Ion temperature measurements in a tokamak using active neutral particle analyzers diagnostics

Abstract

Active ion temperature measurement in the core plasma of a tokamak using active neutral particle analyzers (NPA) diagnostics is considered. Two approaches for local ion temperature reconstruction are reviewed: semi-analytical and iterative. A semi-analytical approach allows the calculation of ion temperature using simple expression, while a more complex iterative approach provides more flexibility. Problems associated with active NPA measurements and their possible solutions are discussed. An example of the core ion temperature profile reconstruction in the compact spherical tokamak Globus-M2 using both approaches is shown. Problems associated with active ion temperature measurements in a compact reactor and possible solutions are considered.

Energy confinement in the spherical tokamak Globus-M2 with a toroidal magnetic field reaching 0.8 T

“…the same plasma shape, the same isotopic composition (deuterium plasma and deuterium beam), the same wall conditioning technique using boronization and the same NB power and energy. From figure one can see the significant increase of the electron and ion temperature measured by the Thomson scattering [24] and neutral particle analyzer [25]. A double increase in the plasma current and toroidal magnetic field results in four-fold T e increase in the plasma core that led to rise of the plasma total stored energy, see figure 1(b).…”

The first observation of the hot ion mode at the Globus-M2 spherical tokamak

“…The value of the toroidal magnetic field in the experiment described in this paper is as high as 0.9 T. A further increase in the toroidal magnetic field to the design values of 1 T and current to 0.5 MA is a task of the following campaigns. The ion temperature was measured by charge exchange recombination spectroscopy (CXRS) [16,17] and a neutral particle analyzer (NPA) [18] reached 4 keV, which was 2.5 times higher than the electron temperature in the plasma center measured using the Thomson scattering (TS) diagnostics [19], see figure 1(b). In these experiments the plasma current as well as the auxiliary heating power were lower than the values of the Globus-M2 design parameters for which predictive calculations (figure 1(a)) were performed.…”

Analysis of toroidal Alfven eigenmode-induced fast ion losses in Globus-M2 spherical tokamak

“…In the experiments at Globus-M2 [9,21,22], where toroidal Alfven eigenmodes were found to arise during neutral beam injection, the first NBI with energy E NBI = 28 keV and beam power P beam about 0.85 MW was applied. ACORD-24M NPA was used to measure neutral flux and ACORD-12 analyzer was applied to measure ion temperature [23]. Single TAE bursts, observed on magnetic probe signal caused short-time drawdowns in NPA channel, set up to register neutrals with energy close to the energy of neutral beam (28.5 ± 1.5 keV).…”