Hydrogen-deuterium Mixtures Research Articles

Introducing Machine-Learning in Spectroscopy for Plasma Diagnostics and Predictions

Artificial Intelligence (AI) and data science techniques are increasingly introduced in physics including plasma physics where Machine Learning (ML) is applied to emission spectroscopy for plasma parameter determination. Recently, the open-access python-based Sickit-Learn ML platform was used to analyze line intensities in the order to infer the plasma electron densities and temperatures for conditions relevant to tokamak divertors. In this paper, we discuss the application of deep-learning (DL) to synthetic line spectra for conditions of magnetic fusion plasmas with hydrogen-deuterium (H-D) mixtures. The idea will be illustrated through application of Artificial Neural Networks (ANN) to spectra of the Balmer-α line emitted by H-D mixtures, the aim being to obtain the isotopic ratios. The objective of our approach is to provide a new method to infer the hydrogen isotopic ratio sufficiently fast that can be exploited for real-time applications. We will demonstrate the proof-of-principle of our method through the application of a TensorFlow DL regression algorithm to theoretical line spectra generated with predetermined parameters.

Application of Deep Learning to Spectroscopic Features of the Balmer-Alpha Line for Hydrogen Isotopic Ratio Determination in Tokamaks

We propose in this paper the use of artificial intelligence, especially deep learning algorithms, for the isotopic ratio determination for hydrogen–deuterium mixtures. Our approach is based on the Balmer-α line emitted by hydrogen and deuterium, but unlike the standard method, it does not consist of fitting the Hα/Dα line spectra. Instead, only some basic spectroscopic features such as the line peak-to-dip wavelength separation, peak-to-peak and dip-to-peak intensity ratios of the Zeeman–Doppler-broadened Hα/Dα line spectra are used by the regression algorithm for training. We demonstrate the proof-of-principle of our approach by applying deep learning from the open-access machine-learning platform TensorFlow to Hα/Dα line profiles, which we have synthetized with pre-determined parameters such as neutral temperatures, the magnetic field strength and the H/(H+D) isotopic ratio. The used regression algorithm allowed us to retrieve with a good accuracy the isotopic ratios used for the synthetized line profiles.

Dynamic simulation of a cryogenic batch distillation process for hydrogen isotopes separation

The operational flexibility of cryogenic batch distillation may propel its application in the Isotope Separation System of the fusion reactor. The batch distillation, unlike continuous distillation, is not a steady-state process. In order to obtain improved separation efficiency, a reasonable dynamic model of batch distillation should be developed. In this paper, dynamic simulations of the batch distillation separation process of a hydrogen-deuterium mixture were performed utilizing Aspen Plus and Aspen Dynamics. The validity of the established simulation model was firstly verified by our experimental results. Following that, two dynamic control structures, i.e., composition control and temperature control, were added to improve the recovery efficiency of batch distillation light component products. In comparison with the distillation without dynamic control structure, the distillation with composition control and temperature control can improve the H 2 recovery ratio by 5.45% and 5.09%, respectively. • A batch distillation dynamic model was built for hydrogen isotopes separation. • The experimental concentration variations agreed well with that of the simulation. • The composition control and the temperature control enhanced the recovery efficiency.

Possible heat production in some Ni-H and Ni-D systems, revised

The paper concludes two year research on the topic of the possible heat production in nickel-hydrogen (Ni-H) and nickel-deuterium (Ni-D) systems during heating that was initially announced by S Focardi, R Habel, F Piantelli and later reported by A Rossi and A G Parkhomov. The authors developed a new methodology and new testing units that could provide consistent results for the physical community due to high importance of such reports in the wake of the energy crisis. The testing units were engineered with such a design that both nonlinear heat losses (convection and radiation) during the experiment were minimized. The experimental methodology is based on the statistical hypothesis testing of the normal distribution from experimental heater power consumption data samples while the temperature is stabilized by the PID controller according to the provided experimental program. This methodology was tested by artificially supplied heat sources and sufficient accuracy was confirmed around 1.5%–3.0%. Around 50 experiments with fuel were conducted with various additional ingredients, different forms of Ni, pure hydrogen and hydrogen-deuterium mixtures according to the experiments cited above. No statistically significant levels of the heat production were found in any of the experiments, with less than 1.5% accuracy in terms of heater power consumption.

Characteristics of plasma parameters and turbulence in the isotope-mixing and the non-mixing states in hydrogen–deuterium mixture plasmas in the large helical device

Characteristics of plasma parameters and turbulence in the isotope-mixing and the non-mixing states in hydrogen-deuterium mixture plasmas in the large helical device are discussed. The isotope mixing state is characterized by the uniform isotope ratio profile regardless of the location of the particle source of each species in the isotope mixture plasma. The isotope non-mixing state is identified by the non-uniform isotope ratio profile measured with bulk charge exchange spectroscopy when the beam fueling isotope species differs from the recycling isotope species. The effect of collisionality, ratio, sign of density gradient on transition between isotope mixing and non-mixing is discussed. The plasma parameters preferable for the non-mixing state are found to be lower collisionality, higher , and negative or zero density gradient (peaked or flat density profile). The time scale of transition from non-mixing to mixing is evaluated by the hydrogen and deuterium pellet injection near the plasma edge and is found to be less than 5 ms, which is much shorter than the particle confinement time. The strong correlation between isotope mixing and turbulence characteristics is observed. This strong correlation suggests the change in turbulence is a strong candidate for the mechanism causing the transition between uniform and non-uniform isotope density ratio profiles.

Transition between Isotope-Mixing and Nonmixing States in Hydrogen-Deuterium Mixture Plasmas

The transition between isotope-mixing and nonmixing states in hydrogen-deuterium mixture plasmas is observed in the isotope (hydrogen and deuterium) mixture plasma in the Large Helical Device. In the nonmixing state, the isotope density ratio profile is nonuniform when the beam fueling isotope species differs from the recycling isotope species and the profile varies significantly depending on the ratio of the recycling isotope species, although the electron density profile shape is unchanged. The fast transition from nonmixing state to isotope-mixing state (nearly uniform profile of isotope ion density ratio) is observed associated with the change of electron density profile from peaked to hollow profile by the pellet injection near the plasma periphery. The transition from nonmixing to isotope-mixing state strongly correlates with the increase of turbulence measurements and the transition of turbulence state from TEM to ion temperature gradient is predicted by gyrokinetic simulation.

Measurement of multiple physical parameters of dense gaseous hydrogen-deuterium mixture under double-shock compression: Evaluating theoretical models from multiple views

A series of reverberating shock experiments on the precompressed hydrogen-deuterium (H-D) mixture were performed by using a two-stage light gas gun, and an elaborately designed diagnostic configuration was presented to probe the multishock states of dense fluid H-D mixtures. The particular diagnostics allowed multiple physical parameters, including the equation of state (EOS), refractive index, reflectivity, molecular polarizability, and energy gap, of H-D mixtures under double-shock compression to be simultaneously determined in a single shot. The multiple parameters obtained provide a comprehensive evaluation for existing theoretical models from multiple perspectives. It is found that, compared with the semilocal Perdew–Burke–Ernzerhof xc functional, the EOS data predicted by a nonlocal van der Waals exchange-correlation (xc) functional (vdW-DF1) are in much better agreement with the experimental results. Furthermore, the commonly used Gladstone–Dale relation is not appropriate for describing the refractive index in high-pressure-temperature regions, and the refractive index and reflectivity can be well reproduced by the Heyd–Scuseria–Ernzerhof hybrid xc functional. These observations may provide insights into future theoretical developments and a better understanding of material properties under extreme pressure-temperature conditions.

Quantum molecular dynamics study on the proton exchange, ionic structures, and transport properties of warm dense hydrogen-deuterium mixtures.

Comprehensive knowledge of physical properties such as equation of state (EOS), proton exchange, dynamic structures, diffusion coefficients, and viscosities of hydrogen-deuterium mixtures with densities from 0.1 to 5g/cm^{3} and temperatures from 1 to 50 kK has been presented via quantum molecular dynamics (QMD) simulations. The existing multi-shock experimental EOS provides an important benchmark to evaluate exchange-correlation functionals. The comparison of simulations with experiments indicates that a nonlocal van der Waals density functional (vdW-DF1) produces excellent results. Fraction analysis of molecules using a weighted integral over pair distribution functions was performed. A dissociation diagram together with a boundary where the proton exchange (H_{2}+D_{2}⇌2HD) occurs was generated, which shows evidence that the HD molecules form as the H_{2} and D_{2} molecules are almost 50% dissociated. The mechanism of proton exchange can be interpreted as a process of dissociation followed by recombination. The ionic structures at extreme conditions were analyzed by the effective coordination number model. High-order cluster, circle, and chain structures can be founded in the strongly coupled warm dense regime. The present QMD diffusion coefficient and viscosity can be used to benchmark two analytical one-component plasma (OCP) models: the Coulomb and Yukawa OCP models.

Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating

We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed ‘three-ion’ scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of $^3$He ions to high energies in dedicated hydrogen–deuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast $^3$He ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular, $^3$He-rich solar flares.

Infrared Peak Splitting from Phonon Localization in Solid Hydrogen.

We show that the isotope effect leads to a completely different spectroscopic signal in hydrogen-deuterium mixtures, compared to pure elements that have the same crystal structure. This is particularly true for molecular vibrations, which are the main source of information about the structure of high-pressure hydrogen. Mass disorder breaks translational symmetry, meaning that vibrations are localized almost to single molecules, and are not zone-center phonons. In mixtures, each observable infrared (IR) peak corresponds to a collection of many such molecular vibrations, which have a distribution of frequencies depending on local environment. Furthermore discrete groups of environments cause the peaks to split. We illustrate this issue by considering the IR spectrum of the high-pressure phase III structure of hydrogen, recently interpreted as showing novel phases in isotopic mixtures. We calculate the IR spectrum of hydrogen-deuterium mixtures in the C2/c and Cmca-12 structures, showing that isotopic disorder gives rise to mode localization of the high-frequency vibrons. The local coordination of the molecules leads to discrete IR peaks. The spread of frequencies is strongly enhanced with pressure, such that more peaks become resolvable at higher pressures, in agreement with the recent measurements.

Compact Determination of Hydrogen Isotopes

Scanning calorimetry of a confined, reversible hydrogen sorbent material has been previously proposed as a method to determine compositions of unknown mixtures of diatomic hydrogen isotopologues and helium. Application of this concept could result in greater process knowledge during the handling of these gases. Previously published studies have focused on mixtures that do not include tritium. This paper focuses on modeling to predict the effect of tritium in mixtures of the isotopologues on a calorimetry scan. The model predicts that tritium can be measured with a sensitivity comparable to that observed for hydrogen-deuterium mixtures, and that under some conditions, it may be possible to determine the atomic fractions of all three isotopes in a gas mixture.

Hydrogen isotope separation with an alkaline membrane fuel cell

The separation of deuterium from a hydrogen–deuterium mixture was carried out using an alkaline membrane fuel cell (AMFC) with a Pt catalyst. This novel use of an AMFC to separate deuterium from a mixture of H2 and D2 was demonstrated by the production of deuterium-enriched water during power generation by the AMFC. The deuterium separation factor increased with output current (i) to a maximum value of 1.64 attained at i=30mAcm−2.

Speed of sound in solid molecular hydrogen-deuterium: Quantum Molecular Dynamics Approximation

Uniformity of the solid layer is one of the critical points for an efficient ignition of the Deuterium-Tritium (DT) target. During the compression process this layer, perturbations grow as the Rayleigh-Taylor instability. Knowing the mechanical properties of this layer and its thermo-mechanical limits is necessary if we want to control or to minimize these instabilities. In this work we have used a simplified approach, replacing the DT ice system with a mixture of hydrogen-deuterium (HD) because beta decay of tritium complicates the analysis in the former case. Through simulation with ab initio methods we have calculated the elastic constants, the bulk modulus and sound velocity for hydrogen isotopes in solid molecular state. In this work we present the results for hydrogen-deuterium mixtures 50%-50%, at 15 K and with a compression which covers the range of 1 to 15 GPa. This system is interesting for study the early stages of the dynamic compression and provides conditions that are close to the manufacture of DT target in inertial confinement fusion. Discontinuities in the curve that have been observed on pure hydrogen, which are associated with phase transitions and the phase hysteresis.

Phonon localization by mass disorder in dense hydrogen-deuterium binary alloy.

Using a combination of the Raman spectroscopy and density functional theory calculations on dense hydrogen-deuterium mixtures of various concentrations, we demonstrate that, at 300 K and above 200 GPa, they transform into phase IV, forming a disordered binary alloy with six highly localized intramolecular vibrational (vibrons) and four delocalized low-frequency (<1200 cm(-1)) modes. Hydrogen-deuterium mixtures are unique in showing a purely mass-induced localization effect in the quantum solid: chemical bonding is isotope-independent while the mass varies by a factor of 2.

Dynamical effects in solid hydrogen and hydrogen-deuterium mixtures at elevated pressures.

We employed molecular dynamics simulations together with some novel theoretical techniques to calculate finite temperature Raman spectra in both hydrogen (H) and hydrogen-deuterium (HD) mixtures. By conditioning the simulations with the experimental data, we have discovered the true nature of Phase IV in solid hydrogen. X-ray and neutron diffraction measurements are virtually impossible in current state of the art experiments. The experimental investigation, thus, relies mainly on spectroscopic methods which provide minimal data about crystallography. Extensive work done so far [1] has led to an impressive amount of Raman and IR data up to pressures of almost 400 GPa. By carefully investigating the positions and widths of the peaks, they discovered phase IV of solid hydrogen and mapped out the melting curve up to very high pressures. Phase IV is only stable at elevated temperatures and therefore static relaxation calculations cannot reproduce the correct crystal structure. Previous theoretical work has predicted a class of exotic crystal structures with alternating layers of different character: B (well-defined molecules) and G (poorly-defined molecules) [2] that could qualitatively describe the Raman signal. By means of MD simulations we show that at high temperature, the Pc structure acquires higher symmetry which is sufficient to reproduce the exact position of the Raman peaks. It had been suggested that in a mixed hydrogen-deuterium alloy, the heavier atoms would segregate in the B layers which would decrease the overall zero-point energy and stabilise the Pc structure. Joining efforts with the experimental team we thoroughly investigated this problem. We found no evidence of isotopic layer segregation, but our theoretical model correctly described the Raman spectra found experimentally. We concluded that the phase boundaries in HD mixtures are slightly offset which we attribute to the inhomogeneous mass effect on the temperature of the broken symmetries, but the general behaviour is similar to that of solid hydrogen. We uncovered a new effect in HD, namely mass induced phonon localization. Matching experimental and theoretical results in this respect are yet another validation of the crystallographic conformation of phase IV.

Preliminary Results of IS Plasma Focus as a Breeder of Short-Lived Radioisotopes 12C(d,n)13N

Modified IS (Iranian Sun) plasma focus (10 kJ,15 kV, 94 μF, 0.1 Hz) has been used to produce the short-lived radioisotope 13N (half-life of 9.97 min) through 12C(d,n)13N nuclear reaction. The filling gas was 1.5–3 torr of hydrogen (60%) deuterium (40%) mixture. The target was solid nuclear grade graphite with 5 mm thick, 9 cm width and 13 in length. The activations of the exogenous target on average of 20 shots (only one-third acceptable) through 10–13 kV produced the 511 keV gamma rays. Another peak found at the 570 keV gamma of which both was measured by a NaI portable gamma spectrometer calibrated by a 137Cs 0.25 μCi sealed reference source with its single line at 661.65 keV and 22Na 0.1 μCi at 511 keV. To measure the gamma rays, the graphite target converts to three different phases; solid graphite, powder graphite, and powder graphite in water solution. The later phase approximately has a doubled activity with respect to the solid graphite target up to 0.5 μCi of 511 keV and 1.1 μCi of 570 keV gamma lines were produced. This increment in activity was perhaps due to structural transformation of graphite powder to nano-particles characteristic in liquid water.

On the role of graphite chamber-wall lining in experiments on the ion-cyclotron resonance plasma heating in the globus-M spherical tokamak

Comparative results of experiments on the ion-cyclotron resonance (ICR) heating of plasma in the Globus-M spherical tokamak using a hydrogen-deuterium mixture are presented. The experimental data are analyzed over a long period of time during which the internal surface of the chamber walls was gradually coated with graphite plates. The observed monotonic decrease in the efficiency of ICR plasma heating in the chamber with increasing graphite coverage can be explained by a growth in the high-frequency power absorption in the coating material. Results of numerical simulation of this process are reported.

Kinetics of muon catalyzed fusion processes in solid H/D mixture

This paper presents the final results of an experimental study of the kinetics of the muon catalysed fusion (MCF) in solid hydrogen-deuterium mixtures (H/D) at a temperature of 3 K. The experiment E742 was carried out on a TRIUMF meson facility in Canada. Four exposures were performed at different deuterium concentrations in the H/D mixture: cd = 0.0005, 0.02, 0.15 and 0.75. A simultaneous analysis of the measured time distributions of the 5.5 MeV γ-quanta and the 5.3 MeV conversion muons obtained from nuclear fusion in the pdμ molecule allowed to extract the values of MCF chain parameters in the H/D mixture: the fusion partial rates for different nuclear spin states of the pdμ molecule, and the pdμ molecule formation rate. The experimental data fitting procedure was conducted in two ways: using solely the analytical formulae describing the kinetics of the MCF processes in the H/D mixture, and the detailed Monte Carlo simulation of the entire experiment. The results obtained by these two methods are consistent with each other and confirm the existence of the Wolfenstein-Gerstein effect.

Formation and Properties of Iron-Phosphorus and Iron-Phosphorus-Hydrogen Complexes in Silicon

Hitherto unreported ESR signal, labeled TU10, was detected after annealing of electronirradiated silicon samples doped with phosphorus, iron and hydrogen. The ESR spectrum corresponds to a complex having monoclinic-I symmetry and S = 3/2 spin-state. Hyperfine structure of the TU10 spectrum suggests participation of two nucleus with spin I = 1/2 and 100% abundance in the core of the related defect. Doping of samples with hydrogen-deuterium mixture revealed presence of one hydrogen atom in the complex. The second nucleus with I = 1/2 is apparently a phosphorus atom. Presence of single iron atom was verified by doping with iron heaving modified isotope content. An intensity of the previously reported TU6 signal, related to iron-phosphorus complex, was significantly suppressed in hydrogen-doped samples.

Investigation of Isotope Effects in the Gas Streams Supplied by a 1:1 ITER Storage Bed Using a Micro Gas Chromatography

In the present design of the Storage and Delivery System of the ITER Tritium Plant deuterium, tritium and their mixtures are stored in hydrogen storage beds with a storage capacity of 100 g. During plasma operation it is required that deuterium-tritium gases with well defined ratios of D/T are supplied by the different hydrogen storage beds. Due to the isotope effects the composition of the hydrogen gas mixture supplied by the getter bed may be different from the one absorbed in the getter and may even change during unloading of the bed depending on the variation of the isotope effect with the actual amount of hydrogen isotopes stored in the bed.At the Forschungszentrum Karlsruhe a 1:1 prototype of ITER hydrogen storage bed with a capacity of 100 g tritium and a target supply rate of up to 200 Pam3s-1 was designed and manufactured. The getter bed is currently filled with zirconium-cobalt and is installed in an experimental rig coupled with a micro gas chromatograph in order to perform texts under different operation conditions and to characterize the possible isotope effects. In this work a first data on the isotope effect during loading and unloading of the getter bed with the different hydrogen-deuterium mixtures is presented.