Reconstruction of Distribution Functions of Fast Ions and Runaway Electrons in ITER Plasmas Using Gamma-Ray Spectrometry
Use of gamma-ray spectrometers on ITER could allow solving one of the most important issues for the safe tokamak operations - diagnosing runaway electrons. 2-D hard X-ray (HXR) emission measurements can provide important information on the runaway beam location in the ITER plasmas and allow estimating the value of the runaway current in the MeV energy range. The DEGAS code has been developed for deconvolution of gamma-ray spectra emitted from plasmas. Using the recorded HXR spectra, the code can reconstruct the runaway electron energy distribution. Results of Monte-Carlo modelling of the gamma-ray spectrometer response functions and bremsstrahlung spectra calculated for electrons in wide energy range are used in the DEGAS code. The deconvolution of spectra allows identifying nuclear reactions, which take place during plasma discharges, calculate their gamma-ray line intensities and determine the maximal energy of runaway electrons with accuracy, which satisfies the ITER Project Requirements. The DEGAS code was used for processing of spectra recorded in JET experiments. Application of the deconvolution technique for 2-D gammaray emission measurements, which can facilitate reconstruction of fast ion spatial distributions in ITER plasmas, is discussed.