Engineering aspects of new generation tokamak devices: spectroscopic diagnostics and vacuum auxiliary system
Author(s)
Belpane, Andrea
Date Issued
February 13, 2025
Type
Doctoral Thesis
Abstract
This thesis is conducted within the framework of nuclear fusion research, a promising alternative energy source
which aims to generate sustainable and clean power. It is the process by which two light atomic nuclei combine
to form a heavier nucleus, releasing a significant amount of energy. The European roadmap for fusion energy
focuses on achieving controlled fusion reactions using toroidal devices known as tokamaks, which are the subject
of intensive scientific research supported by advanced diagnostics and complex auxiliary systems. Advances in
scientific research and technological innovation are driving the development of larger superconducting tokamaks,
as increasing their size improves plasma confinement, enhances energy retention. Unlike earlier designs, where
diagnostics were largely external, the new-generation superconductive tokamaks integrate diagnostic systems
directly into the vacuum vessels where the fusion reactions occur. These harsh nuclear environments, characterized
by high neutron fluxes, high vacuum, and intense heat loads, demand increased complexity, robustness, and
reliability of diagnostic systems as well as complex integration with other tokamak components. Within this
context, the work presented in this thesis focuses on the design of spectroscopy diagnostics and the pumping
systems for two new superconducting tokamaks: DTT and JT-60SA
Part I firstly introduce the global energy landscape and the fundamentals of nuclear fusion, emphasizing the
urgent need for low-carbon energy alternatives and detailing the plasma confinement methods used in fusion
research. The section concludes with an overview of DTT and JT60-SA which are the devices on which the
thesis work is focused.
Part II of this work focuses on the Visible Spectroscopy diagnostic system designed to measure the effective
charge (Zeff ) radial profile time evolution and the visible imaging diagnostic of the DTT’s divertor. This system
is integrated to fit within limited vessel space and includes a setup for Bremsstrahlung radiation measurement
along ten lines of sight in the poloidal plane, a toroidal line of sight for average Zeff evaluation and a dualtelescope
to observe the divertor. In both systems the collected light is transmitted to external spectrometers
and filter devices for flexible monitoring of impurity influx, plasma positioning, and detachment evolution. The
conceptual design was completed, incorporating both the mechanical and optical structures, along with an estimation
of the laboratory setup required for data acquisition and post-processing.
Part III presents the preliminary design of the DTT vacuum system. This section presents the study undertaken
to develop a layout capable of achieving the required pressure levels inside the vacuum vessel. The
analysis begin with an evaluation of the vessel geometry in terms of pumping capacity to identify the optimal
configuration, taking into account the integration of other subsystems such as additional heating systems and
diagnostic equipment. The conceptual design is then finalized, incorporating the technical specifications necessary
to prepare a tender document for the facility’s procurement.
Part IV introduces the Vacuum Ultraviolet Spectrometer (VUV) specifically designed to monitor the JT-
60SA divertor region. This diagnostic supports the broader objectives of ITER and DEMO by investigating
impurity-induced radiation and plasma detachment in the divertor region. The spectrometer is based on the
double SPRED system originally used on Textor which has been significantly upgraded with two new toroidal
gratings for 1D imaging detection, 2D CCD detectors, a dual pair of gold-coated toroidal mirrors, and a new
pumping system. Additionally, a custom-designed chassis was developed to integrate the spectrometer into the
tokamak structure, ensuring precise alignment of the line of sight (LoS). The gratings have been installed within
the spectrometer vessel, and their performance has been verified through a dedicated calibration setup.
Additional information
Dottorato di ricerca in Engineering for Energy and Environment
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