An upgrade of the magnetic diagnostic system of the DIII-D tokamak for non-axisymmetric measurements.

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.

[1]  E. Strait,et al.  Measurement of the electromagnetic torque in rotating DIII-D plasmas , 2010 .

[2]  K. Burrell,et al.  Observation of plasma rotation driven by static nonaxisymmetric magnetic fields in a tokamak. , 2008, Physical review letters.

[3]  K. Tritz,et al.  Active stabilization of the resistive-wall mode in high-beta, low-rotation plasmas. , 2006, Physical review letters.

[4]  L. Segal.  John , 2013, The Messianic Secret.

[5]  R. L. Haye,et al.  Measurement and modeling of three-dimensional equilibria in DIII-D , 2011 .

[6]  F. Milani,et al.  Feedback stabilization of multiple resistive wall modes. , 2004, Physical review letters.

[7]  M E Fenstermacher,et al.  Suppression of large edge-localized modes in high-confinement DIII-D plasmas with a stochastic magnetic boundary. , 2004, Physical review letters.

[8]  G Serianni,et al.  Active-feedback control of the magnetic boundary for magnetohydrodynamic stabilization of a fusion plasma. , 2006, Physical review letters.

[9]  S. Zweben.  Principles of Plasma Diagnostics , 1990 .

[10]  C. Greenfield,et al.  A multilaser system for a fast sampling Thomson scattering diagnostic , 1990 .

[11]  M. F. F. Nave,et al.  Mode locking in tokamaks , 1990 .

[12]  E. D. Fredrickson,et al.  Chapter 2: Magnetic Diagnostics , 2008 .

[13]  Michio Okabayashi,et al.  Stabilization of the external kink and the resistive wall mode , 2010 .

[14]  J. Manickam,et al.  Control of the resistive wall mode with internal coils in the DIII–D tokamak , 2005 .

[15]  K. Burrell,et al.  Plasma rotation driven by static nonresonant magnetic fields , 2008 .

[16]  Bengt Lennartson,et al.  Feedback stabilization of nonaxisymmetric resistive wall modes in tokamaks. I. Electromagnetic model , 2000 .

[17]  L. L. Lao,et al.  Equilibrium analysis of current profiles in tokamaks , 1990 .

[18]  J. Scoville,et al.  Measurement of the resistive-wall-mode stability in a rotating plasma using active MHD spectroscopy. , 2004, Physical review letters.

[19]  J. C. Whitson,et al.  Steepest‐descent moment method for three‐dimensional magnetohydrodynamic equilibria , 1983 .

[20]  T. Osborne,et al.  Validation of the linear ideal magnetohydrodynamic model of three-dimensional tokamak equilibria , 2010 .

[21]  Roberts,et al.  Magnetic field pitch-angle measurments in the PBX-M tokamak using the motional Stark effect. , 1989, Physical review letters.

[22]  E. J. Strait,et al.  Magnetic diagnostic system of the DIII-D tokamak , 2006 .

[23]  A. Boozer,et al.  Computation of three-dimensional tokamak and spherical torus equilibria , 2007 .

[24]  R. Isler,et al.  An overview of charge-exchange spectroscopy as a plasma diagnostic , 1994 .

[25]  J. A. Leuer,et al.  Anomalies in the applied magnetic fields in DIII-D and their implications for the understanding of stability experiments , 2003 .

[26]  K. Burrell,et al.  Multichordal charge‐exchange recombination spectroscopy on the DIII‐D tokamak , 1986 .

[27]  K. Wong,et al.  A review of Alfvén eigenmode observations in toroidal plasmas , 1999 .

[28]  E. W. Herold,et al.  Controlled fusion , 1959, IRE Transactions on Electron Devices.