INTO THE FAST TOMOGRAPHIC POSTPROCESSING IN TOKAMAKS

The collaboration of authors led to implementing advanced and fast systems for diagnostics of plasma content in tokamaks. During the development of systems it is planned to add new functionalities, in particular, the algorithms of tomographic reconstruction to obtain information on three dimensional distribution of plasma impurities. In the article the idea of tomographic reconstruction is introduced and issues of performance and adequate hardware selection are presented.

Feasibility of FPGA to HPC computation migration of plasma impurities diagnostic algorithms

We present a feasibility study of fast events parameters estimation algorithms regarding their execution time. It is the first stage of procedure used on data gathered from gas electron multiplier (GEM) detector for diagnostic of plasma impurities. Measured execution times are estimates of achievable times for future and more complex algorithms. The work covers usage of Intel Xeon and Intel Xeon Phi - high-performance computing (HPC) devices as a possible replacement for FPGA with highlighted advantages and disadvantages. Results show that less than 10 ms feedback loop can be obtained with the usage of 25% hardware resources in Intel Xeon or 10% resources in Intel Xeon Phi which leaves space for future increase of algorithms complexity. Moreover, this work contains a simplified overview of basic problems in actual measurement systems for diagnostic of plasma impurities, and emerging trends in developed solutions.

Measuring plasma impurities in Alcator C-Mod as a function of time in the extreme ultraviolet1This article is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas.

A flat-field grazing-incidence grating spectrometer has been installed on the MIT Alcator C-MOD tokamak, following the installation of such a spectrometer on the Livermore electron beam ion trap facility and on the National Spherical Torus Experiment at Princeton. The spectrometer employs a variable space grating with an average spacing of 2400 lines/mm and covers the 10–70 Å wavelength band. It is being used to monitor the presence of impurity ions such as boron, oxygen, fluorine, argon, calcium, iron, molybdenum, and tungsten, and to calibrate spectral diagnostics of astrophysical plasmas. The Alcator instrument provides spectral emission data in a density regime that is one to three orders of magnitude higher than that covered by the other two instruments and thus produces complementary data.