Study of signal ratio dependence on Doppler shift in the plasma rotation velocity diagnostic of the Tcabr Tokamak

Abstract

The neoclassical theory predicts that plasmas confined in magnetic systems with toroidal geometry must rotate both poloidal and toroidal directions, being the values of these velocities approximately 10^{5}-10^{6} cm/s in the poloidal direction and 10^{6}-10^{7} cm/s in the toroidal direction. The gradient of the poloidal component of the velocity has a direct relationship with the confinement of particles and energy and can suppress the turbulence if the shear of the flow is accentuated. The toroidal component has a direct relation with the threshold for excitation of the tearing modes and resistive wall modes. Therefore, to optimize the performance of the fusion reactor, it is extremely important to understand the mechanisms that produce plasma rotation (its sources and sinks), its connection to the energy and particle transport coefficients and the suppression of the wall resistive modes. With the support of FAPESP, in the Plasma Physics Laboratory was constructed a diagnostic to measure the plasma rotation velocity that is based on the detection of different parts of the same spectral line where the ratio of the corresponding signals is directly connected to the rotation velocity. In this project we intend to create a simple mathematical model to describe the Doppler shift of the spectral lines as a function of the signal ratio and thus better estimate the uncertainties in the velocity measurements.