Deuterium Depth Profiles Research Articles

Deuterium depth profiling in JT-60U W-shaped divertor tiles by nuclear reaction analysis

Deuterium concentrations and depth profiles in plasma-facing graphite tiles used in the divertor of JAERI Tokamak-60 Upgrade (JT-60U) were investigated by nuclear reaction analysis (NRA). The highest deuterium concentration of D/ 12C of 0.053 was found in the outer dome wing tile, where the deuterium accumulated probably through the deuterium–carbon co-deposition. In the outer and inner divertor target tiles, the D/ 12C data were lower than 0.006. Additionally, the maximum (H + D)/ 12C in the dome top tile was estimated to be 0.023 from the results of NRA and secondary ion mass spectroscopy (SIMS). Orbit following Monte-Carlo (OFMC) simulation showed energetic deuterons caused by neutral beam injections (NBI) were implanted into the dome region with high heat flux. Furthermore, the surface temperature and conditions such as deposition and erosion significantly influenced the accumulation process of deuterium. The deuterium depth profile, scanning electron microscope (SEM) observation and OFMC simulation indicated the deuterium was considered to accumulate through three processes: the deuterium–carbon co-deposition, the implantation of energetic deuterons and the deuterium diffusion into the bulk.

Deuterium trapping near vanadium surface bombarded with hydrogen ions

Depth profiles of deuterium near surface of a vanadium sample were observed by nuclear reaction analysis. Irradiation defects were introduced in the sample by bombardment of 0.3-MeV H ions with a dose of 3.9 × 10 21 m −2. During the experiment, the sample was continuously exposed to a rf plasma to be charged with deuterium atoms. The result showed that deuterium trapping sites (traps) were produced by the bombardment and the deuterium concentration increased by several times. The depth profile of trapped deuterium was similar to the distribution of atomic displacement. The traps began to decrease at 470 K, which agreed with the recovery temperature for point defects. From these results, the traps were considered to be vacancies, probably stabilized by impurity atoms or the irradiation defects. The ratio of the number of the traps to the displaced host atoms was estimated to be 0.026 at lower bombarding doses, which became lower at higher doses.

Differential cross-section of the D( 3He, p) 4He nuclear reaction and depth profiling of deuterium up to large depths

The differential D( 3He, p) 4He reaction cross-section was determined at a laboratory angle of 135° for 3He energies between 0.5 and 6 MeV. Deuterium depth profiles are determined from the measurement of the proton yield as a function of incident 3He energy with following deconvolution of the obtained yield function. This allows deuterium depth profiling to very large depths. Deuterium depth profiling to a depth of 7 μm in W and 50 μm in B 4C is demonstrated. The accuracy of the method is discussed.

Depth Profile Measurements of Hydrogen Isotopes near the Surface of the TFTR Plasma Facing Component using Nuclear Reaction Analysis

Tritium and deuterium depth profiles of the TFTR tile exposed to deuterium-tritium plasmas have been measured to reveal the hydrogen isotope behavior at the surface region by means of deuteron induced nuclear reaction analysis. The analyzed sample was a part of a tile made of a four-dimensional carbon fiber composite, which was placed at K bay, column C, row 16 of the TFTR vacuum vessel. Four kinds of elements, deuterium, tritium, lithium -6 and lithium -7, were identified. The tritium concentration had a peak at 0.5 μm with an atomic density of 7.4×1025 T/m3 in depth profile, whereas the deuterium showed a broad distribution up to the depth of 1.5 μm with atomic densities of 3.4×1027 D/m3. It is found that a fraction of the retained tritium from the surface to 1.5 μm, 8.1×1019 T/m2, corresponded to 2% of that from the surface to 1 mm, 1.0×1021 T/m2, which was measured for the KC-18 tile using the combustion method.

Depth distribution of deuterium in single- and polycrystalline tungsten up to depths of several micrometers

Depth profiles of deuterium trapped in W single crystals and polycrystalline W irradiated with 200eV D ions at 300–323K have been measured up to a depth of 7μm using the D(3He,p)4He nuclear reaction in a resonance-like technique. The proton yield as a function of incident 3He energy was measured and the D depth profile was obtained by deconvolution of the measured proton yields using the program simnra. The depth at which deuterium is retained can be tentatively divided into three zones: (i) the near-surface layer (up to a depth of ∼0.2μm), (ii) the sub-surface layer (from ∼0.5 to ∼2μm), and (iii) the bulk (>5μm). Low-energy D ion irradiation modifies the W structure to depths of up to about 5μm, both for W single crystals and polycrystalline W. Up to this depth trapping sites are created at a fluence of 5×1022/m2 for the retention of deuterium at about 0.1at.%.

Depth profile and retention of hydrogen isotopes in graphite tiles used in the W-shaped divertor of JT-60U

Depth profiles of deuterium and hydrogen retained in graphite tiles placed in the divertor region of JT-60U were investigated by secondary ion mass spectroscopy. The deuterium in the near surface of all graphite tiles was replaced by hydrogen due to exposure to hydrogen plasmas at the final stage operations. The depth profiles of the H/ 12C and D/ 12C signal intensity ratios varied not only with the location of the tile but also with the existence of redeposited layers. The integrated intensity of (H + D)/ 12C within the depth of 1.7 μm for the deposition dominated tiles was much smaller than that for the erosion dominated tiles. This suggests that thermal contact of the redeposited layer might be too poor to remove the heat loads from plasma to the substrate resulting in the surface temperature of the redeposited layer becoming much higher than that of the substrate.

Measurement of deuterium and tritium retentions on the surface of JT-60 divertor tiles by means of nuclear reaction analysis

It is important to measure retentions and depth profiles of deuterium and tritium on plasma facing materials to understand plasma-wall interactions. The nuclear reaction analysis (NRA) has been established using a deuteron beam with an adjustable energy. By means of the NRA, depth profiles of deuterium and tritium on the surface of JT-60 divertor graphite tiles irradiated with DD burning were obtained. The NRA method showed that the average concentrations of the deuterium retained in the surface of two different were 1.3 × 10 16 and 0.3 × 10 16 cm −2. α-particles from the T(d, α)n reaction were measured from a dome unit tile of JT-60U W-shaped divertor and the measured activity of tritium was about 18 kBq/cm 2. The peak energy of the α spectrum obtained with the NRA was about 1.2 MeV. This result implies that energetic tritons were implanted in the divertor graphite tile.

A small and compact AMS facility for tritium depth profiling

A dedicated AMS facility for depth profiling of tritium in carbon samples has been installed, tested and applied to routine measurements in the Forschungszentrum Rossendorf. It is based on an SF6-insulated 100 kV tandem accelerator equipped with a thin diamond-like carbon (DLC) stripper foil of about 1 μg/cm2. With this setup carbon samples with tritium concentrations in the range of 5×1010–1019 atoms/cm3 can be analysed. In first routine measurements carbon samples cut from tiles of the inner wall of the fusion experiments ASDEX-upgrade Garching/Germany, JET Culham/UK and TFTR Princeton/USA have been analysed. In addition, depth profiles of deuterium and other light elements can be measured using the Faraday cup at the entrance of the accelerator (SIMS mode of the facility) or in the case of very low concentrations after acceleration using a particle detector (AMS mode).

A small and compact AMS facility for tritium depth profiling

A dedicated AMS facility for depth profiling of tritium in carbon samples has been installed, tested and applied to routine measurements in the Forschungszentrum Rossendorf. It is based on an SF6-insulated 100 kV tandem accelerator equipped with a thin diamond-like carbon (DLC) stripper foil of about 1 μg/cm2. With this setup carbon samples with tritium concentrations in the range of 5 × 1010–1019 atoms/cm3 can be analysed. In first routine measurements carbon samples cut from tiles of the inner wall of the fusion experiments ASDEX-upgrade Garching/Germany, JET Culham/UK and TFTR Princeton/USA have been analysed. In addition, depth profiles of deuterium and other light elements can be measured using the Faraday cup at the entrance of the accelerator (SIMS mode of the facility) or in the case of very low concentrations after acceleration using a particle detector (AMS mode).

Point defect distributions and their electrical effects on (Ba,Sr)TiO3/Pt thin films

Deuterium annealing effects on the electrical properties of (Ba,Sr)TiO3 (BST) thin films were investigated using electrical measurements and x-ray photoelectron spectroscopy (XPS) band bending analysis as a function of Pt surface coverage. In combination with the results from secondary ion mass spectroscopy (SIMS) depth profiling, these results suggest that the majority of deuterium defects incorporated during low temperature D2/N2 anneals is electrically inactive. Therefore, there are quite likely other contributors, in addition to charged interstitial deuterium defects, to the observed leakage current degradation after deuterium/hydrogen forming gas annealing, such as oxygen vacancies formed under reducing D2 annealing conditions and annealing-induced changes in the BST/Pt interface state density. The XPS band bending analysis provides information on the electrostatic potential difference across BST thin films with a Pt bottom electrode. With this boundary condition as input, simulations based on a previously developed equilibrium point defect model and the static (annealing time independent) deuterium depth profiles obtained by SIMS analysis have been performed to predict equilibrium defect distributions across BST thin films.

The Depth Profiles of Deuterium and Hydrogen in Graphite Tiles Exposed to DD Plasma Discharges of JT-60U

Depth profiles of deuterium and hydrogen retained in plasma facing graphite tiles placed in the divertor region of JT-60U, and chemical bonding states of carbon on the surface of the tiles, were respectively investigated by SIMS and XPS. The deuterium in the near surface of all graphite tiles was replaced by hydrogen due to exposure to hydrogen plasma in the clean-up stage after the D-D operation. The depth profiles of the H/12C and D/12C signal intensity ratios varied with the location of the tile. The integrated (H + D)/12C intensity ratio, Σ(H + D)/12C, in the outer divertor tile was the lowest at the strike point, and increased with the distance from the strike point. At the inner divertor tile with a thick re-deposition layer, Σ(H + D)/12C was very low (values in the range of 0.01 ~ 0.07). After the removal of the re-deposition layer, the integrated ratios Σ(H + D)/12C and ΣD/12C increased by factors of 4 and 70, respectively. In the cases of the baffle plates and the dome top tiles, Σ(H + D)/12C was higher. The intensity ratios, D/12C and H/12C, were strongly influenced by the temperature of the tile, the existence of redeposition layers or eroded regions, and the fluxes of hydrogen isotope ions and charge exchange particles during the D-D operation.

Trapping of Hydrogen in Tantalum Bombarded with Helium-3 Ions

Hydrogen trapping in tantalum was experimentally studied using an in-situ observation technique. One side of a tantalum membrane was continuously exposed to a deuterium plasma and was bombarded with 0.8 MeV 3He ions to introduce traps. After the bombardment, the deuterium depth profiles near the surface were observed by nuclear reaction analysis with the reaction of D(3He, p)4He. The result indicated that many deuterium atoms were present in traps which were associated with radiation damages. The temperature dependence of the deuterium concentration showed that there were two kind of traps, called trap 1 and trap 2 here. The difference in the peak shape of the depth profiles and the difference in the trapping energy suggested that traps 1 and 2 were caused by vacancy clusters and monovacancy sites, respectively. The concentration of the trapped deuterium was found to be of the same order of magnitude as those in molybdenum and nickel under the same experimental conditions.

Deuterium Retention in Tungsten Trioxide Irradiated with D Ions

The depth profiles of deuterium trapped as D atoms and D2 molecules in WO3 films both exposed to D plasma at temperatures in the range from 300 to 650 K and implanted with 10 keV D ions at 300 K and 650 K respectively have been determined by means of secondary ion mass spectrometry and residual gas analysis. After plasma exposure at 350–550 K and ion implantation at 300 K, most of the deuterium is accumulated as D2 molecules. The appearance of molecular deuterium in the D implanted WO3 film is considered to be related to the formation of cavities filled with deuterium. D atoms seem to be chemically bonded to O atoms forming deuterium tungsten bronze and captured by grain boundaries. Further irradiation with 10 keV D ions at both 300 K and 650 K leads to the reduction of WO3 to metallic W within the ion stopping zone.

Deuterium Retention and Diffusion in ETP-10 Graphite Exposed to RF Plasma at Room Temperature

ABSTRACTIsotropic graphite of ETP-10 was exposed to a deuterium rf-plasma at room temperature and depth profiles of deuterium near the plasma-facing surface were observed by a nuclear reaction analysis. The depth profile consisted of two parts, which were a peak at the surface and a gradual slope downward to the depths. The surface density of deuterium estimated from the peak area was saturated with longer time and hardly decreased after the exposure. This was explained by that the incident deuterium atoms from the plasma were absorbed on deuterium-free sites and absorbed atoms were not desorbed. The deuterium concentration in the bulk increased nearly in proportion to the square root of time and gradually decreased after the plasma exposure. This was explained by a simple diffusion model and an apparent diffusion coefficient was found to be 2x10−18 m2s−1 from the depth profile.

Trapping of Hydrogen in Molybdenum Bombarded with Helium-3 Ions

ABSTRACTHydrogen trapping in molybdenum was studied by use of an in-situ observation technique of deuterium depth profiling. A sample sheet was exposed to a deuterium plasma and deuterium permeation through it was monitored. The plasma-facing side was bombarded with 3He ions and deuterium depth profiles were observed by a nuclear reaction analysis under the plasma exposure. The result showed that traps, probably vacancies associated with radiation damages, were produced by the ion bombardment. From consideration of an equilibrium between trapped and dissolved deuterium, the equilibrium constant was estimated from the experimental data and the trapping energy of 1.1 eV was obtained. The production rate of the traps was found to be 0.007 from evolution of the concentration of trapped deuterium with the number of atomic displacements.

Upgrading of the ultra-clean injector for depth profiling at the Munich AMS facility

At the Accelerator Laboratory of Ludwig Maximilian University (LMU) and Technical University Munich (TUM) Garching, Germany, the ultra-clean injector of the accelerator mass spectrometry facility was upgraded in order to permit depth profiling of sample materials. The facility was tested and then routinely used in measurements of depth profiles of tritium and deuterium in vessel wall samples from the fusion experiments Joint European Torus (JET) in Culham, Great Britain and from the Axial Symmetric Divertor Experiment (ASDEX-Upgrade) in Garching, Germany.

H- and D distribution in metallic multilayers studied by 3-dimensional atom probe analysis and secondary ion mass spectrometry

Pd/Nb- and Fe/V multilayers were prepared by either ion sputtering or laser ablation. They were deposited on tungsten tips for field ion microscopy using the 3-dimensional atom probe. D was added by doping from the gas phase. In agreement with thermodynamic data D is accumulated in the metal with the more negative heat of solution, i.e. V or Nb. However, SIMS depth profiles of H concentration measured at room temperature show a pronounced enrichment in the top regions of both Nb- and V layers. This is also observed in a deuterium depth profile obtained by the 3d atom probe measured at 60 K despite the moderate removal of atoms by field evaporation which does not give rise to the formation of lattice defects when compared to sputtering. Thus we assume that surface segregation is the reason for H/D accumulation in surface near regions. The effect vanishes if measurements by the atom probe were made at 20 K where the D mobility is too low to allow D transport to the surface during the time of measurements. With the superior depth resolution of the 3d atom probe being less than 0.5 nm we were able to show that at both the V/Fe and the Nb/W interface depletion of deuterium occurs in a range of about 0.5 nm within the Nb- or V layer due to intermixing of adjacent metals.

Fuel accumulation in co-deposited layers on plasma facing components

The work is focused on the determination of the distribution and the total content of deuterium in co-deposits formed in the TEXTOR tokamak on a toroidal belt limiter which is the machine's major plasma facing component (PFC). Limiter tiles in use for 14 100 s of plasma operation were dismounted for examination with surface analysis and microscopy methods. Mapping of the deuterium distribution by means of nuclear reaction analysis (NRA) revealed the presence of deposition zones covering about 35% of the tiles'surface area. Besides C and D, other constituents of the layers were boron, silicon and inconel components. The co-deposit, with a stratified structure and a thickness of up to 50 μm , could be detached from the tiles. Deuterium depth profiling on both sides of the detached flakes and in the underlying graphite substrate enabled the D content in the deposition zones to be estimated at a level of 3.5×10 19 cm −2 . Adding the fuel content found in the erosion zone (3–7×10 17 cm −2) and on the back side of the tile (0.9–1.8×10 17 cm −2) , the total amount of D atoms trapped in all the limiter tiles was assessed to be about 2×10 23 atoms. D content in the co-deposits accounted for approximately 10 at.% ( C D/ C C∼0.1) which was considered to be low in comparison to much greater values observed in other devices. The results of the ion beam analyses (IBA) agree well with the determination by thermal desorption spectrometry (TDS).

Deuterium retention in single crystal tungsten

The retention of deuterium in single crystal tungsten (SCW) has been measured at 300 and 500 K, as a function of incident ion fluence over the range 10 21–10 24 D +/ m 2 . Irradiation of SCW with 1.5 keV D 3 + ions at 300 K leads to saturation at a much lower incident fluence than seen in polycrystalline tungsten (PCW), but with the same levels of D retention at saturation, ≈5×10 20 D/ m 2 . Implantations at 500 K reached saturation at a very low incident fluence, below 10 21 D +/ m 2 , with the amount of D retained at saturation ≈1.5×10 20 D/ m 2 . This level is 3–4 times lower than the saturation value for 300 K implantation of the same single crystal of tungsten. Deuterium depth profile analysis by secondary ion mass spectrometry (SIMS) shows D trapping primarily within the 500 eV D + ion implantation range for both 300 and 500 K profiles. SIMS also revealed that the depth profiles for oxygen and deuterium were similar. When the tungsten was annealed at 500 K for 1 h after implantation at 500 K, SIMS indicated that the deuterium retention decreased by an order of magnitude.

An isotope effect in electrolytic hydrogen absorption of some transition metals studied by ERDA and SIMS techniques

The depth profiles of protium and deuterium which were charged electrolytically, were measured by elastic recoil detection analysis (ERDA) and secondary ion mass spectrometry (SIMS) techniques in order to study the isotope effect in hydrogen absorption of Ti, Zr, Nb, Ni and Pd. The absolute loading ratios of H(D)/metal were calculated from the ERDA spectra and the depth profiles of SIMS were compared with the results of the ERDA. The isotope absorption ratios are estimated to be (D/H) Ti=0.43, (D/H) Zr=0.53, (D/H) Nb=0.17 and (D/H) Pd=0.10. The content in Ni is below the detection limit. The mass balance equations based on the transport–absorption model, were applied to analysis of the experimental results. This model reveals that the isotope absorption ratios for the Nb and Pd cases are governed mainly by the flux of hydrogen ions flowing to the surface of the metal electrode. However, the competition between the absorption–conversion process and the recombination process mainly determine the isotope ratio for the Ti and Zr cases.