Spatial Areas of Potential and Density Fluctuation Measurements Using HIBP on the T-15MD Tokamak

The paper presents a numerical analysis of the possibility of performing local measurements of potential and plasma density fluctuations in the T-15MD tokamak using the Heavy Ion Beam Probe (HIBP) diagnostic. Four types of fluctuations are considered in the frequency range up to 500 kHz: Geodesic Acoustic Mode (GAM), Quasi-Coherent Mode (QCM), Tearing Mode (TM), and Alfvén eigenmode (AE). For each type of fluctuation, spatial measurement areas are defined for regimes with different values of average density \({{\bar {n}}_{e}}\) and toroidal magnetic field \({{B}_{T}}\). Regimes with flat and peaked density profiles are considered. It is shown that high-Q fluctuations (GAM, AE, TM) can be measured in the peripheral region of the plasma \(\rho < 0.8\) up to density \({{\bar {n}}_{e}} \leqslant 7 \times {{10}^{{19}}}\;{{{\text{m}}}^{{ - 3}}}\), while low-Q QCMs can be measured up to \({{\bar {n}}_{e}} \leqslant 5 \times {{10}^{{19}}}\;{{{\text{m}}}^{{ - 3}}}\). In the plasma gradient region \(\rho = 0.5{-} 0.9\) the measurement of high-Q fluctuations is possible at a density of \({{\bar {n}}_{e}} \leqslant 5 \times {{10}^{{19}}}\;{{{\text{m}}}^{{ - 3}}}\), and of the low-Q QCM at a density of \({{\bar {n}}_{e}} \leqslant 3 \times {{10}^{{19}}}\;{{{\text{m}}}^{{ - 3}}}\).