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We demonstrate that geometric deformation of flux-surface induced by a magnetic island can trigger the bifurcation to an electron internal transport barrier (eITB) through a novel positive feedback loop arising from the nonlinear coupling between the neoclassical tearing mode (NTM) and collisionless trapped electron mode (CTEM). The magnetic island-induced deformation enhances the precession drift frequency of trapped electrons, resulting in suppression of the CTEM turbulence. The consequent reduction in turbulent heat transport steepens the electron temperature gradient, which in turn amplifies the magnetic island via an increase in bootstrap current, thereby closing and reinforcing the feedback loop. The key features of this NTM-triggered eITB theory are qualitatively consistent with the experimental observations from J-TEXT (Mao et al 2025 Nucl. Fusion 65 066018).

This paper develops a self-consistent one-dimensional (1D) spatiotemporal model to investigate the interactions between full-energy helium (He) ions and drift wave–zonal flow (DW–ZF) system. The model integrates three physical components: (1) the interactions between He ions and the DW–ZF system, wherein the dilution of He ions modulates DW–ZF dynamics and in turn DW-driven transport simultaneously alters the profile of the He ion dilution factor; (2) the explicit inclusion of dilution effects on the growth rate in addition to the real frequency of DW; and (3) a turbulence spreading term added into the evolution equation of DW. Numerical results reveal that compared with the case with a fixed dilution profile and constant linear growth rate of DW, evolving He ion dilution factor and considering the corresponding dilution-modified linear growth rate in the self-consistent 1D model decreases the saturated value of He ion dilution factor—especially the contribution from lower energy He ash, increases the DW energy, decreases and even causing a reversal radial profile of ZF energy. These findings show that He ash removal may be more achievable even though the increase in the DW energy indicates that the improvement of plasma confinement might not be as substantial as the prediction with fixed dilution factor. Moreover, analytical expressions for the saturated He ion dilution factor, DW energy and ZF energy under a zero-dimensional local approximation are derived, which can qualitatively explain the corresponding 1D results. Overall, these findings highlight the importance of self-consistent modeling for reliably assessing He ash accumulation and confinement performance in future burning plasmas.

The timescale of thermal quench (TQ) remains a long-lasting issue in tokamak plasmas, which has not been fully understood yet. In this work, based on our previous thermal diffusion model and further considering the scattering caused by the electrostatic turbulence into account, a more generalized evolution equation of the electron temperature is derived from the electron drift-kinetic equation. This equation is applicable to all collisional regimes and a wide range of the stochastic magnetic fields (SMF) amplitude b~r. On the one hand, the heat flux induced by the E~×B drift is comparable to that induced by the SMF under DIII-D parameters, but becomes negligible under International Tokamak Experimental Reactor (ITER)-like parameters. However, the overall impact of electrostatic turbulence appears to be insignificant in both scenarios. This is because the direct transport caused by E~×B drift is basically counterbalanced by the reduction of the transport induced by the SMF due to the modification effect of electrostatic turbulence. On the other hand, numerical results indicate the timescale of the TQ is strongly dependent on the SMF amplitude and can reach the order of 100 us when b~r∼10−2. The scaling of TQ timescale being approximately proportional to device size remains invariant under varying SMF amplitudes, and the extrapolations from DIII-D to ITER-like case based on this scaling demonstrate alignment with numerical results. It is also shown that the collisionality-dependent and SMF amplitude-dependent of thermal diffusivity should be carefully considered to predict the TQ timescale. Moreover, it is also discussed that SMF amplitude exceeding 4 × 10−3 would lead to unacceptable thermal loading on divertor target during TQ in ITER.

The impurity transport driven by kinetic ballooning mode (KBM) is theoretically studied in the DIII-D H-mode strong gradient pedestal plasmas. From the electromagnetic gyrokinetic equation, including the correction of the strong radial electric field, the dispersion relationship of KBM instability with non-trace impurity is firstly derived. Then, the turbulent impurity flux and ion heat flux, as well as the associated transport coefficients, are further calculated. Through the parametric dependence analysis of analytical results, it is found that dilution effects of light fully ionized impurities can reduce the drive of KBM by affecting the kinetic pressure gradient parameter α and diamagnetic effects, thus leading to a decrease in both the absolute value of the real frequency |ωr′| and the growth rate γk′ of KBM instability. Stronger dilution effects by increasing the impurity charge number Z or steepening the impurity density profile correspond to stronger effects. Moreover, the removal efficiency of light fully ionized impurities, quantified by the ratio between the impurity diffusivity and effective ion heat conductivity Dzχieff≈1−bz+4ωDz/ωr′3(1+1/ηi)/2, increases with an increase of Z mainly due to the smaller impurity finite Larmor radius (FLR) effects reflected by bz∝1/Z. Besides, the increase of the impurity density gradient can significantly enhance Dz/χieff, and this is because stronger impurity dilution effects make a larger magnetic drift term |ωDz|/|ωr′| ( ωDz is the magnitude of impurity magnetic drift frequency) and ηi (the ratio of ion density gradient scale length to ion temperature gradient scale length). For heavy metal impurities with a concentration of 10−4, the peaking factor (PF) is positive, which means that its density profile is inwardly peaked, and the PF decreases with the enhancement of impurity FLR effects. These results may provide some theoretical reference on understanding the physical mechanism of impurity transport in the pedestal of H-mode plasmas.

In this work, the source of helium (He) ash is explicitly defined in terms of the full energy distribution function of He ions in deuterium–tritium burning plasmas, and the He ash density profile is subsequently predicted by considering both source and radial transport. By numerically solving the Fokker–Planck equation, including the energy diffusion term, we obtain the distribution function of He ions fHe in the full energy range and propose a method to quantitatively define the demarcation energy between energetic alpha ( α) particles and He ash in energy space. The corresponding source of He ash is then calculated. On the one hand, fHe in the low-energy region is significantly higher than the classical slowing down distribution function due to energy diffusion, which indirectly enhances the source of He ash. On the other hand, the directly introduced source term by energy diffusion makes He ions diffuse from the low-energy to the high-energy range, which reduces the source and plays the role of a sink for He ash. Combining the competition between the source and sink, the total source Sash,tF is increased compared to that without energy diffusion. Consequently, the corresponding He ash density profile with the total source is also higher than that without energy diffusion, and closer to that with the source defined by the density of energetic α particles (Angioni et al 2009 Nucl. Fusion 49 055013). These results underscore the significance of complete kinetic calculations. Moreover, the complete kinetic calculations presented in this work show that a simple source defined by the density of energetic α particles provides an accurate description, and therefore leads to a predicted density profile of He ash close to that obtained with the full kinetic calculated source.

The effects of finite β (the ratio of plasma kinetic pressure to magnetic pressure) and three-dimensional (3D) magnetic perturbations (MPs) on the instability of toroidal ion temperature gradient (ITG) mode are studied in this work. The expression of ion magnetic drift frequency ωdi modified by the effects from both finite β and 3D MPs is firstly derived based on the local 3D equilibrium model. Then, under the assumptions of adiabatic electrons and localized mode structure around the outboard mid-plane ( ϑp=0), the dispersion equation of the long wavelength toroidal ITG mode with considering the parallel ion dynamics is derived and solved. The results show that the distribution of ωdi around the outboard mid-plane, including both ωdi,0=ωdi|ϑp=0 and ωdi,0′′≡(d2ωdi/dϑp2)|ϑp=0 (twist parameter quantifying the degree of concave or convex of ωdi), is the key for affecting the toroidal ITG mode instability. The diamagnetic effects from finite β and the effects from 3D MPs can suppress the instability by reducing |ωdi,0|. Via reducing |ωdi,0′′| under the prerequisite of unchanged sign of ωdi,0′′, there also exist stabilization effects on the instability from 3D MPs and the modification of local magnetic shear by finite β effects. In addition, the stabilization effects induced by reducing |ωdi,0′′| are closely associated with the global magnetic shear. The mechanisms for the effects of finite β and 3D MPs on the instability of toroidal ITG mode revealed in this work are helpful to the comprehensive understanding of the relationship between internal kink mode induced non-axisymmetric flux surface distortion and internal transport barrier physics in tokamak plasmas.

In this work, most of the weakly coherent mode (WCM) characteristics and the level of transport coefficients observed in I-mode pedestal plasmas of C-Mod are reproduced theoretically. The dispersion relation of drift-Alfvén wave (DAW) is analytically solved for both drift-wave (DW) and Alfvén wave branches, and the WCM is identified to be the DW branch. The frequency of DW branch in the laboratory frame is about 200 kHz, the poloidal phase velocity propagating in the direction of electron diamagnetic drift is around 7.0km⋅s−1, and the relative magnitude of normalized fluctuations of electron temperature, density and magnetic field are |T~eTe0|/|n~en0|≈0.1 and |b~|/|n~en0|≈8.3×10−4, respectively, which are all consistent with the characteristics of WCM observed in C-Mod experiment. Moreover, the modulation-induced transport coefficients in the presence of DAW turbulence are calculated. It is found that the electromagnetic part of transport coefficient is about 10% of the electrostatic part. The particle diffusivity is 0.21m2⋅s−1, which is about twice of the experimental value. Meanwhile, the electron thermal conductivity is 0.27m2⋅s−1, and is in very good agreement with the corresponding experimental and simulation values. These results may advance the understanding of the underlying physics of turbulence and transport in the I-mode pedestal plasmas.

The 11th Asia-Pacific Transport Working Group meeting was held at Shenzhen University, Shenzhen, China, from 27 to 30 May 2025. Five technical working groups with topics closely related to plasma turbulence and transport were as follows: (A) impurity transport in core and pedestal plasmas, (B) turbulence spreading and coupling in the core-edge-scrape-off layer, (C) transport and turbulence in 3D magnetic topology, (D) interaction between energetic particles, magnetohydrodynamic stability and turbulence, and (E) model reduction and experiments for verification and validation. This report presents a summary of the contributed papers in the five technical working groups and discussions and future prospects on these topics are also given.

We report on comprehensive experimental studies of turbulence spreading in edge plasmas. These studies demonstrate the relation of turbulence spreading and entrainment to intermittent convective density fluctuation events or bursts (i.e. blobs and holes). The non-diffusive character of turbulence spreading is thus elucidated. The turbulence spreading velocity (or mean jet velocity) manifests a linear correlation with the skewness of density fluctuations, and increases with the auto-correlation time of density fluctuations. Turbulence spreading by positive density fluctuations is outward, while spreading by negative density fluctuations is inward. The degree of symmetry breaking between outward propagating blobs and inward propagating holes increases with the amplitude of density fluctuations. Thus, blob-hole asymmetry emerges as crucial to turbulence spreading. These results highlight the important role of intermittent convective events in conveying the spreading of turbulence, and constitute a fundamental challenge to existing diffusive models of spreading.

Mesenchymal stem cell‐based therapy has emerged as a promising approach for the treatment of peripheral arterial disease. The purpose of this study was to examine the potential effects of human placenta‐derived mesenchymal stem cells (PMSCs) on mouse hindlimb ischemia. PMSCs were isolated from human placenta tissue and characterized by flow cytometry. An in vivo surgical ligation‐induced murine limb ischemia model was generated with fluorescent dye (CM‐DiI) labelled PMSCs delivered via intramuscular injection. Our data show that PMSCs treatment significantly enhanced microvessel density, improved blood perfusion and diminished pathologies in ischemic mouse hindlimbs as compared to those in the control group. Further immunostaining studies suggested that injected PMSCs can incorporate into the vasculature and differentiate into endothelial and smooth muscle cells to enhance angiogenesis in ischemic hind limbs. This may in part explain the beneficial effects of PMSCs treatment. Taken together, we found that PMSCs treatment might be an effective treatment modality for treatment of ischemia‐induced injury to mouse hind limbs by enhancement of angiogenesis.