Tomographic Inversion Techniques Incorporating Physical Constraints for Line Integrated Spectroscopy in Stellarators and Tokamaks
Authors: N.A. Pablant, R.E. Bell, M. Bitter, L. Delgado-Aparicio, K.W. Hill, S. Lazerson, and S. Morita
Abstract: Accurate tomographic inversion is important for diagnostic systems on stellarators and tokamaks which rely on measurements of line integrated emission spectra. A tomographic inversion technique based on spline optimization with enforcement of constraints is described that can produce unique and physically relevant inversions even in situations with noisy or incomplete input data. This inversion technique is routinely used in the analysis of data from the x-ray imaging crystal spectrometer (XICS) installed at LHD. The XICS diagnostic records a 1D image of line integrated emission spectra from impurities in the plasma. Through the use of Doppler spectroscopy and tomographic inversion, XICS can provide profile measurements of the local emissivity, temperature and plasma flow. Tomographic inversion requires the assumption that these measured quantities are flux surface functions, and that a known plasma equilibrium reconstruction is available. In the case of low signal levels or partial spatial coverage of the plasma cross-section, standard inversion techniques utilizing matrix inversion and linear-regularization often cannot produce unique and physically relevant solutions.
_________________________________________________________________________________________________
Presented at: The 20th Topical Conference on High-Temperature Plasma Diagnostics, Atlanta, Georgia, June, 2014.
Procedings published in: Review of Scientific Instruments 85, 11E424 (2014)
http://dx.doi.org/10.1063/1.4891977
_________________________________________________________________________________________________
Download PPPL-5048 (pdf 3 MB / 3pp)
_________________________________________________________________________________________________