Magnetic error field analysis by measurement of local rotational transform in a low aspect ratio torsatron

• Published in: Review of scientific instruments 1993-08, Vol.64 (8), p.2262-2266
• Main Authors: Hartwell, Gregory J., Gandy, Rex F., Hanson, James D., Knowlton, Stephen F., Owens, Monte A.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 700430 - Fusion Technology- Magnet Coils & Fields- (1992-); CLOSED PLASMA DEVICES; Exact sciences and technology; Magnetic confinement and equilibrium; MAGNETIC FIELD CONFIGURATIONS; MAGNETIC FLUX; MAGNETIC ISLANDS; MAGNETIC SURFACES; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; ROTATIONAL TRANSFORM; STELLARATORS; Stellarators, spheromaks, compact tori, bumpy tori, and other toroidal confinement devices; Stellarators, torsatrons, heliacs, bumpy tori, and other toroidal confinement devices; THERMONUCLEAR DEVICES; TORSATRON STELLARATORS
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.1143920

In magnetic fusion toroidal confinement devices, the confining magnetic fields may have errors which produce magnetic islands. The standard method of investigating magnetic field errors involves measuring the maximum radial spatial extent of a given magnetic island at a fixed toroidal location and calling this measurement the island width. However, because of magnetic flux conservation inside an island, the spatial width of the island is not toroidally invariant. Magnetic error fields and their associated islands have been investigated in the Compact Auburn Torsatron through the measurement of the local rotational transform about the fixed points of the island. This method of magnetic field error investigation is valid at any poloidal or toroidal angle because the local rotational transform is spatially invariant. The technique of measuring the local rotational transform is described and the results are compared to those obtained using standard methods of measuring island widths.