Deuterium-tritium Mixture Research Articles

High Te discrepancies between ECE and Thomson diagnostics in high-performance JET discharges

The present paper is dedicated to the study of the discrepancies encountered in electron temperature (Te) measurements carried out with electron cyclotron emission (ECE) and Thomson scattering (TS) diagnostics in the core of the JET tokamak. A large database of discharges has been collected, including high-performance scenarios performed with deuterium only and deuterium–tritium mixtures. Discrepancies have been found between core Te measurements taken with an X-mode ECE interferometer (TECE) and a LIDAR TS system (TLID) for Te>5 keV. Depending on the plasma scenario, TECE has been found to be systematically higher or lower than TLID. Discrepancies have also been observed between the peaks of the ECE spectrum in the second (X2) and third (X3) harmonic domains, even in high optical thickness conditions. These discrepancies can be interpreted as evidence of the presence of non-Maxwellian features in the electron energy distribution function (EEDF). In order to investigate the relation between the shape of the EEDF and the measured discrepancies, a model for bipolar perturbations of Maxwellian EEDF has been developed. The model allows analytical calculations of ECE absorption and emission coefficients; hence, the comparison of modeled ECE spectra with experimental data. The different experimental results observed for the various JET scenarios have been found to be qualitatively reproducible by adapting the model parameters, suggesting that bipolar distortions of the bulk EEDF could play a role in giving rise to the reported discrepancies between ECE and TS measurements.

Refractive Index Measurements of Solid Hydrogen Isotopologues

Fuel pellets made of a solid deuterium-tritium (D-T) mixture are supplied for inertial confinement fusion. Characterization of the D-T mixture is fundamental for the design and production of high-quality fuel pellets. However, during the phase transition, isotopologue fractionation may lead to fractional crystallization in the solid phase of the hydrogen isotopologue mixture. If this phenomenon occurs in solid D-T fuel, it will reduce the reaction efficiency of nuclear fusion. Currently, there is no effective observation method for fractional crystallization. This study aims to quantify the degree of fractional crystallization of the hydrogen isotopologues mixture in the solid phase using the refractive index measurement. For this method, refractive index information on the hydrogen isotopologues is necessary, therefore the temperature and wavelength dependences of the refractive index of hydrogen isotopologues need to be measured. Then, using the refractive index distribution of the solid D-T will show the composition distribution of isotopologues for assessing the fractional crystallization. Particularly, as far as we know, this is the first time that the measured values of the refractive index versus wavelength of solid D2 have been obtained. Understanding the wavelength dependence of the refractive index for the dispersion compensation allows for a wider application of the fractionated crystallographic observation method.

Characterisation of divertor detachment onset in JET-ILW hydrogen, deuterium, tritium and deuterium–tritium low-confinement mode plasmas

Measurements of the ion currents to and plasma conditions at the low-field side (LFS) divertor target plate in low-confinement mode plasmas in the JET ITER-like wall materials configuration show that the core plasma density required to detach the LFS divertor plasma is independent of the hydrogenic species protium, deuterium and tritium, and a 40%/60% deuterium-tritium mixture. This observation applies to a divertor plasma configuration with the LFS strike line connected to the horizontal part of the LFS divertor chosen because of its superior diagnostic coverage. The finding is independent of the operational status of the JET cryogenic pump. The electron temperature (Te) at the LFS strike line was markedly reduced from 25 eV to 5 eV over a narrow range of increasing core plasma density, and observed to be between 2 eV and 3 eV at the onset of detachment. The electron density (ne) peaks across the LFS plasma when Te at the target plate is 1 eV, and spatially moves to the X-point for higher core densities. The density limit was found approximately 20% higher in protium than in tritium and deuterium-tritium plasmas.

Radiochemical reaction products of T2/DT and CO under different tritium pressures

The radiochemical reaction products of T2/DT-CO system with different tritium pressures were studied in this work. The results show that the pressure of tritium and reactant was the key factor affecting the reaction rate of T2/DT-CO system, and the reaction products were closely related to the initial tritium concentration. Gradual evolution of reaction products including multi-carbon and multi-oxygen organic compounds were jointly affected by tritium decay in reactant molecules and bond breaking of reactant molecules by β-rays released from tritium decay. In addition, the tritium concentration in the deuterium-tritium mixture also affected the reaction products. High tritium concentration was conducive to the formation of multi-oxygen organics, while low tritium concentration was helpful to produce multi-carbon organics.

Roles of resonant muonic molecule in new kinetics model and muon catalyzed fusion in compressed gas

Muon catalyzed fusion (muCF) in which an elementary particle, muon, facilitates the nuclear fusion between the hydrogen isotopes has been investigated in a long history. In contrast to the rich theoretical and experimental information on the muCF in cold targets, there is relatively scarce information on the high temperature gas targets of deuterium-tritium mixture with high-thermal efficiency. We demonstrate new kinetics model of muCF including three roles of resonant muonic molecules, (i) changing isotopic population, (ii) producing epi-thermal muonic atoms, and (iii) inducing fusion in-flight. The new kinetics model reproduces experimental observations, showing higher cycle rate as the temperature increasing, over a wide range of target temperatures (T<800 K) and tritium concentrations. Moreover, it can be tested by measurements of radiative dissociation X-rays around 2 keV. High energy-resolution X-ray detectors and intense muon beam which are recently available are suitable to reveal these dynamical mechanism of muCF cycles. Towards the future muCF experiments in the high-temperature gas target we have clarified the relationship between the fusion yield and density-temperature curve of adiabatic/shock-wave compression.

Pressure change dynamics of plasma focus chambers as a part of the pulse neutron generators

The dynamics of working gas pressure changes in the plasma focus (PF) chambers were studied by using the chamber with a built-in manometer as part of the ING-102 neutron generator (2.5 MeV neutron yield 106÷107 neutrons/pulse). Investigations were carried out during high-voltage training and neutron emission operation mode. The studies were executed while filling the chamber with various gas mixtures. For operation with a deuterium-tritium mixture, a sealed-off chamber with a built-in gas generator was used. After the primary filling of the PF chambers with a gas mixture, there is a systematic decrease in pressure by Δp = (5 ÷ 50) ·10−3 Torr (∼0,7 ÷ 7 Pa) after each shot of the chamber.The change in the shape of breakdown curves Ubr(p) in the interelectrode gap of the chamber after each series of shots was studied. That made it possible to assess the optimal number of shots during high-voltage training of the PF chamber.

Simulating fusion alpha heating in a stellarator reactor

Gyrocenter following simulations of fusion born alpha particles in a stellarator reactor are preformed using the BEAMS3D code. The Wendelstein 7-X high mirror configuration is scaled in geometry and magnetic field to reactor relevant parameters. A m−3 density plasma with 20 keV core temperatures is assumed and fusion birth rates calculated for various fusion products assuming a 50/50 deuterium-tritium mixture. It is found that energetic He4 ions comprise the vast majority of the energetic particle inventory. Slowing down simulations of the He4 population suggest plasma heating consistent with scaled energy confinement times for a stellarator reactor. Losses for this configuration appear large suggesting optimization beyond the scope of the W7-X device is key to a future fusion reactor. These first simulations are designed to demonstrate the capability of the BEAMS3D code to provide fusion alpha birth and heating profiles for stellarator reactor designs.

Tritium retention in displacement-damaged tungsten exposed to deuterium-tritium gas mixture at elevated temperatures

Abstract W samples, previously irradiated with 20 MeV W ions at room temperature to a displacement-damage level of 0.23 displacements per atom (dpa) at the peak of displacements, were exposed to a deuterium-tritium (D2 ― DT ― T2) gas mixture with a tritium content of 6% at a total pressure of 1.2 kPa and temperatures of 773 K and 973 K for 3 h. The concentration of tritium retained in the displacement-damage zone of these W samples was determined by a method combining chemical etching and subsequent analysis of tritium in the etching solution using liquid scintillation counting (CE-LSC). (Some figures may appear in colour only in the online journal)

Unified first-principles equations of state of deuterium-tritium mixtures in the global inertial confinement fusion region

Accurate knowledge of the equation of state (EOS) of deuterium–tritium (DT) mixtures is critically important for inertial confinement fusion (ICF). Although the study of EOS is an old topic, there is a longstanding lack of global accurate EOS data for DT within a unified theoretical framework. DT fuel goes through very wide ranges of density and temperature from a cold condensed state to a hot dense plasma where ions are in a moderately or even strongly coupled state and electrons are in a partially or strongly degenerate state. The biggest challenge faced when using first-principles methods for obtaining accurate EOS data for DT fuel is the treatment of electron–ion interactions and the extremely high computational cost at high temperatures. In the present work, we perform extensive state-of-the-art ab initio quantum Langevin molecular dynamics simulations to obtain EOS data for DT mixtures at densities from 0.1 g/cm3 to 2000 g/cm3 and temperatures from 500 K to 2000 eV, which are relevant to ICF processes. Comparisons with average-atom molecular dynamics and orbital-free molecular dynamics simulations show that the ionic strong-coupling effect is important for determining the whole-range EOS. This work can supply accurate EOS data for DT mixtures within a unified ab initio framework, as well as providing a benchmark for various semiclassical methods.

Expected Environmental Effects of Long-Term Tritium Supply—Lessons Learned

Fusion reactors are considered an almost unlimited source of power for the future, with tritium [deuterium-tritium (D-T) mixture] being the most convenient fuel for these facilities. Due to tritium-specific features and its self-radioactivity there are a number of issues when handling a large amount of tritium for long-term operations of fusion reactors. This paper presents research results of tritium behavior in the D-T mixture and in the environment during operations at tritium facilities. The results provide the basis for an assessment of the future environmental effects of long-term operation of a fusion reactor/tritium facility. The results of experimental and modeling studies include tritium reactions with carbon oxides under radiolysis, radiolysis of DTO, tritium dispersion in atmosphere under rough terrain, tritium oxide washout from atmosphere, tritium oxidation in soil with soil bacteria, tritium oxide migration in the unsaturated soil layer, and tritium uptake by plants, crops, and lichens. Both experimental and observational data have been used to develop models to predict tritium behavior in the environment under similar conditions. The models have been verified and validated.

The Expansion of the Dense Plasma of a Mixture of Deuterium and Tritium into the Empty Space in which There is a Magnetic Field

The work is aimed at determining parameters of a deuterium-tritium mixture expanding into a vacuum with an external magnetic field, the output of thermonuclear energy from which compensates or exceeds the initial thermal energy of the plasma. This type of assessment is usually based on the Lawson criterion. In the paper the parameters are determined on the basis of the model of adiabatic expansion into the surrounding homogeneous magnetic field of the plasma ball in the magnetohydrodynamic approximation for some special modes of expansion, providing a self-similar distribution of gas-dynamic quantities. The obtained minimum values of the energy expended for the initial heating of the plasma, providing its equality to the resulting integrated fusion energy, are compared with the known estimates within the framework of inertial confinement fusion.

Hydrogen Isotope Dissolution and Release Behavior of Rare Earth Oxides

Hydrogen release behavior from rare earth oxides (REOs) (Y2O3, Sm2O3, Eu2O3, Gd2O3, Dy2O3, Er2O3, and Yb2O3) exposed to 133 Pa of deuterium (D2) gas or 2 kPa of heavy water (D2O) vapor at 873 K for 5 h was examined using thermal desorption spectroscopy. Hydrogen solubility and diffusivity in Y2O3, Gd2O3, Dy2O3, Er2O3, and Yb2O3 exposed to a deuterium-tritium gas mixture (5% to 7% T, 133 Pa) at 873 K and 973 K for 5 h were determined using a tritium imaging plate method. The structural and morphological properties of sintered disk specimens of those REOs were evaluated using an X-ray diffractometer and a scanning electron microscope. From the obtained results, the REO materials were clearly categorized into two kinds in terms of their crystal structure and hydrogen solubility: Monoclinic specimens of Sm2O3, Eu2O3, and Gd2O3 had relatively high hydrogen solubility and diffusivity, while cubic Y2O3, Dy2O3, Er2O3, and Yb2O3 had lower ones. The present study suggests that the cubic REOs could be suitable in a nuclear fusion reactor as the tritium barrier materials.

1997 JET DT experiments revisited—comparative analysis of DD and DT stationary baseline discharges

This paper compares the stationary ELMy H-mode baseline 50%–50% deuterium-tritium (DT) mixture discharges in the first high -power JET DT experimental campaign in 1997 (JET-DTE1) with the counterpart 100% deuterium (DD) baseline discharges which have the same engineering parameters, i.e. Ip, Bt, q95, NBI power, plasma shape, no gas dosing, divertor structure, and the carbon wall. There is no difference in profile peaking of Te, Ti, and ne between the DT and the counterpart DD baseline discharges, indicating that there was no isotopic effect on the core transport in the stationary baseline DT discharges in the 1997 JET-DTE1. The core values of Te, Ti, and ne are higher in some DT discharges compared to their counterpart DD discharges, but this is attributed to the higher pedestal values, rather than any improvement in the core transport. The interpretive TRANSP simulations also show that the local heat diffusivity is not consistently different between the DT and the counterpart DD baseline discharges.The baseline discharges in the 1997 JET-DTE1 are also compared to the latest high-power ELMy H-mode baseline DD discharges with an ITER-like wall (ILW) in 2016. Despite the similar effective collisionality and ion heat deposition in the core, it was observed that Ti/Te is consistently close to unity in the 1997 JET-DTE1 discharges, while the 2016 JET baseline discharges have high Ti, exceeding Te, which enabled the highest fusion performance in the ITER-Like Wall. The high rotation frequency was the key factor in increasing Ti/Te in the 2016 JET baseline discharges, and it is also the main difference compared to the stationary baseline discharges in the 1997 JET-DTE1. Based on this, it is prospected that higher rotation frequency is the key factor to achieving high fusion power in the stationary baseline discharges in the 2020 JET-DTE2, and the plasma operation with the low gas dosing and increased torque available in the present NBI system would enable such a high rotation frequency.

A Thin Alumina Film as a Tritium Adsorption Inhibitor for Stainless Steel 316

The effect of a thin alumina coating on stainless steel 316 (SS316) samples on tritium adsorption and transport are reported. Compact films of alumina were produced on the surfaces of pristine SS316 samples using an atomic layer deposition (ALD) technique. Subsequently, these samples were exposed for 24 h to a deuterium-tritium gas mixture (PT = 0.5 atm, 25°C). A combination of methods including selective etching and programmed thermal desorption were employed to assess both the depth profile of the tritium concentration in the sample and the total quantity of tritium absorbed, respectively. Tritium was quantitatively determined through the measurement of beta radioactivity using liquid-scintillation counting techniques. Data suggest that SS316 with a thin film of alumina reduces the total tritium uptake by ~25% relative to uncoated samples. Importantly, such films appear to reduce, by a factor of 200, tritium diffusion into SS316 and therefore constitute an effective barrier against tritium transport. This observation is of practical importance for tritium and, generally, reactive gas handling.

Modeling the Edge-Plasma Interface for Liquid-Lithium Walls in FNSF

The viability of using liquid-lithium walls for the divertor and main chamber surfaces for a Fusion Nuclear Science Facility (FNSF) is analyzed from the point of view of the edge-plasma region that separates the hot core plasma from the surrounding material walls. The edge plasma is modeled by the UEDGE two-dimensional multifluid transport code that evolves equations for the density, momentum, and temperature of a 50%/50% mixture of deuterium-tritium (DT) ions, impurity ions, and electrons. Neutral DT and impurity gases are represented by neutral fluid equations. The primary inputs from the FNSF design are the magnetic configuration, plasma-facing-surface locations, core plasma exhaust power, and core boundary DT ion density. Lithium sources and sinks due to evaporation and condensation on the plasma-facing surfaces are parameters. The results show that a highly radiating divertor plasma, detached from the divertor plates, can be formed where >90% of the exhaust power is radiated by lithium with a broad deposition profile on plasma-facing surfaces that yields peak heat fluxes in the range of 2 MW/m2. The detached configuration is dominated by lithium plasma in the divertor and by hydrogen plasma upstream adjacent to the core boundary. A nonnegligible low level of lithium is found upstream at the outer midplane, typically in the range of 3% to 20%, that represents a potential core DT fuel dilution problem. An important physical mechanism is the collisional thermal force acting between ion species that can push impurities upstream along the magnetic field lines. Results show that the effect of reduced DT recycling at lithium surfaces due to hydride formation does not significantly affect the stability and radiative efficiency of the lithium divertor.

The dud detector: An empirically-based real-time algorithm to save neutron and T budgets during JET DT operation

Operations using deuterium-tritium (DT) mixtures are envisaged in JET device in the forthcoming 2020 experimental campaign. These experiments will offer a unique possibility to study several open issues in support to ITER and DEMO, such as alpha particle heating, and to improve the high plasma performance obtained in the previous DT campaign Keilhacker et al. [1]. During DT operation, each plasma discharge will be a precious resource, being both T and neutron budget limited. It will be thus mandatory to promptly detect and safely terminate those plasma discharges which do not achieve the expected target parameters. A real-time detector of underperforming discharges has been developed for this purpose and it is named the dud detector. The dud detector calculates and monitors the time evolution of plasma performance indicators, which can be used to trigger an alarm and a proper plasma termination. The experience gained on the algorithm's behavior during DD operation will allow the use of this tool during DT operations and can be used as a guide to design dud detectors for ITER and future fusion reactors.

Protium removal from deuterium-tritium mixture with displacement chromatography method: Experiments and simulations

The displacement chromatography technique with a tri-column system was used to reduce the protium (H) in the deuterium-tritium (D-T) mixture, and the separation performance was studied numerically by ANSYS FLUENT. The experimental results showed that the isotopic abundance of H in the D-T mixture dropped from 2.7% to an acceptable level of 0.88%. The simulation results showed that a lower porosity (θ) of the filling material made a higher separation factor, but a lower separation efficiency. The velocity of the product gas at the outlet of the separation column approximately had a linear relationship with θ5/3/(1-θ)2, which partly indicated the pore diffusion resistance. The mixed gas could contact the filling materials more sufficiently under a lower flow rate resulting in a lower protium concentration in the product gas. The separation column with a thin and long shape had a better separation performance and a lower product gas loss.

Microphysics studies for direct-drive inertial confinement fusion

Accurate and self-consistent knowledge of material properties under high-energy-density (HED) conditions is crucial to reliably understand and design inertial confinement fusion (ICF) targets through radiation–hydrodynamic simulations. For direct-drive ICF target designs, the fuel deuterium–tritium mixtures and ablator materials can undergo a wide range of density and temperature conditions. Their properties under extreme HED conditions, including the equation of state, thermal conductivity, opacity, and stopping power, are the necessary inputs for ICF simulations. To improve the predictive capability of radiation–hydrodynamic codes for direct-drive ICF simulations, we have performed systematic ab initio studies on the static, transport, and optical properties of deuterium (D2) and ablator materials such as polystyrene (CH), beryllium (Be), and silicon (Si), using first-principles methods. The obtained material properties, being favorably compared with existing experimental data, have been implemented into radiation–hydrodynamic codes. This article gives a brief review on how these microphysics studies affect the 1D radiation–hydrodynamic predictions of direct-drive ICF implosions on the OMEGA Laser System.

Overview of the JET operation reliability

The JET tokamak has been in operation since 1983. Information on every shutdown, commissioning phase and experimental campaign has been logged electronically since the year 2000, a model for RAMI analyses in fusion experiments. The JET operation reliability statistics record the time taken to install major upgrades, commission systems with plasma, the downtime for maintenance and the achieved experimental campaign days. On average, JET achieves 82% of the planned experimental days during a calendar year. For unplanned interventions the systems that failed are identified together with the impact on machine availability. A total of 14 unplanned interventions are recorded over 19 years with durations of up to 8 weeks. During experimental campaigns, delays from essential subsystems are recorded; computer systems, power supplies, neutral beam systems and delays attributed to human operators. On average 21% of the time is lost due to delays during operations. From the operation reliability data, refurbishments and maintenance are planned at JET to prepare for the upcoming campaigns using deuterium-tritium mixtures.

Isotope effects on L-H threshold and confinement in tokamak plasmas

The dependence of plasma transport and confinement on the main hydrogenic ion isotope mass is of fundamental importance for understanding turbulent transport and, therefore, for accurate extrapolations of confinement from present tokamak experiments, which typically use a single hydrogen isotope, to burning plasmas such as ITER, which will operate in deuterium–tritium mixtures. Knowledge of the dependence of plasma properties and edge transport barrier formation on main ion species is critical in view of the initial, low-activation phase of ITER operations in hydrogen or helium and of its implications on the subsequent operation in deuterium–tritium. The favourable scaling of global energy confinement time with isotope mass, which has been observed in many tokamak experiments, remains largely unexplained theoretically. Moreover, the mass scaling observed in experiments varies depending on the plasma edge conditions. In preparation for upcoming deuterium–tritium experiments in the JET tokamak with the ITER-like Be/W Wall (JET-ILW), a thorough experimental investigation of isotope effects in hydrogen, deuterium and tritium plasmas is being carried out, in order to provide stringent tests of plasma energy, particle and momentum transport models. Recent hydrogen and deuterium isotope experiments in JET-ILW on L-H power threshold, L-mode and H-mode confinement are reviewed and discussed in the context of past and more recent isotope experiments in tokamak plasmas, highlighting common elements as well as contrasting observations that have been reported. The experimental findings are discussed in the context of fundamental aspects of plasma transport models.