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The influence on the loss of energetic passing ions by the n = 4 resonant magnetic perturbation (RMP) is investigated through numerical simulations (here, n is the toroidal mode number of the RMP field). Dedicated efforts have been made to uncover how the plasma response modifies the loss fractions and underlying mechanisms. The stochastization of the drift surfaces and the particle loss fractions increase significantly under the response field, in which the resonant component is significantly shielded. In order to better understand how the response field contributes a considerable drift island width, the respective effect of each poloidal component $m_\mathrm{b}$ on the outermost drift island $m_\mathrm{p}/n = 9/4$ are compared (here, $m_\mathrm{b}$ and $m_\mathrm{p}$ are poloidal mode numbers of the RMP components and drift island, respectively). Contrary to the intuition that the components with $m_\mathrm{b} = m_\mathrm{p} \pm 1$ should dominate the sideband resonance, some of the components which fulfill $|m_\mathrm{p}-m_\mathrm{b}|\gg 1$ have the dominant contributions under the response field. There are mainly two reasons accounting for this phenomenon, i.e. the drift motion of particles and the enhancement of amplitudes of non-resonant high- m components by the plasma response near the edge due to the resonant field amplification (RFA) effect. The former made it possible for particles to resonate with the far non-resonant components, and the latter significantly enhanced the perturbation field experienced by particles. The above results imply that the RFA effect is more critical than the stochastization of magnetic topology in the fast ion losses under RMP.

An experiment was conducted to study the mode penetration of $n = 1$ resonant magnetic perturbation (RMP) in EAST under low neutral beam injection torque in the co-current direction (Co-NBI). The experimental results indicate that the threshold current ${I_{{\text{RMP,th}}}}$ for field penetration decreases with higher input torque ${T_{{\text{NBI}}}}$ . Furthermore, it is observed that the plasma mode frequency $| {{f_{{\text{MHD}}}}} |$ at counter-current direction is greatly reduced when the plasma toroidal rotation frequency ${f_\phi }$ increases. The theoretical scaling of mode frequency $( {{I_{{\text{RMP,th}}}} \propto {{| {{f_{{\text{MHD}}}}} |}^{0.70}}} )$ predicted by the field penetration theory is in good agreement with the experimental observation ( ${I_{{\text{RMP,th}}}} \propto {| {{f_{{\text{MHD}}}}} |^{0.53}}$ ). The role of $| {{f_{{\text{MHD}}}}} |$ and ${f_\phi }$ on the mode onset threshold was separately investigated using the full toroidal geometry initial value code MARS-Q (Liu et al 2013 Phys. Plasmas 20 042503). The numerical scaling based on the experimental mode frequency is consistent with the experimental and theoretical ones. Numerical results suggest that evaluating the total mode frequency $| {{f_{{\text{MHD}}}}} |$ is crucial in field penetration analysis, in contrast to toroidal rotation frequency ${f_\phi }$ . With the increase of ${T_{{\text{NBI}}}}$ , the decreasing $| {{f_{{\text{MHD}}}}} |$ leads to a reduction in the field penetration threshold. This suggests that more attention should be paid to error field tolerance in low Co-NBI torque scenarios, where the electron diamagnetic frequency may be canceled out by NBI-driven toroidal plasma rotation.

Density scaling of error field penetration in EAST is investigated with different n  =  1 magnetic perturbation coil configurations in ohmically heated discharges. The density scalings of error field penetration thresholds under two magnetic perturbation spectra are and , where br is the error field and ne is the line averaged electron density. One difficulty in understanding the density scaling is that key parameters other than density in determining the field penetration process may also be changed when the plasma density changes. Therefore, they should be determined from experiments. The estimated theoretical analysis ( in lower density region and in higher density region), using the density dependence of viscosity diffusion time, electron temperature and mode frequency measured from the experiments, is consistent with the observed scaling. One of the key points to reproduce the observed scaling in EAST is that the viscosity diffusion time estimated from energy confinement time is almost constant. It means that the plasma confinement lies in saturation ohmic confinement regime rather than the linear Neo-Alcator regime causing weak density dependence in the previous theoretical studies. [ABSTRACT FROM AUTHOR]

Using a tangentially viewing x-ray imaging crystal spectrometer, substantial co-current rotation driven by lower hybrid current drive (LHCD) at 4.6 GHz is observed on EAST tokamak. This study presents plasma rotation behaviors with 4.6 GHz LHCD injection. Typically, the 10–20 km/s co-current rotation change and the transport of rotation velocity from edge to core are observed. The relationship between plasma parameters and rotation is also investigated, indicating that rotation decreases with increasing internal inductance (li) and increases with increasing safety factor (q0). Hysteresis between rotation and Te plasma stored energy is observed, suggesting different response times between the electron heating and rotation acceleration by LHCD. A comparison between the rotations driven by 4.6 G LHCD and 2.45 G LHCD on EAST is also presented, in which higher frequency LHCD could induce more rotation changes. [ABSTRACT FROM AUTHOR]

We observe the spectra of molybdenum for the first time since the first wall of our experimental advanced superconducting tokamak (EAST) was changed mainly to molybdenum tiles. A large amount of molybdenum accumulated in the central plasma where the long-lived m = 1 mode instability bursts is shown. Molybdenum is proved to be the main impurity species observed during the formation and lifetime of impurity-induced long-lived m = 1 mode. This may indicate that a close relationship exists between the high-Z impurity accumulation and the occurrence of long-lived m = 1 mode in EAST plasmas. [ABSTRACT FROM AUTHOR]