High-energy Part Research Articles

Development of a Probe System for Measuring the Plasma Parameters and the High-Energy Part of the Electron-Energy Distribution Function

—A probe system has been developed on the basis of an external ADC/DAC module (ADC is the analog-to-digital converter and DAC is the digital-to-analog converter). Using this system, it is possible to determine all the main plasma parameters of continuous and pulsed gas discharges. A program for the Windows operating system has been developed in C++ to control the probe system. The probe system can be used for diagnostics of plasma devices and can be included in modern microplasma analyzers of gas mixtures.

Benchmark of a multi-physics Monte Carlo simulation of an ion guide for neutron-induced fission products

To enhance the production of medium-heavy, neutron-rich nuclei, and to facilitate measurements of independent yields of neutron-induced fission, a proton-to-neutron converter and a dedicated ion guide for neutron-induced fission have been developed for the IGISOL facility at the University of Jyväskylä. The ion guide holds the fissionable targets, and the fission products emerging from the targets are collected in helium gas and transported to the downstream experimental stations. A computer model, based on a combination of MCNPX for modeling the neutron production, the fission code GEF, and GEANT4 for the transport of the fission products, was developed. The model will be used to improve the setup with respect to the production and collection of fission products. In this paper we benchmark the model by comparing simulations to a measurement in which fission products were implanted in foils located at different positions in the ion guide. In addition, the products from neutron activation in the titanium foil and the uranium targets are studied. The result suggests that the neutron flux at the high-energy part of the neutron spectrum is overestimated by approximately 40%. However, the transportation of fission products in the uranium targets agrees with the experiment within 10%. Furthermore, the simulated transportation of fission products in the helium gas achieves almost perfect agreement with the measurement. Hence, we conclude that the model, after correction for the neutron flux, is well suited for optimization studies of future ion guide designs.

Constraining the NuMI neutrino flux using inverse muon decay reactions in MINERvA

Inverse muon decay, $\nu_\mu e^-\to\mu^-\nu_e$, is a reaction whose cross-section can be predicted with very small uncertainties. It has a neutrino energy threshold of $\approx 11$ GeV and can be used to constrain the high-energy part of the flux in the NuMI neutrino beam. This reaction is the dominant source of events which only contain high-energy muons nearly parallel to the direction of the neutrino beam. We have isolated a sample of hundreds of such events in neutrino and anti-neutrino enhanced beams, and have constrained the predicted high-energy flux.

Antiferromagnetic Kitaev interaction inJ eff = 1/2 cobalt honeycomb materials Na3Co2SbO6 and Na2Co2TeO6

Finding new materials with antiferromagnetic (AFM) Kitaev interaction is an urgent issue for quantum magnetism research. We conclude that Na3Co2SbO6 and Na2Co2TeO6 are new honeycomb cobalt-based systems with AFM Kitaev interaction by carrying out inelastic neutron scattering experiments and subsequent analysis. The spin–orbit excitons observed at 20–28 meV in both compounds strongly support the idea that Co2+ ions of both compounds have a spin-orbital entangled J eff = 1/2 state. Furthermore, we found that a generalized Kitaev–Heisenberg Hamiltonian can describe the spin-wave excitations of both compounds with additional 3rd nearest-neighbor interaction. Our best-fit parameters show significant AFM Kitaev terms and off-diagonal symmetric anisotropy terms of a similar magnitude in both compounds. We also found a strong magnon-damping effect at the higher energy part of the spin waves, entirely consistent with observations in other Kitaev magnets. Our work suggests Na3Co2SbO6 and Na2Co2TeO6 as rare examples of the AFM Kitaev magnets based on the systematic studies of the spin waves and analysis.

Reconstruction of high-energy part of the gamma-ray spectrum in thermal neutron capture by 113Cd

The average gamma-ray spectrum of 114Cd after thermal neutron capture in 113Cd was evaluated in units of mb/MeV. Two approaches are considered for estimation of the average gamma-ray spectrum with normalization of the experimental data: mean spectra for all gamma-energies were found by averaging frequency polygon for experimental data histogram, and mean spectra were estimated as the combination of theoretical values at low gamma-ray energies and averaging experimental data in high-energy range. The experimental spectra were evaluated from the gamma-intensities presented by Mheemeed et al. [A. Mheemeed et al. Nucl. Phys. A 412 (1984) 113] and Belgya et al. [T. Belgya et al. EPJ Web of Conf. 146 (2017) 05009]. They were normalized to the average theoretical spectrum which was calculated using EMPIRE and TALYS codes. The procedure of normalization of the high-energy part of the spectrum was described. Estimated gamma-spectra for 113Cd(n, {xγ}) reaction induced by thermal neutrons were presented.

Photon-axion mixing in thermal emission of isolated neutron stars

Thermally emitting neutron stars represent a promising environment for probing the properties of axion-like particles. Due to the strong magnetic fields of these sources, surface photons may partially convert into such particles in a large magnetospheric region surrounding the stars, which will result in distinctive signatures in their spectra. However, the interaction depends on the polarization state of the radiation and is rather weak due to the low experimentally allowed values of the coupling constant gγa. In this work, we compute the degree of photon-axion transition in the case of 100% O-mode polarization and spectral energy distribution of an isotropic blackbody with uniform surface temperature. The stellar magnetic field is assumed to be dipolar. We show that for the magnetic fields ∼1013 – 1014 G, typical for X-ray dim isolated neutron stars, the maximum effect is reached at gγa=2×10−11 GeV−1: the optical flux is reduced by 30 – 40%, while the high-energy part of the spectrum is not affected. The low-energy decrease exceeds 5% at gγa≥2×10−12 GeV−1 and ma≤2×10−6 eV, which is below the present experimental and astrophysical limits on axion parameters. To obtain the actual observational constraints, rigorous treatment of the radiative surface layers is required.

Crystal synthesis and Debye temperature determination of PdSb2: Usefulness of single crystal precise structure analysis

Single crystals of pyrite-type PdSb2 were grown by sealing a stoichiometric proportion of the elements in an evacuated silica glass tube and heating the tube in a furnace at 930 K for 20 days. The crystal structure of PdSb2 [space groupPa3¯, a = 6.4659(2) Å, u = 0.37331(3), Z = 4] was refined to R1 = 0.0171 for 374 unique reflections obtained by single-crystal X-ray diffraction experiments. The lattice constant, a, and anion-anion distance of 2.8677(3) Å are slightly different from the previously reported values. The single crystal diffraction method has excellent advantages such that the Debye temperature can be determined for each crystallographically independent site. The obtained ΘD values for Pd and Sb in PdSb2 are 258 K and 214 K, respectively. Characteristically, the Debye temperatures, ΘD, of both atoms in PdSb2 were found to be very low among the pyrite-type transition metal pnictides and chalcogenides. Certain regularities between the cation–anion bonding distances and Debye temperatures were found in pyrite-type compounds. The vibration of anion contributes to the highest energy part of the normal mode of thermal vibration, when the cation–anion bonding distances in pyrite-type compounds are shorter than 2.6 Å.

Electron sink on the Langmuir probe in plasma, its influence on measurements and methods to account for it

The influence of the electron sink effect on the probe on the results of measurements of the electron energy distribution functions (EEDFs), plasma potential, and electron concentration was studied. The studies were carried out for helium in a discharge with a hollow cathode at a gas pressure of ⩽1 Torr for cathode–anode distances of 1 cm and 3 cm; measurements were carried out at several distances from the cathode. The distribution functions were obtained by processing the probe volt–ampere characteristics using the standard Druyvesteyn method. The form of the measured EEDFs changed with distance from the cathode. According to test calculations performed using the Monte Carlo method, this was due to the nonlocal nature of the EEDF formation under the considered conditions. Calculations also showed that the nonlocality effect manifests itself mainly in the region of the high-energy part of the EEDF, while in the low-energy region the form of the EEDF is close to local one. The latter fact was used to correct the measured EEDFs with allowance for the effect of electron sinking to the probe. In standard probe measurements, the sink (flux, flow) of electrons to the probe leads to underestimated values of the EEDFs in the region of low electron energies. The paper analyzes various known methods (formulas) for calculating the amount of sink in relation to the experimental conditions under consideration. The correction of the measured EEDFs was carried out taking into account the indicated effect. The errors in determining the macroscopic parameters of the plasma and the rates of elementary processes using the EEDFs obtained by processing the probe characteristics without taking into account the sink effect were analyzed.

Longitudinal acoustic and higher-energy excitations in the liquid phase-change materialGe2Sb2Te5

The dynamic structure factor $S(Q,E)$ of liquid ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$ has been obtained by inelastic x-ray scattering, where $Q$ and $E$ are momentum and energy transfer, respectively. The dispersion curve of the longitudinal acoustic excitation energy exhibits flat-topped $Q$ dependence similarly to that in liquid GeTe and liquid Bi, where the local structure is modulated by Peierls distortion. The flat-topped energy in liquid ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$ is split into low and high energy parts arising from Sb-Te and Ge-Te correlations, respectively. Furthermore, the high energy part depends on $Q$ like an optical mode with decreasing $Q$ to zero, and it approaches the vibrational energy of fourfold coordinated Ge atoms with octahedral configurations. The result indicates that a majority of Ge in the liquid stays in octahedral order as predicted by first-principles molecular dynamics simulations.

Magnetic excitations of diagonally coupled checkerboards* *Project supported by the National Key R&D Program of China (Grant Nos. 2018YFA0306001 and 2017YFA0206203), the National Natural Science Foundation of China (Grant No. 11974432), GBABRF-2019A1515011337, and Leading Talent Program of Guangdong Special Projects.

By using quantum Monte Carlo based stochastic analytic continuation (QMC-SAC) and spin wave theory, we study magnetic excitations of Heisenberg models with diagonally coupled checkerboard structures. We consider three kinds of checkerboard models (DC 2 × 2, DC 3 × 3, and CDC 3 × 3) consisting nearest-neighbor strong J 1 and weak J 2 antiferromagnetic interactions. When the coupling ratio g = J 2/J 1 approaches 1, all three diagonal checkerboards have the same long-range antiferromagnetic Néel order at T = 0. When g decreases, the quantum fluctuation can drive DC 2 × 2 model to quantum paramagnetic state, while DC 3 × 3 and CDC 3 × 3 models still have the long-range Néel order. By calculating the magnetic excitations at different coupling ratios, we find that the low-energy part of magnetic excitations calculated by QMC-SAC can be well explained by the spin wave theory. However, the high-energy parts even deep in the long-range antiferromagnetic phase are beyond the spin wave description. Compared to the g = 1 uniform square lattice, the high-energy excitations are more rich in our models. Our study may also draw the attention to the high-energy exctitaions beyond the spin wave theory.

Electron-molecule scattering in a bichromatic elliptically polarised laser field: Plateau structures and two-centre interference minima

Scattering of electrons off diatomic molecules in a bichromatic elliptically polarised laser field is considered by applying the S-matrix theory within the second Born approximation. Two characteristic plateaus appear in the energy spectrum of scattered electrons. The higher plateau is observed in the low-energy part of the spectrum and describes the single scattering, while the lower plateau extends to the high-energy part of the spectrum and describes the double scattering. Scattering and rescattering of electrons off molecular targets may occur at any molecular centre and in any order. Interference of contributions results in increasing/decreasing the differential cross section in particular regions of the energy spectrum of scattered electrons. Two contributions for single scattering and four contributions for double scattering exist in the case of diatomic molecules. For some molecular orientations, a sequence of declining maxima may be observed instead of the plateaus in the electron energy spectrum. We have also observed parabolic structures in the angle-resolved energy spectra. Analytical formulas that explain these structures have been provided. We have also explored the impact of the laser-field ellipticity on the scattered-electron energy spectra. The bichromatic ω– and ω– laser fields have been considered.

Potential origin of the state-dependent high-energy tail in the black hole microquasar Cygnus X-1 as seen with INTEGRAL

Context. 0.1–10 MeV observations of the black hole microquasar Cygnus X-1 have shown the presence of a spectral feature in the form of a power law in addition to the standard black body (0.1–10 keV) and Comptonization (10–200 keV) components observed by INTEGRAL in several black-hole X-ray binaries. This so-called “high-energy tail” was recently shown to be strong in the hard spectral state of Cygnus X-1, and, in this system, has been interpreted as the high-energy part of the emission from a compact jet. Aims. This result was nevertheless obtained from a data set largely dominated by hard state observations. In the soft state, only upper limits on the presence and hence the potential parameters of a high-energy tail could be derived. Using an extended data set, we aim to obtain better constraints on the properties of this spectral component in both states. Methods. We make use of data obtained from about 15 years of observations with the INTEGRAL satellite. The data set is separated into the different states and we analyze stacked state-resolved spectra obtained from the X-ray monitors, the gamma-ray imager, and the gamma-ray spectrometer (SPI) onboard. Results. A high-energy component is detected in both states, confirming its earlier detection in the hard state and its suspected presence in the soft state with INTEGRAL, as seen in a much smaller SPI data set. We first characterize the high-energy tail components in the two states through a model-independent, phenomenological analysis. We then apply physical models based on hybrid Comptonization (eqpair and belm). The spectra are well modeled in all cases, with a similar goodness of the fits. While in the semi-phenomenological approach the high-energy tail has similar indices in both states, the fits with the physical models seem to indicate slightly different properties. Based on this approach, we discuss the potential origins of the high-energy components in both the soft and hard states, and favor an interpretation where the high-energy component is due to a compact jet in the hard state and hybrid Comptonization in either a magnetized or nonmagnetized corona in the soft state.

Simulated design of neutron ambient dose equivalent meter with gadolinium core plastic scintillator using Geant4 code

It has been demonstrated that the gadolinium-core plastic scintillator sphere is a stable, highly sensitive, transportable, and cost-efficient neutron detector made of environmentally friendly components. This detector comprises a metal gadolinium core inserted at the center of a high-scale plastic scintillator sphere. In this study, we conducted simulations to investigate the feasibility of obtaining accurate neutron ambient dose equivalent measurements using this type of detector. The Geant4 code based on the Monte Carlo method was employed to calculate the detector light output spectra for different neutron energies and the response function of the high energy part above 3 MeVee. The neutron energy responses of the detector were combined in an appropriate manner to match the energy-dependent neutron fluence to the ambient dose equivalent conversion coefficients. The Monte Carlo simulation results were used to optimize the thickness of the metal gadolinium core and plastic scintillator. The simulation results showed that a metal gadolinium core with a thickness of several hundred microns is a suitable choice considering manufacturing costs and the detector's efficiency. In addition, this type of detector with the plastic scintillator sphere size of 8″ can predict the neutron ambient dose equivalent with good accuracy over a wide energy range from 0.01 eV to 20 MeV, Although it underestimated the neutron dose equivalent in the energy range from 10 keV to about 5 MeV and overestimated it in the energy interval from 5 MeV to 20 MeV.

Synthesis, spectroscopic, electrochemical and photophysical properties of high band gap polymers for potential applications in semi-transparent solar cells

BackgroundThe design of new polymers able to filter the electromagnetic spectrum and absorb distinctly in the UV and high-energy part of visible spectrum is crucial for the development of semi-transparent solar cells. Herein, we report on the synthesis and spectroscopic, electrochemical, and photophysical characteristics of three new polymers, namely (i) Poly(triamterene-co-terephthalate), (ii) Poly[triamterene-co- 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-p,p′-disulfonamide], and (iii) Poly(5-hydroxyindole-2-carboxylate) that might show promise as materials for semi-transparent solar cells.ResultsThe energy band gap, refractive index, dielectric constant, and optical conductivity of the electron donor polymer, poly(triamterene-co-terephthalate), were determined to be 2.92 eV, 1.56, 2.44 and 2.43 × 104 S cm−1, respectively. The synthesized electron acceptor polymers showed a relatively high refractive index, dielectric constant, and optical conductivity. The presence of a direct allowed transition was confirmed between intermolecular energy bands of the polymers.ConclusionsThe polymers showed relatively high energy gap and deep HOMO levels, making them strong absorbers of photons in the UV region and high energy part of the visible region. The synthesized donor and acceptors performed well relative to P3HT and fullerenes due to the close match of the HOMO and LUMO levels. With further development, the polymers could be viable for use as the active layers of semi-transparent solar cells.

Scaling of magnetic dissipation and particle acceleration in ABC fields

Using particle-in-cell numerical simulations with electron–positron pair plasma, we study how the efficiencies of magnetic dissipation and particle acceleration scale with the initial coherence length $\lambda _0$ in relation to the system size $L$ of the two-dimensional ‘Arnold–Beltrami–Childress’ (ABC) magnetic field configurations. Topological constraints on the distribution of magnetic helicity in two-dimensional systems, identified earlier in relativistic force-free simulations, that prevent the high- $(L/\lambda _0)$ configurations from reaching the Taylor state, limit the magnetic dissipation efficiency to about $\epsilon _{\textrm {diss}} \simeq 60\,\%$ . We find that the peak growth time scale of the electric energy $\tau _{E,{\textrm {peak}}}$ scales with the characteristic value of initial Alfvén velocity $\beta _{A,{\textrm {ini}}}$ like $\tau _{E,\textrm {peak}} \propto (\lambda _0/L)\beta _{A,{\textrm {ini}}}^{-3}$ . The particle energy change is decomposed into non-thermal and thermal parts, with non-thermal energy gain dominant only for high initial magnetisation. The most robust description of the non-thermal high-energy part of the particle distribution is that the power-law index is a linear function of the initial magnetic energy fraction.

Generation of intense single short attosecond pulse with a multicycle spatially inhomogeneous field

We theoretically study the high-order harmonics and single attosecond pulse generation from a pre-excited He+ ion in a multicycle two-color spatially inhomogeneous field. It is shown that the broadband supercontinuum spectrum and single quantum path selection can be realized, and then a single 15.2 as pulse is directly obtained. By appending a uv attosecond pulse to the two-color spatially inhomogeneous field at a proper time, the conversion efficiency of the high-energy part of the supercontinuum is improved by at least an order of magnitude, which enables the production of an intense single 17.3 as pulse.

New reconstruction of event-integrated spectra (spectral fluences) for major solar energetic particle events

Aims. Fluences of solar energetic particles (SEPs) are not easy to evaluate, especially for high-energy events (i.e. ground-level enhancements, GLEs). Earlier estimates of event-integrated SEP fluences for GLEs were based on partly outdated assumptions and data, and they required revisions. Here, we present the results of a full revision of the spectral fluences for most major SEP events (GLEs) for the period from 1956 to 2017 using updated low-energy flux estimates along with greatly revisited high-energy flux data and applying the newly invented reconstruction method including an improved neutron-monitor yield function. Methods. Low- and high-energy parts of the SEP fluence were estimated using a revised space-borne/ionospheric data and ground-based neutron monitors, respectively. The measured data were fitted by the modified Band function spectral shape. The best-fit parameters and their uncertainties were assessed using a direct Monte Carlo method. Results. A full reconstruction of the event-integrated spectral fluences was performed in the energy range above 30 MeV, parametrised and tabulated for easy use along with estimates of the 68% confidence intervals. Conclusions. This forms a solid basis for more precise studies of the physics of solar eruptive events and the transport of energetic particles in the interplanetary medium, as well as the related applications.

One-dimensional hydrodynamic simulations of low convergence ratio direct-drive inertial confinement fusion implosions.

Indirect drive inertial confinement fusion experiments with convergence ratios below 17 have been previously shown to be less susceptible to Rayleigh–Taylor hydrodynamic instabilities, making this regime highly interesting for fusion science. Additional limitations imposed on the implosion velocity, in-flight aspect ratio and applied laser power aim to further reduce instability growth, resulting in a new regime where performance can be well represented by one-dimensional (1D) hydrodynamic simulations. A simulation campaign was performed using the 1D radiation-hydrodynamics code HYADES to investigate the performance that could be achieved using direct-drive implosions of liquid layer capsules, over a range of relevant energies. Results include potential gains of 0.19 on LMJ-scale systems and 0.75 on NIF-scale systems, and a reactor-level gain of 54 for an 8.5 MJ implosion. While the use of 1D simulations limits the accuracy of these results, they indicate a sufficiently high level of performance to warrant further investigations and verification of this new low-instability regime. This potentially suggests an attractive new approach to fusion energy.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

Sources and space-time distribution of the electromagnetic pulses in experiments on inertial confinement fusion and laser-plasma acceleration.

When high-energy and high-power lasers interact with matter, a significant part of the incoming laser energy is transformed into transient electromagnetic pulses (EMPs) in the range of radiofrequencies and microwaves. These fields can reach high intensities and can potentially represent a significative danger for the electronic devices placed near the interaction point. Thus, the comprehension of the origin of these electromagnetic fields and of their distribution is of primary importance for the safe operation of high-power and high-energy laser facilities, but also for the possible use of these high fields in several promising applications. A recognized main source of EMPs is the target positive charging caused by the fast-electron emission due to laser-plasma interactions. The fast charging induces high neutralization currents from the conductive walls of the vacuum chamber through the target holder. However, other mechanisms related to the laser-target interaction are also capable of generating intense electromagnetic fields. Several possible sources of EMPs are discussed here and compared for high-energy and high-intensity laser-matter interactions, typical for inertial confinement fusion and laser-plasma acceleration. The possible effects on the electromagnetic field distribution within the experimental chamber, due to particle beams and plasma emitted from the target, are also described. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Recent progress in quantifying hydrodynamics instabilities and turbulence in inertial confinement fusion and high-energy-density experiments.

Since the seminal paper of Nuckolls triggering the quest of inertial confinement fusion (ICF) with lasers, hydrodynamic instabilities have been recognized as one of the principal hurdles towards ignition. This remains true nowadays for both main approaches (indirect drive and direct drive), despite the advent of MJ scale lasers with tremendous technological capabilities. From a fundamental science perspective, these gigantic laser facilities enable also the possibility to create dense plasma flows evolving towards turbulence, being magnetized or not. We review the state of the art of nonlinear hydrodynamics and turbulent experiments, simulations and theory in ICF and high-energy-density plasmas and draw perspectives towards in-depth understanding and control of these fascinating phenomena. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.