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 br∝ne0.5 and br∝ne0.6, 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 (br∝ne0.54 in lower density region and br∝ne0.40 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
This paper presents the penetration of
n
= 2 magnetic field perturbations, where
n
is the toroidal mode number. The
n
= 2 intrinsic error field (IEF) is measured in an ohmic heating plasma ...using the compass scan method, i.e. the toroidal asymmetry in the threshold current for the penetration of
n
= 2 resonant magnetic perturbations (RMPs). Its amplitude is 55.5 A in equivalent coil current or
B
r,3/2
= 0.1 G and the toroidal phase of the IEF is around 170.6° (129°). Phasing scans (scans of the phase difference between the upper and lower coil currents) of the
n
= 2 RMPs are carried out to obtain the
e
ffects of the
n
= 2 spectrum on field penetration. The observed dependence of the field penetration on the spectrum is consistent with those of simulations using the MARS-F code. One of the interesting phenomena is that the
n
= 2 mode often stimulates an
n
= 1 mode. The dominant poloidal harmonic of the
n
= 1 mode is
m
= 2, and the dominant poloidal harmonic of the
n
= 2 mode is
m
= 3. The evolution of the
n
= 1 mode has two stages, i.e., an initial small island growth stage, and a later saturation stage. In the initial stage, the amplitude of the
n
= 1 magnetic island grows, while the phase remains fixed. When the amplitude of the magnetic island exceeds a certain threshold, it enters the second stage, in which the magnetic island is locked into another phase and its amplitude starts to saturate. The phase in the initial small island stage depends linearly on the phase of the applied
n
= 2 RMP, which suggests that the
n
= 2 mode is directly driven by the coupling between the
n
= 1 and
n
= 2 modes. The phase in the second stage is either locked to the phase close to the previously measured
n
= 1 IEF, or is locked to the phase close to the
n
= 2 response field. This suggests that the final phase of the
n
= 1 mode depends on competition between the locking effect induced by the
n
= 1 IEF and the nonlinear coupling effect between the two modes. This might be an issue in the MHD control application using high-
n
RMPs in the future ITER device.
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 br21/BT∝BT−1.0 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 br21∝q951.66 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.
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 br2,1/BT≃10−5 and the toroidal phase of intrinsic error field is around 60°. 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.
The experimental advanced superconducting tokamak (EAST) is a superconducting tokamak, which successfully achieved the first plasma discharge in 2006. The major radius of EAST plasma is 1.9 m, and ...its central magnet field is 3.5 T. In the past few years, EAST has made many achievements, such as 60-s double-null divertor configuration plasma and 1-MA plasma. In 2012, 411-s long-pulse discharge with 0.28-MA plasma current and 32-s H-mode operation was achieved at the seventh campaign. In addition, various means for mitigating ELMs have also been demonstrated to facilitate long-pulse operation. The experimental results and engineering experience obtained from EAST can be used as a reference for fusion next step. To make further progress, much optimization work should be done in next step. Based on the present EAST heating system, two sets of 4-MW neutral beam injection, one set of electron cyclotron resonance heating, and lower hybrid current drive will be installed to achieve more than 30-MW total heating power. The upper divertor will be updated to W-Cu divertor, which consists of monoblock structure and tungsten armor that can withstand 10- MW·m -2 heat load. To increase the upper divertor's ash removal efficiency, one new cryopump will be added on the behind of it. Aiming to improve plasma configuration and enhance its stabilization, the EAST resonant magnetic perturbation (RMP) coils will be designed, fabricated, and installed. The RMP coils will integrate the functions of error field correction, edge localized mode, and resistive wall mode. About 45 kinds of diagnostics will be used in the next campaign and all of them will be integrated on six ports as port plug. In addition, some fusion technologies are also considered in EAST to validate for ITER and future reactor.
► The IR thermography diagnostic equipment is playing an important role in tokamak. ► The IR thermography diagnostic equipment with wavefront coding is applied in tokamak. ► Because of the ...application of wavefront coding, the optical is less sensitive to the change of the temperature and the depth of field is enlarged.
This article describes the principle of wavefront coding (WFC) technology and the role it plays in optical system. The infrared optical system in tokamak includes three parts: (1) the combination of the concave aspheric mirror and flat mirror; (2) the Cassegrain system; (3) the relay group lenses. Because of the application of wavefront coding, the optical system is less sensitive to the change of the temperature and the depth of field is enlarged. Comparing the modulation transfer function (MTF) of the original optical system and the improved system in different temperatures, the results show that the new system can be used in a larger range of temperature.
An optimal solution of multi-objective optimization has been proposed for the measure project of automatic test system (ATS) because of the formation complexity and the factors diversity. The method ...is used to select the optimal measure project for ATS. First a quasi-ideal solution is defined using maximum subjection principle from fuzzy theory. Then calculate the subjection of the existing projects and get their maximum subjection under specific weight set. Finally the optimal measure project has been obtained. The signal integrity, data throughput, cost, degree of automation, volume scale and expansion capabilities are regarded as integrated key factors according to bus forms and system architecture. The optimal measure project of ATS is determined by finding maximum subjection. Therefore the selection method enhances the cost-effectiveness of ATS formation.
The shield tunnel is typically simplified as an infinite beam with two free ends in existing analytical models, which are used to calculate the longitudinal deformation of the underlying shield ...tunnel induced by the excavation of a foundation pit. However, the applicability of those analytical models is limited due to the simplification. The current study is aimed at estimating analytically the longitudinal deformation of the underlying shield tunnel induced by the excavation of a foundation pit adjacent to the station (working shaft). The constraint on the shield tunnel generated by the joint between the station (working shaft) and the tunnel is treated as a rotation spring with the rotation stiffness of K and a vertical rod support. The Winkler foundation–Timoshenko beam model for calculating the longitudinal deformation of the shield tunnel adjacent to the station (working shaft) induced by the foundation pit excavation is proposed. The finite difference solution of the proposed model is strictly derived based on the basic principles of the force method. The reliability and applicability of the proposed analytical model are verified via the comparison with the finite element numerical solution of one-dimensional elastic foundation beam model and the global finite element simulation results of the longitudinal deformation of the underlying tunnel induced by the excavation of a foundation pit adjacent to the station. The parametric studies indicate the following conclusions. (i) The longitudinal deformation and internal forces of the shield tunnel are significantly influenced by the rotation stiffness, K, of the joint between the station (working shaft) and the tunnel. The internal forces and the longitudinal deformation (i.e. rotation angle) at the end of the tunnel increase and decreases nonlinearly with a increasing K, respectively. In addition, when the flexible connection is adopted at the joint between the station (working well) and tunnel, the working performance of the shield tunnel at the joint can be better guaranteed. (ii) The constraint effect of the joint on the end of the tunnel is non-negligible, when the distance from the center of the foundation pit to the station-tunnel joint ranges from 4 to 5 times the width of the pit along the tunnel axis. In this condition, the proposed analytical model should be adopted to evaluate the longitudinal working performance of the tunnel. (iii) The influence of the overlying foundation pit excavation on the underlying tunnel mainly exerts within 2 times the length of the pit perpendicular to the tunnel axis away from the center of the pit.
The control of large edge localized modes (ELMs) is a critical issue for the successful operation of future burning plasma devices, such as the international thermonuclear experimental reactor (ITER) ...and China fusion engineering test reactor (CFETR). In this paper, we present a new active and effective means of ELM suppression using ion cyclotron resonant heating (ICRH) on the experimental advanced superconducting tokamak (EAST). We obtained the key role of the external
E
×
B
velocity shear near the pedestal top and the scrape-off-layer (SOL) induced by the RF sheath potential of ICRH in ELM suppression. The experimental results showed a positive correlation between the RF sheath and the
E
×
B
shear rate in SOL. BOUT++ simulations indicate that increased
E
×
B
velocity shear rates in the pedestal and SOL regions promote ELM suppression; thereby, supporting the experimental observations on EAST. These findings suggest a new simple approach to access the ELM suppressed regimes in plasma with low torque input as ITER baseline discharges.
