Implementation and Review of the Axisymmetric Equilibrium System of RFX-Mod2 within the MARTe2 Framework

A major refurbishment of the toroidal complex of the RFX-mod device is in progress and it will include the removal of the Inconel vacuum vessel and a modification of the stainless steel supporting structure to be made vacuum-tight. The axisymmetric equilibrium control in RFX-mod was responsible for the control of the plasma current, horizontal and vertical position along with its stability and the plasma shape. The new implementation framework, both hardware and software, is described. The system has been fully reviewed and modified, if needed, for its prospective use in RFX-mod2. In order to run tests in an operation-like context, the updated system has also been implemented in the MARTe2 framework, to be deployed for the real-time applications of RFX-mod2. The results of the previous versions were reproduced and the cycle-time requirements were met

Studies on the impact of the ITER Pulsed Power Supply System on the Pulsed Power Electrical Network

ITER experiment will be built at Cadarache (France) and its main goal will be to prove the viability of fusion as an energy source. In a fusion reactor, the plasma (an ionized gas of Deuterium and Tritium) has to be heated up to temperatures of millions of Celsius degrees in order to sustain the fusion reaction. No materials are able to withstand these temperatures; therefore the plasma is kept away from the walls of the reactor vacuum vessel by means of appropriate magnetic fields, produced by the currents flowing in the superconducting coils, which interact with the charged particles of the plasma. Besides the ohmic heating, two additional sources are foreseen in ITER, based on radiofrequency electromagnetic waves and neutral beam injection. Two Neutral Beam Injectors (NBIs) will heat the plasma; each of them is based on five 200 kV stages in series accelerating negative ions of deuterium or hydrogen, which are neutralized and injected in ITER plasma. The high energy (1 MeV) and beam power (16.7 MW) make this design very complex, close to the state of the art of the components. The ac/dc conversion system necessary to supply the superconducting coils of the magnet system and the auxiliary systems (as the NBIs) may consume a total active and reactive power respectively up to 500 MW and 900 Mvar. In the past years many studies have been carried out on the ITER power supply system and its impact on the electrical network (called Pulsed Power Electrical Network PPEN). Several methods have been considered to improve the power factor, based both on Q reduction and compensation techniques. As for the first, sequential and asymmetric controls, with internal bypass or external freewheeling have been evaluated. Concerning the compensation approach, the current reference design is based on Static Var Compensation System with nominal power of 750 Mvar based on Thyristor Controlled Reactor (TCR) + Tuned Filter (as fixed capacitor). Nevertheless, studies are still in progress aimed to further improvements. This PhD thesis aims to investigate two topics related to the impact on the PPEN of the ITER power supply system with a novel approach. The former concerns the study of the stability of the PPEN and mainly aims to investigate interaction phenomena among the ac/dc conversion and Q compensation and filtering systems, due in particular to the relatively high power ratings and operating scenarios with significant power transients during the plasma pulses. It is not an easy task: the overall system is very complex, the numerical simulation of its operation via programs capable of reproducing the instantaneous current and voltage profiles requires very long calculation time and most of all it does not provide any sensitivity data concerning the stability of the whole power system. Therefore I have followed an analytical approach. The study took the starting points from the methods developed for the HVDC applications, which however can not be directly applied to the ITER case; therefore I have developed specific analytical models. The former model is a Quasi Static Model, which aims to evaluate the strength of the electrical network feeding the ITER power supply system by sensitivity analysis. I have derived the equations of the model by the power flow equations as a function of some relevant parameters in order to carry out sensitivity analysis. This model allows the calculation of some indexes as the Critical Short Circuit Ratio (CSCR) and Voltage Sensitivity Factor (VSF). No critical conditions have been found. The latter is a Dynamic Model; it is based on the state space formulation and it aims to investigate the dynamic stability of the whole system, including also the control system. Nevertheless the ac/dc conversion and the TCR systems are non-linear and discrete, thus difficult to be modelled; therefore, taking the starting point from the methods described in literature, I have approximated the discrete phenomena by continuous transfer functions, and I have worked out the linearization around an equilibrium point such that the small signal analysis approach can be used. I have adopted a modular approach, developing an analytical Dynamic Model for each subsystem (Tuned Filters, TCR and ac/dc conversion system). Then I have built numerical models of the subsystems with a program (PSIM) capable to reproduce the instantaneous waveforms for the validation of the analytical Dynamic Models (run in Matlab Simulink program, state space tool) in frequency and time domain by a comparison between the simulation results. Finally I have built the Dynamic Model of the whole system and validated by comparison with the PSIM one. From the results of the frequency analysis, the dynamic model is accurate for frequency range less than 50 Hz, but it may be used to obtain some insight about the system stability also for frequency range up to 100 Hz. Some unstable operating conditions have been discovered, and the cause has been identified due to resonance between the tuned filters and the grid. It is highlighted that this model may be easily implemented with more detail to the whole ITER power supply system and it can be a very useful and fast tool to aid the design of the power supply system and set the parameters of the control system. As the second topic of my PhD thesis, I have studied the feasibility of adopting a more advanced technology based on the Active Front End approach for the design of the main ac/dc conversion system (called AGPS) of the NBI power supply (56 MW, 88 MVar) to improve its impact in ITER PPEN in terms of current harmonic and reactive power minimization. After giving a short description of the AGPS reference design, based on thyristor technology, the conceptual design of the AFE alternative topology that I have developed for the input ac/dc rectifier is illustrated; its feasibility, and the advantages and drawbacks with respect to the thyristor solution are evaluated and discussed. The results obtained by the analysis show that the AFE solution is feasible and it significantly improves the impact of the AGPS on the Pulsed Power Electrical Network of ITER with respect to thyristor one. The modifications of the present design parameters to allow the full compliance with the requirements of the technical specifications with the implementation of the AFE solution are also proposed and discussed. This thesis is organized as follows. In the Chapter 1 a brief introduction to the fusion research framework is given. The ITER power supply system is described in the chapter 2. The first part of the PhD thesis related to the development of the analytical model starts in the chapter 3, with the description of the simplified equivalent scheme of the ITER Power Supply. The Quasi-Static and Dynamic Models are described in chapter 4 and 5 respectively, and in the chapter 6 are given the conclusions related to this part. The second part of the PhD thesis related to Study of Active-Front-End design for the Acceleration Grid Power Supply of ITER Neutral Beam Injector start in the chapter 7, describing the reference design of the AGPS based on thyristor solution. Then an overview of the AFE converter topologies and control systems is given and their application to AGPS is discussed in the chapter 8. In chapter 9 the conceptual design of the AGPS based on AFE approach is described in detail. In the chapter 10 the AFE and thyristor solution are compared in terms of impact on the PPEN (reactive power and ac current harmonic)L’esperimento ITER sarà costruito a Cadarache (Francia) e il suo obiettivo principale sarà quello di dimostrare la fattibilità tecnologica di produzione di grandi quantità d’energia attraverso la fusione in un plasma di deuterio e trizio In un reattore a fusione, il plasma (un gas ionizzato di deuterio e trizio) deve essere riscaldato fino a temperature di milioni di gradi Celsius al fine di sostenere la reazione di fusione. Non vi sono materiali in grado di resistere a tali temperature, per cui il plasma è tenuto lontano dalle pareti della camera da vuoto del reattore per mezzo di opportuni campi magnetici, prodotto dalle correnti nelle bobine superconduttrici, che interagiscono con gli ioni del plasma. Oltre al riscaldamento ohmico, altri due sistemi di riscaldamento sono previsti nel progetto di ITER, basati sulle onde elettromagnetiche a radiofrequenza e iniezione di neutri. Due iniettori di fasci di neutri (Neutral Beam Injectors NBIs) saranno utilizzati per scaldare il plasma; ciascuno è composto da un sistema di griglie che formano cinque stadi di accelerazione da 200 kV ciascuno, che accelerano gli ioni negativi di deuterio o idrogeno, che vengono poi neutralizzati e iniettati nel plasma di ITER. L'alta energia (1 MeV) e la potenza del fascio (16,7 MW) rendono questo progetto molto complesso, vicino alla stato dell'arte dei componenti. Il sistema di conversione ac/dc necessario per alimentare le bobine superconduttrici del sistema di magneti e dei sistemi ausiliari (come i NBIs) può consumare complessivamente una potenza attiva e reattiva rispettivamente fino a 500 MW e 900 Mvar. Negli ultimi anni molti studi sono stati effettuati sul sistema di alimentazione ITER e sul suo impatto sulla rete elettrica (chiamata Pulsed Power Electrica Networ PPEN). Diverse tecniche sono state considerate per migliorare il fattore di potenza dei sistemi di conversione ac/dc a tiristori di ITER. Per quanto riguarda la riduzione dell’assorbimento sono state studiate tecniche quali il controllo sequenziale ed asimmetrico, con bypass interno o con freewheeling esterno. Per quanto riguarda invece la compensazione, l’attuale progetto di riferimento è basato sulla tecnologia Static Var Compensator (SVC) con potenza nominale di 750 Mvar, composto da Thyristor Controlled Reactor (TCR) + Filtri per le armonche di corrente (che hanno la funzione di fornire potenza reattiva). Tuttavia, gli studi sono ancora in corso con l'obiettivo di ulteriori miglioramenti. Questa tesi di dottorato studia due aspetti legati all'impatto sulla rete PPEN del sistema di alimentazione di ITER, con un approccio diverso rispetto a quelli già effettuati. Il primo riguarda lo studio della stabilità della rete elettrica PPEN e principalmente si propone di studiare i fenomeni di interazione tra i sistemi di conversione ac/dc e di compensazione della reattiva, dovuti in particolare all’elevato consumo di potenza durante gli scenari di funzionamento di ITER. Non è un compito facile: il sistema di alimenatzione di ITER è molto complesso, le simulazioni numeriche del suo funzionamento attraverso programmi in grado di riprodurre i profili istantanei di tensione e corrente richiede tempi di calcolo molto lunghi e soprattutto non forniscono alcuna sensibilità riguardo la stabilità del sistema. Ho quindi applicato un approccio analitico e, considerando i metodi sviluppati per le applicazioni HVDC che però non possono essere direttamente applicati al caso ITER, ho sviluppato specifici modelli analitici. Il primo modello è il “Quasi-Static Model”, che ha lo scopo di valutare l’adeguatezza della rete elettrica del sistema di alimentazione di ITER attraverso un’analisi di sensibilità. Ho ricavato le equazioni del modello dalle equazioni ai flussi di potenza in funzione di alcuni parametri rilevanti per l’analisi di sensibilità. Con questo modello ho potuto calcolare alcuni indici come il rapporto critico cortocircuito (Critical Short Circuit Ratio) e il fattore di sensibilità di tensione (Voltage Sensitivity Factor). Nessuna condizione criticha è stata trovata. Il secondo è un modello dinamico (chiamato Dynamic Model), ed è basato sulla formulazione alle variabili di stato e si propone di indagare la stabilità dinamica di tutto il sistema, tra cui anche il sistema di controllo. Tuttavia il sistema di conversione ac/dc e i TCR sono componenti non lineari e discreti, e sono difficili da modellare; considerando i metodi descritti in bibliografia, ho approssimato i fenomeni discreti con funzioni di trasferimento continue, e ho eseguito la linearizzazione attorno ad un punto di equilibrio, utilizzando così l’approccio ai piccoli segnali. Ho adottato un approccio modulare, sviluppando cioè un modello dinamico per ogni sottosistema (i filtri delle armoniche di corrente, i TCR e il sistema di conversione ac/dc). Poi ho costruito modelli numerici dei sottosistemi, con un programma (PSIM) in grado di riprodurre le forme d'onda istantanee per la validazione dei modelli dinamici (implementato con il programma Matlab Simulink, state space tool) attraverso il confronto dei risultati nel dominio della frequenza e del tempo. Infine ho costruito il modello dinamico di tutto il sistema e validato con il modello equivalente in PSIM. Dai risultati delle analisi in frequenza, il modello dinamico è accurato per frequenze inferiori a 50 Hz, ma può essere utilizzato per ottenere qualche informazione circa la stabilità del sistema anche per frequenze fino a 100 Hz. Alcune condizioni di funzionamento instabili sono state individuate e sono dovute alla risonanza tra i filtri e la griglia. Questo modello può essere facilmente implementato con maggiori dettagli per l'intero sistema di alimentazione ITER e può essere uno strumento molto utile e veloce per aiutare la progettazione del sistema di alimentazione e impostare i parametri del sistema di controllo. Come secondo argomento della mia tesi di dottorato, ho studiato la fattibilità tecnologica di utilizzare una tecnologia più avanzata basata su un approccio di rettificazione attiva (Active Front End AFE) per la progettazione del principale sistema di conversione ac/dc (chiamato Acceleration Grid Power Supply AGPS) del sistema di alimentazione del NBI (56 MW , 88 MVAr) per migliorare il suo impatto in sulla rete PPEN in termini di minimizzazione della potenza reattiva e delle armoniche di corrente. In questa parte della tesi, dopo una breve descrizione del progetto di riferimento dell’AGPS basato sulla tecnologia a tiristori, ho descritto il progetto concettuale del sistema di rettificazione dell’AGPS basato sulla soluzione alternativa AFE che ho sviluppato; la sua fattibilità ed i vantaggi e gli svantaggi rispetto alla soluzione tiristori sono stati valutati e discussi. I risultati ottenuti dalle analisi mostrano che la soluzione AFE è fattibile e migliora significativamente l'impatto della AGPS sulla rete PPEN di ITER rispetto a quella a tiristori. Inoltre sono state proposte e discusse alcune modifiche di alcuni parametri del progetto di riferimento per consentire la piena conformità con i requisiti delle specifiche tecniche con l'implementazione della soluzione AFE. Questa tesi è organizzata come segue. Nel capitolo 1, una breve introduzione descrive la ricerca sulla fusione. Il sistema di alimentazione di ITER è descritto nel capitolo 2. La prima parte della tesi di dottorato relativa allo sviluppo dei modelli analitici inizia nel capitolo 3, con la descrizione dello schema equivalente semplificato del sistema di alimentazione ITER. I modelli quasi-statico e dinamico sono descritti rispettivamente nei capitoli 4 e 5, e nel capitolo 6 sono presenti le conclusioni relative a questa parte. La seconda parte della tesi di dottorato relativa allo studio di una soluzione di rettifficazione attiva applicata al sistema d’alimentazione dell griglie (AGPS) dell’iniettore di fasci di neutri inizia nel capitolo 7, che descrive il progetto di riferimento della AGPS basato sulla soluzione tiristori. Poi sono descritte diverse soluzioni AFE e dei sistemi di controllo trovati in bibliografia, e la loro applicazione alla AGPS è discussa nel capitolo 8. Nel capitolo 9 il progetto concettuale della AGPS basato sull’approccio AFE è descritto in dettaglio. Nel capitolo 10 la soluzioni AFE e tiristori sono confrontati in termini di impatto sulla rete PPEN (potenza reattiva e armoniche di corrente

Return and Liquidity Relationships on Market and Accounting Levels in Brazil

ABSTRACT This article discusses profitability-liquidity relationships on accounting and market levels for 872 shares of publicly-traded Brazilian companies, observed between 1994 and 2013. On the market level, the assumption is that share liquidity is able to reduce some of the risks incurred by investors, making them more willing to pay a higher price for liquid shares, which would lower expected market returns. On the accounting level, the basic hypothesis argues that a firm's holding more liquid assets is related to a conservative investment policy, possibly reducing accounting returns for shareholders. Under the assumption of financial constraint, however, more accounting liquidity would allow positive net present value investments to be carried out, increasing future accounting returns, which would positively affect market liquidity and share prices in an efficient market, resulting in a lower market risk/expected return premium. Under the assumption of no financial constraint, however, more accounting liquidity would only represent a carry cost, compromising future accounting returns, which would adversely affect market liquidity and share prices and result in a higher market risk/expected return premium. Among the hypotheses, the presence of a negative market liquidity premium was verified in Brazil, with shares that traded more exhibiting a higher expected market return. On the margins of the major theories on the subject, only two negative relationships between excess accounting liquidity and market liquidity and accounting return, supporting the carry cost assumption for financially unconstrained firms, were verified. In terms of this paper's contributions, there is the analysis, unprecedented in Brazil as far as is known, of the relationship between liquidity and return on market and accounting levels, considering the financial constraint hypothesis to which the firms are subject

Modeling of the magnetic field errors of RFX-mod upgrade

After several years of successful RFX-mod operations, both in RFP and Tokamak configurations, an upgrade of the machine has been conceived. In particular, the vacuum vessel might be removed with the aim of improving passive MHD control and enabling plasma rotation at higher currents. In this paper, a detailed analysis of the new magnetic front-end is presented, with particular emphasis on the computation of the magnetic field errors generated at the poloidal gaps during transient phases of the discharge. At this purpose, a non-linear MHD equilibrium code, MAXFEA, has been used to provide the input data for the 3D electromagnetic analyses in the time domain carried out with the CAFE code. \ua9 2017 Elsevier B.V

New insights into the Shwachman-Diamond Syndrome-related haematological disorder: Hyper-activation of mTOR and STAT3 in leukocytes

Shwachman-Diamond syndrome (SDS) is an inherited disease caused by mutations of a gene encoding for SBDS protein. So far little is known about SBDS exact function. SDS patients present several hematological disorders, including neutropenia and myelodysplastic syndrome (MDS), with increased risk of leukemic evolution. So far, the molecular mechanisms that underlie neutropenia, MDS and AML in SDS patients have been poorly investigated. STAT3 is a key regulator of several cellular processes including survival, differentiation and malignant transformation. Moreover, STAT3 has been reported to regulate neutrophil granulogenesis and to induce several kinds of leukemia and lymphoma. STAT3 activation is known to be regulated by mTOR, which in turn plays an important role in cellular growth and tumorigenesis. Here we show for the first time, to the best of our knowledge, that both EBV-immortalized B cells and primary leukocytes obtained from SDS patients present a constitutive hyper-activation of mTOR and STAT3 pathways. Interestingly, loss of SBDS expression is associated with this process. Importantly, rapamycin, a well-known mTOR inhibitor, is able to reduce STAT3 phosphorylation to basal levels in our experimental model. A novel therapeutic hypothesis targeting mTOR/STAT3 should represent a significant step forward into the SDS clinical practice

Implementation and Review of the Axisymmetric Equilibrium System of RFX-Mod2 within the MARTe2 Framework

A major refurbishment of the toroidal complex of the RFX-mod device is in progress and it will include the removal of the Inconel vacuum vessel and a modification of the stainless steel supporting structure to be made vacuum-tight. The axisymmetric equilibrium control in RFX-mod was responsible for the control of the plasma current, horizontal and vertical position along with its stability and the plasma shape. The new implementation framework, both hardware and software, is described. The system has been fully reviewed and modified, if needed, for its prospective use in RFX-mod2. In order to run tests in an operation-like context, the updated system has also been implemented in the MARTe2 framework, to be deployed for the real-time applications of RFX-mod2. The results of the previous versions were reproduced and the cycle-time requirements were met

Regulation of IL-8 gene expression in gliomas by microRNA miR-93

Background: Different strategies have been proposed to target neoangiogenesis in gliomas, besides those targeting Vascular Endothelial Growth Factor (VEGF). The chemokine Interleukin-8 (IL-8) has been shown to possess both tumorigenic and proangiogenic properties. Although different pathways of induction of IL-8 gene expression have been already elucidated, few data are available on its post-transcriptional regulation in gliomas. Methods: Here we investigated the role of the microRNA miR-93 on the expression levels of IL-8 and other pro-inflammatory genes by RT-qPCR and Bio-Plex analysis. We used different disease model systems, including clinical samples from glioma patients and two glioma cell lines, U251 and T98G. Results: IL-8 and VEGF transcripts are highly expressed in low and high grade gliomas in respect to reference healthy brain; miR-93 expression is also increased and inversely correlated with transcription of IL-8 and VEGF genes. Computational analysis showed the presence of miR-93 consensus sequences in the 3′UTR region of both VEGF and IL-8 mRNAs, predicting possible interaction with miR-93 and suggesting a potential regulatory role of this microRNA. In vitro transfection with pre-miR-93 and antagomiR-93 inversely modulated VEGF and IL-8 gene expression and protein release when the glioma cell line U251 was considered. Similar data were obtained on IL-8 gene regulation in the other glioma cell line analyzed, T98G. The effect of pre-miR-93 and antagomiR-93 in U251 cells has been extended to the secretion of a panel of cytokines, chemokines and growth factors, which consolidated the concept of a role of miR-93 in IL-8 and VEGF gene expression and evidenced a potential regulatory role also for MCP-1 and PDGF (also involved in angiogenesis). Conclusion: In conclusion, our results suggest an increasin