Z{sub eff} profile diagnostics using visible bremsstrahlung continuum for nonaxisymmetric plasmas with finite {beta} in large helical device

Journal Article · Mon Mar 15 00:00:00 EDT 2010 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.3326970· OSTI ID:21476379

Zhou, H Y; Dong, C F ^[1]; Morita, S; Goto, M ^[2]

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1. Department of Fusion Science, Graduate University for Advanced Studies, Toki, Gifu 509-5292 (Japan)
2. National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan)

An astigmatism-corrected Czerny-Turner-type visible spectrometer coupled with a charge-coupled device has been installed in large helical device (LHD) to measure visible bremsstrahlung continuum. A full vertical profile has been observed from the elliptical plasmas at horizontally elongated plasma cross section through a 44 fiber parallel array with vertical observation length of {approx}1 m. Line emissions can be easily eliminated by use of the visible spectrometer instead of an interference filter. A nonmonotonic bremsstrahlung emission profile, which is originated in the thick ergodic layer surrounding the main plasma, has been observed for normal discharges in all the magnetic configurations of LHD. After analyzing the detailed structure, the lower half of the vertical bremsstrahlung emission profile is found to be free of the strong edge bremsstrahlung emission in inwardly shifted magnetic configurations (R{sub ax{<=}}3.60 m). The nonmonotonic bremsstrahlung emission disappeared in extremely high-density discharges (n{sub e{>=}}10{sup 14} cm{sup -3}) because of the reduction of the plasma outside boundary. When the local emissivity is calculated using Abel inversion, the solution is very sensitive to the distortion of the magnetic surface structure. The influence of the magnetic surface distortion based on the finite {beta} effect is examined as error estimation in addition to unclear edge plasma boundary due to the presence of the ergodic layer. The result indicates that the determination of the normalized minor radius for each observation chord gives a larger influence on the Abel inversion rather than the determination of the chord length. When the observed chord-integrated bremsstrahlung intensity profile is flat, the resultant uncertainty seen in the bremsstrahlung emissivity profile becomes large, in particular, at the plasma center. The Z{sub eff} profile calculated with consideration of density and temperature profiles is verified in neutral-beam-heated discharges with H{sub 2} and C pellet injections, where the Z{sub eff} values should be close to 1 and 6, respectively. Analysis on the flat and hollow electron density profiles results in a fairly flat Z{sub eff} profile.

• OSTI ID: 21476379
• Journal Information: Journal of Applied Physics, Vol. 107, Issue 5; Other Information: DOI: 10.1063/1.3326970; (c) 2010 American Institute of Physics; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BETA RATIO
BOUNDARY LAYERS
BREMSSTRAHLUNG
CHARGE-COUPLED DEVICES
ELECTRON DENSITY
EMISSIVITY
HYDROGEN
LHD DEVICE
MAGNETIC SURFACES
PELLET INJECTION
PLASMA
PLASMA CONFINEMENT
PLASMA DENSITY
PLASMA DIAGNOSTICS
PLASMA RADIAL PROFILES
STELLARATORS
CLOSED PLASMA DEVICES
CONFINEMENT
DIMENSIONLESS NUMBERS
ELECTROMAGNETIC RADIATION
ELEMENTS
LAYERS
MAGNETIC FIELD CONFIGURATIONS
NONMETALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
SEMICONDUCTOR DEVICES
SURFACE PROPERTIES
THERMONUCLEAR DEVICES