Deuterium Release Research Articles

Retention and recycling of plasma edge hydrogen isotopes in C and TiC

The retention, release, and isotopic exchange of hydrogen, deuterium, and tritium incident on room temperature C and TiC with Maxwellian velocity and isotropic angular distributions have been calculated using the Local Mixing Model. The calculations are based on the hydrogen saturation concentration, range distributions and isotopic exchange behavior, all of which have been verified experimentally by monoenergetic implants. Particle fluences (10 16 to 10 20/cm 2) and characteristic Maxwellian energies (50 eV to 3200 eV) were chosen in the range of interest for tokamak plasma edge conditions. The results of these calculations are used to estimate tritium inventory buildup and to predict tritium changeout rates by isotopic exchange in tokamaks and other fusion devices. Tritium inventories in the TiC components (which comprise ≳ 20% of the TFTR first-wall surface) are anticipated to remain at reasonable levels in TFTR, and isotopic exchange is shown to be a feasible method to reduce these tritium inventories.

Trapping and Surface Recombination of Deuterium in Fusion Reactor Metals

Ion implantation and ion beam analysis were used to examine bulk trapping and surface recombination for deuterium in Fe, Ni, and austenitic stainless steel. Irradiation-defect traps were characterized in the three metals, and substantially stronger traps were shown to be associated with small He bubbles. The rate of deuterium release at stainlesssteel and Fe surfaces was measured as a function of temperature and solution concentration. Trapping and surface recombination parameters were extracted by applying established theory for solute diffusion within a field of traps.

Dynamic measurements of implanted deuterium retention and release in stainless steel and carbon

The TFTR limiter is graphite. It is possible to decrease the amount of D trapped in the limiter by making plasma discharges with gas injected only as a prefill. When the limiter is deuterium depleted well enough by this technique for supershots (with Rd∼0.5–0.6) it pumps noble gases. The effective confinement time τp* ranges from ≤1 s for He down to 0.08 s for Kr. These noble gases escape from the limiter slowly after the run. The partial pressures of Ar and Ne decay with time constants of several hours, and the data for Ar show evidence of two trapping sites.

Ion-induced release of deuterium from carbon

The ion-induced release of deuterium from carbon was studied by first implanting carbon targets with a high fluence of low-energy (150–600 eV) deuterium to saturate a thin near-surface region and then bombarding the targets with higher-energy ions which penetrate through the deuterium implanted region. Measurements were made of the deuterium release caused by bombardment by hydrogen and helium ions at 3 keV, by helium and carbon ions at 30 keV and by carbon ions at 60 keV. A strong correlation is observed between the ion-induced release rate and the energy lost to atomic collisions by the incident ions. A model for the ion-induced release is described which includes retrapping of the deuterium. Two features of this model are that retrapping results in a non-exponential dependence of the release on incident ion fluence, and in a dependence of the release on the thickness of the deuterium implanted layer. Both of these features are observed in the data which indicates that ion-induced release of deuterium from carbon involves retrapping.

Influence of damage on the thermal release of deuterium implants in graphite

Trapping and release of keV deuterium in pyrolytic graphite has been the subject of several investigations because of its relevance to the problem of interaction of a hot fusion plasma with the solid wall. In the present work the influence of He-induced damage on implantation profiles for deuterium in pyrolytic graphite is investigated for either a smaller (9 keV D +, 3 keV He +) or larger He range (1.5 keV D +, 13 keV He +). During annealing, the implanted D is found to be retained more strongly at depths where He-damage has been introduced. The results show that the trapping sites of deuterium in pyrolytic graphite are at least partly connected with radiation damage.

Dose and energy dependence of ion-induced release of deuterium from molybdenum by low energy hydrogen ions

The ion-induced release of deuterium trapped in molybdenum at room temperature was investigated by subsequent bombardment with protons using incident energies ranging from 0.5 to 6 keV for deuterons and protons. The release curve of deuterium pre-implanted at 1 keV due to proton bombardment at energies from 1 to 6 keV consisted of two exponential decay curves. The two decay constants, i.e., release cross sections, decreased with increasing dose of the implanted deuterium. Two distinct peaks were observed in the release spectra of deuterium pre-implanted at energies from 3 to 6 keV due to proton bombardments at the corresponding energies. The release spectra and the amount of release of D 2 were dependent on the implanted deuteron dose, deuteron energy, proton energy and condition of pre-implanted target. The results are discussed in view of radiation damage effects.

Liberation of deuterium gas from molybdenum upon heating after penetration of D+ ions

A series of peaks of liberation of deuterium gas from molybdenum has been discovered in this paper upon the heating of a sample after ion penetration. The maxima of these peaks lie, in the 230–650°K range. The diffusion coefficient and the activation energy in the individual peaks of j(T) have been measured. It has been discovered that D in the individual peaks covers a range of at least 10 orders of magnitude when the temperature is constant, and the discrete activation energy series comprises 45–126 kJ/mole. The measured values of D and Q can be larger or smaller than those which are measured in experiments on hydrogen transport. At high irradiation doses an interrelationship has been discovered in the first group of peaks between secondary defects in molybdenum and the liberation of captured deuterium gas. It is suggested that secondary defects can serve, in different cases both as centers for deuterium retention and as the means for its easier escape to the surface. It has been assumed possible to explain the high-temperature peaks as the release of deuterium from radiation vacancy-deuterium atom complexes with a different content of vacancies and deuterons.

Deuterium trapping and release in titanium-based coatings for TFTR

We have measured the deuterium trapping and thermal release characteristics of three candidate armor and limiter materials for TFTR: Ti explosively bonded onto Cu; TiB 2 and TiC chemically vapor deposited on C. The re-emission rate of deuterium was monitored during bombardment with 10 keV D + 3 and the post-implantation retention was measured with D( 3He, α)H nuclear reaction profiling and linear ramp thermal desorption. Titanium claddings showed no thermal release of deuterium for fluences of 10 19 D/cm 2 at 375 K; at 775 K, only 65% of the fluence was released during implantation to 10 18 D/cm 2. This high retention is shown to result from titanium deutende precipitation and the formation of a bulk deuterium solid solution. In contrast, the TiB 2 and TiC coatings showed a rapid saturation in deuterium retention of < 10 17 D/cm 2.

Experimental measurements of hydrogen isotope exchange in carbon surfaces under ion bombardment

Carbon has been bombarded to saturation with deuterons at energies from 10 to 25 keV. The deuterium concentration was then depleted using protons of corresponding energy. Also, 10 keV deuterons implanted to saturation were removed using a range of proton energies from 10 to 30 keV. The deuterium release rate per incident proton was determined and shown to be a result of lattice saturation and not energy transfer to the lattice. The emitted deuterium from carbon saturated by 20 keV deuterons was analysed under 20 keV deuteron bombardment. A chopping technique was employed to detect the directly released particles and these were primarily D 2 molecules. This result is shown to be consistent with the previous results.

Low-Energy D(d,p)T Spectroscopy for Studying Dynamic Deuteron Implant Effects

Hydrogen isotope buildup and migration during implantation are difficult to study in many materials because of its high mobility. In addition, under high fluence conditions much of the damage produced by the ion beam is annealed during the implant and is thus unobservable by post-mortem analysis. A system is-described for implanting deuterium at 40 keV and simultaneously evaluating the deuterium retention and release under various target conditions. Semi-quantitative deuterium profiling by D(d,p)T spectroscopy is shown useful at 40 keV, where the approach to a dynamic equilibrium is rapid. Experimental data on ScD2 and Cu-Be are presented which illustrate the utility of the technique for investigating bombardment effects on the deuterium binding, surface retention barriers, damage-enhanced mobility, and impurity-produced depletion.

Ion-induced release of deuterium trapped in stainless steel

The release of deuterium atoms which have been trapped in stainless steel, by subsequent bombardment with protrons, has been investigated over the range of incident ion energies from 5 to 30 keV. It is shown that at 77 K ion induced release occurs with “cross sections” for release in the range 10 −18 to 10 −17 cm 2. This mechanism appears to be important in determining the saturation level of surfaces under ion bombardment in cases where diffusion is not important. At 300 K the release cross section is ~5 × 10 −17 cm 2 and it is suggested that this is due to a combination of ion induced release and simple diffusion. Some different models, including trap filling and radiation enhanced fissuion, are proposed as the physical mechanisms responsible for ion induced release. Each of the models has some success in explaining the experimental results but there is still insufficient data to decide between them.

Thermal desorption and bombardment-induced release of deuterium implanted into stainless steels at low energy

Thermal desorption spectra have been obtained for low energy (15–750 eV) deuterons implanted into types 321 and 304 stainless steel, to total fluences in the range 10 13–10 17 deuterons/cm 2. In each case the spectra show a peak at about 350 K, but in the 321 steel there is a second peak in the region of 900 K, the population and peak temperature of which increase with energy. Activation energies of 0.99 and 2.39 eV and a rate constant of 7 × 10 15/ s have been derived for the peaks, and it is thought that the first peak corresponds to release from sites close to the surface, while the second peak may be related to trapping at impurities such as Ti. Measurements have also been made of the release of deuterium resulting from post-implantation bombardment with hydrogen ions. It is found that depletion of the first peak in the 321 steel is the result of gas sputtering, but depletion of the second peak is the result of the formation of HD during desorption, while depletion of the peak in the 304 stainless steel also results from HD formation even though this peak is the same as the first peak in the 321 steel. Estimates have also been made of the deuterium self-sputtering cross section at various energies, which show a monotonie decrease as energy increases.

Studies on the phenylalanine hydroxylase system in vivo. An in vivo assay based on the liberation of deuterium or tritium into the body water from ring-labeled L-phenylalanine.

The rate of release of deuterons into the body water from 2,3,4,5,6-pentadeutero-L-phenylalanine has been shown to be a valid measure of the activity of the phenylalanine hydroxylase system in vivo. At a dose of 0.5 g/kg, the rate of release of deuterons is linear for 60 to 90 min. Male rats, which had previously been shown to have 22 to 25% more phenylalanine hydroxylase activity in liver extracts than female rats, produced deuterons from deuterated phenylalanine at a rate 20 to 30% greater than female rats. p-Chlorophenylalanine, which irreversibly inhibits phenylalanine hydroxylase in vivo, caused a similar degree of inhibition of the rate of deuteron formation as was found when phenylalanine hydroxylase was measured in extracts from the same group of animals. Methotrexate, which inhibits the phenylalanine hydroxylase system by preventing regeneration of the tetrahydropteridine cofactor, caused parallel inhibition of the in vivo assay as well as when the conversion of phenylalanine to tyrosine was measured in liver slices. Randomly ring-tritiated phenylalanine can be used interchangeably with ring-deuterated phenylalanine if greater sensitivity is needed in the in vivo assay for phenylalanine hydroxylase. However, a dose of 20 to 30 muCi/kg is required. The in vivo deuterium release assay described in this paper should be useful in studying the physiological control of the phenylalanine hydroxylating system. It also may be of value in differentiating between individuals who are heterozygotes for phenylketonuria and those who are homozygotes for hyperphenylalaninemia.

Diffusion of Hydrogen and Deuterium in Fused Quartz

A mass spectrometer was used to record the transfer of hydrogen and deuterium through hollow, thinwalled cylinders of fused quartz over the temperature range of 300–1000°C. Steady-state gas permeation measurements resulted in permeability values which agree well with the literature; however, results of transient experiments which provide a direct means of measuring diffusion coefficients did not agree with so-called ``normal'' diffusion. The deviation from normal diffusion increases with increasing temperature. Measurements were made of the temperature variation in the rate of release of deuterium from fused quartz resulting from replacement by dissolved hydrogen. A chemical exchange between the diffusing molecules (H2 or D2) and one or more species of trapped gas within the fused quartz is thought to be the principal cause of the nondiffusion-like character of the high-temperature gas transport. Activation energies were calculated for the permeability (H2:8.88 kcal/mole. D2:9.05 kcal/mole), diffusion (H2:10.37 kcal/mole D2:10.52 kcal/mole), and chemical exchange (15.5 kcal/mole) mechanisms. Experimental solubilities were compared with the so-called normal solubilities (Sn=permeability/diffusion coefficient) and were found to exceed the normal to a greater extent with increasing temperature.