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Experiments have achieved high confinement discharges in tokamaks with a negative triangularity (NT) plasma shape accompanied by a lower pedestal and smaller and more frequent edge localized modes (ELMs) compared with positive triangularity (PT). Some existing theories emphasize the linear instability variations result from the change of pedestal. However, NT can directly bring significant changes on magnetic field structures which may also influence the instability of ELMs. Based on a series of equilibria constructed with different triangularities and pressure profiles, the influence of NT on peeling-ballooning mode (P–B mode) is investigated. It is found that NT can increase the growth rates of low to intermediate n (toroidal mode number) modes in the linear stage and lead to a larger pedestal collapse in the nonlinear stage if its pressure profile is the same with the PT shape. Further analyses demonstrate that NT enlarges the unfavorable curvature area, which provides stronger driving source and larger unstable region for the instability. Meanwhile, the diamagnetic effect and local magnetic shear helps to stabilize high n modes in the linear phase, and the E × B shearing rate at the top of the pedestal contributes to suppress the transport of turbulence into the plasma core in the nonlinear phase for the NT shape. What’s more, further simulations with different pedestal heights demonstrate that there exists a threshold value of pressure ratio, below which the ELM energy loss in NT shapes can be smaller than that in PT shapes, suggesting that the smaller energy loss with NT in experiment mainly results from the lower pedestal heigh. The results reveal behaviors of P–B modes and provide possible mechanisms for the phenomenon of lower pedestal height with negative triangularities in experiments.

The Chinese first quasi-axisymmetric stellarator (CFQS), which will be the first quasi-axisymmetric (QA) stellarator in the world, is now under construction. The primary task of the CFQS project is to realize a QA configuration and to examine its physical properties. Based on this task, two important issues were investigated in this work in order to estimate the robustness of the CFQS design from a physical perspective. One was the toroidal field (TF) ripple due to the discreteness of modular coils (MCs) which could potentially degrade the charged particle confinement in the CFQS configuration. The other was a possible MC misalignment in the assembly that would affect the magnetic field and charged particle confinement in the CFQS. Moreover, since the stellarator symmetry might be broken by the MC misalignment, such a case was also investigated in this work. By performing a magnetic field line tracing and charged particle orbit tracing calculation, it was found that the TF ripple does not affect the confinement property significantly and the magnetohydrodynamics equilibrium was robust against possible MC misalignments. These results are helpful in defining the reasonable tolerance of assembly accuracy.

We studied the work function of cesium deposition and co-deposition with the electronegative element on the plasma grid (PG) using the first-principles calculations. The impurity particles may exist in the background plasma and vacuum chamber wall, and the work function of the PG will be affected. The results indicate that the minimum work functions of pure cesium deposition on Mo (110), W (110), and Mo (112) are reached at a partial monolayer. They are 1.66 eV (σ = 0.56 θ), 1.69 eV (σ = 0.75 θ), and 1.75 eV (σ = 0.88 θ), respectively. An appropriate co-deposition model consisting of cesium with electronegative elements can further decrease the work function. The coverage of cesium and electronegative elements are both 0.34 θ in all the co-deposition models. The F-Cs co-deposition model where the Cs atom and F atom are aligned along the surface normal obtains the lowest work function. They are 1.31 eV for F-Cs on Mo (110), and 1.23 eV for F-Cs on W (110), respectively. The change in work function is linearly related to the change in dipole moment density with a slope of −167.03 VÅ. For pure cesium deposition, two factors control the change in dipole-moment density, one is the electron transfer between adsorbates and the substrate, and another one is the restructuring of surface atoms. There are two additional factors for the co-deposition model. One is the intrinsic dipole moment of the double layer, the other is the angle between the intrinsic dipole moment and the surface. The latter two factors play important roles in increasing the total dipole moment.

The effects of positive and negative bias voltages on the turbulence characteristics in the edge plasmas of J-TEXT are studied using Langmuir probe arrays. The experimental results illustrate that the turbulent particle transport fluxes are suppressed in both positive and negative bias cases, while the suppression mechanisms are quite different. For positive bias (+300 V), long-range correlation (LRC) structures with frequencies of about 10–30 kHz are generated, which are beneficial for turbulent transport suppression. In the −300 V bias case, no LRCs appear, while a strong mean flow shear exists which can reduce the amplitudes of potential and density fluctuations and thus decrease the turbulent transport.

The structural, mechanical and thermodynamic properties of tungsten-based alloys, including W0.5Ti0.5,W0.67Zr0.33,W0.666Ti0.1667Zr0.1667,W0.67Hf0.33 and W0.666Ti0.1667Hf0.1667, have been investigated in this paper by first-principles calculations based on density functional theory (DFT). The calculated elastic constants and mechanical stability criteria of cubic crystals indicated that all of these cubic alloys are mechanical stable. The mechanical properties, including bulk modulus (B), shear modulus (G), Young’s modulus(E), ratio B/G, Poisson’s ratio, Cauchy pressure and Vickers hardness are derived from the elastic constants Cij. According to calculated elastic modulus and Vickers hardness, the W0.666Ti0.1667Hf0.1667 alloy has the greatest mechanical strength. The Vickers hardness of these cubic alloys rank as follows: W0.666Ti0.1667Hf0.1667 > W0.67Zr0.33 > W0.666Ti0.1667Zr0.1667 > W0.5Ti0.5 > W0.67Hf0.33. Moreover, calculated ratio B/G, Poisson’s ratio, Cauchy pressure indicated that the ductility of W0.666Ti0.1667Hf0.1667 alloy is the worst among these alloys. The ductility of these cubic alloys rank as follows: W0.67Hf0.33 > W0.5 Ti0.5 > W0.67Zr0.33 > W0.666Ti0.1667Zr0.1667 > W0.666Ti0.1667Hf0.1667. What is noteworthy is that both mechanical strength and ductility of W0.666Ti0.1667Hf0.1667 are greater than pure W. Finally, Debye temperature, melting point and thermal conductivity have been predicted through empirical formulas. All these results will provide scientific data for the study on new product development of electrode materials.

In the particle-in-cell simulation study of this paper, it is found that the high-power terahertz radiation at twice the plasma frequency can be generated by the interaction between a weakly relativistic, large-radius, focused electron beam and an overdense plasma. The terahertz radiation is emitted from a multi-filament structure in the electron beam, which is caused by the coupling of the longitudinal two-stream instability and the transverse filamentation instability. The analysis of the k space of the plasma waves indicates that the radiation can be explained by the mode coupling among a forward oblique mode, a backward oblique mode, and a second harmonic radiation mode. The influences of the beam Lorentz factor and plasma density on the radiation power, efficiency, and coherence are also investigated. The present results not only contribute to the development of novel megawatt-level narrowband terahertz radiation sources, but also propose a potential terahertz radiation mechanism for the fundamental research of the beam-plasma system.

It is found that the plasma waves driven by an electron beam rotating in a magnetized overdense plasma can be converted into terahertz electromagnetic radiation by new mechanisms. According to the particle-in-cell simulation results, the radiation modes include a dominant extraordinary (X) mode at twice the plasma frequency [Formula: see text] and a subordinate X mode at [Formula: see text]. The [Formula: see text] radiation can be generated by the coupling of a beam mode and a scattered upper-hybrid (UH) mode, or by the coupling of a beam mode and a right-handed X mode. Here, the beam mode can be a UH mode or a left-handed X mode driven by the beam under the Cherenkov condition, and the right-handed X mode can be induced by high-order electron cyclotron maser instability. The [Formula: see text] radiation is the right- or left-handed fundamental X mode escaping from the plasma boundary. This study also shows that the breakdown of beam modulation is responsible for the radiation attenuation. The scheme proposed in this paper can be applied in high-power THz radiation sources and diagnosis of magnetized plasmas.

We report on an analysis of the decay J/ψ→γπ0η′ using a sample of (1310.6±7.0)×106J/ψ events collected with the BESIII detector. We search for the CP-violating process ηc→π0η′ and a dark gauge boso ...

The cross section for the process e(+)e(-)-> pi(+) pi(-) J/psi is measured precisely at center-of-mass energies from 3.77 to 4.60 GeV using 9 fb(-1) of data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in a fit to the cross section. The first resonance has a mass of (222.0 +/- 3.1 +/- 1.4) MeV/ c(2) and a width of (44.1 +/- 4.3 +/- 2.0)MeV, while the second one has a mass of (4320.0 +/- 10.4 +/- 7.0)MeV/c(2) and a width of (101.4(- 19.7)(+25.3) +/- 10.2) MeV, where the first errors are statistical and second ones are systematic. The first resonance agrees with the Y(4260) resonance reported by previous experiments. The precision of its resonant parameters is improved significantly. The second resonance is observed in e(+)e(-)-> pi(+) pi(-) J/psi for the first time. The statistical significance of this resonance is estimated to be larger than 7.6 sigma. The mass and width of the second resonance agree with the Y(4360) resonance reported by the BABAR and Belle experiments within errors. Finally, the Y(4008) resonance previously observed by the Belle experiment is not confirmed in the description of the BESIII data.

Electron cyclotron resonance heating and current drive (ECRH/ECCD) are deemed to be one of the best option to control the neoclassical tearing modes (NTMs), which are potential danger for steady state operation in fusion reactors. Recently, one of the two ECRH equatorial launchers on HL-2A tokamak has been upgraded to satisfy the real-time control requirements. The upgrade of the rotation and driving mechanism accelerates the tuning speed of poloidal injection angle of EC beam significantly, which permits the modification of the EC power deposition position in real time. Analyses on the beam injection angles and wave power losses, together with calibration results on test bed indicate that the new launcher has a good launching performance. The upgraded No. 2 ECRH launcher was successfully applied in the first proof-of-principle experiment for NTM real-time control, in which within 250 ms suppression of the classical tearing modes (CTMs) by ECRH/ECCD was realized for the first time on HL-2A.

In this study, the plasma-photonic-crystal-like beam–plasma system has been proposed. Two types of plasma-photonic-crystal-like beam–plasma systems, namely plasma-vacuum-plasma-vacuum-plasma (PVPVP) beam–plasma system and plasma-vacuum-plasma (PVP) beam–plasma system, have been simulated using the particle-in-cell method. The simulation results show that the beam electrons can be focused without an external magnetic field, and the electromagnetic (EM) radiation can be observed. For the PVPVP beam–plasma system, the EM radiation frequency is 0.9035 THz, and the electron efficiency that the beam electrons give out their energy to the EM wave is 3.06%. For the PVP beam–plasma system, the EM radiation frequency is also 0.9035 THz, but the electron efficiency can be up to 10.5%. This work can contribute to the engineering practice of the beam–plasma system.

A quasi-axisymmetric stellarator, the CFQS, has been designed as a joint project of the National Institute for Fusion Science and Southwest Jiaotong University to prove intrinsic advantages of quasi-axisymmetry. Principal parameters of the CFQS are as follows: the major radius is 1 m, the magnetic field strength is 1 T, the aspect ratio is 4, and the toroidal periodic number is 2. The magnetic field configuration is designed based on that of the CHS-qa. Enhanced confinement properties within the context of neoclassical theory are achieved by its quasi-axisymmetric configuration. In the entire radial range, the magnetic well is retained to keep favourable stability features in the magnetohydrodynamic equilibrium. A magnetic field coil system was designed for the CFQS, which consists of 16 modular coils, 12 toroidal field coils, and 4 poloidal field coils. The supporting structure is designed to withstand strong electromagnetic force under 1 T operation, maintaining enough space for heating and diagnostic systems. The mock-up modular coil with the most complicated shape was constructed by Hefei Keye Electro Physical Equipment Manufacturing Co., Ltd. to check manufacturability and the achieved accuracy. A heat-run test was performed to check the temperature rise of conductors, and the capability of 1 T operation was confirmed. After various tests for the mock-up coil, construction of actual modular coils and the vacuum vessel has begun.

In this work, the O impurity particle adsorption on the Cs/Mo(110) surface, to determine the influence of O on Cs stability on Mo(110) surface and also the work function of Cs/O/Mo(110) surface, has been investigated by performing density functional theory (DFT). There are four independent adsorption sites on Cs/Mo(110) surface for O atom. No matter which adsorption site O was adsorbed, the surface adsorption energy of Cs increased. O atoms attract more charges due to the difference in electronegativity. Although this weakens the interaction between the Cs and Mo atoms, the O atom does connect them like a bridge, resulting in enhanced adsorption of Cs atom. In our model, the surface work function of Cs/Mo(110) is calculated as 1.835 eV. In some cases, the adsorption of O can dramatically reduce the surface work function to 1.633 eV. Conversely, O may also increase it, but this increase is not pronounced. This result suggests that the appropriate addition of O atoms may be beneficial to the development of high-efficiency negative ion sources.

The toroidal flow damping has been investigated in the edge plasma of J-TEXT tokamaks with an electrode biasing (EB). The estimated viscosity of the toroidal flow after the bias turning off is about 67 times of the classical viscosity and four times of the neo-classical viscosity, which infers that the flow damping is anomalous in the transition phase. In the equilibrium phase, the torque densities driven by the EB, the momentum transport, and the neo-classical toroidal viscosity (NTV) under different bias conditions are calculated, which show that the NTV torques are comparable with the other terms. According to the angular momentum balance equation, the remnant damping torque densities and the effective damping coefficients have been obtained. Considering that the remnant damping is mainly contributed by the neutral particle damping, this investigation provides a method to estimate the neutral particle density ( nH), which gives that the nH in the edge plasma of J-TEXT is in the range of 1–4 (×1017 m−3).

A new scheme of generating high power terahertz (THz) radiation by using two obliquely colliding electron beams in plasma is proposed. The particle-in-cell simulation finds that a small beam intersection of high electron density is formed within a plasma wavelength when two thin electron beams collide. Meanwhile, the beam intersection can oscillate in a strong plasma wave driven by the two beams to produce THz radiation at double plasma frequency. A theoretical model is established showing that the radiation mechanism is the second-order current generated by the beam intersection oscillation. The angular distribution of the THz radiation is calculated by the theory, which agrees well with the particle-in-cell simulation. Compared with the existing high power THz sources, the scheme provided in this letter has advantages of simple structure and no need of extreme parameter conditions, which is hopeful to be applied in kilowatt-level coherent compact THz sources.

The ion (T i) and electron (T e) temperatures at the last closed flux surface (LCFS) during density scanning discharges and in the scrape-off layer (SOL) with a constant plasma density have been measured in the J-TEXT tokamak using a retarding field analyzer and four-tip Langmuir probe, respectively. Both the LCFS T i and T e are found to reduce with increasing central line-averaged density ( n ˉ e ). The temperature ratio (τ = T i/T e) is about 2 for a low n ¯ e (1.5 → 2.5 × 1019 m−3), decays in a moderate n ˉ e (2.5 → 3.5 × 1019 m−3) and tends to unity at a high n ˉ e (3.5 → 4.2 × 1019 m−3). This suggests that the ions and electrons at the LCFS (even in the SOL) are thermally decoupled at low or moderate n ˉ e and tend to full thermal coupling in the high-density plasmas. In addition, both T i and T e decrease with the radius and T e falls more steeply than T i due to faster parallel energy loss of electrons in the SOL. In contrast, τ rises with the radius, which indicates that the ions and electrons are much more thermally decoupled in the deeper SOL.

The effect of the toroidal flow and flow shear on the m/n = 2/1 tearing mode (TM) has been investigated in J-TEXT tokamak, where m and n are the poloidal and toroidal mode numbers. It is found that the toroidal flow increment is linearly modulated by the bias current/return current. The frequency of the 2/1 TM is also found to be proportional to the toroidal flow during the bias phase, which is consistent with the theoretical expectation. The electron diamagnetic drift frequency is almost constant before and during the bias phase. Moreover, the statistical analysis shows that the saturated island width of the TM is more correlated to the toroidal flow amplitude than the flow shear, which reveals that the effect of the TM depends on the magnitude of the toroidal flow rather than the flow shear. This result may illustrate the process of the 2/1 TM controlled by the electrode biasing, and suggests that changing the magnitude of toroidal flow is a possible method for stabilizing the TM.

The lattice structure, mechanical properties, electronic structure and thermodynamic properties of W1−xVx alloys (x = 0, 0.0625, 0.125, 0.25, 0.3125, 0.5 and 1) were calculated and simulated by first-principles method based on DFT. The mechanical properties including Poisson’s ratio, elastic moduli and B/G ratio were analysed via V concentration. The simulated results showed the ductility of alloys getting improved while the strength decreased with the addition of vanadium. And we calculated the anisotropy of Young’s modules and ideal tensile strength. The projected density of states is calculated to analyse the electronic structure. Furthermore, thermodynamic properties like Debye temperature and low temperature heat capacity were also calculated in this work. All the results can provide reference for selecting plasma facing materials in fusion reactor design.

In this paper, the mechanism by which current reflux forms from a plasma-focused electron beam is studied theoretically and numerically by considering nonlinear interactions between the beam and plasma. We demonstrate that a moving virtual cathode can be generated at the end of a plasma ion channel due to the influence of the boundary plasma electrons on the beam, and that this accounts for reflux formation. In addition, the reflux formation condition is derived and analyzed via the beam envelope and space-charge-limited current theories. The results indicate that the virtual cathode tends to form at defocusing positions of the beam. Particle-in-cell simulations are used to verify the theoretical results and to show that the beam divergence and energy spread increase during current reflux formation.

In order to support the design and manufacture the cesium (Cs) oven for the prototype negative ion source in the Chinese Fusion Engineering Test Reactor-Negative Ion Based Neutral Beam Injection (CFETR-NNBI) system, an advanced cesium oven is being set up at IFS. The design scheme is proposed based on the characteristics of the prototype negative ion source in the CFETR-NNBI system and combined with the international frontier research related to this aspect. Based on the reference to the Padova cesium oven, this article has designed a dedicated nozzle for the cesium oven and a transport channel more conducive to steam transport. A corrosion-resistant Cs reservoir and delivery tube is utilized. Precise control of cesium flux is achieved via remotely controlled switching valves and heating systems. The surface ionization detector is used to detect the cesium flux of the nozzle. And the thermal stability analysis, thermal transient analysis, thermal stress analysis and thermal deformation analysis were carried out on the design. The feasibility of the design is demonstrated through finite element analysis, which provides a theoretical basis for the next step of manufacturing. The cesium flux of oven is simulated and calculated, which provides reference for the subsequent device testing.

The characteristics of various quasi-single helicities (QSHs) in the Keda Torus eXperiment (KTX) are investigated in ideal magnetohydrodynamics (MHD) simulations with self-organized helical equilibria. It is found that in the core plasma region the negative magnetic shear imposes a substantial influence on the stabilization of interchange modes, which can enhance the magnetic fluctuations of the dominant single mode. The prominent reversal shear plays a critical role on the transition to the QSH phase. This paper shows that the QSH state with a toroidal field periodicity N fp = 6 is expected to stably achieve by the negative magnetic shear in the future KTX experiments. In addition, the plasma confinement effected by subdominant modes is estimated using particle drift computations in the KTX. As the amplitude of residual subdominant modes increases the radial drift is significantly enhanced, which indicates a drastic loss of ions arises from the subdominant modes with sufficient amplitudes. The result appears to agree with experimental observations in the Madison Symmetric Torus (MST) (Bonofiglo 2019 Phys. Rev. Lett. 123 055001). This work may shed a light on the transition mechanism between the multiple helicities (MH) phase and the QSH phase in reversed-field pinch (RFP) facilities. Moreover, to improve the confinement of RFP in the QSH scenario, the critical importance of subdominant mode amplitudes on the ion confinement should be greatly considered.

The Chinese First Quasi-axisymmetric Stellarator (CFQS) will be the first operational quasi-axially symmetric stellarator in the world. The physical and engineering complexities led to the cancellation of two famous quasi-axisymmetric stellarators, CHS-qa and NCSX. Therefore, the major mission of the CFQS is to experimentally achieve the canonical quasi-axisymmetric configuration. The CFQS has been designed to possess a number of advanced features in fixed and free-boundary equilibria. It is a compact stellarator with an aspect ratio R/a ∼4.0. The neoclassical diffusion coefficient is similar to that of tokamaks in the collisionless regime. The MHD equilibrium of the CFQS configuration is stable up to volume-averaged normalized pressure β ∼1.1%. A region of the second ballooning stability exists in this facility with a large region of plasma, becoming second stable for β ∼2.7% in free-boundary equilibria. The gap between the first and second stability boundaries is very narrow, which is greatly beneficial for the CFQS operation in the second stable regime with high β plasma. A modular coil system with 16 coils is designed which robustly reproduces the standard quasi-axisymmetric magnetic field.

To date, almost all coil-design codes, e.g. NESCOIL, COILOPT, FOCUS codes, etc, have been primarily attributed to the optimization of filament coils for stellarators. However, evolving to a practical/finite-sized coil from a filament coil, the finite-size effect of coils significantly constrains the fabrication tolerances of a coil system. This paper presents a novel approach that emphasizes the optimization of practical modular coils to reduce sensitivity to fabrication tolerances and to achieve the expected magnetic configurations precisely. A new evaluation parameter, surface twist, is defined in this paper and applied to the optimization sequence in addition to the practical coil line torsion and curvature. The approach has been applied to the framework of the filament coil scheme in the Chinese first quasi-axisymmetric stellarator. This practical coil system without surface twists has been accomplished. Compared to the original finite-sized coil design, the new result is a more considerable simplification of coil shapes, such that in a certain direction view each finite-sized coil becomes a planar-like one. Moreover, this method can also be implemented for the estimation of stochastic deviations of practical coils during the fabrication and assembly of the coil system.

The Chinese First Quasi-axisymmetric Stellarator (CFQS) is now under design and construction. It will be the first quasi-axisymmetric (QA) configuration device to be operated in the world. The main parameters of the CFQS are as follows: the toroidal periodic number Np = 2, major radius R = 1.0 m, aspect ratio Ap = 4.0 and magnetic field strength Bt = 1.0 T. The low Ap makes it quite challenging to design a supporting structure because of the limited space and strong electromagnetic (EM) force. In this paper, a cage-like supporting structure is proposed for the CFQS modular coil (MC) system to sustain the EM force and the weight of entire device. A finite element analysis is carried out for ensuring the reliability of the supporting structure. The analysis results of the CFQS global model indicate that the cage-like supporting structure can basically satisfy the requirement.

The structural, elastic constants, mechanical properties and thermodynamic properties of WTi, WV, W2Zr, WVTi and WVZr alloys were investigated in this paper by using first-principles calculation based on density functional theory(DFT). Bulk modulus, shear modulus, radio B/G, Poisson's ratio and Young’s were derived from elastic data Cij. And the Debye temperature, melting point and minimum thermal conductivity can be obtained by empirical formulas. The Vickers hardness and Cauchy pressure of WTi, WV, W2Zr, WVTi and WVZr alloys were also calculated in this work. This work provides a theoretical basis for employing and further developing WTi, WV, W2Zr, WVTi and WVZr alloys.

The retarding field analyzer (RFA) is considered as one of the most effective tools to measure the ion temperature (T i) in the plasma boundary. However, there are some inaccuracies in the measured T i by RFA, due to impurities in the plasma. In this paper, the influences of impurities on the measured T i by RFA have been analyzed in hydrogen isotope plasmas with both low-Z and high-Z impurities. The analytical results show that the T i is underestimated in H+ (also D+ and T+) plasma when the fuel ion charge is taken as the charge number and the analyzed T i in H+ are all larger than that in D+ and T+ plasmas, exhibiting the isotope effect. With the concentration of low-Z impurity (η l) increasing, the analyzed T i decreases and it is about 20% underestimated with η l~12%. Comparison of different charge numbers and masses of low-Z impurities, it is found that larger charge number and smaller mass of low-Z impurities lead to the analyzed T i being more underestimated. The high-Z impurities make almost no impact on the T i, due to their small current contribution. Moreover, the T i is measured by RFA and edge rotational diagnostic (ERD) system through experiments. The results show good agreement with the analytical evaluations.

The nonresonant and stochastic heating of ions with a Kappa (κ) velocity distribution by an Alfven wave is investigated by means of both extremum method and test-particle simulation. Due to energetic-ion population, κ ions are picked up in the perpendicular (to the background magnetic field) direction via wave-ion nonresonant interaction and the ion energy gain depends on the thermal non-equilibrium factor (κ factor) and the ratio of the wave electric-field energy to background magnietic-field energy. With heating ion in perpendicular direction, the stochastic heating is to be sufficient and the maximal average parallel ion speed is the Alfven wave velocity, independent of initial ion velocity distribution. This phenomenon may have relevance to the heating in the solar wind, and there is a close link between heating, differential flow, and temperature anisotropy.

Based on a sample of 1.31 billion J/psi events collected with the BESIII detector, we report the study of the doubly radiative decay eta' -> gamma gamma pi(0) for the first time, where the eta' meson is produced via the J/psi -> gamma eta' decay. The branching fraction of eta' -> gamma gamma pi(0) inclusive decay is measured to be B(eta' -> gamma gamma pi(0))(Incl) = (3.20 +/- 0.07(stat) +/- 0.23(sys)) x 10(-3), while the branching fractions of the dominant process eta' -> gamma omega and the non-resonant component are determined to be B(eta' -> gamma omega) x B(omega -> gamma pi(0)) = (23.7 +/- 1.4(stat) +/- 1.8(sys)) x 10(-4) and B(eta' -> gamma gamma pi(0))(NR) = (6.16 +/- 0.64(stat) +/- 0.67(sys)) x 10(-4), respectively. In addition, the M-gamma gamma(2)-dependent partial widths of the inclusive decay are also presented.

The cross section for the process e(+)e(-)-> pi(+) pi(-) J/psi is measured precisely at center-of-mass energies from 3.77 to 4.60 GeV using 9 fb(-1) of data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in a fit to the cross section. The first resonance has a mass of (222.0 +/- 3.1 +/- 1.4) MeV/ c(2) and a width of (44.1 +/- 4.3 +/- 2.0)MeV, while the second one has a mass of (4320.0 +/- 10.4 +/- 7.0)MeV/c(2) and a width of (101.4(- 19.7)(+25.3) +/- 10.2) MeV, where the first errors are statistical and second ones are systematic. The first resonance agrees with the Y(4260) resonance reported by previous experiments. The precision of its resonant parameters is improved significantly. The second resonance is observed in e(+)e(-)-> pi(+) pi(-) J/psi for the first time. The statistical significance of this resonance is estimated to be larger than 7.6 sigma. The mass and width of the second resonance agree with the Y(4360) resonance reported by the BABAR and Belle experiments within errors. Finally, the Y(4008) resonance previously observed by the Belle experiment is not confirmed in the description of the BESIII data.

The effects of misalignment of modular coils on various physical properties in the Chinese first quasi-axisymmetric Stellarator (CFQS) are discussed in this study. To estimate the effects quantitatively, simple assumptions are made regarding the structure of coil displacement. We consider the following three cases: displacement in radial direction (Case A), displacement in the vertical direction (Case B), and displacement by tilting (Case C). In all cases, we assume that the displacement structure has a stellarator symmetry. These assumptions are employed to calculate the change in the magnetic surfaces, rotational transform profile, magnetic well depth profile, and the effective helical ripple. Calculation results show that if the magnitude of displacement is less than 10 mm, the effects on these physical properties are small, and the good neoclassical transport property is retained.