flux density of 3 × 1020 m−2 s−1 at temperatures of 370 and 670 K. The irradiation doses varied from 5 × 1021 to 1024 m−2. To heat the target and to ionize impurities near its surface the target was irradiated with an electron beam. The deuterium concentration at the target center exceeds its concentration at the periphery by a factor of more than two under all irradiation conditions. The target center was enriched with carbon up to 16–24 at %, as compared to 4–6 at % at the target periphery. The [D]: [Be] atomic concentration ratios at the target center were equal to 0.054 and 0.036 against 0.024 and 0.016 at the periphery at temperatures of 370 and 670 K, respectively. It has been found that these ratios depend on the concentration of carbon atoms which trapped deuterium atoms.

Thermal Stability of Deuterated C60 Films

The thermal stability and electronic structure of deuterated C60 films were studied by temperature-resolved mass spectroscopy and ultraviolet photoionization/photoelectron spectroscopy, UPS. The films were prepared by exposing C60 layers predeposited onto HOPG to a flux of thermal energy atomic deuterium. The initial stage of on-top deuteration at room temperature is associated with the formation of a capping layer that exhibits a higher thermal stability than pristine C60 films. The sublimation heat of the capping layer increases with the deuterium dose applied and levels off at a value of 2.15 ± 0.05 eV/cage at deuterium exposures in the range of 1016 D/cm-2. Capping layers appear to kinetically hinder further deuteration of subsurface C60. This hindrance can be reduced by performing the initial (and subsequent) deuteration at elevated sample temperatures. Further deuterium exposure leads to the formation of higher deuterofullerenes (e.g., C60D36). These exhibit sublimation enthalpies of 1.39 ± 0.1 eV/cage, considerably lower than the capping layers but comparable to pristine C60 films. Capping layers are air-resistant and amenable to the fabrication of stable multilayered [C60/C60Dx]m structures.

Numerical modelling and experimental study of ICR heating in the spherical tokamak Globus-M

In spherical tokamaks the conventional ICR plasma heating has a number of specific features and therefore requires additional investigations. For this aim the modelling of wave propagation and absorption was performed by the 1-D code developed at the Ioffe institute. All possible mechanisms of RF absorption (cyclotron absorption at fundamental and second harmonics, TTMP, Landau) were taken into account. The calculations demonstrated the possibility of effective RF power absorption both by ions and electrons in a broad range of plasma parameters (including relative hydrogen concentration).The ICRH experiments were performed on the low aspect ratio tokamak Globus-M (R = 0.36 m, a = 0.24 m, B0 = 0.3–0.4 T, Ip = 0.15–0.25 MA, vertical elongation 1.2–2, at RF power input level up to 200 kW at frequencies of 7.5–9.2 MHz. A 12-channel neutral particle analyser measured simultaneously hydrogen and deuterium fluxes and relative concentration of ion components. In the experiment the ion temperature increases twice, but the ion heating efficiency depends on the location of the second hydrogen cyclotron harmonic and on the concentration of the light ion component. It is shown that the position of the second hydrogen harmonic in front of the antenna decreases the efficiency of the ion heating. The increase in H-concentration in deuterium target plasma from 10% up to 70% does not influence ion heating efficiency essentially but seems to increase it moderately. The first results on 1.5-D transport ASTRA Modelling are described. They are in reasonable agreement with experimental data. The electron heating was not detected in the experiment due to comparatively low absorbed power with respect to OH one.

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).

Characterization of the deuterium recycling flux in front of a graphite surface in the TEXTOR tokamak

In the TEXTOR tokamak, experiments were performed to simultaneously determine the molecular, atomic and total particle flux of deuterium in front of a graphite limiter, the temperature of which can be controlled independently of the plasma conditions. With rising limiter temperatures, TTL, but constant plasma conditions an increase in Balmer emission and a decrease in Fulcher-band emission were observed. This variation is associated with a change in the type of released species: molecules dominate at low temperatures (550 K < TTL < 1100 K), whereas at temperatures TTL ⩾ 1100 K the direct atomic release starts to become important. The total number of deuterons remains constant for all temperatures. Since not all molecules dissociate into two potentially radiating atoms, it is necessary to take into account the ratio of atoms to molecules when deducing the total particle flux from the Balmer emission. We present a spectroscopic method which allows the determination of the atomic, molecular and total deuterium particle flux and which also gives effective conversion factors, (S/XB)eff, to deduce the total deuterium flux from Balmer-α emission alone.Analysis of the spectroscopic data of both species can be performed to determine the rotational and vibrational populations for the molecules by means of Fulcher-α spectroscopy, and the penetration depth and energy for the atoms using Balmer spectroscopy. This further analysis gives additional information about the release mechanism, showing that both species, atoms and molecules, are released predominantly as thermalized particles.

Modeling and analysis of mixed-material surface evolution and sputtering

Analysis of near-surface compositional changes in materials exposed to ion fluxes is important to a number of technological applications. These applications include preferential sputtering of multi-component materials, ion implantation, plasma contamination, and erosion of plasma facing components in future tokamak devices such as ITER. A model is developed that addresses the dynamics of compositional changes in the near surface region of a plasma facing component where the synergistic effects of sputtering, implantation, and re-deposition are taken into account self consistently. The Monte Carlo binary collision methodology is combined with phenomenological kinetics modeling to study the evolution of the near surface region and the mixing of incident particles with the target material. To show the model capabilities, example model calculations simulated the evolution of beryllium in the sub-surface region of a tungsten divertor that is exposed to multiple fluxes of deuterium, tritium, oxygen, and beryllium. The calculations show that Be can remain in sub-surface region only if the re-deposition fraction is near 1.0 and the confinement of most implanted Be to that region. The calculations also show that the time needed for Be fraction to reach equilibrium is within 1s after the start of irradiation.

High‐Energy Deuteron Measurement with the CAPRICE98 Experiment

We report the first measurement of the deuterium abundance in cosmic rays above 10 GeV nucleon � 1 of kinetic energy. The data were collected by the balloon-borne experiment CAPRICE98, which was flown on 1998 May 28–29 from Fort Sumner, New Mexico. The detector configuration included the NMSU-WiZard/CAPRICE superconducting magnet spectrometer equipped with a gas RICH detector, a silicon-tungsten calorimeter, and a time-of-flight system. By combining the information from the spectrometer and the RICH detector, it was possible to separate deuterons from protons in the kinetic energy range from 12 to 22 GeV nucleon � 1 .I n order to estimate the proton background and the deuteron selection efficiency, we developed an empirical model for the response of the instrument, based on the data collected in this experiment. The analysis procedure is described in this paper, and the result on the absolute flux of deuterium is presented. We found that the deuterium abundance at high energy is consistent with the hypothesis that the propagation mechanism of light nuclei is the same as that of heavier secondary components. Subject headings: balloons — cosmic rays — Galaxy: abundances — ISM: abundances

A Chinese View on Summary of Condensed Matter Nuclear Science

Investigation on tritium was one of the recommendations in Energy Research Advisory Board (ERAB) report of U. S. Department of Energy (DOE) in November, 1989. Fifteen years evolution of the related research proved that it was an important recommendation. A selective resonant tunneling model is attempted to explain this discovery. Deuterium flux might be a key issue to solve the problem of the reproducibility. A further investigation is suggested based on this model.

Chemical Erosion Measurements in Tokamaks by Spectroscopy

The paper focusses on the conversion of photon fluxes into particle fluxes by means of photon efficiencies in tokamaks. Both flux contributions to the chemical erosion yield, the deuterium flux, as well as the eroded hydrocarbon flux, are critically investigated, and possible uncertainties in the data evaluation are identified. Inverse photon efficiencies, so-called S/XB or D/XB values, are critical factors in the conversion of the fluxes. For deuterium, the flux determination is influenced by the presence of a molecular source. In contrast, the hydrocarbon flux is also uncertain due to the indirect conversion from photon to particle fluxes. In particular, the conversion of CD photon fluxes into CD4 particle fluxes can lead to misinterpretation, because C2Dy and CD4 can finally contribute to the flux of CD radicals. A correction formula for the total hydrocarbon flux which includes the contribution of different hydrocarbon sources is introduced.We also present results from spectra simulations of the A-X transition of CD, which show that the usual observation of the CD band (429.4 nm–430.9 nm) may lead to an underestimation of the total photon flux from the whole A-X transition of more than a factor of two. Up to now, the modelling with erosion and deposition codes only takes the complete electronic transition into account. A unification of the quantities is necessary to compare modelling and experiment.