Helium Atoms Research Articles

Electron diffraction of foam-like clusters between xenon and helium in superfluid helium droplets.

We report electron diffraction results of xenon clusters formed in superfluid helium droplets, with droplet sizes in the range of 105-106 atoms/droplet and xenon clusters from a few to a few hundred atoms. Under four different experimental conditions, the diffraction profiles can be fitted using four atom pairs of Xe. For the two experiments performed with higher helium contributions, the fittings with one pair of Xe-He and three pairs of Xe-Xe distances are statistically preferred compared with four pairs of Xe-Xe distances, while the other two experiments exhibit the opposite preference. In addition to the shortest pair distances corresponding to the van der Waals distances of Xe-He and Xe-Xe, the longer distances are in the range of the different arrangements of Xe-He-Xe and Xe-He-He-Xe. The number of independent atom pairs is too many for the small xenon clusters and too few for the large clusters. We consider these results evidence of xenon foam structures, with helium atoms stuck between Xe atoms. This possibility is confirmed by helium time-dependent density functional calculations. When the impact parameter of the second xenon atom is a few Angstroms or longer, the second xenon atom fails to penetrate the solvation shell of the first atom, resulting in a dimer with a few He atoms in between the two Xe atoms. In addition, our results for larger droplets point toward a multi-center growth process of dopant atoms or molecules, which is in agreement with previous proposals from theoretical calculations and experimental results.

A hydrodynamic approach to reproduce multiple spinning vortices in horizontally rotating three-dimensional liquid helium-4

This paper reports a three-dimensional (3D) simulation of a rotating liquid helium-4, using a two-fluid model with spin-angular momentum conservation. Our model was derived from the particle approximation of an inviscid fluid with residual viscosity. Despite the fully classical mechanical picture, the resulting system equations were consistent with those of the conventional two-fluid model. We consider bulk liquid helium-4 to be an inviscid fluid, assuming that the viscous fluid component remains at finite temperatures. As the temperature decreased, the amount of the viscous fluid component decreased, ultimately becoming a fully inviscid fluid at absolute zero. Weak compressibility is assumed to express the volume change because some helium atoms do not render fluid owing to Bose–Einstein condensations or change states because of local thermal excitation. One can solve the governing equations for an incompressible fluid using explicit smoothed-particle hydrodynamics, simultaneously reproducing density fluctuations and describing the fluid in a many-particle system. We assume the following fluid–particle duality: a hydrodynamic interfacial tension between the inviscid and viscous components or a local interaction force between two types of fluid particles. The former can be induced in the horizontal direction when non-negligible non-uniformity of the particles occurs during forced two-dimensional rotation, and the latter is non-negligible when the former is negligible. We performed a large-scale simulation of 3D liquid helium forced to rotate horizontally using 32 graphics processing units. Compared with the low-resolution calculation using 2.4 × 106 particles, the high-resolution calculation using 19.6 × 106 particles showed spinning vortices close to those of the theoretical solution. We obtained a promising venue to establish a practical simulation method for bulk liquid helium-4.

State selective total and angular differential cross sections for positronium formation in [formula omitted]+[formula omitted] collisions

State-selective total and angular differential cross sections for positronium formation are presented in the collision of positron with helium atoms in their ground state by using the four-body formalism of the boundary-corrected continuum-intermediate-states approximation. The main purpose of the present study is to investigate the relative importance of intermediate ionization continuum states that has been incorporated with a suitable choice of distorting potential. In addition, the nine-dimensional integrals of the transition amplitude are analytically reduced to a one-dimensional real integral, which can be easily calculated numerically. The influence of the target static electron correlations on the capture probability is investigated using the different bound-state wave functions of He. The theoretical model for the calculation is fairly accurate and predicts a number of interesting features of the state-selective total and differential cross sections in the range of positron impact energy varies from 20 to 250eV. The total cross sections are highly peaked at an impact energy of 50 eV. The results are compared with those of other theories and the available experimental data. The present theoretical results and other measurements show satisfactory agreement in the wide energy range. Moreover, surface plots for the state-selective differential cross sections are also presented to illustrate the interesting feature of the positronium formation in this collision process.

Theoretical Modeling of Sr(q+) He (q = 0, 1, 2) van der Waals Systems Including Spin-Orbit Coupling.

Using an ab initio methodology that incorporates pseudopotential technique in conjunction with pair potential approaches, core polarization potentials (CPP), large basis sets of Gaussian type, and full configuration interaction calculations, we investigate interaction of neutral and charged Srq+(q = 0,1,2) with helium atom. In this context, the core-core interaction of Sr2+-He is included using an accurately performed potential for the ground state at CCSD(T) level of calculation. Also, the potential energy curves and permanent and transition dipole moments of the ground state and numerous excited states have been performed respectively for Sr+He and SrHe systems. Subsequently, the spin-orbit effect is considered by utilizing a semiempirical method for states dissociating into Sr+(5p) + He, Sr+(6p) + He, Sr+(4d) + He, Sr+(5d) + He, Sr(5s5p) + He, and Sr(5s4d) + He. The spectroscopic constants of the Srq+(q = 0, 1, 2) He states, with and without spin-orbit interaction, are derived and assessed in comparison to the existing theoretical and experimental studies. Such comparison has revealed good agreement, especially, for the Sr+He ionic system. Additionally, the spin-orbit effect is considered for the X2Σ+ → 22Π1/2,3/2 and X2Σ+ → 32Σ1/2 + transition dipole moments for Sr+He.

Behavior of Foreign Interstitial Hydrogen and Helium Atoms at Tungsten/Beryllium Interface from First-Principles Calculations

The behavior of foreign interstitial hydrogen and helium atoms and its effect on the physical properties of the tungsten/beryllium interface structure were computationally studied by first-principles calculations. Briefly, as part of our study of helium irradiation damage and hydrogen detention, the following properties were calculated: (1) the electronic properties of the tungsten/beryllium interface structure with a single interstitial hydrogen or helium atom and Hen vacancy or Hn vacancy complexes, and (2) the isotropy (polycrystalline) elastic modulus (bulk, torsion, Young’s modulus), anisotropy factor and minimum thermal conductivity of the previously described tungsten/beryllium interface systems. This study found that defect atoms are more likely to be concentrated in beryllium, but the tungsten layer is more sensitive to changes in mechanical properties caused by interstitial atoms. The ability of the beryllium vacancies to capture interstitial atoms is smaller than that of the tungsten vacancies. Based on the computational results, a preliminary assumption of the judgment of the tungsten/beryllium interface structure on the resistivity for plasma-facing materials is introduced. These computational studies provide a critical evaluation of the radiation resistivity and hydrogen retention of tungsten/beryllium interface materials. The calculated interface properties can be incorporated into radiation damage resistance property evaluation systems to develop and test tungsten-based composite materials.

Impact of electronic correlation on strong laser-induced bound-state transitions

Electron correlation (EC) plays a crucial role in all multi-electron systems and dynamic processes. In this work, we focus on strong laser-induced bound-bound transitions (BBT), which are fundamental to optical absorption measurements. We use the helium atom, the simplest two-electron system, as our test case, utilizing the ab initio code package HeTDSE. We examined the bound state energy levels, transition dipole moments (TDMs), and the dynamics of strong laser-induced BBT, both with and without considering EC. Our results indicate that EC significantly impacts the energy levels of the bound states and the TDMs. These effects collectively influence the transition dynamics of the excited states. Although EC does not alter the quantum transition pathways between resonance states, it generally increases the probability of resonance transitions in most cases. Our findings provide a quantitative description of EC in laser-induced BBT.

Full-quantum calculations of the pressure broadening $$D_{1}$$ and $$ D_{2}$$ lines of Mg$$^{+}$$ magnesium ion in a gas of ground-state He helium atoms

Full-quantum calculations of the pressure broadening $$D_{1}$$ and $$ D_{2}$$ lines of Mg$$^{+}$$ magnesium ion in a gas of ground-state He helium atoms

The hybrid anti-symmetrized coupled channels method (haCC) for the tRecX code

We present a new implementation of the hybrid antisymmetrized Coupled Channels (haCC) method in the framework of the tRecX (Scrinzi, 2022 [6]). The method represents atomic and molecular multi-electron functions by combining CI functions, Gaussian molecular orbitals, and a numerical single-electron basis. It is suitable for describing high harmonic generation and the strong-field dynamics of ionization. Fully differential photoemission spectra are computed by the tSurff method. The theoretical background of haCC is outlined and key improvements compared to its original formulation are highlighted. We discuss control of over-completeness resulting from the joint use of the numerical basis and Gaussian molecular orbitals by pseudo-inverses based on the Woodbury formula. Further new features of this tRecX release are the iSurff method, new input features, and the AMOS gateway interface. The mapping of haCC into the tRecX framework for solving the time-dependent Schrödinger equation is shown. Use, performance, and accuracy of haCC are discussed on the examples of high-harmonic generation and strong-field photo-emission by short laser pulses impinging on the Helium atom and on the linear molecules N2 and CO. Program summaryProgram title: tRecX — time-dependent Recursive indeXing (tRecX=tSurff+irECS)CPC Library link to program files:https://doi.org/10.17632/m9g2jc82sw.1Developer's repository link:https://gitlab.physik.uni-muenchen.de/AG-Scrinzi/tRecXLicensing provisions: GNU General Public License 2Programming language: C++External libraries: Eigen, arpack, lapack, blas, boost, FFTW (optional)Journal Reference of previous version: A. Scrinzi, Comp. Phys. Comm., 270:108146, 2022.Does the new version supersede the previous version: YesReasons for the new version: Major new functionality: haCC — hybrid antisymmetrized coupled channels methodSummary of revisions: Main additions are haCC and iSurff. Code usage and compilation were improved.Nature of problem: tRecX is a general solver for time-dependent Schrödinger-like problems, with applications mostly in strong field and attosecond physics. There are no technical restrictions on the spatial dimension of the problem with up to 6 spatial dimensions realized in the strong-field double ionization of Helium. Gaussian-based quantum chemical multi-electron atomic and molecular structure can be combined with the numerical basis. A selection of coordinate systems is available and any Hamiltonian involving up to second derivatives and arbitrary up to three dimensional potentials can be defined on input by simple scripts.Solution method: The method of lines is used with spatial discretization by a flexible combination of one dimensional basis sets, DVR representations, discrete vectors, expansions into higher-dimensional eigenfunctions of user-defined operators, and Gaussian based molecular orbitals. Multi-electron Gaussian-based CI (configuration interaction) functions for neutrals and ions are combined with the numerical basis. Photo-emission spectra are calculated using the time-dependent surface flux method (tSurff) in combination with infinite range exterior complex scaling (irECS) for absorption. The code is object oriented and makes extensive use of tree-structures and recursive algorithms. Parallelization is by MPI. Code design and performance allow use in production as well as for graduate level training.

Present Status of Spectroscopy of the Hyperfine Structure and Repolarization of Muonic Helium Atoms at J-PARC

The mass mμ− of the negative muon is one of the parameters of the elementary particle Standard Model and it allows us to verify the CPT (charge–parity–time) symmetry theorem by comparing mμ− value with the mass mμ+ of the positive muon. However, the experimental determination precision of mμ− is 3.1ppm, which is an order of magnitude lower than the determination precision of mμ+ at 120ppb. The authors aim to determine mμ− and the magnetic moment μμ− with a precision of O(10ppb) through spectroscopy of the hyperfine structure (HFS) of muonic helium-4 atom (4Heμ−e−) under high magnetic fields. He4μ−e− is an exotic atom where one of the two electrons of the He4 atom is replaced by a negative muon. To achieve the goal, it is necessary to determine the HFS of He4μ−e− with a precision of O(1ppb). This paper describes the determination procedure of the HFS of He4μ−e− in weak magnetic fields reported recently, and the work towards achieving the goal of higher precision measurement.

Probability of He+ Ion at Quantum Number 3 ≤ n ≤ 4 in Momentum Space

Ions resulting from the ionization of helium atoms are known as helium ions. Atom of Helium The probability distribution of the particle locations and velocities inside a helium atom is referred to as probability. Using theoretical study methods, the goal of this research is to find the probability of an electron's position in a helium atom at the quantum number 3 ≤ n ≤ 4. This type of research is non-experimental research by developing previously existing theories. This type of research is non-experimental research by transforming the radial wave function of hydrogenic atoms in position space into a radial wave function in momentum space using the Fourier transformation, then including a number of Gegenbauer functions and using the probability equation of finding an electron in a Helium ion in momentum space. The results of this research provide information regarding the position and probability of the existence of electrons in the helium atom. The probability value for the Helium ion is obtained using the equation P(p) = which is used to indicate the probability of finding an electron in a helium atom is directly proportional to the principal quantum number (n) and the value of the electron's momentum. The larger the electron momentum interval, the greater the probability.

Approximate Analytical Solution of the Ground State Problem of He and He-like Ions using Symmetrized-Hydrogenic States

The matrix method using three symmetrized-hydrogenic basis states has been applied to analytically obtain an approximate solution to the Schrödinger equation of the Helium atom and some He-like ions (2<Z<10). This study aims at obtaining more accurate ground state energies of the systems compared to our previous calculation using un-symmetrized basis states and some other simple calculations in the literature. The contribution of the symmetrized basis states on the ground state energies of the systems is also investigated. The time-independent Schrödinger equation involving a 3×3 Hamiltonian matrix, formed by hydrogenic s-states, was analytically solved to obtain three energy eigenvalues of the systems as well as their corresponding eigenvectors. Results showed that the 1s2 energies of the systems were more accurate than our previous unsymmetrized basis calculations, with significant error reduction observed for He and Li+. With the same matrix size, the ground state energies of He and He-like ions obtained from three symmetrized basis states in this study were found to be closer to the exact and experimental energies than those obtained from unsymmetrized basis states. It was also demonstrated that the |100;100> state made the largest contribution to the ground state energies of the systems, i.e. about 90.9% for He and around 99.9% for Ne8+, and consequently the smallest contribution came from the other two symmetrized states (less than 1%). To conclude, the calculated ground state energies were more accurate than some other simple calculations reported in the literature.

A comparative study on the spectral characteristics of nanosecond pulsed discharges in atmospheric He and a He+2.3%H2O mixture

Nanosecond pulsed discharges at atmospheric pressure in a pin-to-pin electrode configuration are well reproducible in time and space, which is beneficial to the fundamentals and applications of low-temperature plasmas. In this experiment, the discharges in helium (He) and He with 2.3% water vapor (H2O) are driven by a series of 10 ns overvoltage pulses (~13 kV). Special attention is paid to the spectral characteristics obtained in the center of discharges by time-resolved optical emission spectroscopy. It is found that in helium, the emission of atomic and molecular helium during the afterglow is more intense than that in the active discharge, while in the He+2.3%H2O mixture, helium emission is only observed during the discharge pulse and the molecular helium emission disappears. In addition, the emissions of OH(A-X) and Hα present similar behavior that increases sharply during the falling edge of the voltage pulse as the electrons cool down rapidly. The gas temperature is set to remain low at 540 K by fitting the OH(A-X) band. A comparative study on the emission of radiative species (He, He2, OH and H) is performed between these two discharge cases to derive their main production mechanisms. In both cases, the dominant primary ion is He+ at the onset of discharges, but their He+ charge transfer processes are quite different. Based on these experimental data and a qualitative discussion on the discharge kinetics, with regard to the present discharge conditions, it is shown that the electron-assisted three-body recombination processes appear to be the significant sources of radiative OH and H species in high-density plasmas.

Ground state properties of the screened helium atom under harmonic confinement

In this contribution, we show electronic property results for the ground state of the helium atom screened by a Debye plasma under an isotropic harmonic confinement as a function of the screening length (λD) and the angular frequency (ω0). The associate Hamiltonian is solved by expanding the wave function in the Hylleraas basis to incorporate the electron correlation in a simple manner. Furthermore, in order to compare with other findings the Hartree–Fock approach is implemented using a numerical grid method. The main results show that the total energy reaches the ionization threshold by the action of the electron coupling with the plasma medium and the strength of the harmonic confinement. The electron–electron average distance shows the compression of the system as the Debye plasma and the harmonic interactions become strongest (low λD and large ω0 values). We found acceptable results for the electron correlation energy when separate interactions are considered. In the absence of both interactions, the findings are in excellent agreement with other theoretical results.

High electron mobility in heavily sulfur-doped 4H-SiC

The Hall electron mobility in sulfur-doped 4H-SiC over a wide range of S concentration was investigated. Sulfur (S) works as a double donor in SiC. The electron concentration in the S+-implanted layers saturates when the S concentration exceeds 1×1018 cm−3 and the net donor concentration of the S+-implanted layer with S concentration of 1×1019 cm−3 is 4×1018 cm−3, indicating that the solubility or activation limit of S+-implanted SiC is about 2×1018 cm−3. The S+-implanted SiC with a S concentration of 1×1018 cm−3 exhibits an electron mobility of 598 cm2/V s, which is more than twice as high as that in N-doped SiC with the same doping concentration (268 cm2/V s). The temperature dependence of the electron mobility in S+-implanted SiC is reproduced in the wide temperature range by the calculation of the electron mobility adopting the helium atom model for neutral-impurity scattering.

In-situ TEM characterization and atomistic simulation of cavity generation and interaction in tungsten at 800 °C under dual W2+/He+ irradiation

In this work, we have investigated the role of pre-existing nano-scale cavities and irradiation sequence in helium clustering, and in the evolution of the cavity population in tungsten at 800 °C, by performing in-situ Transmission Electron Microscopy (TEM) characterizations under dual-beam W2+(600 keV)/He+(10 keV) irradiation to a total dose of 0.351 dpa, and supported by atomistic simulations. Pre-existing cavities, induced by single W2+ irradiation to 0.256 dpa, were seen to attract induced defects from subsequent irradiations, resulting in enhanced cavity size and a reduced number density in sequential irradiation when compared to concurrent irradiation. Such cavities developed faceted geometries and saturated in number density at an additional 0.051 dpa induced by He+ exposure in the sequential irradiation. In contrast, concurrent irradiations generate a denser cavity distribution that showed no sign of saturation or faceting up to the total irradiation damage of 0.351 dpa. In addition, Molecular Dynamics and Statics simulations were performed using LAMMPS software. These showed the pre-existing cavities to be trapping sites for helium atoms. Despite the large binding energy of ∼6 eV of those cavities, He-He interactions still occurred beyond the effective radius of such sinks, leading to additional He-He clustering not seeded by neighbouring cavities. These results point to the importance of selecting the irradiation conditions to simulate synergistic ion effects on cavity formation and evolution in plasma-facing tungsten-base materials.

Effect of H+ pre-irradiation on irradiation hardening and microstructure evolution of FeCoCrNiAl0.3 alloy with He2+ irradiation

FeCoCrNiAlx-based high entropy alloys (HEAs) exhibit excellent high-temperature strength, good radiation tolerance and corrosion resistance. However, studies on light-ion irradiation damage are relatively lacking. The influence of hydrogen and helium effect on HEAs deserves further study, given their complex interaction during different sequence irradiation at different irradiation conditions. In the present study, FeCoCrNiAl0.3 HEA was irradiated under two different modes at 723 K, one is single He2+ and the other is pre-iradiation of H+ followed by He2+. Microstructure evolution and irradiation hardening were studied by transmission electron microscopy and nanoindentation technique. There is no distinct difference of the irradiation hardening rate between sequential H+-He2+ and single He2+ irradiated samples. A large number of irradiation-induced nano-defects were observed after pre-irradiation of H+, which act as sinks to trap the subsequent helium atoms in the H+-He2+ irradiated sample. Fine helium bubbles and dislocation loops with high density dispersed in both irradiated samples. Compared with single He2+ irradiation, pre-irradiation of H+ resulted in a decrease in bubble density and an increase in loop density in H+-He2+ irradiated sample, but had little effect on their size. It is speculated that the critical concentration of bubble formation originating from H-He-V clusters is supposed to be higher than that of HeV clusters at elevated temperatures in FeCoCrNiAl0.3 alloy, leading to the aggregation and redistribution of He atoms at the H-He-V clusters rather than the formation of stable bubble nucleus after succeeding He2+ irradiation. The influence of pre-irradiation of H+ on FeCoCrNiAl0.3 alloy on the formation of helium bubbles and the relationship between bubble, loop and irradiation hardening are discussed.

Singular vibronic interaction in liquids: manifestation in the optical spectrum of impurity atoms in superfluid helium

The zero phonon line (ZPL) and its phonon-roton wing have been studied both experimentally and theoretically in the optical spectrum of the inner shell transition in the Dy atom in superfluid helium. It is shown that the linear vibronic interaction of impurity atom with long-wave acoustic phonons in the liquid phase is singularly enhanced. As a result, the ZPL of both the superfluid and normal components of liquid helium has a finite width. The temperature dependence of the spectrum is a consequence of the redistribution of the superfluid and normal components of the liquid helium and the temperature dependence of the spectrum of its normal component. Our calculations of the ZPL and its phonon-rotor wing are consistent with the experiment.

Accurate Scaling Functions of the Scaled Schrödinger Equation. II. Variational Examination of the Correct Scaling Functions with the Free Complement Theory Applied to the Helium Atom.

In a previous paper [Phys. Rev. Lett. 2004, 93, 030403.], one of the authors introduced the scaled Schrödinger equation (SSE), g(H - E)ψ = 0 for atoms and molecules, where the scaling function g is the positive function of the electron-nuclear (e-n) and electron-electron (e-e) distances. The SSE is equivalent to the Schrödinger equation (SE), (H - E)ψ = 0, that governs the chemical world but does not have the divergence difficulty that occurs when we try to solve the SE to obtain the exact solution. The g function is essential not only to prevent this divergence difficulty but also to obtain the exact wave function of the SE or SSE. In paper I of this series [J. Chem. Phys. 2022, 156, 014113.], we introduced five analytical g functions that behave correctly at both the coalescence and asymptotic regions, but we examined them only for the e-e part. In this paper, we examine these correct g functions for both e-n and e-e parts by applying the free complement (complete-element) (FC) theory variationally to the He atom. However, even for the two-electron He atom, the analytical integral formulas were not obtained when we use the correct g functions for both e-n and e-e parts, except for g = 1 - exp(-γr), but we were able to perform variational FC calculations by employing numerical integration schemes. We examined not only the energy and wave function but also the H-square error (defined by eq 14 of the text), energy lower bound, and e-n and e-e cusp properties. For the energy lower bound, we applied our FC wave functions to the method proposed recently by Pollak, Martinazzo, and others and could obtain good results. With the use of the correct-group g functions, the convergence of the FC theory to the exact analytical solution of the SE or SSE became efficient, and the performance was particularly good with the g functions, r/(r + 1/γ), Ei, and 1 - exp(-γr) in this order. These results were always superior to those obtained with g = r.

Quantum calculation of the pressure broadening of H and K lines of Ca+ calcium ion in a gaz of ground-state He helium atoms

In this theoretical study, we have conducted calculations to investigate the pressure broadening of the H ( 4 s 2 S 1 / 2 − 4 p 2 P 1 / 2 ) and the K ( 4 s 2 S 1 / 2 − 4 p 2 P 3 / 2 ) lines of the Ca + calcium ion in a gas of ground-state He helium atoms. The focus of our work is to determine the profiles of the pressure-broadened resonance lines and analyse their behaviour under the influence of binary collisions between Ca + ions and He atoms. To achieve this, we constructed accurate potential energy curves for the ground X 2 Σ 1 / 2 + and the excited D 2 Π 1 / 2 , D 2 Π 3 / 2 and E 2 Σ 1 / 2 + states. Additionally, we constructed the corresponding transition dipole moments based on the data obtained through high-level ab initio methods, including SA-CASSCF, MRCI, and SO coupling, with Davidson and BSSE corrections. The study spans a range of temperatures from 4000 K to 12,000 K and wavelengths from 200 nm to 500 nm . The theoretical profile is characterised by dominant free-free transitions. In the vicinity of the 436 nm wavelength position, there is a satellite peak in the red wing, attributed to the contribution of D 2 Π 1 / 2 ⟵ X 2 Σ 1 / 2 + and D 2 Π 3 / 2 ⟵ X 2 Σ 1 / 2 + transitions. Our findings are in good agreement with previous theoretical results.

The temperature effect on the formation and growth of helium-vacancy clusters in bcc iron: A comprehensive molecular dynamics simulation

Bubble generation can significantly degrade the performance of fusion reactor structural materials. In this work, the temperature effects on the initial clustering of helium (He) atoms, the formation of helium-vacancy clusters (HenVm) and the subsequent growth of the clusters into bubbles in bcc iron under different conditions were simulated by molecular dynamics. The results show that He behaviors are primarily dominated by coalescence at temperature range from 400 K to 500 K, which leads to a preference for He to bind together. Conversely, when temperature is higher than 500 K, dissociation become more prominent, causing large He clusters to be hard to form. Under the conditions of increasing He concentration and irradiation dose, the higher the temperature, the higher the density of HenVm clusters at He concentration around 100 appm. However, the temperature dependence reversed at high He concentration. The detailed analysis of formation cases revealed the percentage of nucleation sites for He bubbles at defects during He segregation. In addition, there is no significant difference among the He/V ratio of HenVm clusters formed at vacancies, interstitial dislocation loops (IDLs) and interstitial sites during the cluster growth. However, the He/V ratio of He bubbles growing on edge dislocation (ED) is overall lower than those growing at other formation sites, since the growth of HenVm clusters on ED requires a lower pressure to kick out self-interstitial atoms (SIAs) or SIA clusters. The average He/V ratio of He bubbles in bulk decreases as temperature rises from 400 K to 800 K, while that of He bubbles growing on ED is independent of temperature.