Tritium Ions Research Articles

Investigations into penetration depth profiles of hydrogenic species in beryllium plasma-facing components via molecular dynamics simulations

During the operation of nuclear fusion reactors, plasma-facing components lining the reactor vessel are continually bombarded by plasma species. The penetration and subsequent trapping of these bombarding plasma ions has implications for component damage as well as in-vessel inventory. Accurately predicting the expected ion penetration depth profiles at a range of plasma ion and surface temperatures typical of fusion reactor operating conditions will inform the scrape-off layer design to limit particle radiation damage and tritium trapping in order to prolong the lifetime of the plasma-facing components and satisfy the DT fuel cycle requirements. By defining a statistical distribution for ion penetration depth and describing the evolution of its parameters across the fusion parameter space of interest, the expected ion deposition depth profiles can be calculated for any subset of ion and surface temperature ranges as needed. Molecular dynamics simulations were used to study the bombardment of beryllium lattices with surface temperatures of up to 1100 K by 5 eV–150 eV deuterium and tritium ions, and the resulting ion penetration depths were investigated. The distributions of two penetration depth quantities, considered from the perspectives of lattice damage and hydrogen retention are defined and their distribution parameter dependence on surface and ion temperature is identified. The expected positive correlation between penetration depth and ion temperature is observed, where the non-linear relationship between these quantities indicates the expected form of the velocity dependence of nuclear stopping power at low bombardment energies. Isotope effects on the distributions are also investigated, with results suggesting that heavier ions have comparably lower mobility within the sample and will generally accumulate closer to the surface. A short study on ion deposition rates is also performed; a non-linear increase of deposition rate with increasing bombarding ion energy has been observed, and evidence of a weak positive surface temperature correlation has been noted.

High-Energy Tritium Ion and α-Particle Release from the Near-Surface Layer of Lithium During Neutron Irradiation in the Nuclear Reactor Core

This paper examines in situ spectroscopic measurements of nuclear-excited plasma of noble gases excited by 6Li(n,α)3H nuclear reaction products in the core of a nuclear reactor. A thin layer of lithium applied on the walls of the experimental device, stabilized in the matrix of the capillary-porous structure, serves as a source of gas excitation. During in-pile tests conducted at the IGR research reactor, thermal neutrons interact via the 6Li(n,α)3H reaction, and the emergent α-particles with a kinetic energy of 2.05 MeV and tritium ions with a kinetic energy of 2.73 MeV excite the noble gas (Ar) medium. The intensity of tritium release from the lithium layer in noble gases was estimated by the intensity of the α-line of the Balmer series of the tritium atom 3Hα (656.2 nm). A tritium release was observed at 710 K due to the beginning of desorption of thermalized tritium atoms dissolved in the liquid phase of lithium. The results are of interest in terms of clarifying the mechanisms and developing models that allow for describing the processes of generation, diffusion, and release of tritium from lithium during neutron irradiation.

The magnetic field design of a solenoid for the cold-cathode Penning ion source of a miniature neutron tube

A high-yield and beam-stable neutron tube can be applied in many fields. It is of great significance to the optimal external magnetic field intensity of the cold-cathode Penning ion source (PIS) and precisely controls the movement of deuterium (D), tritium (T) ions and electrons in the source of the neutron tubes. A cold-cathode PIS is designed based on the solenoidal magnetic field to obtain better uniformity of the magnetic field and higher yield of the neutron tube. The degree of magnetic field uniformity among the magnetic block, double magnetic rings and solenoidal ion sources is compared using finite element simulation methods. Using drift diffusion approximation and a magnetic field coupling method, the plasma distribution of hydrogen and the relationship between plasma density and magnetic field intensity at 0.06 Pa pressure and a solenoid magnetic field are obtained. The results show that the solenoidal ion source has the most uniform magnetic field distribution. The optimum magnetic field strength of about 0.1 T is obtained in the ion source at an excitation voltage of 1 V. The maximum average number density of monatomic hydrogen ions (H+) is 1 × 108 m−3, and an ion-beam current of about 14.51 μA is formed under the −5000 V extraction field. The study of the solenoidal magnetic field contributes to the understanding of the particle dynamics within the PIS and provides a reference for the further improvement of the source performance of the neutron tube in the future.

Computer simulation of the sputtering energy thresholds for some plasma-facing component materials irradiated with helium, deuterium, and tritium ions

Simulations for low-energy irradiation of nuclear Fusion plasma’s ion species on several plasma-facing materials were performed. This study is devoted to determining the minimum incident ion energy to cause sputtering or what is known as the “sputtering energy threshold” Eth. The simulations have been performed on various materials such as tungsten, graphite, and beryllium irradiated with various light ionic species such as helium, deuterium, and tritium. Two different Monte-Carlo-based simulation programs were used to perform this task. One of the latest versions of the state-of-the-art SDTrimSP simulation program was used in this study and complemented by the RDS-BASIC simulation program which was specifically designed to perform reasonably accurate and detailed calculations for the low–energy ions irradiation. The later simulation program also adopts a special and more realistic treatment accounting for the reduction in the atomic displacement threshold in the top surface monolayer. The simulation results were also compared with experimental data and theoretical data fittings.

Extension of the energetic particle transport kick model in TRANSP to multiple fast ion species

Alfvénic instabilities (AEs) are well known to cause enhanced transport of energetic particles (EPs) in fusion devices. Most studies until now have focused on characterizing and understanding AE stability in single-species plasmas heated by neutral beams (NB), where deuterium is typically used as both main plasma species and NB fuel. As the fusion community moves toward fusion reactors that target burning plasma conditions, such as ITER, the single-species picture breaks down. Burning plasmas, which will use a mix of deuterium and tritium (DT) as main fuel, also feature the presence of several supra-thermal fusion products such as alpha particles, protons, helium isotopes and high-energy tritium ions. This work presents the extension of the EP transport kick model implemented in the TRANSP time-dependent tokamak transport code to study the combined effect of multiple EP species on AE stability and, in turn, the response of different EP species to plasma instabilities in terms of their redistribution and losses. Further validation of the enhanced model is planned based on experimental results expected from the JET DT campaign scheduled for 2021, in preparation for ITER plasmas and beyond.

On the definition of the deuterium-tritium ion beam parameters for the SORGENTINA-RF fusion neutron source

The SORGENTINA-RF project aims to develop a 14 MeV fusion neutron source to produce medical radioisotopes with special focus on ^{99}Mo. The facility is based on a positive ion source with an acceleration stage to produce a deuterium (D^{+}) and tritium (T^{+}) ion beam that, impacting on a titanium-coated rotating target, allows fusion reactions to take place. Maximizing the neutron production rate is one of the main issues to be addressed in the project and the optimization of some key parameters of the ion beam is of paramount importance in this regard. In this study, a methodology is discussed to reach a definition of the beam characteristics for an effective and sustainable operation of the plant. The most convenient layout that has been found out is based on a single ion source fed by a deuterium and tritium gas mixture. Eventually, a series of considerations about the operation of the ion source and fuel cycle have been drawn.

Preliminary Assessment of Radiolysis for the Cooling Water System in the Rotating Target of SORGENTINA-RF

The SORGENTINA-RF project aims at developing a 14 MeV fusion neutron source featuring an emission rate in the order of 5–7 × 1013 s−1. The plant relies on a metallic water-cooled rotating target and a deuterium (50%) and tritium (50%) ion beam. Beyond the main focus of medical radioisotope production, the source may represent a multi-purpose neutron facility by implementing a series of neutron-based techniques. Among the different engineering and technological issues to be addressed, the production of incondensable gases and corrosion product into the rotating target deserves a dedicated investigation. In this study, a preliminary analysis is carried out, considering the general layout of the target and the present choice of the target material.

An Assessment Via Computer Simulation of the Sputtering Energy Thresholds for Some Plasma-Facing Component Materials Irradiated with Helium, Deuterium, and Tritium Ions

An Assessment Via Computer Simulation of the Sputtering Energy Thresholds for Some Plasma-Facing Component Materials Irradiated with Helium, Deuterium, and Tritium Ions

Optical Radiation from the Sputtered Species under Excitation of Ternary Mixtures of Noble Gases by the 6Li(n,α)3H Nuclear Reaction Products

The present paper examines the luminescence of ternary Ar-Kr-Xe and Ne-Ar-Kr mixtures of noble gases in the spectral range from 300 to 970 nm, excited by the 6Li(n,α)3H nuclear reaction products in the core of a nuclear reactor. A thin layer of lithium applied on the walls of the experimental device, stabilized in the matrix of the capillary-porous structure, serves as a source of gas excitation. During in-pile tests, conducted at the IVG.1M research reactor, thermal neutrons interact via the 6Li(n,α)3H reaction, and the emergent alpha particles with a kinetic energy of 2.05 MeV and tritium ions with a kinetic energy of 2.73 MeV excite gaseous medium. The study was carried out in a wide temperature range. The temperature dependence of the intensity of the emission of the atoms of noble gases and alkali metals, heteronuclear ionic molecules of noble gases were studied. The obtained values of the activation energy of the emission process 1.58 eV for lithium and 0.72 eV for potassium agree well with the known values of evaporation energy. Excitation of alkali metals atoms occurs consequently of the Penning process of alkali metals atoms on noble gas atoms in the 1s-states and further ion-molecular reactions.

Polarized proton acceleration in ultraintense laser interaction with near-critical-density plasmas.

The production of polarized proton beams with multi-GeV energies in ultraintense laser interaction with targets is studied with three-dimensional particle-in-cell simulations. A near-critical density plasma target with prepolarized proton and tritium ions is considered for the proton acceleration. The prepolarized protons are initially accelerated by laser radiation pressure before injection and further acceleration in a bubblelike wakefield. The temporal dynamics of proton polarization is tracked via the Thomas-Bargmann-Michel-Telegdi equation and it is found that the proton polarization state can be altered by both the laser field and the magnetic component of the wakefield. The dependence of the proton acceleration and polarization on the ratio of the ion species is determined and it is found that the protons can be efficiently accelerated as long as their relative fraction is less than 20%, in which case the bubble size is large enough for the protons to obtain sufficient energy to overcome the bubble injection threshold.

Thermal decoupling of deuterium and tritium during the inertial confinement fusion shock-convergence phase.

A series of thin glass-shell shock-driven DT gas-filled capsule implosions was conducted at the OMEGA laser facility. These experiments generate conditions relevant to the central plasma during the shock-convergence phase of ablatively driven inertial confinement fusion (ICF) implosions. The spectral temperatures inferred from the DTn and DDn spectra are most consistent with a two-ion-temperature plasma, where the initial apparent temperature ratio, T_{T}/T_{D}, is 1.5. This is an experimental confirmation of the long-standing conjecture that plasma shocks couple energy directly proportional to the species mass in multi-ion plasmas. The apparent temperature ratio trend with equilibration time matches expected thermal equilibration described by hydrodynamic theory. This indicates that deuterium and tritium ions have different energy distributions for the time period surrounding shock convergence in ignition-relevant ICF implosions.

Application of High-Energy Tritium Ions and Alpha Particles Formed in 6Li(n,α)T Nuclear Reaction to Excite the Luminescence of Inert Gas Mixtures

The paper describes the technology of creating a surface source of high-energy tritium ions and alpha particles formed as a result of a nuclear reaction of the interaction of the 6Li isotope with thermal neutrons . Different design versions of the developed irradiating ampoule devices are presented, and a description of the experimental reactor facility is given. The paper also describes the scheme of reactor experiments to study the spectral-luminescent characteristics of nuclear-excited plasma of argon. The results of test experiments are presented, and they show the applicability of high-energy tritium ions and alpha particles for nuclear excitation of luminescence of inert gas mixtures.

Direct-drive target designs as energetic particle sources for the Laser MégaJoule facility

This work aims to analyse the possibility of directly driven imploding spherical targets in order to create a source of energetic particles (neutrons, protons, alphas, tritium and 3He ions) for the Laser MégaJoule facility. D3He gas-filled spherical SiO2 glass pellets, irradiated by an absorbed laser intensity of 1014 W cm−2 or 1015 W cm−2 have been considered. Depending on the absorbed laser intensity and the amount of the ablated glass layer two distinct regimes have been identified: a massive pusher and an exploding pusher. Both regimes are analysed in terms of hydrodynamics and fast particle spectra. Energetic particle time-resolved spectra are calculated and used to infer ionic temperatures and total areal densities. A parametric study has been performed by varying the shell thickness and target inner radius for both laser absorbed intensities.

Isotope and chemical composition of monthly precipitation collected at Sapporo, northern part of Japan during 2015-2019

The aim of this study is to measure tritium concentrations, δ2H, δ18O and ion concentration in monthly precipitation collected at Sapporo, the northern part of Japan and to understand the regional precipitation chemistry. Tritium concentrations of monthly precipitation in Sapporo from July 2015 to the end of 2019 ranged from 0.24 to 1.59 Bq/L with a mean value (±S.D.) of 0.68 ± 0.30 Bq/L. Tritium seasonal patterns were determined with higher tritium concentrations in spring and lower tritium concentrations in summer. It was higher than the reported values in the southern area of Japan. It seemed that tritium concentrations changed with the meteorological conditions depending on the air masses of continental or marine origin and the contribution of cosmogenic tritium from the upper atmosphere. The strong correlation was found between tritium concentrations and NO3− and NH4+ (p < 0.05). It is necessary to accumulate more data as to long-term monitoring for a reliable analysis of ambient tritium concentrations.

The role of collisionless trapped electron mode turbulence on removal of helium ash and transport of deuterium-tritium ions

Removal of helium ash and the anomalous transport of deuterium (D) and tritium (T) ions driven by collisionless trapped electron mode (CTEM) turbulence in tokamak plasmas with weak magnetic shear are studied. We derive the eigenvalue of CTEM with helium ash, and calculate the quasi-linear turbulent fluxes of helium ash, D and T ions simultaneously. Based on the analytical results, the parametric dependence of CTEM instability as well as the anomalous transport of helium ash and D-T ions is investigated, in order to explore the parameter region that is favorable for expelling more helium ash than D and T ions. It is found that helium ash with higher temperature and steeper density profile plays a role of destabilizing CTEM instability, and has higher transport level than that of T ions. We also find that increasing electron temperature and flattening electron density profile are favorable for exhausting helium ash. Isotopic effects (i.e. increasing the fraction of T ions) enhance the transport of both helium ash and D-T ions. Moreover, the trend of stronger transport level of helium ash than that of D-T ions is enhanced by raising electron temperature and flattening electron density profile as well as isotopic effects. Besides, the diffusivity is much larger than the convection. This indicates that the CTEM turbulence driven helium ash transport is favorable for removing helium ash under the parameter region used in the present paper. The possible relevance of our theoretical results to experimental observations is also discussed.

Numerical Calculation on Recycling Ratio of Tritium from Tungsten Wall Used in Current CFETR Design

The recycling of tritium from plasma facing wall is an important neutral fuel source (in atomic and molecular form) for plasma confinement and particle control. In this study, the recycling process at tungsten wall based on current CFETR design was modeled. Monte Carlo code SRIM was used to model the implantation of energetic tritium ions into pure tungsten and to get back-scattering fraction of ions and the distribution of implanted tritium ions. The diffusion process of atoms in materials, with recombination at surface as boundary condition, was simulated using numerical approach for both stead and transient state. The total recycling ratio was contributed by fast process (implantation and back scattering) and slow process (diffusion and recombination) and its value nearly equals to 1 for stead state. Temporal dependence of total recycling ratio mainly depended on the slow process and was limited by diffusion coefficient in the bulk near surface and existence of traps in material. For tungsten material with good surface condition, the time of 90% recycling was characterized as 1 ms and affected by temperature, recombination coefficient and concentration of traps while the thickness of material had less affection. Isotope effect that recycling ratio of tritium was larger than that of deuterium at the same situation was also found in the simulation and this effect may affect particle balance and fueling in D-T plasma operation. A collection of theoretical models to estimate the recycling ratio and its time dependence were also summarized and validated by the simulation results.

Absorbed doses from GCR and albedo particles emitted by the lunar surface

When high energy galactic cosmic ray (GCR) particles collide with the lunar regolith, they eject “albedo” particles from the surface. The albedo particles could be either scattered incident ions, or secondary ions and neutrons produced by the collisions of incident ions with the lunar regolith. In an effort to understand the nature of these albedo particles, we use the MCNP6 transport code to estimate the angular and energy distribution of albedo particles at an altitude of 50 km to calculate the resulting total absorbed dose rates, which are compared with measurements from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument aboard the Lunar Reconnaissance Orbiter (LRO) spacecraft. MCNP6 simulations estimate that the albedo particles account for 19.9% of the total absorbed dose rate. The albedo photons account for 8.81% of the total absorbed dose rate, the highest among albedo species followed by protons (4.97%), electrons (2.47%), positrons (1.89%), neutrons (1.17%), deuterons (0.5%), tritium ions (0.07%), helium-3 ions (0.02%), and alphas (0.01%). In addition, recent studies indicate the presence of hydrogen on the Moon. We simulate a hypothetical lunar regolith enriched with hydrogen to study its effect on the lunar albedo. The results herein show that the proton absorbed dose rate is slightly increased if hydrogen is present in the regolith, which is primarily caused by the increased flux of energetic albedo protons leaving the lunar surface.

Influence of Lithium Vacancy Defects on Tritium Diffusion in β-Li2TiO3.

Lithium metatitanate, Li2TiO3, is a leading candidate for application as a tritium breeding material in a future fusion reactor. Following transmutation of lithium, the tritium must escape the crystal in order to be extracted for use in the fusion plasma. The rate-limiting step to release tritium from the Li2TiO3 pebbles is diffusion through the crystal grains. In this work, the activation barriers for tritium diffusion have been calculated using density functional theory. The results show that tritium can diffuse as an interstitial with a barrier of 0.52 eV. However, when a tritium ion becomes bound to a lithium vacancy defect, the energy required to either detrap the tritium from the vacancy or for the cluster to diffuse increases to >1 eV. Overall, these results suggest that the introduction of lithium vacancies due to Li burn-up may lead to an increase in tritium retention in the pebbles.

Theoretical evaluation of tritium release parameters from Near-Surface layer of the Li15.7Pb eutectics under neutron irradiation at the IVG.1 M reactor

The studies described in this paper are devoted to the study of the mechanisms of tritium ions formation in the near-surface layer of the Li15.7Pb lithium–lead eutectic under irradiation at the IVG.1 M reactor; studying the process non-diffusion output of tritium ions from the eutectic due to its own high energy. The paper describes the tritium release from the near-surface layer of the eutectic in detail. The calculations of the length and volume of the near-surface layer of the sample are presented. The rate of tritium generation in this material during its irradiation at the IVG.1 M reactor was determined. Based on the obtained data, a theoretical estimation of tritium release from the near-surface layer of the Li15.7Pb lithium–lead eutectic has been done and a comparison with experimental data has been presented.

1S-2S energy shift in muonic hydrogen

We calculate corrections of orders α4, α5, α6 to the (1S – 2S) fine structure interval in muonic hydrogen (μp), muonic tritium (μt) and muonic helium ion $$((\mu _2^3He) + )$$. They are determined by the effects of vacuum polarization, nuclear structure and recoil and relativistic corrections. The nuclear structure effects are taken into account in terms of the charge radii of the nuclei in one-photon interaction and in terms of electromagnetic form-factors in the case of two-photon interaction. The obtained results for the (1S – 2S) splitting can be used for a comparison with future experimental data.