Dottorato in ENERGIA E AMBIENTE

Titolo della tesi: Characterization of a new pixelated diamond detector for fast neutron diagnostics on fusion reactors

This research activity focuses on characterizing an innovative pixelated diamond detector utilizing Timepix3 (TPX3) chip technology. This detector combines a polycrystalline diamond with the TPX3 chip. Future versions will feature a monocrystalline diamond covering a 14 × 14 mm² area, achieving a remarkable spatial resolution of 55 μm. The TPX3 chip empowers pixel-wise simultaneous counting, charge measurement, and time recording, enabling precise monitoring of neutron interactions within the diamond, which are manifested as tracks. This capability proves invaluable for multiparametric analysis along a designated line of sight in a Tokamak machine. This is a central objective of this research. We aim to investigate the detector's response to neutrons within the 1-20 MeV energy range, which is critically relevant in nuclear fusion. Furthermore, TPX3's capacity to discriminate against signals from intense background sources, primarily gamma rays and scattered neutrons, is of paramount importance for designing diagnostic systems and the interpretation of data. Equally significant is the detector's ability to capture the temporal evolution of neutron emissions, offering real-time monitoring prospects that can be seamlessly integrated into feedback systems. A pivotal facet of this research involves the development of an algorithm. This algorithm, informed by laboratory measurements and Monte Carlo simulations, elucidates the distribution of pixel patterns generated in the diamond by primary neutron reactions. Its application to experimental data will facilitate the determination of the neutron spectrum. Specifically, the thesis is organized as follows. The first two chapters introduce the scientific context in which this research unfolds, presenting essential insights into the fundamental properties of neutron emissions from fusion plasmas. Chapter 3 reviews neutron detection systems, focusing on the Timepix3 detector. Its unique capabilities are showcased through two applications: radon decay product and thermal neutron monitoring using a 6LiF converter. These applications highlight the potential of these detectors as track detectors, particularly their ability to discriminate particles through morphological track analysis. Chapter 4 provides a comprehensive overview of the Diamondpix detector. The chapter discusses the properties of diamonds and presents the results of characterization studies of the Diamondpix detector. Finally, in Chapter 5, the potential of Diamondpix as a detector for fast neutrons is explored. Measurements were conducted at FNG (ENEA Frascati) and n_TOF (CERN). At FNG, the response of Diamondpix to 2.5 and 14 MeV neutrons from D-D and D-T reactions was characterized. The neutron efficiency at the two energies was also estimated. At n_TOF, time-of-flight measurements with Diamondpix were performed. Track analysis was carried out at different neutron energies, and Diamondpix was energy calibrated. The Diamondpix charge response was analyzed, and the FNG and n_TOF results were compared. Charge profiles were analyzed and compared with Monte Carlo simulations.