A new branch of the m/n = 2/1 fishbone-like mode is found to be excitated by trapped energetic ions when the tearing mode is unstable. An energy-principle-based dispersion relation is derived and analyzed, which incorporates the wave-particle resonance and the resistive layer physics. Once the beta amplitude of trapped energetic ions exceeds a critical value, 2/1 fishbone-like instabilities would appear. The mode transition from tearing mode to 2/1 fishbone-like mode will be triggered with the increasing beta of trapped energetic ions. The total effects of the ideal magnetohydrodynamic potential energy and the adiabatic contribution of trapped energetic ions on the real frequency and growth rate of 2/1 fishbone-like modes are investigated; the effects of magnetic Reynolds number and magnetic shear are also studied. Both resistivity and magnetic shear play a stable role on 2/1 fishbone-like modes. An implication of the theory is conducive to understanding the 2/1 fishbone-like activities observed recently in HL-2A.

The influence of trapped energetic ions (TEIs) on m/n=2/1 low-frequency magnetohydrodynamic (MHD) instabilities with reversed shear profile is investigated by a global kinetic–MHD hybrid simulation. For low energetic-ion beta, TEIs have a stabilizing effect on the double tearing mode (DTM). When the energetic-ion beta is larger than a threshold, an energetic-particle-driven mode, the fishbone-like mode (FLM), is excited; that is, a mode transition from the DTM to the FLM occurs. The threshold increases with increasing resistivity, and the growth rate of the FLM is reduced by the presence of resistivity. In addition, the dependences on energetic-ion beta, gyroradius, and injection velocity of the effects of TEIs are studied systematically.

Gyrokinetic simulations in the collisionless limit demonstrate the physical mechanisms and the amplitude of the current driven by turbulence. Simulation results show the spatiotemporal variation of the turbulence driven current and its connection to the divergence of the Reynolds stress and the turbulence acceleration. Fine structures (a few ion Larmor radii) of the turbulence induced current are observed near the rational surfaces with the arbitrary wavelength solver of the quasi-neutrality equation. The divergence of the Reynolds stress plays a major role in the generation of these fine structures. The so-called spontaneous current is featured with large local magnitude near the rational surfaces.

Using 980 fb −1 of data at and around the ϒðnSÞ (n ¼ 1, 2, 3, 4, 5) resonances collected with the Belle detector at the KEKB asymmetric-energy e þ e − collider, the two-photon process γγ → γψð2SÞ is studied from the threshold to 4.2 GeV for the first time. Two structures are seen in the invariant mass distribution of γψð2SÞ: one at M R 1 ¼ 3922.4 AE 6.5 AE 2.0 MeV=c 2 with a width of Γ R 1 ¼ 22 AE 17 AE 4 MeV, and another at M R 2 ¼ 4014.3 AE 4.0 AE 1.5 MeV=c 2 with a width of Γ R 2 ¼ 4 AE 11 AE 6 MeV; the signals are parametrized with the incoherent sum of two Breit-Wigner functions. The first structure is consistent with the Xð3915Þ or the χ c2 ð3930Þ, and the local statistical significance is determined to be 3.1σ with the systematic uncertainties included. The second matches none of the known charmonium or charmoniumlike states, and its global significance is determined to be 2.8σ including the look-elsewhere effect. The production rates are Γ γγ BðR 1 → γψð2SÞÞ ¼ 9.8 AE 3.6 AE 1.3 eV assuming ðJ PC ; jλjÞ ¼ ð0 þþ ; 0Þ or 2.0 AE 0.7 AE 0.2 eV with ð2 þþ ; 2Þ for the first structure and Γ γγ BðR 2 → γψð2SÞÞ ¼ 6.2 AE 2.2 AE 0.8 eV with ð0 þþ ; 0Þ or 1.2 AE 0.4 AE 0.2 eV with ð2 þþ ; 2Þ for the second. Here, the first errors are statistical and the second systematic, and λ is the helicity.

The mechanism of excitation of beta-induced Alfvén eigenmodes (BAEs) with magnetic islands larger than a threshold without energetic ions is studied. It is found that the nonlinear coupling between geodesic acoustic mode and magnetic islands can drive the pair of BAEs. The phase of BAEs to island should be π/2 to excite the BAEs and the magnetic island is larger than a threshold. The results are consistent with the experimental results shown in EAST(#86309). It implies that similar experimental results in other tokamaks, that BAEs excitation by magnetic islands without energetic ions, may be from the nonlinear coupling between islands and waves. It also implies that the existence of magnetic islands can make the excitation of BAEs easier in plasma with energetic ions, since the magnetic island can also increase the pressure gradient of energetic ions near the island separatrix. This predicts that BAEs may appear more frequently in the presence of magnetic islands in ITER.