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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]

Collapse hazards occur frequently in mountainous areas. Geosynthetics-reinforced soil (GRS) wall, combing the damping characteristics of soil and the tensile properties of reinforcement materials, can effectively resist rockfall impact through its flexible deformation. However, excessive deformation is easy to occur near the impact point of reinforced soil retaining wall subjected to impact loading, resulting in instantaneous instability and long repair time as well as high repair cost of the structure. Therefore, the prestressed GRS wall with buffer layer was proposed in this paper. Four retaining walls with different types and the impactor consist of pendulum device and solid steel ball was designed to study the impact resistance and dynamic stability of the retaining wall. The results show that the cumulative deformation of the wall panel experiences acceleration phase, deceleration phase and stable stage subjected to the impact loading. The application of buffer layer and prestress member can effectively improve the impact resistance and dynamic stability of retaining wall, and further control the deformation of retaining wall under the impact loading, in comparison with ordinary reinforced retaining wall. The peak impact stress of the retaining wall and the responsive strain of the reinforcement increase gradually as the distance between the measure point and the impact point decreases. The research results can provide reference for the design and the application of prestressed GRS wall under the impact of rockfall. [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]