Interpretation of spatially resolved helium line ratios on MAST

• Published in: Journal of nuclear materials Vol. 390; pp. 1078 - 1080
• Main Authors: Lisgo, S., Börner, P., Counsell, G.F., Dowling, J., Kirk, A., Scannell, R., O’Mullane, M., Reiter, D.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 15-06-2009; Elsevier
• Subjects: Applied sciences; Controled nuclear fusion plants; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Fuels; Installations for energy generation and conversion: thermal and electrical energy; Nuclear fuels; 52.20.H; 52.65; 52.55; Tokamak; Plasma; Nuclear fusion reactor; Impurity; Filter; Divertor; Helium; Spectrometer; Nuclear reactor
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2009.01.292

The tokamak boundary plasma is inherently 2D/3D, which impedes the detailed validation of transport models due to the limited spatial coverage of most diagnostics. A potential method for determining the 2D profiles of
n
e and
T
e in the plasma volume is to resolve spatially the emission ratios of atomic helium, principally the lines at 667, 706 and 728 nm. Unfortunately, there are several challenges associated with this approach: the traditional use of line-of-sight spectrometer data; crowding by other impurity lines; low signal levels; reliance on accurate atomic physics; and He I meta-stables. Several of these issues are explored in the present study, which utilises tomographic reconstruction of filtered CCD camera images to measure He emission throughout the divertor. Plasma gradients are resolved and compared with results from the OSM–EIRENE code. The near-target
n
e and
T
e values agree with Langmuir probe measurements to within a factor ∼2.