The Divertor Tokamak Test facility (DTT) [1] is a new tokamak device, the construction of which is starting in Italy. Its main goal is to investigate alternative power exhaust solutions for DEMO. Indeed, in ITER it is planned to test standard baseline techniques for the power exhaust issue, but these solutions could be inappropriate for the operating conditions of DEMO. In magnetically confined fusion experiments, laser interferometer/polarimeter systems allow to determine plasma density, give valuable information on the internal magnetic fields, contribute to evaluate the plasma magnetic equilibrium and to the real time estimation of the q profile. It is underlined that measuring the Cotton-Mouton effect together with the Faraday rotation angle allows recovering the plasma density directly from polarimetric data. This guarantees for the redundancy of the plasma density measurements, useful when fringe jump occurs in interferometric data, e.g. due to Edge Localized Modes (ELMs) or pellet injection. In the present work, a 14 chord, double pass, interferometer/polarimeter system for DTT is considered and the polarimetric and interferometric signals are investigated for laser source solutions of the order of 100/50 ?m. In particular, an analysis of both the Faraday rotation and of the Cotton-Mouton effect depending upon different initial polarization states of the laser beam is carried out for each chord in order to identify the most appropriate initial polarization condition. This is done by numerically solving the equation describing the evolution of the laser beam polarization inside the plasma, through the exploitation of the Mueller formalism. Detection techniques of the interferometric and polarimetric signals are also analyzed and the expected SNR of the measurements is evaluated. In addition, possible crosstalks between interferometric and polarimetric measurements and Faraday rotation and Cotton-Mouton effect measurements are studied.
Characterization of the polarimetric and interferometric signals for a DTT interferometer/polarimeter system
Innocente P;Terranova D;
2020
Abstract
The Divertor Tokamak Test facility (DTT) [1] is a new tokamak device, the construction of which is starting in Italy. Its main goal is to investigate alternative power exhaust solutions for DEMO. Indeed, in ITER it is planned to test standard baseline techniques for the power exhaust issue, but these solutions could be inappropriate for the operating conditions of DEMO. In magnetically confined fusion experiments, laser interferometer/polarimeter systems allow to determine plasma density, give valuable information on the internal magnetic fields, contribute to evaluate the plasma magnetic equilibrium and to the real time estimation of the q profile. It is underlined that measuring the Cotton-Mouton effect together with the Faraday rotation angle allows recovering the plasma density directly from polarimetric data. This guarantees for the redundancy of the plasma density measurements, useful when fringe jump occurs in interferometric data, e.g. due to Edge Localized Modes (ELMs) or pellet injection. In the present work, a 14 chord, double pass, interferometer/polarimeter system for DTT is considered and the polarimetric and interferometric signals are investigated for laser source solutions of the order of 100/50 ?m. In particular, an analysis of both the Faraday rotation and of the Cotton-Mouton effect depending upon different initial polarization states of the laser beam is carried out for each chord in order to identify the most appropriate initial polarization condition. This is done by numerically solving the equation describing the evolution of the laser beam polarization inside the plasma, through the exploitation of the Mueller formalism. Detection techniques of the interferometric and polarimetric signals are also analyzed and the expected SNR of the measurements is evaluated. In addition, possible crosstalks between interferometric and polarimetric measurements and Faraday rotation and Cotton-Mouton effect measurements are studied.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
