ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
Passive charge exchange (PCX) between neutral deuterium entering the plasma from the walls and ionized light impurities in a Tokamak Fusion Plasma have been investigated, and a comparison between the synthetic spectra and the experimental data is performed. In the core light impurities are fully stripped and may only be detected by the use of charge exchange recombination spectroscopy. Using a multichord spectrometer viewing various radial points from the edge to the plasma center intersecting the neutral beam injection path, a strong localized signal from active charge exchange (ACX) will be detected during the deexcitation process in the plasma ion. However, it is well known that passive charge exchange emission from neutral deuterium in the plasma blends the signal, and since calculations of particle densities are performed on the ACX, it is therefore of crucial importance to separate the ACX from the PCX. The spectra from the PCX component will carry line of sight integrated information about the plasma rotation velocity and the ion temperature throughout the plasma. By taking an initial estimate of the radial emissivity for the PCX into account as well as the ion temperature and plasma rotation profiles, one may perform the line integrated emission calculation over the various viewing lines through the plasma, and reconstruct a synthetic spectra for each viewing line. Since the emissivity is given by the reaction rate cross section and the densities of the participating ions one may, by inserting the synthetic emission into the measured spectra and performing a nonlinear least squares fit of the intensity, establish a more accurate assessment of the D0 density. The investigation shows good agreement between the experimentally observed PCX and the theoretical model, both in wavelength position and in spectral shape. The accuracy on the absolute value of the measured neutral density will be 50%, depending on the model of the decrease of the neutrals from the wall, and the error in the charge exchange cross section. © 1999 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1149451
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