The development of charge exchange recombination spectroscopy diagnostics for the T-15MD tokamak

Abstract

In 2020 a modernized tokamak T-15MD (R=1.5 m, a=0.67 m, κ=1.8, Ipl≤2 MA, Bt≤2 T, discharge duration ≤10 s, Paux≤24 MW) will be launched in the National Research Center “Kurchatov Institute”. For this installation, a modern Charge eXchange Recombination Spectroscopy (CXRS-diagnostics) has been developed. It can function both on a diagnostic injector (EDNB=60 keV) and heating injector (ENBI=80 keV) . CXRS-diagnostics of T-15MD can be used to measure local values of the following plasma parameters with high spatial (≈1 cm) and temporal (≈1 ms) resolutions: ion temperature (Ti), density of main gas and light impurities nuclei (nz), toroidal and poloidal rotation velocity (Vpol, Vtor) and the fast-ion spectrum. The composition of the CXRS-diagnostic complex and its schematic is presented. Its main components are the DNB (H, 60 keV, 150 kW), four spectrometers (two of them based on Echelle gratings, one based on holographic grating and another utilizes both types of gratings), and EMCCD-cameras. The attenuation of the diagnostic beam in the plasma is calculated considering its ionization and charge exchange by the main gas and impurities (C, O), as well as electron impact ionization. The intensities of active and passive components of λ=5291 Åline of C5+ ion are calculated considering the line fine structure, Doppler, and Zeeman effects. The active and passive signals emitted by C5+ ion are estimated for toroidal and poloidal registration systems. It is established that the acquisition time of 1 – 3 ms is enough to achieve the valid signal level to measure Ti with a statistical error ≈ 3 %. The calculated ratio between the active and passive CXRS-signal in the plasma center is 2.2 – 3.7. Measurement error is estimated for λ=5291 ÅCX-line and calculations show low measurement errors for Ti and nz (around 2 – 5 %), Vpol and Vtor (around 2 km/s). This indicates that CXRS-diagnostics have potential to provide reliable and accurate measurements of the named plasma parameters on T-15MD.