title: An upgrade of the magnetic diagnostic system of the DIII-D tokamak for non-axisymmetric measurements.
abstract: The DIII-D tokamak magnetic diagnostic system [E. J. Strait, Rev. Sci. Instrum. 77, 023502 (2006)] has been upgraded to significantly expand the measurement of the plasma response to intrinsic and applied non-axisymmetric "3D" fields. The placement and design of 101 additional sensors allow resolution of toroidal mode numbers 1 ≤ n ≤ 3, and poloidal wavelengths smaller than MARS-F, IPEC, and VMEC magnetohydrodynamic model predictions. Small 3D perturbations, relative to the equilibrium field (10(-5) < δB/B0 < 10(-4)), require sub-millimeter fabrication and installation tolerances. This high precision is achieved using electrical discharge machined components, and alignment techniques employing rotary laser levels and a coordinate measurement machine. A 16-bit data acquisition system is used in conjunction with analog signal-processing to recover non-axisymmetric perturbations. Co-located radial and poloidal field measurements allow up to 14.2 cm spatial resolution of poloidal structures (plasma poloidal circumference is ~500 cm). The function of the new system is verified by comparing the rotating tearing mode structure, measured by 14 BP fluctuation sensors, with that measured by the upgraded B(R) saddle loop sensors after the mode locks to the vessel wall. The result is a nearly identical 2/1 helical eigenstructure in both cases.
authors.affiliation: Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 378300-8050, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: King
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Strait
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: R L
authors.initials: RL
authors.lastname: Boivin
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: D
authors.initials: D
authors.lastname: Taussig
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: M G
authors.initials: MG
authors.lastname: Watkins
authors.affiliation: Department of Applied Physics and Applied Mathematics, Columbia University, 116th and Broadway, New York, New York 10027, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Hanson
authors.affiliation: Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451, USA.
authors.forename: N C
authors.initials: NC
authors.lastname: Logan
authors.affiliation: Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 378300-8050, USA.
authors.forename: C
authors.initials: C
authors.lastname: Paz-Soldan
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Pace
authors.affiliation: Department of Applied Physics and Applied Mathematics, Columbia University, 116th and Broadway, New York, New York 10027, USA.
authors.forename: D
authors.initials: D
authors.lastname: Shiraki
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Lanctot
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: La Haye
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: L L
authors.initials: LL
authors.lastname: Lao
authors.affiliation: Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Battaglia
authors.affiliation: Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Sontag
authors.affiliation: Plasma Research Laboratory, Research School of Physical Sciences and Engineering, The Australia National University, Canberra, ACT 0200, Australia.
authors.forename: S R
authors.initials: SR
authors.lastname: Haskey
authors.affiliation: Research and Development Division, National Fusion Research Center, Daejeon, South Korea.
authors.forename: J G
authors.initials: JG
authors.lastname: Bak