Study for a tangential dispersion interferometer/polarimeter for DTT

Abstract

The Divertor Tokamak Test (DTT) facility [1], whose construction is starting in Frascati, will require robust and reliable diagnostics for the correct operation of the machine and the characterization of the plasma discharge. For this purpose, we are studying a common-path dispersion interferometer/polarimeter for the detection of plasma electron density and magnetic field in two different tangential chords in the equatorial plane. The physical principle is based on the generation of a second harmonic which crosses the plasma collinearly with the beam at its fundamental. Being the plasma a dispersive medium, the two beams are subject to different phase shifts from which it is possible to retrieve the plasma free electron density. Moreover, the unconverted part of the fundamental can be used for polarimetric measurement. Two different implementations of the interferometer have been considered, one with a CO2 laser (λ = 10.6/5.3 µm) and another one with Nd:YAG (λ = 1.064/0.536 µm). The former is more sensitive to lower plasma densities and to Faraday rotation, while the latter is more robust to fringe jumps. We have studied the main aspects of these two possible solutions. In particular, we analysed the optics to be used and the expected maximum signals for the interferometry and the polarimetry in a possible plasma scenario of DTT. A tentative draft of the layout of the optics inside the machine will be also presented.

Applications of nuclear physics to energy: the INFN-E project of the National Institute of Nuclear Physics (INFN)

“…INFN is contributing to the development of several components of DTT, i.e. the Neutral Beam Injector (NBI) source [26], the NBI accelerator [27], the RF system [28], the interferometry/polarimetry plasma diagnostics [29], the reflectometry plasma diagnostics [30] and the soft X-ray plasma diagnostics. It is worth emphasizing that in the development of the NBI accelerator as well as the RF transmission systems and launchers, extensive use of the Additive Manufacturing technology is being pursued, specifically studying how to optimize the procedure in order to get the best material characteristics and performances.…”