Hydrogen Isotope Ions Research Articles

Investigation of Hydrogen Isotope Conductivity through Single- and Multi-Layer Graphene

Since its discovery, the outstanding properties of graphene regarding electrical and thermal conductivity as well as mechanical stability have increased the interest of the scientific community in this versatile material. The intensive investigations on the material uncovered even more unique properties that were previously thought to be physically impossible. In 2014 Hu et al. had shown that pristine graphene, which was prior thought to be an impermeable barrier, could be penetrated by ions.[1] Especially ions of hydrogen isotopes seem to be able to penetrate graphene at a fast rate. This permeation is supposed to cause a separation where protium passes more easily than the other isotopes which is still thoroughly discussed in recent literature. Contrary to single layer graphene, the permeability through multiple layers of graphene as an A-B-stacking seems to be less discussed nor investigated. Theoretical calculations of Eren et al. proposed a possible and fast interstitial movement of ions through multi-layered 2D-materials.[2] Within this work we were able to prove that in fact, several layers of graphene could be penetrated by protons and deuterons. By utilizing impedance spectroscopy, it was possible to show that the ions pass through the graphene layers. The currents produced in this electrochemical ion pump exceeded 500 mA/cm2 and showed that the graphene added almost no additional resistance. Combining impedance spectroscopy with mass spectrometry, we were also able to analyze whether isotope separation occurred for protons and deuterons. With electrochemical measurements we validated conduction of ions through graphene but were unable to find any separation. Therefore, our results are challenging a lot of recent results in this field.

Study of hydrogen exchange between the Zr–1%Nb alloy and the gaseous ambient through the oxidized surface under ion and atomic irradiation

In the article, a hydrogen exchange between the Zr–1%Nb alloy (E110) and the gas ambient was experimentally studied when the samples were irradiated with deuterium and argon plasma ions. It has been established that, upon irradiation with deuterium plasma ions with an energy of E = 650 eV/at, the enhanced absorption of deuterium exceeds the release of hydrogen initially contained in the samples, which leads to their loading with hydrogen isotopes. Adding 30 at.% oxygen to the plasma-forming gas or raising the sample temperature from T = 450 K to T = 600 K, significantly reduces the content of hydrogen isotopes in the sample. Based on the aggregate data obtained by atomic and ion irradiation, a mechanism of hydrogen exchange between zirconium alloy and gas ambient is proposed. The process includes three stages: reactions on the oxidized surface of the zirconium alloy (surface hydroxylation and formation of water molecules); reactions at the metal-oxide interface; transfer of hydrogen isotopes through the surface oxide layer in both directions due to hopping between neighboring oxygen ions. Surface reactions caused by irradiation of atoms and ions trigger the hydrogen exchange. The proposed model agrees with the experimental data on the irradiation of the E110 alloy with atoms and ions of hydrogen isotopes.

Difference of co-extracted electron current and beam acceleration in a negative ion source with hydrogen-isotope ions

Improvement of the performance on a hydrogen/deuterium negative ion source for a nuclear fusion device is reported. In particular, the suppression of the co-extracted electron current, Ie, is an important issue to ensure the stable beam acceleration. Improvement of the Ie has been confirmed by optimizing the magnetic field of the electron deflection magnet in the extraction grid. Two other new methods for reduction of the Ie were validated. The first was an electron fence whose rods were set between the rows of apertures on a plasma grid. The electron and negative ion current ratio, approximately Ie/I acc, was greatly improved from 0.7 to 0.25 in deuterium. The second was an outer iron yoke which enhanced the magnetic flux density 19% inside the arc discharge chamber. The Ie/Iacc using the outer yoke decreased by 0.1 compared with using a normal magnetic filter in a deuterium operation. These attempts have improved the total deuterium injection beam power of 8.4 MW by three negative ion based NBIs.

Hydrogen atom-ion synergy in surface lattice modification at sub-threshold energy

Low-energy hydrogen-isotope (HI) plasma is widely applied for industrial surface processing. Here we demonstrate that HI plasma - even with ion energies far below the threshold for stable Frenkel pair production - can strongly modify crystalline materials by forming heavily lattice-distorted surface layers with a thickness of several nanometers and a HI content of several atomic percent. We experimentally reproduce the identical lattice modification at deuterium and hydrogen plasma-irradiated tungsten (W) surfaces when the sub-threshold HI ion energies are adjusted such as to transfer equal amounts of kinetic energy in collisions with W lattice atoms. A physical model for the low-energy generation of primary defects is proposed, which involves the synergy between temporary Frenkel pair creation by sub-threshold HI ion collisions and vacancy stabilization by trapping of solute HI atoms. Such synergistic defect generation is generally expected upon injection of energetic projectiles (ions, neutrons) into HI-containing solids and likely contributes to material degradation. As a means of surface modification, the fabrication of nanometer-scale hydrogen-rich surface layers on materials (even those with negligible hydrogen solubility) via low-energy H plasma exposure promises utilization potential in catalysis and electrochemistry.

Cathode and plasma phenomena in vacuum-arc sources of hydrogen isotope ions. II. Ionization processes in the arc plasma

An experimental and theoretical study of the content of deuterium ions in arc discharge plasma was performed for deuterated zirconium cathodes. It was found experimentally that the deuterium ion percentage increased significantly with increasing arc current and decreasing arc duration, reaching 85% at kiloampere currents and few microsecond durations. In this case, a clear correlation was found between the content of deuterium ions in the arc plasma and the mean charge of zirconium ions: the higher the mean Zr ion charge, the greater the amount of deuterium ions in the plasma. A model was developed to describe the ionization processes that occur in the plasma of a vacuum arc with a deuterated cathode. It was shown that the relative content of deuterium ions in the plasma jet ejected from an individual cathode spot cell is not over 50%. The deuterium atoms are additionally ionized when the plasma jets of individual cells are mixed within a group cathode spot with high average current density. Conditions for additional ionization arise when the density of cells on the cathode surface is high, that is, at the initial stage of the discharge operation.

Cathode and plasma phenomena in vacuum-arc sources of hydrogen isotope ions: I. Desorption of hydrogen isotopes during the operation of vacuum arc cathode spots

A model is proposed to describe the desorption of deuterium from a deuterated cathode during the operation of the vacuum arc cathode spot. The model treats a cathode spot as consisting of individual cells and involves a numerical simulation of the temperature fields that arise during the hydrodynamic processes responsible for the formation of microcraters on the cathode surface. Using a deuterated ZrD0.67 cathode as an example, it is shown that the amount of deuterium desorbed immediately from the crater formed during the operation of the cathode spot cells is several times smaller than the total amount of desorbed deuterium. The main portion of deuterium is desorbed from the hot cathode region adjacent to the crater and from the crater at the stage of its cooling. For a deuterated ZrD0.67 cathode, the percentage of desorbed deuterium can reach 80% of the total number of evaporated atoms, and it can be even greater if the cathode spot cells operate in the immediate vicinity of each other.

Ion Angular and Initial Energy Distributions in Arc Discharge Deuterium Ion Source

Ion beams of hydrogen isotopes are of interest for accelerator and surface modification technologies. One of the methods of the generation of hydrogen-isotope ion beams is by using a high-current arc discharge ion source with hydrogen-saturated electrodes. The divergence of an ion beam is determined by the initial energy and angular distributions of ions. Some applications require ion beams with a divergence of 100 mrad or less. This paper analyzes the initial energy and angular distributions of ions in an ion source based on an arc discharge with a deuterated zirconium electrode. The analysis shows that the angular distribution of deuterium ions, compared to zirconium ions, is much broader and that the initial energy of zirconium ions in the ion beam is greater than the initial energy of deuterium ions.

Hydrogen Isotope Separation via Ion Penetration through Group-IV Monolayer Materials in Electrochemical Environment.

Based on density functional theory calculations, the chemical penetration behaviors and separation properties of hydrogen isotope ions through pristine and fully hydrogenated group-IV monolayer materials are investigated. Both the penetration energy profiles and kinetic isotope effects are studied to evaluate the performance of four group-IV (C, Si, Ge, and Sn) monolayer materials for hydrogen isotope separation. To examine the thermodynamically stable morphologies of these monolayer materials in electrochemical aqueous environment, the Pourbaix diagrams varying with pH and external bias are constructed. The fully hydrogenated monolayer materials are found to be thermodynamically favorable in some conditions, and the proton penetration and hydrogen isotope separation behaviors are different from their pristine counterparts. The silicene is found to be a suitable candidate material for hydrogen isotope separation in an electrochemical environment.

Gyrokinetic microinstability analysis of high-Ti and high-Te isotope plasmas in Large Helical Device

Transport and confinement characteristics, and microinstabilities for high- and high- isotope plasmas in Large Helical Device are explored by using the gyrokinetic Vlasov simulation GKV with hydrogen isotope ions and real-mass kinetic electrons. The experimental data indicate that the thermal diffusivity is reduced in the deuterium-dominated plasmas, where the deviation from the gyro-Bohm scaling in the overall tendency and the strong anomaly of the electron heat transport are identified. Linear gyrokinetic analyses identify that the growth rates of the ion temperature gradient and trapped electron mode (TEM) instabilities in the deuterium plasmas are reduced due to the change in the profile gradients and/or the isotope ion mass, and the radial dependence of the mixing-length diffusivity is qualitatively consistent with the experimental tendency. Also, TEM-like turbulent fluctuations are examined by the using the phase contrast imaging measurement and the linear gyrokinetic calculation for the high- deuterium plasma.

Meson-catalyzed fusion in ultradense plasmas

We first argue that negative muons in the MeV energy range can be fully stopped in warm-dense-matter and fast ignition scenario ultradense plasmas on a picosecond time scale by taking into account the slowing down of partially degenerate electrons and charged hydrogen isotope ions taken as classical. Atomic and molecular recombinations within these plasmas on the lowest available exoatom bound states are then demonstrated. The very existence of in situ produced exoatoms can be proved with x-ray line Stark broadening. Finally, a former conjecture about the negligibility of meson sticking on fusion-produced particles is reinforced. Mesonic catalysis of deuterium-tritium fusion reactions is then shown to be possible in short-lived plasma targets with rates that are orders of magnitude above cold deuterium reactions. The dipole exoatom orientations clearly favor the cold and long-lived warm-dense-matter option.

Quantum tunneling of thermal protons through pristine graphene.

Engineering of atomically thin membranes for hydrogen isotope separation is an actual challenge which has a broad range of applications. Recent experiments [M. Lozada-Hidalgo et al., Science 351, 68 (2016)] unambiguously demonstrate an order-of-magnitude difference in permeabilities of graphene-based membranes to protons and deuterons at ambient conditions, making such materials promising for novel separation technologies. Here we demonstrate that the permeability mechanism in such systems changes from quantum tunneling for protons to quasi-classical transport for heavier isotopes. Quantum nuclear effects exhibit large temperature and mass dependence, modifying the Arrhenius activation energy and Arrhenius prefactor for protons by more than 0.5 eV and by seven orders of magnitude correspondingly. Our findings not only shed light on the separation process for hydrogen isotope ions passing through pristine graphene but also offer new insights for controlling ion transport mechanisms in nanostructured separation membranes by manipulating the shape of the barrier and transport process conditions.

Accelerated procedure to solve kinetic equation for neutral atoms in a hot plasma

The recombination of plasma charged components, electrons and ions of hydrogen isotopes, on the wall of a fusion reactor is a source of neutral molecules and atoms, recycling back into the plasma volume. Here neutral species participate, in particular, in charge-exchange (c-x) collisions with the plasma ions and, as a result, atoms of high energies with chaotically directed velocities are generated. Some fraction of these hot atoms hit the wall. Statistical Monte Carlo methods normally used to model c-x atoms are too time consuming for reasonably small level of accident errors and extensive parameter studies are problematic. By applying pass method to evaluate integrals from functions, including the ion velocity distribution, an iteration approach to solve one-dimensional kinetic equation [1], being alternative to Monte Carlo procedure, has been tremendously accelerated, at least by a factor of 30-50 [2]. Here this approach is developed further to solve the 2-D kinetic equation, applied to model the transport of c-x atoms in the vicinity of an opening in the wall, e.g., the entrance of the duct guiding to a diagnostic installation. This is necessary to determine firmly the energy spectrum of c-x atoms penetrating into the duct and to assess the erosion of the installation there. The results of kinetic modeling are compared with those obtained with the diffusion description for c-x atoms, being strictly relevant under plasma conditions of low temperature and high density, where the mean free path length between c-x collisions is much smaller than that till the atom ionization by electrons. It is demonstrated that the previous calculations [3], done with the diffusion approximation for c-x atoms, overestimate the erosion rate of Mo mirrors in a reactor by a factor of 3 compared to the result of the present kinetic study.

An assessment for the erosion rate of DEMO first wall

In a fusion reactor a significant fraction of plasma particles lost from the confined volume will reach the vessel wall. The recombination of these charged species, electrons and ions of hydrogen isotopes, is a source of neutral molecules and atoms, recycling back into the plasma. Here they participate, in particular, in charge-exchange (c-x) collisions with the plasma ions and, as a result, atoms of high energies with chaotically oriented velocities are generated. A significant fraction of these hot neutrals will hit the wall, leading, as well as the outflowing fuel and impurity ions, to its erosion, limiting the reactor operation time. The rate of the wall erosion in DEMO is assessed by applying a one-dimensional model which takes into account the transport of charged and neutral species across the flux surfaces in the main part of the scrape-off layer, beyond the X-point vicinity and divertor, and by considering the shift of the centers of flux surfaces, their elongation and triangularity. Atoms generated by c-x of recycling neutrals are modeled kinetically to define firmly their energy spectrum, being of particular importance for the erosion assessment. It is demonstrated the erosion rate of the DEMO wall armor of tungsten will have a pronounced ballooning character with a significant maximum of mm per full power year at the low field side, decreasing with an increase in the anomalous perpendicular transport in the ‘far’ SOL or the plasma density at the separatrix.

Isotope Effects on Trapped-Electron-Mode Driven Turbulence and Zonal Flows in Helical and Tokamak Plasmas.

Impacts of isotope ion mass on trapped-electron-mode (TEM)-driven turbulence and zonal flows in magnetically confined fusion plasmas are investigated. Gyrokinetic simulations of TEM-driven turbulence in three-dimensional magnetic configuration of helical plasmas with hydrogen isotope ions and real-mass kinetic electrons are realized for the first time, and the linear and the nonlinear nature of the isotope and collisional effects on the turbulent transport and zonal-flow generation are clarified. It is newly found that combined effects of the collisional TEM stabilization by the isotope ions and the associated increase in the impacts of the steady zonal flows at the near-marginal linear stability lead to the significant transport reduction with the opposite ion mass dependence in comparison to the conventional gyro-Bohm scaling. The universal nature of the isotope effects on the TEM-driven turbulence and zonal flows is verified for a wide variety of toroidal plasmas, e.g., axisymmetric tokamak and non-axisymmetric helical or stellarator systems.

Radiation-induced hydrogen transfer in metals

The paper presents processes of hydrogen (deuterium) diffusion and release from hydrogen-saturated condensed matters in atomic, molecular and ionized states under the influence of the electron beam and X-ray radiation in the pre-threshold region. The dependence is described between the hydrogen isotope release intensity and the current density and the electron beam energy affecting sample, hydrogen concentration in the material volume and time of radiation exposure to the sample. The energy distribution of the emitted positive ions of hydrogen isotopes is investigated herein. Mechanisms of radiation-induced hydrogen transfer in condensed matters are suggested.

In-Situ Observation of Sputtered Particles for Carbon Implanted Tungsten during Energetic Hydrogen Isotope Ion Implantation

The effect of carbon implantation for the dynamic recycling of deuterium, which demonstrates tritium recycling, including retention and sputtering, was investigated using in-situ sputtered particle measurements. The C+ implanted W, WC and HOPG were prepared and dynamic sputtered particles were measured during H2 + irradiation. It was found that the major hydrocarbon species for C+ implanted tungsten was found to be CH3, although those for WC and HOPG were CH4. The chemical state of hydrocarbon is controlled by the H concentration in a W-C mixed layer. The amount of C-H bond and the retention of H trapped by carbon atom should control the chemical form of hydrocarbon sputtered by H2+ irradiation and the desorption of CH3 and CH2 was due to chemical sputtering, although that for CH was physical sputtering. The activation energy for CH3 desorption was estimated to be 0.4 eV, corresponding to the trapping process of hydrogen by carbon through the diffusion in W. It was concluded that the chemical states of hydrocarbon sputtered by H2+ irradiation for W was determined by the amount of C-H bond on the W surface.

Method for determining the tritium concentration using the effects of dissociation of molecular beams of hydrogen isotopes on thin carbon films

Physical foundations of a new method for mass-spectrometric determination of tritium concentration in hydrogen-containing media, which is based on the effect of dissociation of molecular ions of hydrogen isotopes passing through thin carbon films, are formulated. The effects accompanying the interaction of particles with a solid (angular scattering, change in the charge state, energy losses in protons, deuterons, and tritons) are analyzed. The corresponding theoretical and experimental data indicate that the proposed technology can be implemented in practice for a comparatively low particle energy of ∼10 keV/nucleus.

Influence of beryllium carbide formation on deuterium retention and release

The inconel cladding tiles of the ITER-like-wall to be tested at JET will be coated by a beryllium layer. Carbon containing tiles will be also present. These materials are sputtered in the high flux (1022m−2s−1 or higher) of the deuterium–tritium plasma. Ionized by the energetic electrons and with hydrogen isotope ions they will be implanted or re-deposited, creating composite layers.In order to study the deuterium retention and release, mixed layers were prepared using the thermionic arc method.Deuterium implantation was performed using a high current ion source at room temperature using a deuterium ion beam with energy of 200eV/D. Thermal Desorption Spectroscopy (TDS) analyses were correlated with the beryllium/carbon relative concentrations of the prepared films. At higher carbon concentrations the peak value from TDS spectra corresponding to beryllium was lower and an increased peak corresponding to the carbon was observed.

Hydrogen isotopic effects on the chemical erosion of graphite induced by ion irradiation

This theoretical study investigates the dynamic behavior of chemical erosion of graphite due to hydrogen-isotope ion bombardment. The ion energy ranges from 10 to 1000eV and the target temperature ranges from 300 to 1100K. The chemical erosion processes under investigation included surface-related and thermally activated hydrocarbon emission processes. The computer code TRIDYN was employed. The proposed simulation model was fitted to experimental data by implementing surface-related and thermally activated coefficients. It is improved compared to our previous model by incorporating a depth-dependent probability for out-diffusion of hydrocarbons. The local reduction of carbon density due to either physical sputtering or chemical erosion was also taken into account. Furthermore, the erosion for all three hydrogen isotopes – hydrogen, deuterium, and tritium – was modeled. All the calculated and fitted results are in good agreement with measured data. The results from the current simulation model surpass previous ones in the low ion energy region in which chemical erosion is of vital importance.

Influence of irradiation conditions on the retention of hydrogen isotopes in structural materials

The influence of irradiation conditions on the retention of hydrogen isotopes in structural materials (austenitic steel) under heating is considered. The specimens under study were irradiated either in a reactor or by bombarding them with hydrogen-isotope ions of variable fluence and energy at accelerators. An investigation of irradiated specimens with an EM-300 transition electron microscope was accompanied by studying the kinetics of hydrogen release from samples with a high-vacuum mass spectrometer. Also, the kinetics of hydrogen-isotope release from specimens of structural materials treated with a deuterium plasma was studied. It was found that, under the effect of irradiation, the materials being studied develop radiation defects, which appear to be efficient traps for hydrogen atoms, retaining them up to rather high temperatures (650 K). It is also shown that blisters formed in the materials treated with a hydrogen plasma contain both molecular hydrogen and hydrocarbons—in particular, methane.