Beam emission spectroscopy studies in a H-/D- beam injector

The limited availability of the present energetic resources and the climate changes induced by the increase of the level of CO2 in the atmosphere are pushing humanity to completely rethink the ways to produce and consume energy. In the long term, a significant contribution to the solution of the world energy issue may come from nuclear fusion: the raw materials, deuterium and lithium, are worldwide accessible and in sufficient quantity to feed the future fusion reactors for several centuries. The largest fusion experiment is ITER, in phase of construction in France. The ITER machine is designed to produce a fusion power of 500 MW, 10 times the input power. Moreover ITER will be the first experiment to continuously operate with deuterium-tritium plasmas, and will have to stand the neutron irradiation produced by nuclear fusion. To reach the desired performances various additional heating systems are foreseen to heat the plasma core up to 10-15 keV. One of the most important heating systems will be composed by 2 neutral beam injectors (NBIs), which produce 2x16.7 MW beams, composed by H/D atoms. To obtain the beams H-/D- ions produced by an ion source will be accelerated at high energy (870 keV for hydrogen, 1 MeV for deuterium) and then neutralized thanks to the charge exchange interaction with the molecules of a H2/D2 gas. The construction of such a system is very challenging and 2 prototypes will be built and tested in Padua at Consorzio RFX. The first one, SPIDER (Source for the Production of Ions o Deuterium Extracted from an Rf plasma), operative in 2016, aims at studying the source part of the NBI, accelerating ions at lower energies, up to 100 keV. The prototype of the full ITER negative NBI system is MITICA (Megavolt ITer Injector Concept and Advancement), it will start operating in 2019. Both SPIDER and MITICA will be equipped with a large number of diagnostics: in particular, the Beam Emission Spectroscopy (BES) will measure the spectrum of the radiation produced by the beam when interacting with the background gas in order to measure the divergence and the uniformity of the beam produced by the ion source. The divergence is a key parameter for the safety of the test facilities, since it is related to the power deposition of the beam on the beam line component. The beam uniformity is crucial for the heating effectiveness of the beam itself. The PhD activity was mostly devoted to develop the BES diagnostics of SPIDER and MITICA, with the target to measure divergence in the range 3- 7 mrad (e-folding) with a relative error below 10%, and values of uniformity in the range 90-100%. In particular, the work consisted in: • developing a set of codes (dBES) for the simulation of the behavior of the BES diagnostics; • studying and improving the methods of analysis for the data that will be collected by BES. • completing the design of the BES diagnostics, also selecting and testing its hardware components; Experimental data of the test facilities BATMAN (BAvarian Test MAchine for Negative ions), MANITU (Multi Ampere Negative Ion Test Unit) and ELISE (Extraction from a Large Ion Source Experiment) at the Max Planck Institut für Plasmaphysik (IPP) in Garching, have been used to validate the numerical model at the base of dBES and to improve the method of analysis of the BES spectra. During my stays at the ITED group of IPP Garching the results of dBES were also benchmarked against those of the BBC-NI code, developed at IPP for similar purposes. Besides SPIDER and MITICA the studies were also addressed to NIO1 (Negative Ion Optimization 1), hosting an RF ion source which produces a 130 mA beam composed by H- ions. The test facility was jointly built by Consorzio RFX and INFN-LNL, with the aim of studying and improving the production of negative ions, as well as testing concepts and instrumentation for SPIDER and MITICA. For NIO1 the BES diagnostic was entirely designed; the tests on NIO1 of this diagnostic will allow a first experimental validation of the design of those for SPIDER and MITICA. The PhD research is described in this thesis as follows: • Chapter [chap:Introduction] gives a briefly describes the ITER reactor. The principle of operation of the neutral beam injectors is then explained, together with the characteristics of the considered experiments: SPIDER and MITICA, BATMAN, MANITU, ELISE and NIO1. The main diagnostics installed in the negative ion sources and more generally in the NBIs are presented, too. • Chapter [chap:Beam-Emission-Spectroscopy] describes the work done on the simulation codes dedicated to Beam Emission Spectroscopy. The physical phenomena at the base of the BES diagnostic operation are explained. The code dBES, developed for the simulation of the BES diagnostic and for the analysis of its measurements, is described. dBES is then benchmarked against the BBC-NI code and with the experimental data of the BES diagnostics in the BATMAN, MANITU and ELISE test facilities. • Chapter [chap:Designtotal] presents the design of the BES diagnostics in the experiments NIO1, SPIDER and MITICA, carried out by means of the dBES code. • Chapter [chap:Experimental-work] presents the experimental activities carried out to test the available instrumentation for the BES and the optical emission spectroscopy diagnostics in NIO1, SPIDER and MITICA; the design activity of some components is also illustrated. • The summary is reported in chapter [chap:Conclusions]. There follows the list of the articles published and of the technical notes written during the PhD

Cardiology of the future: xenotransplantation with porcine heart

The reduced availability of human donor hearts compared with the needs of patients with advanced heart failure refractory to medical therapy has promoted the search for therapeutic alternatives to cardiac allografts. Porcine heart xenotransplantation represents one of the most promising frontiers in this field today. From the first researches in the 1960s to today, the numerous advances achieved in the field of surgical techniques, genetic engineering and immunosuppression have made it possible at the beginning of 2022 to carry out the first swine-to-human heart transplant, attaining a survival of 2 months after surgery. The main intellectual and experimental stages that have marked the history of xenotransplantation, the latest acquisitions in terms of genetic editing, as well as the improvement of immunosuppressive therapy are discussed analytically in this article in order to illustrate the underlying complexity of this therapeutic model

Characterization of cesium and H-/D- density in the negative ion source SPIDER

The Heating Neutral Beam Injectors (HNBs) for ITER will have to deliver 16.7 MW beams of H/D particles at 1 MeV energy. The beams will be produced from H-/D- ions, generated by a radiofrequency plasma source coupled to an ion acceleration system. A prototype of the ITER HNB ion source is being tested in the SPIDER experiment, part of the ITER Neutral Beam Test Facility at Consorzio RFX. Reaching the design targets for beam current density and fraction of coextracted electrons is only possible by evaporating cesium in the source, in particular on the plasma facing grid (PG) of the acceleration system. In this way the work function of the surfaces decreases, significantly increasing the amount of surface reactions that convert neutrals and positive ions into H-/D-. It is then of paramount importance to monitor the density of negative ions and the density of Cs in the proximity of the PG. Monitoring the Cs spatial distribution along the PG is also essential to guarantee the uniformity of the beam current. In SPIDER, this is possible thanks to the Cavity Ringdown Spectroscopy (CRDS) and the Laser absorption Spectroscopy diagnostics (LAS), which provide line-integrated measurements of negative ion density and neutral, ground state Cs density, respectively. The paper discusses the CRDS and LAS measurements as a function of input power and of the magnetic and electric field used to reduce the coextraction of electrons. Negative ion density data are in qualitative agreement with the results in Cs-free conditions. In agreement with simulations, Cs density is peaked in the center of the source; a top/bottom non uniformity is however present. Several effects of plasma on Cs deposition are presented.Comment: 17 pages, 9 figures. Paper (Preprint) following the poster contribution at the SOFT 2022 conference. The destination journal is Fusion Engineering and Desig

Overview on electrical issues faced during the SPIDER experimental campaigns

SPIDER is the full-scale prototype of the ion source of the ITER Heating Neutral Beam Injector, where negative ions of Hydrogen or Deuterium are produced by a RF generated plasma and accelerated with a set of grids up to ~100 keV. The Power Supply System is composed of high voltage dc power supplies capable of handling frequent grid breakdowns, high current dc generators for the magnetic filter field and RF generators for the plasma generation. During the first 3 years of SPIDER operation different electrical issues were discovered, understood and addressed thanks to deep analyses of the experimental results supported by modelling activities. The paper gives an overview on the observed phenomena and relevant analyses to understand them, on the effectiveness of the short-term modifications provided to SPIDER to face the encountered issues and on the design principle of long-term solutions to be introduced during the currently ongoing long shutdown.Comment: 8 pages, 12 figures. Presented at SOFT 202

Beam emission spectroscopy studies in a H-/D- beam injector

The limited availability of the present energetic resources and the climate changes induced by the increase of the level of CO2 in the atmosphere are pushing humanity to completely rethink the ways to produce and consume energy. In the long term, a significant contribution to the solution of the world energy issue may come from nuclear fusion: the raw materials, deuterium and lithium, are worldwide accessible and in sufficient quantity to feed the future fusion reactors for several centuries. The largest fusion experiment is ITER, in phase of construction in France. The ITER machine is designed to produce a fusion power of 500 MW, 10 times the input power. Moreover ITER will be the first experiment to continuously operate with deuterium-tritium plasmas, and will have to stand the neutron irradiation produced by nuclear fusion. To reach the desired performances various additional heating systems are foreseen to heat the plasma core up to 10-15 keV. One of the most important heating systems will be composed by 2 neutral beam injectors (NBIs), which produce 2x16.7 MW beams, composed by H/D atoms. To obtain the beams H-/D- ions produced by an ion source will be accelerated at high energy (870 keV for hydrogen, 1 MeV for deuterium) and then neutralized thanks to the charge exchange interaction with the molecules of a H2/D2 gas. The construction of such a system is very challenging and 2 prototypes will be built and tested in Padua at Consorzio RFX. The first one, SPIDER (Source for the Production of Ions o Deuterium Extracted from an Rf plasma), operative in 2016, aims at studying the source part of the NBI, accelerating ions at lower energies, up to 100 keV. The prototype of the full ITER negative NBI system is MITICA (Megavolt ITer Injector Concept and Advancement), it will start operating in 2019. Both SPIDER and MITICA will be equipped with a large number of diagnostics: in particular, the Beam Emission Spectroscopy (BES) will measure the spectrum of the radiation produced by the beam when interacting with the background gas in order to measure the divergence and the uniformity of the beam produced by the ion source. The divergence is a key parameter for the safety of the test facilities, since it is related to the power deposition of the beam on the beam line component. The beam uniformity is crucial for the heating effectiveness of the beam itself. The PhD activity was mostly devoted to develop the BES diagnostics of SPIDER and MITICA, with the target to measure divergence in the range 3- 7 mrad (e-folding) with a relative error below 10%, and values of uniformity in the range 90-100%. In particular, the work consisted in: • developing a set of codes (dBES) for the simulation of the behavior of the BES diagnostics; • studying and improving the methods of analysis for the data that will be collected by BES. • completing the design of the BES diagnostics, also selecting and testing its hardware components; Experimental data of the test facilities BATMAN (BAvarian Test MAchine for Negative ions), MANITU (Multi Ampere Negative Ion Test Unit) and ELISE (Extraction from a Large Ion Source Experiment) at the Max Planck Institut für Plasmaphysik (IPP) in Garching, have been used to validate the numerical model at the base of dBES and to improve the method of analysis of the BES spectra. During my stays at the ITED group of IPP Garching the results of dBES were also benchmarked against those of the BBC-NI code, developed at IPP for similar purposes. Besides SPIDER and MITICA the studies were also addressed to NIO1 (Negative Ion Optimization 1), hosting an RF ion source which produces a 130 mA beam composed by H- ions. The test facility was jointly built by Consorzio RFX and INFN-LNL, with the aim of studying and improving the production of negative ions, as well as testing concepts and instrumentation for SPIDER and MITICA. For NIO1 the BES diagnostic was entirely designed; the tests on NIO1 of this diagnostic will allow a first experimental validation of the design of those for SPIDER and MITICA. The PhD research is described in this thesis as follows: • Chapter [chap:Introduction] gives a briefly describes the ITER reactor. The principle of operation of the neutral beam injectors is then explained, together with the characteristics of the considered experiments: SPIDER and MITICA, BATMAN, MANITU, ELISE and NIO1. The main diagnostics installed in the negative ion sources and more generally in the NBIs are presented, too. • Chapter [chap:Beam-Emission-Spectroscopy] describes the work done on the simulation codes dedicated to Beam Emission Spectroscopy. The physical phenomena at the base of the BES diagnostic operation are explained. The code dBES, developed for the simulation of the BES diagnostic and for the analysis of its measurements, is described. dBES is then benchmarked against the BBC-NI code and with the experimental data of the BES diagnostics in the BATMAN, MANITU and ELISE test facilities. • Chapter [chap:Designtotal] presents the design of the BES diagnostics in the experiments NIO1, SPIDER and MITICA, carried out by means of the dBES code. • Chapter [chap:Experimental-work] presents the experimental activities carried out to test the available instrumentation for the BES and the optical emission spectroscopy diagnostics in NIO1, SPIDER and MITICA; the design activity of some components is also illustrated. • The summary is reported in chapter [chap:Conclusions]. There follows the list of the articles published and of the technical notes written during the PhD.La disponibilità limitata delle attuali risorse energetiche e i cambiamenti climatici indotti dall’aumento della concentrazione di CO2 nell’atmosfera impongono all’umanità di ripensare completamente i modi di produrre e consumare energia. Nel lungo termine, un contributo importante alla soluzione del problema energetico mondiale potrebbe arrivare dalla fusione nucleare: le materie prime, deuterio e litio, sono accessibili in tutto il globo e in quantità sufficiente per alimentare i futuri reattori a fusione per diversi secoli. Il più grande esperimento a livello mondiale sulla fusione è ITER, in fase di costruzione in Francia. ITER è progettato per produrre dalla fusione fino a 500MW, 10 volte la potenza in ingresso. Inoltre, ITER sarà il primo esperimento a operare permanentemente con plasmi di deuterio e trizio, quindi conterrà materiale radioattivo (il trizio) e dovrà sopportare l’irraggiamento neutronico prodotto dalla fusione nucleare. Per raggiungere le prestazioni volute serviranno varie forme di riscaldamento addizionale, in modo da portare la temperatura centrale del plasma a 10 15 keV. Uno dei sistemi di riscaldamento più importanti sarà costituito da 2 iniettori di neutri (NBI), che producono fasci da 16.7 MW composti da particelle neutre (H/D). Per ottenere i fasci ioni H-/D-, prodotti da un’apposita sorgente, verranno accelerati ad energie elevate (870 keV per l’idrogeno, 1 MeV per il deuterio) e successivamente neutralizzati grazie alle reazioni di scambio carica con le molecole di un gas di idrogeno/deuterio. Costruire un sistema simile è un’operazione complessa, per questo 2 prototipi saranno costruiti e testati a Padova presso il Consorzio RFX. Il primo, SPIDER (Source for the Production of Ions o Deuterium Extracted from an Rf plasma), che sarà operativo dal 2016, verrà utilizzato per studiare la produzione e accelerazione (fino a 100 keV) degli ioni negativi. Il secondo sarà il prototipo di un intero iniettore di neutri per ITER, MITICA(Megavolt ITer Injector Concept and Advancement), che entrerà in funzione nel 2019. Sia SPIDER che MITICA saranno dotati di un gran numero di diagnostiche: in particolare, la Beam Emission Spectroscopy (BES) misurerà lo spettro della radiazione prodotta dall’interazione tra fascio e gas di fondo, con lo scopo di misurare la divergenza e l’uniformità del fascio prodotto dalla sorgente di ioni. La divergenza è un parametro chiave per la sicurezza degli impianti, poichè è legata alla potenza depositata dal fascio sulle strutture degli esperimenti. L’uniformità del fascio è cruciale per l’efficacia del fascio stesso nel riscaldamento del plasma. L’attività di dottorato è stata dedicata in gran parte a sviluppare le diagnostiche BES di SPIDER e MITICA, con l’obiettivo di misurare la divergenza nell’intervallo 3 7 mrad (e-folding) con un errore relativo sotto il 10%, e valori di uniformità nell’intervallo 90 100%. In particolare, il lavoro è consistito nel: • sviluppare un set di codici (dBES) per la simulazione del comportamento della diagnostica BES; • studiare e migliorare i metodi di analisi dei dati che saranno raccolti dalla BES; • completare il design della diagnostica, anche individuando e testando la sua componentistica hardware; Le misure raccolte negli impianti sperimentali BATMAN(BAvarian Test MAchine for Negative ions), MANITU (Multi Ampere Negative Ion Test Unit) ed ELISE (Extraction from a Large Ion Source Experiment) al Max Planck Institut für Plasmaphysik (IPP) a Garching, sono state utilizzate per validare il modello numerico alla base di dBES a per migliorare il metodo di analisi degli spettri BES. Durante le visite al gruppo ITED di IPP Garching i risultati di dBES sono stati confrontati con quelli del codice BBC-NI, sviluppato a IPP per scopi analoghi. Oltre che su SPIDER e MITICA gli studi si sono concentrati anche su NIO1 (Negative Ion Optimization 1), dotato di una sorgente RF che produce un fascio di 130 mA composto da ioni H. L’esperimento è frutto di una collaborazione tra Consorzio RFX e INFN-LNL, con lo scopo di studiare e migliorare la produzione di ioni negativi, nonchè di testare la strumentazione per SPIDER e MITICA. Per NIO1 è stata interamente progettata la diagnostica BES; i test su NIO1 di questa diagnostica permetteranno una prima verifica sperimentale del design delle diagnostiche analoghe per SPIDER e MITICA. Il lavoro di dottorato è descritto nella tesi come segue: • Il capitolo 1 fornisce una breve descrizione del reattore ITER. Viene poi illustrato il principio di funzionamento degli iniettori di neutri, nonchè le caratteristiche dei esperimenti presi in considerazione: SPIDER e MITICA, BATMAN, MANITU, ELISE e NIO1. Vengono inoltre presentate le principali diagnostiche installate nelle sorgenti di ioni negativi e più in generale negli iniettori di neutri. • Il capitolo 2 descrive il lavoro svolto sui codici di simulazione per la Beam Emission Spectroscopy. Vengono illustrati i fenomeni fisici alla base del funzionamento della diagnostica. Viene successivamente presentato il codice dBES, sviluppato per la simulazione della diagnostica BES e per l’analisi dei dati raccolti dalla diagnostica stessa. Segue la verifica delle simulazioni di dBES con i risultati del codice BBC-NI e con i dati delle diagnostiche BES negli esperimenti BATMAN, MANITU ed ELISE. • Il capitolo 3 presenta il design delle diagnostiche BES per gli esperimenti NIO, SPIDER e MITICA, realizzato con il supporto del codice dBES. • Il capitolo 4 presenta le attività sperimentali svolte per caratterizzare la strumentazione disponibile per le diagnostiche BES e optical emission spectroscopy in NIO1, SPIDER e MITICA; viene illustrata anche la progettazione di alcune componenti delle diagnostiche. • Nel capitolo 5 vengono sintetizzati e discussi i risultati presentati nella tesi. Seguono infine la lista degli articoli pubblicati e delle note tecniche scritte durante il dottorat

USE OF SILT-CLAY MIXTURES IN MSW LANDFILLS COVER SYSTEMS

Reuse of excavated soils in MSW landfills liners is not always feasible, due to their geotechnical properties that have to meet the requirements of the existing regulation. This paperdeals with a case history occurred in the north east of Italy and shows an in-situ mixing procedure of a sandy silt with a medium plastic clays, able to achieve a homogenous mineral barriers suitable for landfill. A laboratory investigation was firs carried out to evaluate the best percentages of silt and clay in the mix. Field tests were planned using a soil stabilizer machine for mixing the two soils at different percentages by weight. Laboratory tests, performed on samples collected in situ, showed a very good soil homogenization. In this case history, the reuse of a relevant quantity of excavated silt, has also assumed a strategic importance related to economic issues and environmental sustainability

A feasibility study of a NBI photoneutralizer based on nonlinear gating laser recirculation

The neutralization efficiency of negative ion neutral beam injectors is a major issue for future fusion reactors. Photon neutralization might be a valid alternative to present gas neutralizers, but still with several challenges for a valid implementation. Some concepts have been presented so far but none has been validated yet. A novel photoneutralization concept is discussed here, based on an annular cavity and a duplicated frequency laser beam (recirculation injection by nonlinear gating). The choice of lithium triborate as the material for the second harmonic extractor is discussed and a possible cooling method via crystal slicing is presented; laser intensity enhancement within the cavity is evaluated in order to quantify the achievable neutralization rate. Mockups of the critical components are proposed as intermediate steps toward system realization

Defects in GaN-based LEDs: Impact on internal quantum efficiency and on reliability

This paper reviews the properties of the defects which limit the performance and the reliability of LEDs based on InGaN. More specifically we discuss: (i) the origin and properties of the defects responsible for SRH recombination; (ii) the role of defects in favoring the degradation of InGaN-based LEDs. Original data are compared to previous literature reports to provide a clear understanding of the topic