External magnetic diagnostics for the National Compact Stellarator Experiment

Stratton, B.; Brooks, A.; Brown, T.; Johnson, D.; Labik, G.; Lazarus, E. A.; Pomphrey, N.; Raftopoulos, S.; Zarnstorff, M. C.

doi:10.1063/1.2229227

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“…3 A description of novel concepts in the design of the VV loops is the main purpose of this paper. Magnetic boundary conditions for the reconstruction will be provided by signals from a variety of plasma diagnostics including ϳ200 in-vessel magnetic field probes providing measurements of the field tangential to the vacuum vessel ͑VV͒, 50 flux loops co-wound with all of the independently powered magnets ͑signals from a subset of these loops a͒ Paper UI1 3, Bull.…”

Section: Introduction and Overviewmentioning

confidence: 99%

Novel design methods for magnetic flux loops in the National Compact Stellarator Experiment

et al. 2007

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Articles you may be interested inA novel electron density reconstruction method for asymmetrical toroidal plasmas Rev. Sci. Instrum. 85, 053506 (2014);Magnetic pickup loops on the vacuum vessel ͑VV͒ can provide an abundance of equilibrium information for stellarators. A substantial effort has gone into designing flux loops for the National Compact Stellarator Experiment ͑NCSX͒ ͓Zarnstorff et al., Plasma Phys. Controlled Fusion 43, A237 ͑2001͔͒, a three-field period quasi-axisymmetric stellarator under construction at the Princeton Plasma Physics Laboratory. The design philosophy, to measure all of the magnetic field distributions normal to the VV that can be measured, has necessitated the development of singular value decomposition algorithms for identifying efficient loop locations. Fields are expected to be predominantly stellarator symmetric ͑SS͒-the symmetry of the machine design-with toroidal mode numbers per torus ͑n͒ equal to a multiple of 3 and possessing reflection symmetry in a period. However, plasma instabilities and coil imperfections will generate non-SS fields that must also be diagnosed. The measured symmetric fields will yield important information on the plasma current and pressure profile as well as on the plasma shape. All fields that obey the design symmetries could be measured by placing flux loops in a single half-period of the VV, but accurate resolution of nonsymmetric modes, quantified by the condition number of a matrix, requires repositioning loops to equivalent locations on the full torus. A subarray of loops located along the inside wall of the vertically elongated cross section was designed to detect n =3, m = 5 or 6 resonant field perturbations that can cause important islands. Additional subarrays included are continuous in the toroidal and poloidal directions. Loops are also placed at symmetry points of the VV to obtain maximal sensitivity to asymmetric perturbations. Combining results from various calculations which have made extensive use of a database of 2500 free-boundary VMEC equilibria, has led to the choice of 225 flux loops for NCSX, of which 151 have distinct shapes.

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Section: Introduction and Overviewmentioning

confidence: 99%