Publikationsdatum:
2014-08-08
Beschreibung:
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 〈 δ B / B 0 〈 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 B P 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.
Print ISSN:
0034-6748
Digitale ISSN:
1089-7623
Thema:
Elektrotechnik, Elektronik, Nachrichtentechnik
,
Physik
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