A power-balance model, with radiation losses from impurities and neutrals, gives a unified description of the density limit (DL) of the stellarator, the L-mode tokamak, and the reversed field pinch (RFP). The model predicts a Sudo-like scaling for the stellarator, a Greenwald-like scaling, , for the RFP and the ohmic tokamak, a mixed scaling, , for the additionally heated L-mode tokamak. In a previous paper (Zanca et al 2017 Nucl. Fusion 57 056010) the model was compared with ohmic tokamak, RFP and stellarator experiments. Here, we address the issue of the DL dependence on heating power in the L-mode tokamak. Experimental data from high-density disrupted L-mode discharges performed at JET, as well as in other machines, are taken as a term of comparison. The model fits the observed maximum densities better than the pure Greenwald limit.

Synergetic effects of resonant magnetic perturbation (RMP) and electron cyclotron current drive (ECCD) on stabilizing neoclassical tearing mode (NTM) in reversed magnetic shear (RMS) tokamak plasmas are numerically investigated based on a set of reduced MHD equations. For the moderate separation, it is found that the explosive burst induced by the fast reconnection of double tearing mode (DTM) in the RMS configuration can be completely suppressed by externally applied RMPs. Zonal flows with strong shear induced by a rotating RMP play an important role in this suppression process. Moreover, turning on ECCD in advance is essential to mitigate the NTM. For the large separation without the explosive burst, two strategies, i.e. a continuous ECCD with static RMP and a modulated ECCD with rotating RMP, are separately investigated. It is shown that when the NTM is decelerated by a relatively slow rotating RMP, the modulated ECCD can have a better stabilizing effect. In addition, the ECCD deposition widths in both radial and helical angle directions, as well as the ECCD on-duty time, are analyzed in detail. The best effectiveness of ECCD is obtained and the relevant physical mechanisms are discussed.

Absorbers with light weight, low filler loading, high absorption capacity, and broad absorption bandwidth are highly desirable for electromagnetic (EM) wave absorption application, and extensive efforts in designing excellent performance biomass-derived microwave absorbents using sustainable and renewable materials have been made. Here, for the first time we constructed flexible and high-performance EM-absorbing materials of porous biomass-derived carbon (PBDC) decorated with in-situ grown MnO nanorods (MnOnrs) by a simple process. The chemical composition and microstructural feature of these MnOnrs/PBDC composites are highly dependent on the content of MnOnrs controlled through the concentration of potassium permanganate, and thus their EM properties could be also manipulated. Compared with the pure PBDC, the MnOnrs/PBDC composites exhibited excellent EM wave absorption performance with the minimum reflection loss (RLmin) of −51.6 dB at 10.4 GHz with a thickness of 2.47 mm and a qualified bandwidth of 14.2 GHz with an integrated thickness from 1.00 to 5.00 mm. Notably, the microwave absorption capacity of this new kind of composite is not so susceptible to the content of MnOnrs as those common carbon-based absorbers, which could be attributed to the synergistic effect between PBDC and MnOnrs as well as the hierarchical structure. This work may provide a new guideline for development of biomass as a low-cost, green, and renewable high-performance, carbon-based absorber.

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This paper reviews the effects of resonant magnetic perturbation (RMP) on classical tearing modes (TMs) and neoclassical tearing modes (NTMs) from the theory, experimental discovery and numerical results with a focus on four major aspects: (i) mode mitigation, where the TM/NTM is totally suppressed or partly mitigated by the use of RMP; (ii) mode penetration, which means a linearly stable TM/NTM triggered by the externally applied RMP; (iii) mode locking, namely an existing rotating magnetic island braked and finally stopped by the RMP; (iv) mode unlocking, as the name suggests, it is the reverse of the mode locking process. The key mechanism and physical picture of above phenomena are revealed and summarized.