Improved Three-Dimensional CCS Method Analysis for the Reconstruction of the Peripheral Magnetic Field Structure in a Finite Beta Helical Plasma

Abstract

In the previous 3D Cauchy-condition surface (CCS) method analysis to reconstruct the magnetic field profile in the Large Helical Device (LHD), one assumed an impractically large number of magnetic sensors, i.e., 440 field sensors and 126 flux loops. In the singular value decomposition (SVD) process employed in the CCS method, a gap is found in the magnitude of the singular values. The most accurate field results can be obtained if all the singular values smaller than the gap threshold are eliminated, independent of the number of boundary elements on the CCS and the number of sensors as well. With the reduction in the number of boundary elements, the required numbers of field sensors and flux loops are significantly reduced to 110 and 25, respectively, without losing the solution accuracy. They can be further reduced to 58 and 13 respectively if considering the symmetry of the field profile in the LHD. This result suggests the possibility of actual application to the LHD.

Optimization of the Magnetic Sensor Configuration for JT-60SA Plasma Control

“…The preliminarily unknown eddy current distribution in the vacuum vessel is reconstructed in a reversed field pinch device based on the external magnetic sensor signals [6]. Furthermore, the CCS method has been expanded to reconstruct the 3D magnetic field profile outside the non-axisymmetric plasma in the Large Helical Device (LHD) [7].…”

Visualization of the Plasma Shape in a Force Free Helical Reactor, FFHR

“…The acquisition of the plasma shape has abundant and thorough research with profiles. Itagaki, Masafumi et al [7,8] found an effective way to reconstruct the 3D magnetic field profile outside the non-axisymmetric plasma in a reactor and indicated the plasma boundary precisely. However, they did not build a 3D model but visualized the result with profiles of the magnetic field.…”

Reconstruction of plasma shape and eddy current profile based on modified cauchy condition surface method in merging spherical tokamak

“…Such information should be deduced from signals of magnetic sensors located near the vacuum vessel wall, since the direct measurement of physical quantities inside the plasma is usually difficult. The Cauchy condition surface (CCS) method [16][17][18][19][20][21][22][23] is one such idea for reconstructing the magnetic flux profile outside the plasma and hence the plasma boundary shape. The method has already been established for operating control and diagnosis of JT-60U [16], a tokamak-type device.…”

“…The application of the method has been expanded to other devices such as KSTAR [17], JT-60SA [18] and QUEST [19]. Further, Itagaki et al developed the 3D CCS method [20][21][22] to reconstruct 3D magnetic field profile outside the non-axisymmetric plasma in the LHD. In these methods, the CCS, where both the Dirichlet and the Neumann conditions are unknown, is hypothetically placed in a domain that can be supposed to be inside the plasma.…”