Beam physics via tomographic diagnostics

The goal of this thesis work is the study of the beam physics of the negative ion beam for ITER HNB. A new diagnostics is installed on SPIDER, the full-size prototype of ITER negative ion source: the visible tomography. It is composed by a set of visible cameras which measure the light emitted by the beam particles when they interact with the background gas. An algorithm to reconstruct through tomographic inversion the two-dimensional pattern of the beam emission is developed, and the reconstructed profiles are used to study the homogeneity of the beam current, also with the support of a model to directly correlate the beamlet emission with the beamlet current density. Thanks to the masking of most of the apertures composing SPIDER multi-beamlets negative ion beam, the single-beamlet divergence is estimated through the Gaussian fit of the 1D beam profiles. \\ The results obtained by this new technique are used to investigate the beam features as a function of the main source and accelerator parameters, integrating the information provided by all the other diagnostics available. A strong correlation between the beam properties and the plasma features is found, thus a deep investigation of the source plasma is carried out. The beam homogeneity depends on the uniformity of both electrons and negative ions at the extraction region, in order to obtain identical beamlet optics at all the apertures and to avoid localised heating of the extraction grid due to the co-extracted electrons. The estimation of the single-beamlet current density is exploited to better interpret the spectroscopic measurements both close to the grid system (together with the electrostatic probes data), and inside the drivers. This experience is fundamental for the future operation at full performances, when the characterization of the single beamlet will be more challenging. The various operational regimes explored, both with and without caesium evaporation, are investigated to improve the understanding of the physics behind the generation and extraction of a large negative ion beams, when the principal source and accelerator control parameters are varied. This is the first comprehensive analysis of the experimental data measured during the experimental campaign of SPIDER experiment, and the performances achieved in term of beam divergence and homogeneity, as well as beamlet current density and co-extracted electrons currents are presented.The goal of this thesis work is the study of the beam physics of the negative ion beam for ITER HNB. A new diagnostics is installed on SPIDER, the full-size prototype of ITER negative ion source: the visible tomography. It is composed by a set of visible cameras which measure the light emitted by the beam particles when they interact with the background gas. An algorithm to reconstruct through tomographic inversion the two-dimensional pattern of the beam emission is developed, and the reconstructed profiles are used to study the homogeneity of the beam current, also with the support of a model to directly correlate the beamlet emission with the beamlet current density. Thanks to the masking of most of the apertures composing SPIDER multi-beamlets negative ion beam, the single-beamlet divergence is estimated through the Gaussian fit of the 1D beam profiles. \\ The results obtained by this new technique are used to investigate the beam features as a function of the main source and accelerator parameters, integrating the information provided by all the other diagnostics available. A strong correlation between the beam properties and the plasma features is found, thus a deep investigation of the source plasma is carried out. The beam homogeneity depends on the uniformity of both electrons and negative ions at the extraction region, in order to obtain identical beamlet optics at all the apertures and to avoid localised heating of the extraction grid due to the co-extracted electrons. The estimation of the single-beamlet current density is exploited to better interpret the spectroscopic measurements both close to the grid system (together with the electrostatic probes data), and inside the drivers. This experience is fundamental for the future operation at full performances, when the characterization of the single beamlet will be more challenging. The various operational regimes explored, both with and without caesium evaporation, are investigated to improve the understanding of the physics behind the generation and extraction of a large negative ion beams, when the principal source and accelerator control parameters are varied. This is the first comprehensive analysis of the experimental data measured during the experimental campaign of SPIDER experiment, and the performances achieved in term of beam divergence and homogeneity, as well as beamlet current density and co-extracted electrons currents are presented

NIO1 negative ion beam investigation in view of ITER heating and current drive

Negli ultimi decenni, la ricerca e lo sviluppo di nuove fonti di energia sono state oggetto di crescente interesse scientifico. In particolare, la fusione nucleare potrebbe essere la soluzione al problema energetico mondiale. ITER è attualmente il più grande esperimento di fusione nucleare in via di costruzione. Situato nel sud della Francia, sarà il più grande tokamak costruito al mondo con l'obiettivo di produrre 500 MW di potenza dai 50 MW di potenza fornitagli. Diversi metodi di riscaldamento del plasma sono in via di sviluppo per poter scaldare il core del plasma a temperature dell'ordine dei 15 keV. Tra questi, l'iniezione di fasci neutri è uno dei più importanti. Il progetto PRIMA, costituito dagli esperimenti SPIDER e MITICA in via di costruzione al Consorzio RFX a Padova, si pone come obiettivo lo studio dei futuri iniettori di fasci neutri di ITER. L'esperimento NIO1, anch'esso situato al Consorzio RFX, è una relativamente piccola sorgente a radio frequenza RF di ioni negativi, nato con l'obiettivo di caratterizzare la fisica delle sorgenti di ioni nell'ottica dei futuri utilizzi negli iniettori di fasci neutri, quali lo stesso MITICA. Questo lavoro di tesi, nato da una collaborazione tra i Laboratori Nazionali di Legnaro (LNL) e il Consorzio RFX, caratterizza il fascio di ioni negativi di NIO1. I dati raccolti durante le campagne sperimentali sono stati analizzati e confrontati, per testare le performance della nuova griglia di estrazione installata su NIO1 a maggio 2017. La caratterizzazione è stata fatta in diversi modi: confrontando qualitativamente i dati raccolti dalle varie diagnostiche; ricostruendo tomograficamente l'immagine dei 9 beamlets tramite i dati raccolti dalle telecamere; caratterizzando il plasma formatosi in seguito alla propagazione del fascio nel gas di fondo, tramite il confronto con i dati sperimentali e quelli ottenuti da una simulazione numerica Particles-In-Cell PIC

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

Misure preliminari a temperature variabili su SiPM per future applicazioni nell'esperimento XENON

Negli ultimi decenni la materia oscura è stata oggetto di crescente interesse scientifico: dati sperimentali indicano che essa costituisce il 26.8% della massa totale dell'Universo ma le sue origini e natura rimangono ancora ignote. Essa interagisce solo gravitazionalmente in quanto priva di carica, caratteristica che ne rende molto difficile la rivelazione. Numerosi esperimenti in tutto il mondo sono alla ricerca di maggiori informazioni riguardo la natura della materia oscura tramite metodi di rivelazione indiretta e diretta; questi ultimi sono accumunati da rivelatori molto massivi per sopperire alla piccola sezione d'urto di interazione e situati in ambienti molto isolati per diminuire il rumore di fondo dovuto alla radioattività terrestre. Tra le varie ipotesi avanzate riguardo la natura della materia oscura spiccano le WIMP, Weakly Interacting Massive Particle. L'esperimento XENON, situato ai Laboratori Nazionali del Gran Sasso, si occupa della rivelazione diretta di WIMP studiandone l'urto elastico con i nuclei di Xeno, presente allo stato liquido e gassoso all'interno della TPC, il rivelatore fulcro dell'esperimento. I primi risultati dell'ultima fase del progetto sono attesi per l'inizio del 2016; grazie alla massa fiduciale di circa una tonnellata di Xeno, da cui il nome XENON1T, e a migliorie atte a diminuire il rumore di fondo, quali la scelta accurata di materiali a bassa radioattività e a un sistema di veto dei muoni, si ipotizza che il rivelatore raggiungerà una sensibilità due ordini di grandezza superiore a quelle finora raggiunte. Sono in fase di ricerca soluzioni per incrementare la raccolta di luce del rivelatore, nell'ottica di diminuire l'energia di soglia di rivelazione migliorandone la sensibilità. Una delle possibili soluzioni consiste nell'affiancare i PMT già in uso con fotomoltiplicatori al Silicio SiPM. Essi dovranno essere in grado di lavorare a una temperatura di sim ~170 K ed avere una buona efficienza di rivelazione per fotoni di lunghezza d'onda di ~178 nm. Questo lavoro di tesi si colloca nell'ambito di tale progetto di ricerca e sviluppo. Lo scopo del lavoro di tesi presentato è stato la misura della variazione di guadagno e conteggi di buio dei SiPM a disposizione in funzione della temperatur

Beam physics via tomographic diagnostics

The goal of this thesis work is the study of the beam physics of the negative ion beam for ITER HNB. A new diagnostics is installed on SPIDER, the full-size prototype of ITER negative ion source: the visible tomography. It is composed of a set of visible cameras which measure the light emitted by the beam particles when they interact with the background gas. An algorithm to reconstruct through tomographic inversion the two-dimensional pattern of the beam emission is developed, and the reconstructed profiles are adopted to study the homogeneity of the beam current, also with the support of a model to directly correlate the beamlet emission with the beamlet current density. Thanks to the masking of most of the apertures composing SPIDER multi-beamlets negative ion beam, the single-beamlet divergence is estimated through the Gaussian fit of the 1D beam profiles. The results obtained by this new technique are utilized to investigate the beam features as a function of the main source and accelerator parameters, integrating the information provided by all the other diagnostics available. A strong correlation between the beam properties and the plasma features is found, thus a deep investigation of the source plasma is carried out. The beam homogeneity depends on the uniformity of both electrons and negative ions at the extraction region, in order to obtain identical beamlet optics at all the apertures and to avoid localised heating of the extraction grid due to the co-extracted electrons. The estimation of the single-beamlet current density is exploited to better interpret the spectroscopic measurements both close to the grid system (together with the electrostatic probes data), and inside the drivers. This experience is fundamental for the future operation at full performances, when the characterization of the single beamlet will be more challenging. The various operational regimes explored, both with and without caesium evaporation, are investigated to improve the understanding of the physics behind the generation and extraction of a large negative ion beams, when the principal source and accelerator control parameters are varied. This is the first comprehensive analysis of the experimental data measured during the experimental campaign of SPIDER experiment, and the performances achieved in term of beam divergence and homogeneity, as well as beamlet current density and co-extracted electrons currents are presented

Use of electrical measurements for non-invasive estimation of plasma electron density in the inductively coupled SPIDER ion source

SPIDER is the full-scale prototype of the ITER Neutral Beam Injector ion source. The plasma heating takes place inside eight drivers via inductive coupling, through the radio frequency (RF) coil. To achieve the optimum conditions during source operation it is necessary to know the plasma behaviour under various operational conditions. One of the essential parameter, is the plasma electron density. It is possible to experimentally measure this parameter, and currently, different methods are being explored, like the estimations coming from the Langmuir probe and optical emission spectroscopy. However, these methods are either available for temporary measurements or require dedicated analyses with large uncertainties. In this perspective, an alternative, reliable, and fast diagnostic tools will be beneficial for the estimation of the order of magnitude of electron density inside the driver. Two models for the estimation of electron density are recalled, discussed, and further modified in this work: one is based on the classical power balance equation and the other is recently described in the literature and relies on classical plasma conductivity. Both models use equivalent electrical parameters of the driver derived from available electrical measurements at the output of the RF generator and through the knowledge of the matching network and the transmission line length. This work explicitly focuses on the application of these models to estimate the plasma electron density in a single driver of SPIDER. Furthermore, the estimations are compared with the first experimental results obtained from temporary electrostatic probe measurements and are found to be in good agreement in terms of magnitude and trends

Global variation in postoperative mortality and complications after cancer surgery: a multicentre, prospective cohort study in 82 countries

© 2021 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND 4.0 licenseBackground: 80% of individuals with cancer will require a surgical procedure, yet little comparative data exist on early outcomes in low-income and middle-income countries (LMICs). We compared postoperative outcomes in breast, colorectal, and gastric cancer surgery in hospitals worldwide, focusing on the effect of disease stage and complications on postoperative mortality. Methods: This was a multicentre, international prospective cohort study of consecutive adult patients undergoing surgery for primary breast, colorectal, or gastric cancer requiring a skin incision done under general or neuraxial anaesthesia. The primary outcome was death or major complication within 30 days of surgery. Multilevel logistic regression determined relationships within three-level nested models of patients within hospitals and countries. Hospital-level infrastructure effects were explored with three-way mediation analyses. This study was registered with ClinicalTrials.gov, NCT03471494. Findings: Between April 1, 2018, and Jan 31, 2019, we enrolled 15 958 patients from 428 hospitals in 82 countries (high income 9106 patients, 31 countries; upper-middle income 2721 patients, 23 countries; or lower-middle income 4131 patients, 28 countries). Patients in LMICs presented with more advanced disease compared with patients in high-income countries. 30-day mortality was higher for gastric cancer in low-income or lower-middle-income countries (adjusted odds ratio 3·72, 95% CI 1·70–8·16) and for colorectal cancer in low-income or lower-middle-income countries (4·59, 2·39–8·80) and upper-middle-income countries (2·06, 1·11–3·83). No difference in 30-day mortality was seen in breast cancer. The proportion of patients who died after a major complication was greatest in low-income or lower-middle-income countries (6·15, 3·26–11·59) and upper-middle-income countries (3·89, 2·08–7·29). Postoperative death after complications was partly explained by patient factors (60%) and partly by hospital or country (40%). The absence of consistently available postoperative care facilities was associated with seven to 10 more deaths per 100 major complications in LMICs. Cancer stage alone explained little of the early variation in mortality or postoperative complications. Interpretation: Higher levels of mortality after cancer surgery in LMICs was not fully explained by later presentation of disease. The capacity to rescue patients from surgical complications is a tangible opportunity for meaningful intervention. Early death after cancer surgery might be reduced by policies focusing on strengthening perioperative care systems to detect and intervene in common complications. Funding: National Institute for Health Research Global Health Research Unit

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

© 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licenseBackground: Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide. Methods: A multimethods analysis was performed as part of the GlobalSurg 3 study—a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital. Findings: Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3·85 [95% CI 2·58–5·75]; p<0·0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63·0% vs 82·7%; OR 0·35 [0·23–0·53]; p<0·0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer. Interpretation: Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised. Funding: National Institute for Health and Care Research