Measurement of helicity flux density using the eddy-current diagnostic system in Keda Torus eXperiment device

Chen, Zheng; Li, Hong; Adil, Yolbarsop; Zhang, Yuan; Yan, Wentan; Rao, Xianhao; Tao, Zhen; Mao, Wenzhe; Wei, Zhuangzhuang; Liu, Zixi; Zhou, Chu; Liu, Adi; Lan, Tao; Xie, Jinlin; Zhou, Haiyang; Xu, Wen; Wang, Hai; Zhuang, G.; Xiao, C.; Ding, Weixing; Liu, Wandong

doi:10.1063/5.0073486

Cited by 3 publications

(5 citation statements)

References 26 publications

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“…Figure 8 shows this relationship. The helicity flux density measurement system is implemented in KTX, and a similar linear relationship was obtained [28,32]. For KTX, when the average toroidal magnetic field ⟨B t ⟩ ≈ 0.26 T, we estimate that a plasma current of about 0.6 MA is needed to spontaneously transform into a three-dimensional state and when the current reaches 0.72 MA, the plasma can self-organize to form the SHAx state.…”

Section: Magnetic Field Properties Of Different Self-organized Statesmentioning

confidence: 66%

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Effects of magnetic helicity on 3D equilibria and self-organized states in KTX reversed field pinch

Liu,

Yu,

Huang

et al. 2024

Nucl. Fusion

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The reversed field pinch (RFP) is a toroidal magnetic configuration in which plasmas can spontaneously transform into different self-organized states. Among various states, the ''quasi-single-helical'' (QSH) state has a dominant component for the magnetic field and significantly improves confinement. Many theoretical and experimental efforts have investigated the transitions among different states. This paper employs the multi-region relaxed magnetohydrodynamic (MRxMHD) model to study the properties of QSH and other states. The stepped-pressure equilibrium code (SPEC) is used to compute MHD equilibria for the Keda Torus eXperiment (KTX). The toroidal volume of KTX is partitioned into two subvolumes by an internal transport barrier. The geometry of this barrier is adjusted to achieve force balance across the interface, ensuring that the plasma in each subvolume is force-free and that magnetic helicity is conserved. By varying the parameters, we generate distinct self-organized states in KTX. Our findings highlight the crucial role of magnetic helicity in shaping these states. In states with low magnetic helicity in both subvolumes, the plasma exhibits axisymmetric behavior. With increasing core helicity, the plasma gradually transforms from an axisymmetric state to a double-axis helical (DAx) state and finally to a single-helical-axis (SHAx) state. Elevated core magnetic helicity leads to a more pronounced dominant mode of the boundary magnetic field and a reduced core magnetic shear. This is consistent with previous experimental and numerical results in other RFP devices. We find a linear relationship between the plasma current and helicity in different self-organized states. Our findings suggest that KTX may enter the QSH state when the toroidal current reaches 0.72 MA. This study demonstrates that the stellarator equilibrium code SPEC unveils crucial RFP equilibrium properties, rendering it applicable to a broad range of RFP devices and other toroidal configurations.

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Section: Magnetic Field Properties Of Different Self-organized Statesmentioning

confidence: 66%

“…The KTX with a measurement system of helicity flux density located at the University of Science and Technology of China is a large RFP device [27,28]. The KTX vacuum chamber has a circular cross-section with major radius R = 1.4 m and minor radius a = 0.4 m.…”

Section: Self-organized Equilibrium Simulation Of Ktxmentioning

confidence: 99%

Effects of magnetic helicity on 3D equilibria and self-organized states in KTX reversed field pinch

Liu,

Yu,

Huang

et al. 2024

Nucl. Fusion

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“…Due to the presence of the two vertical gaps, the (0, 0) component of the toroidal vector potential is absent. To compensate for this absence, the loop voltage from the control group is subtracted from the experimental group [27]. Another significant application of the ECDS is the measurement of magnetic and current helicity flux densities.…”

Section: Applications Of the Ecdsmentioning

confidence: 99%

“…Once the radial magnetic helicity flux densities are measured, we can compute the change in the total magnetic helicity within the vacuum chamber. We have previously investigated the characteristics of magnetic and current helicity flux densities [27], which include magnetic helicity flux densities that pass through the passive shell and current helicity flux densities that accumulate on the shell. In this context, we present additional findings concerning the magnetic helicity of plasma during the ohmic discharge.…”

Section: Applications Of the Ecdsmentioning

confidence: 99%

Data analysis methods and applications of the eddy current diagnostic system in the Keda Torus eXperiment device

Chen,

Tao,

Yolbarsop

et al. 2024

J. Inst.

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Since the establishment of the eddy current diagnostic system within the Keda Torus eXperiment (KTX) device, it has unveiled many applications. Recent developments have introduced innovative data analysis techniques alongside compelling experimental results, underscoring the necessity for a comprehensive summary of the system's data analysis approaches and broad applications. Notable features of the system encompass exceptional precision, the ability to encompass shell currents on the entirety of the closed boundary, vector detection of shell currents, and measurement of diverse physical quantities. In terms of data analysis methodologies, meticulous scrutiny of the null field region is conducted, and we reveal a distinctive characteristic within the complex shell current signals, namely the asymmetry of the amplitudes of ±n Fourier coefficients. Moreover, the Hodge decomposition emerges as a pivotal technique, allowing for the distinctive separation of shell currents into three orthogonal components based on their distinct spatial topological properties. With regard to practical applications, an in-depth examination of the vector potential and magnetic helicity flux densities are presented in detail, further highlighting the far-reaching utility of the system's capabilities.

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“…The eddy current diagnostic system provides signals with low common-mode noise suppressed by differential operation and facilitates real-time measurement of the shell current vector on the composite shell. In addition, based on the measured shell currents, the boundary magnetic helicity flux can be calculated to study the magnetic helicity transport during the plasma discharge [27]. This paper proposes to further expand the application of eddy current diagnostics on the KTX by using the Hodge decomposition to decouple the halo and inductive currents.…”

Section: Introductionmentioning

confidence: 99%

The Hodge decomposition of shell current on the Keda Torus eXperiment device

Chen,

Li,

Yolbarsop

et al. 2023

Plasma Phys. Control. Fusion

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The Hodge decomposition is a valuable tool for uniquely decomposing total currents on the composite shell into three types: inductive current, halo current, and harmonic current, each with its specific physical meaning. During plasma disruptions, halo currents appear, essential for studying the wall’s thermal load and electromagnetic force. Furthermore, understanding halo currents is crucial for improving the existing methodologies by removing their effects on equilibrium reconstructions and instability analyses based on boundary magnetic probe data. On the Keda Torus eXperiment (KTX) device, radial and tangent halo currents can be simultaneously provided to locate the contact region during a minor disruption experimentally. Additionally, experimental results demonstrate that, in addition to the occurrence of halo current during minor disruption events, halo current is already present simultaneously with the generation of inductive current when a resistive wall mode exists. For devices that lack the capability to measure the two-dimensional shell current distribution on the entire shell, we propose a method to estimate inductive and halo currents only using a set of shell currents along the toroidal direction. This technique is demonstrated on the KTX device and provides an overall good approximation of the inductive and halo current distribution.

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Measurement of helicity flux density using the eddy-current diagnostic system in Keda Torus eXperiment device

Cited by 3 publications

References 26 publications

Effects of magnetic helicity on 3D equilibria and self-organized states in KTX reversed field pinch

Effects of magnetic helicity on 3D equilibria and self-organized states in KTX reversed field pinch

Data analysis methods and applications of the eddy current diagnostic system in the Keda Torus eXperiment device

The Hodge decomposition of shell current on the Keda Torus eXperiment device

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