3He Concentrations Research Articles

Effect of temperature and heat input on helium isotope separation driven by an entropy filter

To understand the effect of temperature and heat input on helium isotope separation driven by an entropy filter, the thermomechanical flow of superfluid helium through an entropy filter for obtaining high purity 4He is experimentally investigated. For this method, there are two important indicators: separation flow (flow rate) and separation effect (3He concentration). The separation flow rate is examined at various temperatures ranging from 1.6 K to 1.9 K of feed helium. Different heat inputs (Q) are applied to the entropy filter outlet to drive superfluid 4He flowing through the porous element. The results demonstrate that the flow rate increases as the feed helium temperature decreases and heat input increases. Simultaneously, 3He diffusion is detected as the superfluid helium passes through the entropy filter. The concentration of 3He, filtered at different temperature ranging from 1.6 K to 1.9 K, are analyzed using HELIX SFT Static Vacuum Mass Spectrometer. The findings reveal that the 3He concentration decreases with an increase in the temperature of the feed helium bath. 3He concentration of feed helium is around 3.3×10-8. Specifically, the 3He concentration in the filtered helium at 1.6 K is approximately 3.2×10-10, while at 1.9 K, it reduced to 2.2×10-10. This suggests that 3He diffusion in He II is inversely proportional to the He II temperature from 1.6 K to 1.9 K, resulting in a lower 3He concentration at higher temperatures.

Feasibility of 129I groundwater dating calibrated by both 81Kr and 4He for the assessment of deep geological repositories in Japan

Iodine-129, which is a promising tracer for dating old groundwater, has been used as a tracer for deep upwelling groundwater. The nuclide is expected to be one of the key factors for site selection for high-level radioactive waste disposal, which is a global societal issue. The pre-anthropogenic 129I/127I ratio for marine iodine is (1.50 ± 0.15) × 10−12, which could be considered the initial value for 129I dating. This study identifies the challenges in groundwater age dating using 129I/127I. We measured the ratios of 129I/127I and 81Kr/Kr and concentration of 4He in groundwater from boreholes on the northern coast of Japan. The 129I dating results were not coincident with the other groundwater dating results. The iodine in the groundwater was inferred to be released in situ from marine organisms in sediments of various ages. We estimated that the primordial iodine ratio originating from seawater was ~ 1 × 10–13 (8 × 10–14 ~ 2 × 10–13). The groundwater age deduced from the 129I/127I ratio using this value agrees with other groundwater dating results.

New insight into groundwater 4He ages based on Ne isotopic equilibrium in Jianghan Plain, Central China

The change of hydrostatic pressure caused by the fluctuation of groundwater table in the aquifer will lead to the partial dissolution of excess 4He gas, resulting in the isotope imbalance of 3He/4He-4He. The dissolved Ne in groundwater is mainly derived from the atmosphere, and its isotopic composition can correct the isotopic imbalance of 3He/4He-4He. We collected thirty-eight groundwater samples from the second aquifer of the Jianghan Plain, and the isotopic concentrations and ratios of He and Ne were measured. 21Ne/22Ne-20Ne/22Ne illustration is proposed to estimate the shares of atmospheric and mantle components. The 21Ne content and isotopic ratios of atmospheric and mantle components are used to estimate a calculated Ne content. The difference between the calculated Ne content and the measured Ne content (∆Ne) is used to evaluate the percentage of error estimated“excess air”. The accumulation of crustal 4He is corrected with the measured 4He content and the percentage of error estimated “excess air”. We found the maximum percentage of error estimated “excess air” was 7.57 % occurring in the groundwater samples from the second aquifer of Jianghan Plain, and the disequilibrium of 3He/4He-4He led to overestimation of the share of mantle He. The percentage of mantle He in total dissolved components is reassessed and range from 0.03 % to 0.74 %, indicating the mantle component is minor. The reassessed 4He ages (1.79 ka to 21.90 ka) were uniformly older than those estimated by traditional method which only use the measured 3He/4He ratio to distinguish the crust 4He (1.28 ka to 18.74 ka). 4He age is significantly underestimated up to 47.05 %.

Noble gas characteristics of microbial gas in the Qaidam Basin, China: Implications for helium enrichment processes

Helium is a critical, strategic and nonrenewable resource with limited reserves and unstable supplies. However, the helium sources and migration processes in petroliferous basins remain unclear. The Qaidam Basin features multiple reservoir layers, multiple genetic types of natural gas, and varying helium concentrations, providing an ideal natural laboratory for understanding the helium enrichment processes. Here, we present the original noble gas isotopic compositions and major gas components of 11 microbial gas samples from three gas layers in the Sebei No.1 gas field, eastern Qaidam Basin, China. The helium isotopic ratios range from 0.007 to 0.057 Ra, reflecting a predominantly crustal source. The Quaternary Sebei microbial gas features much lower helium concentration (0.0003–0.001%), 21Ne/22Ne ratio (0.031–0.034), and 40Ar/36Ar ratio (292–380) than thermogenic natural gases in the Qaidam Basin. The middle gas layer (II) of the Sebei gas field features higher 21Ne/22Ne and 40Ar/36Ar ratios than the top and bottom gas layers, displaying positive correlations with higher 4He groundwater concentrations before degassing, as calculated from 4He/20Ne ratios and 20Ne concentrations in air-saturated water. However, the correlations between the 4He contents in natural gas and the 21Ne/22Ne and 40Ar/36Ar ratios are unclear, suggesting that 4He dissolves into the groundwater system before degassing into a gas reservoir and that the variations in the 4He concentration in the gas phase are caused by the different levels of hydrocarbon dilution. Quantitative calculations of helium production revealed an external helium flux from the crustal basement except for the in-situ production from sedimentary strata even in this broadly-defined self-generating and self-preserving natural gas system. The helium resources in the Qaidam Basin are mainly distributed in tectonically active zones with uplifted pre-Jurassic basement rocks (providing sufficient helium sources), ancient groundwater systems (accumulating more helium) and suitable hydrocarbon production (acting as a carrier gas but diluting helium as slightly as possible).

Decoding degassing modes of magma chamber of arc volcanoes: Insights from CO2/Cl and Cl/H2O ratios of magmatic fluids in groundwater

The H2O-CO2-Cl composition of the fluids released from the magma chambers for arc volcanoes was calculated based on the solubilities of H2O and CO2 in the silicate melt and the partition coefficient of Cl between the aqueous fluid and melt for the stages defined by a simple evolution model of the magma chamber. The degassing modes consisted of mafic bubbling (MB: first boiling) and felsic bubbling (FB: second boiling) releasing fluids as separate bubbles due to the mafic magma supply and felsic magma formation by differentiation, respectively, and felsic solidification (FS) releasing fluid due to felsic pluton formation. The variations in the CO2/Cl and Cl/H2O ratios of the fluids were examined for each degassing mode at pressures ranging from 150 to 400 MPa and were found to have very large variations at 0.00024–845 for CO2/Cl and 0.00043–0.041 for Cl/H2O. The CO2/Cl is concluded to be a good indicator of magma chamber conditions because each mode has a specific ratio distinguished from that of the other modes; i.e., CO2/Cl > 43 for MB, 0.027–23 for FB, and < 0.62 for FS.The alteration of magmatic composition of fluid during ascent was discussed considering the phase separation of fluid, CO2 bubbling in groundwater, dissolution, and deposition of minerals; furthermore, the limitation of the method when applied to natural groundwater systems were outlined. This method was tested for a natural volcanic system, the Kuju volcano in central Kyusyu, Japan, which is an active volcano complex composed of various magma types from rhyolitic to basaltic, replacing the eruption centers from west to east. Groundwater samples from springs and boreholes were collected and analyzed for chemical and isotopic compositions to determine the magmatic H2O, dissolved inorganic carbon (DIC), and Cl concentrations. The new approach to determine the magmatic CO2 concentration in groundwater using 3He concentration proposed herein cancelled the effect of carbonate deposition/dissolution, addition of DIC from organic matter, and bubbling of CO2. The estimated magmatic CO2/Cl ratios were 0.0009–14, which overlapped consistently with the modeled variation in the CO2/Cl ratio. The spatial variation of magmatic CO2/Cl in groundwater showed that higher-CO2/Cl are found near the central part of the volcanic complex which composed of felsic to mafic volcanoes, and low-CO2/Cl are only found around old felsic volcanoes. The CO2 bubbling springs were found to be associated with younger mafic volcanoes. The condition of the magma chambers, as shown by the spatial variation in CO2/Cl, were consistent with the record of the eruptive activities of the Kuju volcano. The CO2/Cl method proposed in this study using groundwater is useful for estimating magmatic conditions in chambers.

Likely Common Coronal Source of Solar Wind and 3He-enriched Energetic Particles: Uncoupled Transport from the Low Corona to 0.2 au

Parker Solar Probe (PSP) observations of a small dispersive event on 2022 February 27 and 28 indicate scatter-free propagation as the dominant transport mechanism between the low corona and greater than 35 solar radii. The event occurred during unique orbital conditions that prevailed along specific flux tubes that PSP encountered repeatedly between 25 and 35 Rs during outbound orbit 11. This segment of the PSP orbit exhibits almost stationary angular motion relative to the rotating solar surface, such that in the rotating frame, PSP’s motion is essentially radial. The time dispersion often observed in impulsive solar energetic particle (SEP) events continues in this case down to velocities including the core solar-wind ion velocities. Especially at the onset of this event, the 3He content is much larger than the usual SEP abundances seen in the energy range from ∼100 keV to several MeV for helium. Later in the event, iron is enhanced. The compositional signatures suggest this to be an example of an acceleration mechanism for generating the seed energetic particles required by shock (or compression) acceleration models in SEP events to account for the enrichment of various species above solar abundances in such events. A preliminary search of similar orbital conditions over the PSP mission has not revealed additional such events, although favorable conditions (isolated impulsive acceleration and well-ordered magnetic field connection with minimal magnetic field fluctuation) that would be required are infrequently realized, given the small fraction of the PSP trajectory that meets these observation conditions.

New insights into the flow dynamics of a deep freshwater aquifer in the semi-arid and saline Cuvelai-Etosha Basin, Northern Namibia: Results of a multi-environmental tracer study

Study regionA paleo-megafan system of the Cubango River in the northern parts of the semi-arid Cuvelai-Etosha Basin, shared by Angola and Namibia. It hosts a deep freshwater aquifer, the so-called Kalahari-Ohangwena 2 (KOH-2), with the potential to resolve the imminent regional water supply shortages. Study focusHydrogeochemical and multi-environmental tracer studies incorporating the use of age tracers 14C, 36Cl, 81Kr and 4He to determine the age of groundwater and provide insights into the flow dynamics of the KOH-2. New hydrological insights for the regionStable water isotopes and noble gas thermometry show that in a period with higher rainfall and recharge, temperatures were at least 3 – 4 °C lower than today. Several arguments led to the conclusion that younger groundwater, possibly of an age of 35,000 years, is mixed with ancient saline pore water. These include: 1) the correlation of measured 36Cl and 81Kr ratios, as well as 4He concentrations, using a binary mixing model, and 2) the substantial variation in 81Kr ages, ranging from 40,000 to 170,000 years, over relatively short distances—a phenomenon challenging to explain by advective groundwater flow equations. Consequently, the ages derived from 81Kr measurements serve as indicators of the extent of freshening and therefore describe mixing ages rather than absolute travel times.

Steady-State simulation of cryogenic distillation used for helium isotope separation

Helium-3 (3He) is an invaluable and scarce resource with applications in various scientific and industrial fields. It is typically found mixed with helium- 4(4He) in natural gas and nuclear off-gas, which is industrial source of helium. Therefore, separation of the helium isotope is necessary. Cryogenic distillation is a preferred method of separation due to its higher separation coefficient and processing capacity. In this study, a numerical steady-state simulation of cryogenic distillation column for helium isotope has been conducted using programming. The mathematical model for the equilibrium-state cryogenic distillation process was established and solutions of the thermodynamic formulation was proposed. The simulation provided the distribution of 3He and 4He along each distillation column as well as the profiles of temperature and flow rates along the column, based on the designed specifications including the composition of the feeding mixture, feed flow rate and pressure. The required heat duty of the condenser and reboiler was also calculated, and the column dimensions were estimated. Besides, we have studied the effects of the reflux ratio and feed concentration of 3He on the final isotopic contents of the top and bottom products. The results demonstrated that the distillation simulation could provide crucial theoretical support for the smooth execution of future laboratory experiments.

Improving the Accessibility and Efficiency of Proton Irradiations for 4He/3He Thermochronology

AbstractSynthesizing uniform and high concentrations of 3He within minerals via high‐energy proton irradiation is paramount for 4He/3He thermochronology and helium diffusion kinetic studies. Proton irradiations of geological material have hitherto exclusively been routinely conducted at the Francis H. Burr Proton Therapy Center (FHB); we thus explored alternative irradiation protocols at two European‐based facilities with the intention to improve the accessibility and efficiency in obtaining 4He/3He data. We conducted a single irradiation at the Paul Scherrer Institute (PSI) using an approach most similar to that used at FHB (wide, high‐energy beam), and four irradiations at the Helmholtz Zentrum Berlin (HZB) using a newly developed in‐vacuum irradiation protocol in a narrow, lower‐energy but high‐intensity beam. Internal shards of Durango apatite were irradiated in all experiments; 4He/3He release spectra and bulk 3He concentrations of PSI and HZB‐irradiated Durango shards were compared to those from FHB to assess the quality of each experiment in terms of the quantity and uniformity of synthesized 3He. While 3He was uniformly synthesized in PSI‐irradiated Durango shards, the bulk 3He concentration was below the required threshold due to limitations on the maximum allotted proton flux. Over the course of four irradiation experiments at HZB, the protocol evolved to ensure that uniform and high concentrations of 3He can be consistently induced. Furthermore, we demonstrate how HZB irradiations can be replicated using computer simulations, permitting the use of simulations to inform future modifications of the irradiation protocol in order to optimize the uniformity of the 3He distribution across all irradiated samples.

Identification of modern meteoric water, glacial meteoric water, and fossil seawater in a deep borehole at the coastal area of Horonobe, north Japan, using groundwater dating and paleoclimatic proxy methods

Groundwater flow in deep areas of coastal regions has attracted significant attention for geological radioactive waste disposal or geological CO2 storage. To investigate groundwater flow in coastal areas, groundwater dating methods with the potential to assess slow groundwater flow were used at depths of up to 1200 m at Hamasato, Horonobe, northern Japan. Multiple groundwater dating methods were applied using pore water in drilling core and pumping groundwater. This study shows that modern meteoric water, glacial meteoric water, and fossil seawater are distributed in sand and silt layers at 300–360 and 90–300 m in depth and in silt and mud layers below 800 m in depth, respectively. Modern meteoric water infiltrated after and glacial meteoric water infiltrated during the latest glacial period were identified using δD and δ18O values, estimated recharge temperature from noble gas concentrations, and 14C concentrations. The estimated recharge temperatures of modern and glacial meteoric waters were 8.1 ± 2.0 and 2.1 ± 2.0 °C, respectively, whereas the δD and δ18O values were −68 ± 3‰ and −10.3 ± 0.2‰, −81 ± 2‰ and −11.4 ± 0.3‰, respectively. The 14C age of modern meteoric water was 10–16 ka. However, the 14C age of glacial meteoric water could not be estimated because it was highly diluted by 14C-free CO2 from methanogenesis and marine carbonate dissolution. Fossil seawater was identified using δD, δ18O, 36Cl, and 4He. δD and δ18O values underwent water-rock interaction and approached inland fossil seawater with increasing depth. 36Cl/Cl values did not reach secular equilibrium in situ in the Yuchi Formation due to its relatively short geological age and consolidation-induced porosity changes. However, the Yuchi Formation seawater is considered extremely old because its 36Cl/Cl ratio is higher than that of modern seawater as a result of 36Cl production, which also explains the observed 36Cl/Cl increases with depth toward the secular equilibrium ratio (36Cl/Clse). 4He concentrations were in the order of 10−6 ccSTP/gw, corresponding to an in situ accumulation age of 1–2 Ma, neglecting the external flux. The contribution of external flux could be negligible for the short geological age and rapid sedimentation rates. 4He ages were equivalent to the geological age of the Yuchi Formation. Core investigations can interpolate groundwater investigations because cores, particularly those from low-hydraulic conductivity layers, can be collected continuously. In addition, stable and radioactive isotopes and noble gases can help identify modern meteoric water, glacial meteoric water, and fossil seawater, assisting in understanding the groundwater flow velocity.

Terrigenic helium in brackish groundwaters of Kuwait, probable influences from hydrocarbon resources

The presence of helium in groundwater can shed light on its age, migration patterns, and potential recharge locations. The 4He, 3He/4He, 20Ne, and major ions concentrations in groundwater samples were analysed. He concentration in groundwaters of the Kuwait group aquifers ranged from 3.82 × 10−8 to 1.33x−6 cm3STP/g and that of Dammam formation ranged from 9.97 × 10−8 to 1.62 × 10−6 cm3STP/g. The distribution of He was inferred to be influenced by geological structures and it was found that He decreased with Cl concentration and δ18O with few exceptions. The δ18O signatures reflect mixing between aquifers. The higher He fluxes were recorded during the Last Glacial Maximum, but they rose steadily over time. Most of the north Kuwait samples, dating from 1650 to 348 yBP, had a tritiogenic component similar to the present atmosphere, as indicated by RA (Air normalized He ratios) values, which was inferred to be due to the decay of tritium derived from meteoric impact. Magnitude 2–4 earthquake epicenters occurred more frequently in areas with lower RA values. Lateral flow was predominant with insitu (He derived from rock matrix along the flow) and exogenous sources (vertical upward cross formational flow, atmospheric input and from hydrocarbon reservoirs). Groundwater samples near oil fields were found to contain more terrigenic He, suggesting its migration to shallow waters through fault planes. The presence of more He in brackish groundwater at a shallow depth may be indicative of an abundant source beneath. He excess (Heex) and air corrected He excess (ΔHe%) are indicators of non-neuclogenic and radiogenic He sources, such as the exsolution from adjoining hydrocarbon fields through structurally weaker planes.

Estimation of the buildup of He-3 and Li-6 poisoning, He-4 and tritium activity in beryllium oxide reflector block in APSARA-U reactor

The Apsara-U research reactor, situated at the Bhabha Atomic Research Center, began its operation in 2018. This facility employs a fuel core configuration employing low-enriched uranium and reflector assemblies made of beryllium oxide. In neutron-rich environment of a nuclear reactor, these beryllium oxide reflector blocks participate in nuclear reactions identified as 9Be(n,α) and 9Be(n,2n). The 9Be(n,α) reaction initiates the formation of isotopes such as 4He, 6Li, 3He, and 3H in the process. The accumulation of gasses like 3He, 4He, and 3H causes the beryllium oxide reflector to swell, ultimately restricting how long it can effectively serve as a reflector or moderator material within the reactor. Extended periods of reactor shutdown result in a significant increase in the concentrations of 3He, mainly due to the radioactive decay of 3H. 6Li and 3He nuclei have significant neutron capture cross-sections, leading to a reduction in the reactor's reactivity, a phenomenon termed "poisoning". This effect varies depending on factors like neutron flux, neutron flux spectrum, and the reactor's operational history. Thorough investigations have been carried out to gain insights into the accumulation of 4He, 3He, 6Li, and 3H within beryllium oxide and their effects on reactivity considering the diverse levels of neutron exposure it encounters.

Experiments in high-performance JET plasmas in preparation of second harmonic ICRF heating of tritium in ITER

The reference ion cyclotron resonance frequency (ICRF) heating schemes for ITER deuterium–tritium (D-T) plasmas at the full magnetic field of 5.3 T are second harmonic heating of T and 3He minority heating. The wave-particle resonance location for these schemes coincide and are central at a wave frequency of 53 MHz at 5.3 T. Experiments have been carried out in the second major D-T campaign (DTE2) at JET, and in its prior D campaigns, to integrate these ICRF scenarios in JET high-performance plasmas and to compare their performance with the commonly used hydrogen (H) minority heating. In 50:50 D:T plasmas, up to 35% and 5% larger fusion power and diamagnetic energy content, respectively, were obtained with second harmonic heating of T as compared to H minority heating at comparable total input powers and gas injection rates. The core ion temperature was up to 30% and 20% higher with second harmonic T and 3He minority heating, respectively, with respect to H minority heating. These are favourable results for the use of these scenarios in ITER and future fusion reactors. According to modelling, adding ICRF heating to neutral beam injection using D and T beams resulted in a 10%–20% increase of on-axis bulk ion heating in the D-T plasmas due to its localisation in the plasma core. Central power deposition was confirmed with the break-in-slope and fast Fourier transform analysis of ion and electron temperature in response to ICRF modulation. The tail temperature of fast ICRF-accelerated tritons, their enhancement of the fusion yield and time behaviour as measured by an upgraded magnetic proton recoil spectrometer and neutral particle analyser were found in agreement with theoretical predictions. No losses of ICRF-accelerated ions were observed by fast ion detectors, which was as expected given the high plasma density of n e ≈ 7–8 × 1019 m−3 in the main heating phase that limited the formation of ICRF-accelerated fast ion tails. 3He was introduced in the machine by 3He gas injection, and the 3He concentration was measured by a high-resolution optical penning gauge in the sub-divertor region. The DTE2 experiments with 3He minority heating were carried with a low 3He concentration in the range of 2%–4% given the fact that the highest neutron rates with 3He minority heating in D plasmas were obtained at low 3He concentrations of ∼2%, which also coincided with the highest plasma diamagnetic energy content. In addition to 3He introduced by 3He gas injection, an intrinsic concentration of 3He of the order of 0.2%–0.4% was measured in D-T plasmas before 3He was introduced in the device, which is attributed to the radioactive decay of tritium to 3He. According to modelling, even such low intrinsic concentrations of 3He lead to significant changes in ICRF power partitioning during second harmonic heating of T due to absorption of up to 30% of the wave power by 3He.

He Isotopic Composition of Alkaline Intrusions of the Hovsgol Area, Northwestern Mongolia

The He isotopic composition of fluid inclusions in magnetite of alkaline and subalkaline intrusion of the Hovsgol region, Northwestern Mongolia, is studied. The measured 4He content varies from 6.6 × 10–7 to 114 × 10–7 cm3/g. The 3He/4He isotope ratio of most samples is 0.23–0.59 Ra indicating the presence of He from different sources in magmatic fluid. The maximum of mantle He (2.51 Ra) is observed in magnetite of subalkali gabbro. The mantle He component was ~40–60% during the generation of parental magma with possible involvement of subcontinental lithospheric mantle material or a plume-like reservoir less enriched in 3He. The mantle He component did not exceed 10–15% during the evolution of the foidoitic and alkali-syenitic melts because of mixing with crustal radiogenic He. We suggest the interaction of intrusions with fragments of the Precambrian accretionary–collision complexes of the Tuva–Mongolian Terrane. This mixing of He isotopes in melts and fluids can serve as indirect evidence of the development of mantle magmatism at the active continental margin.

Constant 4He Concentration and 190Pt‐4He age of Detrital Pt‐Alloy Grains from the Santiago River, Ecuador: Potential as a 4He Mineral Reference Material

Over the last few decades geo‐ and thermochronological techniques based on the accumulation of radiogenic 4He in minerals have gained popularity. Currently there is no mineral‐based 4He reference material that allows routine screening of gas extraction and measurement procedures. The commonly‐used mineral reference material for (U‐Th)/He thermochronology have variable U and Th contents which result in variable 4He concentrations. Here we demonstrate that native platinum grains (RS‐Pt) from placer deposits in the Santiago River, Ecuador, yield constant 4He contents and may be used as a reference material. Helium concentrations measured at the Scottish Universities Environmental Research Centre (n = 8) and Institute of Precambrian Geology and Geochronology RAS (n = 9) noble gas laboratories yield mean 4He concentrations that overlap at the 95% confidence level. The weighted mean 4He concentration is 215 ± 4 × 1011 at g‐1 (2s) and mean 190Pt‐4He age is 39.6 ± 0.7 Ma (2s). Samples of the Santiago River Pt concentrate are available on request from the SUERC laboratory.

Refractive index measurement of hydrogen isotopologue mixture and applicability for homogeneity of hydrogen solid at cryogenic temperature in fusion fuel system

Deuterium (D)-Tritium (T) nuclear fusion reaction has potential as an energy source in the future. In both magnetic confinement and inertial confinement fusion reactors, solid D–T will generally be supplied as fusion fuel. The efficiency of the nuclear fusion reaction depends on the quality of solid D–T fuel, which is related to the composition, homogeneity, helium-3 (3He) content, and so on. However, there is no technique for in-situ examination of solid D–T fuel. In this study, we consider a simple and precise method for the characterization of solid hydrogen isotopologues at cryogenic temperature using refractive index measurement, and evaluate the distribution of hydrogen isotopologue composition and homogeneity. To evaluate without the effect of tritium decay, the homogeneity of the hydrogen (H2)-deuterium (D2) mixture is measured at first. By the in-situ refractive index measurement at cryogenic temperature, the homogeneity of solid H2–D2 mixture is roughly quantified. The phase diagram of the H2–D2 mixture shows a solid solution type. D2-rich crystal first appears from the liquid phase as a primary crystal. The composition of D2 in liquid phase ias homogeneous, whereas it reduces by obeying the liquidus line in the phase diagram with the crystallization. On the other hand, the composition of the H2–D2 mixture in solid phase is inhomogeneous because the mobility of H2 and D2 in solid phase was too slow to be homogeneous and solid. The compositions of H2–D2 mixture in liquid and solid phases could be evaluated by the in-situ refractive index measurement in time. Consequently, the refractive index measurement shows great potential as an inspection method of solid D–T fuel in fusion reactors.

Multi-Isotope Geochemical Baseline Study of the Carbon Management Canada Research Institutes CCS Field Research Station (Alberta, Canada), Prior to CO2 Injection

Carbon capture and storage (CCS) is an industrial scale mitigation strategy for reducing anthropogenic CO2 from entering the atmosphere. However, for CCS to be routinely deployed, it is critical that the security of the stored CO2 can be verified and that unplanned migration from a storage site can be identified. A number of geochemical monitoring tools have been developed for this purpose, however, their effectiveness critically depends on robust geochemical baselines being established prior to CO2 injection. Here we present the first multi-well gas and groundwater characterisation of the geochemical baseline at the Carbon Management Canada Research Institutes Field Research Station. We find that all gases exhibit CO2 concentrations that are below 1%, implying that bulk gas monitoring may be an effective first step to identify CO2 migration. However, we also find that predominantly biogenic CH4 (∼90%–99%) is pervasive in both groundwater and gases within the shallow succession, which contain numerous coal seams. Hence, it is probable that any upwardly migrating CO2 could be absorbed onto the coal seams, displacing CH4. Importantly, 4He concentrations in all gas samples lie on a mixing line between the atmosphere and the elevated 4He concentration present in a hydrocarbon well sampled from a reservoir located below the Field Research Station (FRS) implying a diffusive or advective crustal flux of 4He at the site. In contrast, the measured 4He concentrations in shallow groundwaters at the site are much lower and may be explained by gas loss from the system or in situ production generated by radioactive decay of U and Th within the host rocks. Additionally, the injected CO2 is low in He, Ne and Ar concentrations, yet enriched in 84Kr and 132Xe relative to 36Ar, highlighting that inherent noble gas isotopic fingerprints could be effective as a distinct geochemical tracer of injected CO2 at the FRS.

Genesis of the Abunabu antimony deposits in the Tethys Himalayan metallogenic belt: Evidence from He–Ar and S isotopes of stibnite

Introduction: The Abunabu antimony mining area is located between the Indus–Yarlung Tsangpo suture and the southern Tibetan detachment system. Ore deposits in the mining area provide an excellent opportunity to understand the nature and genesis of antimony mineralisation in the Tethys Himalayan metallogenic belt.Methods: In this study, we analysed the He–Ar and S isotopic compositions of stibnite-hosted fluid inclusions as a basis for investigating the sources of ore-forming fluids in the Abunabu mining area and the Tethys Himalayan metallogenic belt.Results: The analysed stibnites have 4He contents of 0.016 × 10−7–1.584 × 10–7 cm3 STP/g, 40Ar contents of 1.37 × 10−7–2.94 × 10–7 cm3 STP/g, 40Ar/36Ar ratios of 303.8–320.7, and 3He/4He (Ra) ratios of 0.021–0.351. These isotopic features indicate that the ore-forming fluids were primarily metamorphic fluids of crustal origin, with small amounts of magmatic-derived materials and modified air-saturated water with low 40Ar*/4He ratios. The δ34S values of stibnite vary within a narrow range of −4.9‰ to −3.5‰, with a mean value of −4.31‰, indicating a deep magmatic origin.Discussion: On the basis of these results and a compilation of data for sulphide deposits in the metallogenic belt, we infer that compositional variations in the He and Ar isotopes of the ore-forming fluids of each antimony deposit in the Tethys Himalayan metallogenic belt are independent of each other. This suggests that antimony deposits in the belt had similar ore-forming fluid sources and mixing processes and that differences in the metallogenic tectonic setting within the belt emerged only in the later stages of deposit evolution. Our new results and compiled data also show that antimony–gold deposits and lead–zinc–antimony polymetallic deposits in the Tethys Himalayan metallogenic belt differ in their sulphur isotopic compositions and that multiple sulphur sources were involved in each of these types of deposit.

Cosmogenic 3He paleothermometry on post-LGM glacial bedrock within the central European Alps

Abstract. Diffusion properties of cosmogenic 3He in quartz at Earth surface temperatures offer the potential to directly reconstruct the evolution of past in situ temperatures from formerly glaciated areas, which is important information for improving our understanding of glacier–climate interactions. In this study, we apply cosmogenic 3He paleothermometry to rock surfaces gradually exposed from the Last Glacial Maximum (LGM) to the Holocene period along two deglaciation profiles in the European Alps (Mont Blanc and Aar massifs). Laboratory experiments conducted on one representative sample per site indicate significant differences in 3He diffusion kinetics between the two sites, with quasi-linear Arrhenius behavior observed in quartz from the Mont Blanc site and complex Arrhenius behavior observed in quartz from the Aar site, which we interpret to indicate the presence of multiple diffusion domains (MDD). Assuming the same diffusion kinetics apply to all quartz samples along each profile, forward model simulations indicate that the cosmogenic 3He abundance in all the investigated samples should be at equilibrium with present-day temperature conditions. However, measured cosmogenic 3He concentrations in samples exposed since before the Holocene indicate an apparent 3He thermal signal significantly colder than today. This observed 3He thermal signal cannot be explained with a realistic post-LGM mean annual temperature evolution in the European Alps at the study sites. One hypothesis is that the diffusion kinetics and MDD model applied may not provide sufficiently accurate, quantitative paleo-temperature estimates in these samples; thus, while a pre-Holocene 3He thermal signal is indeed preserved in the quartz, the helium diffusivity would be lower at Alpine surface temperatures than our diffusion models predict. Alternatively, if the modeled helium diffusion kinetics is accurate, the observed 3He abundances may reflect a complex geomorphic and/or paleoclimatic evolution, with much more recent ground temperature changes associated with the degradation of alpine permafrost.

Prediction of ICRF minority heating schemes for JET D–T experiments

Achieving high-performance conditions and maximizing the fusion yield of plasma discharges have been one of the main goals of recent Joint European Torus (JET) campaigns in preparation for its second deuterium–tritium (D–T) campaign. The simulations shown in this work delve into the role of external heating using neutral beam injection (NBI) and radio-frequency waves in the ion cyclotron range of frequencies (ICRF) in order to optimise high fusion performance in the JET tokamak. A baseline discharge with record neutron rate is used as a reference in order to perform a D–T prediction, which considers the NBI+RF synergy. In this work, our focus is on JET’s two main minority schemes, H and 3He. This study tackles the heating mechanisms by which these schemes reach high-performance conditions. The H scheme typically boosts the ICRF fusion enhancement through the second D harmonic heating, whereas 3He minority is characterised by its strong bulk ion heating. Both features are beneficial for increasing the fusion yield. Nevertheless, the minority concentration is a relevant parameter, which needs to be assessed to understand in which concentration ranges the benefits of each particular minority scheme are met. Therefore, the main objective of this work is to assess in which concentration range the ICRF fusion enhancement and bulk ion heating are optimal, for H and 3He, respectively. Under these conditions, our prediction suggests 3He concentration should stay above 1.2% and H should remain below 2.2%.