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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.

The plasma-beta effect on the n = 1 resonant magnetic perturbation (RMP) field penetration in purely radio-frequency (RF) wave heated discharges has been investigated in EAST. The experimental results show that the dependence of the threshold RMP coil current for field penetration, $I_{\textrm {RMP,th}}$ , on the total absorbed power P _tot scales as approximately $I_{\textrm {RMP,th}} \propto P_{\textrm {tot}}^{0.30}$ , indicating that the error-field tolerance is improved with increasing RF power. This is benefited by the increased electron perpendicular flow dominated by a counter-current electron diamagnetic flow with increasing RF power. However, theoretical scaling in cylindrical geometry overestimates the power index. Assuming an additional term $\beta_\textrm N^{\alpha_{\beta_\textrm N}}$ for the normalized beta in the scaling, it is shown that the fitted $\alpha_{\beta_\textrm N}$ from the experimental observation is around −1, indicating a degradation effect of plasma beta. To clarify the underlying physics of the plasma-beta effect that was not included in the theoretical scaling in cylindrical geometry, the MARS-Q code with full toroidal geometry is employed for simulation of nonlinear field penetration (Liu et al 2013 Phys. Plasmas 20 042503). The MARS-Q simulation results reproduce the $\beta_\textrm N$ dependence well, and hence the P _tot scaling of the threshold current in experimental observations. The main reason for this is that the net total torque, which is mainly contributed by the neoclassical toroidal viscosity (NTV), increases with increasing plasma $\beta_\textrm N$ . The results demonstrate that the nonlinear toroidal coupling effect via NTV torque plays an important role in determining field penetration, even in cases with relatively low $\beta_\textrm N \in [0.3,0.6]$ , which is far less than the no-wall beta limit.

The plasma-beta effect on the n = 1 resonant magnetic perturbation (RMP) field penetration in purely radio-frequency (RF) wave heated discharges has been investigated in EAST. The experimental results show that the dependence of the threshold RMP coil current for field penetration, I RMP,th , on the total absorbed power P tot scales as approximately I RMP,th ∝ P tot 0.30 , indicating that the error-field tolerance is improved with increasing RF power. This is benefited by the increased electron perpendicular flow dominated by a counter-current electron diamagnetic flow with increasing RF power. However, theoretical scaling in cylindrical geometry overestimates the power index. Assuming an additional term β N α β N for the normalized beta in the scaling, it is shown that the fitted α β N from the experimental observation is around −1, indicating a degradation effect of plasma beta. To clarify the underlying physics of the plasma-beta effect that was not included in the theoretical scaling in cylindrical geometry, the MARS-Q code with full toroidal geometry is employed for simulation of nonlinear field penetration (Liu et al 2013 Phys. Plasmas 20 042503). The MARS-Q simulation results reproduce the β N dependence well, and hence the P tot scaling of the threshold current in experimental observations. The main reason for this is that the net total torque, which is mainly contributed by the neoclassical toroidal viscosity (NTV), increases with increasing plasma β N . The results demonstrate that the nonlinear toroidal coupling effect via NTV torque plays an important role in determining field penetration, even in cases with relatively low β N ∈ [ 0.3 , 0.6 ] , which is far less than the no-wall beta limit. [ABSTRACT FROM AUTHOR]

Toroidal field and q95 scalings of error field penetration are investigated with n = 1 resonant magnetic perturbation coil in EAST. The toroidal field scalings of error field penetration thresholds under fixed q95 are about in both ohmically and lower hybrid wave heated plasmas, where br21 is the vacuum error field at the q = 2/1 rational surface and BT is the toroidal field. These scalings indicate a favorable tolerance on error field in ITER. To make clear the underlying physics on toroidal field scaling, the theoretical analysis is given. By subtituting penetration related scaling parameters into the theory, the obtained theoretical scalings are consistent with the experimental observations using the vacuum penetration thresholds. To further investigate penetration threshold in larger operation region, the q95 scaling on penetration threshold with has also been observed. The rational surface radius rs and magnetic shear s, which are crucial to q95 scaling, are included in the theoretical analysis. The theoretical analysis is also consistent with the experimental scalings using the vacuum penetration thresholds. Moreover, the obtained theoretical scalings are easy to compare with experimental scalings. These theoretical analyses will stimulate the extrapolation of error field tolerance towards future reactors. [ABSTRACT FROM AUTHOR]

An ultrasensitive electrochemical aptasensor for thrombin (TB) was designed using MoS2 nanoparticles loaded iron-porphyrinic metal-organic framework (PCN-223-Fe) as the electrochemical tracer. Spindle-shaped PCN-223-Fe was synthesized with zirconium ion as node and iron-porphyrin as linker, and in situ loaded with MoS2 nanoparticles to obtain MoS2/PCN-223-Fe composite. MoS2/PCN-223-Fe was characterized by electron microscopies, X-ray diffraction and X-ray photoelectron spectroscopy. Due to the synergistic effect of MoS2 and PCN-223-Fe, MoS2/PCN-223-Fe modified electrode exhibited enhanced electrocatalytic activity to oxygen reduction. Sequentially, MoS2/PCN-223-Fe was combined with TB aptamer 2 to prepare signal probe. A sandwich-type electrochemical aptasensor was constructed for TB detection. TB aptamer 1 was fixed on electrode surface to capture TB molecules, and then TB aptamer 2 functionalized MoS2/PCN-223-Fe tracer was introduced on electrode surface. By detecting the electrochemical signal of oxygen reduction catalyzed by MoS2/PCN-223-Fe, the designed TB sensor was monitored. The proposed TB aptasensor showed a wide linear range from 0.1 pM to 100 nM and a low detection limit of 0.03 pM (S/N = 3). Meanwhile, the aptasensor showed good reproducibility, stability and selectivity, which was successfully applied for TB detection in human serum sample. This strategy broadens application of metal-organic frameworks, and could be used for other biomolecules detection. [ABSTRACT FROM AUTHOR]

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]

Intrinsic error field on EAST is measured using the ‘compass scan’ technique with different n  =  1 magnetic perturbation coil configurations in ohmically heated discharges. The intrinsic error field measured using a non-resonant dominated spectrum with even connection of the upper and lower resonant magnetic perturbation coils is of the order and the toroidal phase of intrinsic error field is around . A clear difference between the results using the two coil configurations, resonant and non-resonant dominated spectra, is observed. The ‘resonant’ and ‘non-resonant’ terminology is based on vacuum modeling. The penetration thresholds of the non-resonant dominated cases are much smaller than that of the resonant cases. The difference of penetration thresholds between the resonant and non-resonant cases is reduced by plasma response modeling using the MARS-F code. [ABSTRACT FROM AUTHOR]

During the tokamak operation, variation of the stored energy can cause internal perturbations of the plasma. These perturbations may develop into large-scale vertical movement of the whole column for the vertically elongated tokamak, eventually generating the hot vertical displacement event (VDE). It will cause considerable damage to the machine. In this work, the hot VDE process due to stored energy perturbations is investigated by a mature non-linear time-evolution code DINA. The influence on the vertical instability, the displacement direction and the electromagnetic loads on in-vessel components during the hot VDE are analyzed. It is shown that a larger perturbation leads to faster development of the vertical instability. Meanwhile the variation of the Shafranov shift, due to the energy change, is related to the VDE direction. The vertical electromagnetic force on the vacuum vessel and the halo current flowing in the divertor baffle become larger in the case of VDE moving towards the X point. [ABSTRACT FROM AUTHOR]

If βN exceeds βNno—wall, the plasma will be unstable because of external kink and resistive wall mode (RWM). In this article, the effect of the passive structure and the toroidal rotation on the RWM stability in the experimental advanced superconducting tokamak (EAST) are simulated with CHEASE and MARS codes. A model using a one-dimensional (1D) surface to present the effect of the passive plate is proved to be credible. The no wall βN limit is about 3li, and the ideal wall βN limit is about 4.5li on EAST. It is found that the rotation near the q = 2 surface and the plasma edge affects the RWM more. [ABSTRACT FROM AUTHOR]