Magnetic reconnection in fusion plasmas

This thesis is devoted to the experimental study of magnetic reconnection and the related phenomena taking place in the plasmas produced in the RFX-mod device, a flexible toroidal facility for the study of magnetic plasma confinement for nuclear fusion. Magnetic reconnection consists in a rearrangement of the magnetic field topology, which results in a conversion of magnetic energy into heat and kinetic energy of charged particles. It occurs everywhere in the universe, being observed in the evolution of solar flares, in the interaction of solar-wind with the Earth’s magnetosphere and in star accretion disks. Magnetic reconnection occurs also in laboratory plasmas, especially in the self-organization processes in current carrying fusion plasmas. In the latter, magnetic reconnection events are particularly evident during sawtooth activities in tokamaks and in the discrete relaxation events (DREs) in Reversed Field Pinchs (RFPs). They are also involved in island formation associated to the stearing instability. During these phenomena, a topology change of the magnetic field lines occurs, leading to new equilibrium configurations of lower magnetic energy. A complete and detailed understanding of magnetic reconnection is still missing, therefore this phenomenon represents an important topic to be studied for a better understanding of a large variety of astrophysical and laboratory phenomena. The research activity, here presented, is based on the analysis of the experimental RFX-mod data, coming mainly from the in-vessel system of electrostatic and magnetic probes. The experimental analyzes have been performed alongside theoretical modelling activities. The overall activity can be divided in two main parts: in the first one, a characterization of reconnection phenomena in fusion plasmas, with special emphasis on the RFP configuration, has been performed; the second one is dedicated to the study of the rotation of magnetic islands in tokamak circular discharges. The characterization of magnetic reconnection has been carried out by analyzing the DREs in RFP discharges. During these phenomena, a toroidally localized m = 0 magnetic perturbation develops, associated with the formation of a poloidal current sheet. The analysis, performed on the high frequency magnetic perturbation data, has shown that the current sheet is naturally subject to a fragmentation process, determining, in turn, a multiscale electric field structure, which has been suggested to be able to efficiently accelerate charged particles. Indeed, the acceleration of supra-thermal ions, mainly localized at the position where magnetic reconnection occurs, has been observed during the discrete relaxation events. Such particles have energies high enough to induce enhanced fusion reactivity, as evidenced by the time behavior of the detected neutron fluxes. These evidences show that magnetic reconnection can efficiently contribute to the plasma heating of RFP plasmas. The second main research activity has been devoted to the analysis of tearing mode dynamics in the RFX-mod plasmas in tokamak configuration. Tearing modes are resistive instabilities, developing both in tokamak and RFP plasmas. In the presence of resistivity, field lines can tear and reconnect, determining a change in the magnetic topology. The resulting magnetic configuration is characterized by the presence of magnetic islands, which, in turn, favor the radial transport of particles and the confinement reduction. Tearing modes are therefore a concern for magnetic confinement and their characterization is important in order to control them and achieve better confinement performances. The study of tokamak circular discharges has included both the analysis of experimental data and a theoretical modeling of mode rotation based on the two-fluid MHD equations. The comparison of experimental and theoretical results has shown that the rotation of magnetic islands in RFX-mod tokamak plasmas is driven mainly by the diamagnetic drift. The variation of the latter can determine the slowing down of tearing mode rotation, a phenomenon which is sometimes associated with the growth of the instability and the sudden loss of magnetic confinement (disruption). Finally, a characteristic quasi-cyclic oscillation of both amplitude and frequency of tearing mode, known as ‘limit cycle’, has been observed. This behavior has been found to be coupled to sawtooth activities occurring in the plasma core

On the Electrical and Optical Features of the Plasma Coagulation Controller Low Temperature Atmospheric Plasma Jet

We report on the electrical and optical characterization of the Plasma Coagulation Controller (PCC) device, a low temperature atmospheric plasma source for biomedical applications. This device, designed for the study of plasma-induced blood coagulation, has been developed to operate flexibly in several operational conditions, since it is possible to vary the applied voltage V p and the pulse repetition rate f in a quite wide range ( V p range: 2–12 kV, f range: 1–40 kHz). Emission spectroscopy measurements were conducted by varying the line of sight along the axis of helium and neon plasma plumes. The increase of the Reactive Oxygen and Nitrogen Species (RONS) has been observed, as one moves from inside the gas pipe to the outside, as a consequence of the gas mixture with the surrounding air. Furthermore, high-speed photographs of the plasma jet were taken, showing that the plasma is not uniformly distributed in a continuous volumetric region, the plasma being concentrated in localized structures called Pulsed Atmospheric-pressure Plasma Streams (PAPS). The propagation velocities of these objects have been examined, noting that they are not related to the propagation of ion sound waves. Rather, we provide indications that the streamer propagation speed is proportional to the electron drift velocity

Efficacy of conventional versus innovative therapies for treating skin wounds in veterinary medicine

open16siINTRODUCTION: The skin is the largest organ of mammals. The loss of skin integrity may induce important dysfunctions or even death. For superficial wounds, the endogenous healing mechanisms in combination with traditional wound care are sufficient to achieve functional repair. In contrast, in larger wounds, like third and fourth degree burns, chronic wound or deep ulcers it is difficult to obtain the restitutio ad integrum and fibrosis and/or scar tissue develops1,2. The aim of this study was to verify the efficacy of conventional and innovative topic treatments on skin regeneration, induced experimentally in sheep. To achieve this goal different types of investigations (clinical, molecular, histological, immunohistochemical) were performed. METHODS: Six skin lesions (4x4cm) were surgically created on the back of six healthy adult sheep; every single wound was destined, in a randomized way, to one of the following treatments: Acemannan gel, Manuka Honey, hyaluronic acid, Plasma3 (ionized gas), allogeneic mesenchymal stem cells isolated from peripheral blood (PB-MSCs). The sixth wound was the placebo. Biopsies were collected with a surgical punch (0,6x0,6 cm) at time T0, T15 and T40 days. Lesions were clinically evaluated considering the presence and color of wound fluid, the state of hydration, the wound surface/surroundings and other parameters. Histological examinations considered crust formation, re-epithelization and epidermal thickness, dermis edema, extension of granulation tissue, acute and chronic inflammation. Immunohistochemistry for evaluation of inflammation, vascularization and cell proliferation was performed using CD3, CD20, MHCII, von Willebrand factor (vWF) and KI67 antibodies. Furthermore, Real time-PCR investigated genes as V ascular endothelial growth factors (VEGF), Transforming growth factor beta 1(TGFβ1), Vimentin (VIM), Collagen 1α1 (Col1α1) and hair Keratin (hKER). RESULTS: Clinically, the lesions treated with plasma healed more rapidly respect to other treatments and a reduced bacterial load was observed. At T7 wounds treated with stem cells and plasma were less macerated than lesions treated with other therapies. At T15 the wounds treated with hyaluronic acid showed a normal state of hydration while lesions treated with Manuka Honey exhibited a normal hydration from the third week only (Acemannan gel at fourth week). From the second week onwards all wounds did not show presence of fluid and exhibited a dry and clean secondary layer. All lesions, excluded wounds treated with acemannan gel, presented a red (hyaluronic acid and plasma) and dark red (Manuka Honey, PB-MSCs) granulation tissue starting from the first week. Molecular analysis showed a correspondence between clinical and molecular/histologic results. For instance, VEGF mRNA expression confirms angiogenetic events observed at histological level while TGF-β, CD3 and CD20 mRNA/protein expression indicated the presence/absence of inflammation in the used treatments. DISCUSSION & CONCLUSIONS: Innovative therapies led to surprising results regarding regeneration of mammalian skin. Indeed, on the basis of clinical analysis, wounds treated with plasma and MSC healed more rapidly. Further examinations are ongoing in order to elucidate possible mechanisms explaining these differences. REFERENCES: 1S.Y. Broeckx, S. Maes, T. Martinello, et al (2014) Equine epidermis: a source of epithelial-like stem/progenitor cells with in vitro and in vivo regenerative capacities Stem Cells Dev, pp 1134-48. 2J.H. Spaas, C. Gomiero, S.Y. Broeckx, et al (2016) Wound healing markers after autologous and allogeneic epithelial-like stem cell treatment Cytotherapy 2016 (in press). 3E. Martines, M. Zuin, R. Cavazzana, et al. (2009) A novel plasma source for sterilization of living tissues, New J. Phys. 11, 115014.openPatruno, MARCO VINCENZO; Gomiero, Chiara; Martinello, Tiziana; Perazzi, Anna; Gemignani, F; DE BENEDICTIS, GIULIA MARIA; Ferro, Silvia; Zuin, M; Martines, E; Cordaro, Luigi; Brun, Paola; Maccatrozzo, Lisa; Broeckx, Sy; Spaas, Jh; Chiers, K; Iacopetti, IlariaPatruno, MARCO VINCENZO; Gomiero, Chiara; Martinello, Tiziana; Perazzi, Anna; Gemignani, F; DE BENEDICTIS, GIULIA MARIA; Ferro, Silvia; Zuin, M; Martines, E; Cordaro, Luigi; Brun, Paola; Maccatrozzo, Lisa; Broeckx, Sy; Spaas, Jh; Chiers, K; Iacopetti, Ilari

How future surgery will benefit from SARS-COV-2-related measures: a SPIGC survey conveying the perspective of Italian surgeons

COVID-19 negatively affected surgical activity, but the potential benefits resulting from adopted measures remain unclear. The aim of this study was to evaluate the change in surgical activity and potential benefit from COVID-19 measures in perspective of Italian surgeons on behalf of SPIGC. A nationwide online survey on surgical practice before, during, and after COVID-19 pandemic was conducted in March-April 2022 (NCT:05323851). Effects of COVID-19 hospital-related measures on surgical patients' management and personal professional development across surgical specialties were explored. Data on demographics, pre-operative/peri-operative/post-operative management, and professional development were collected. Outcomes were matched with the corresponding volume. Four hundred and seventy-three respondents were included in final analysis across 14 surgical specialties. Since SARS-CoV-2 pandemic, application of telematic consultations (4.1% vs. 21.6%; p < 0.0001) and diagnostic evaluations (16.4% vs. 42.2%; p < 0.0001) increased. Elective surgical activities significantly reduced and surgeons opted more frequently for conservative management with a possible indication for elective (26.3% vs. 35.7%; p < 0.0001) or urgent (20.4% vs. 38.5%; p < 0.0001) surgery. All new COVID-related measures are perceived to be maintained in the future. Surgeons' personal education online increased from 12.6% (pre-COVID) to 86.6% (post-COVID; p < 0.0001). Online educational activities are considered a beneficial effect from COVID pandemic (56.4%). COVID-19 had a great impact on surgical specialties, with significant reduction of operation volume. However, some forced changes turned out to be benefits. Isolation measures pushed the use of telemedicine and telemetric devices for outpatient practice and favored communication for educational purposes and surgeon-patient/family communication. From the Italian surgeons' perspective, COVID-related measures will continue to influence future surgical clinical practice

Notas sobre a Carta de Veneza

This paper presents a critical reading of the Venice Charter, an Icomos key document, fruit of a conference held in 1964. The Charter is often quoted in Brazil but is not always properly understood. The conservation and restoration charters - especially those produced by international institutions - are documents that have an indicatory or, at the most, prescriptive character. They constitute the deontological foundation of many professionals involved in preservation, but they are not recipes for immediate use. In order to elaborate a well-founded reading of the document, its ideas must be understood in connection to the theoretical postulates of the time they were engendered and to the developments of the field. Thus this paper will examine these subjects, commenting and enlightening the Charter's articles and pointing out the origins of specific ideas. It also discusses how the Charter relates to previous documents and their theoretical foundations. This approach, based in a critical analysis, is necessary in order to reach a fuller interpretation of the Charter's indications so that they can be used in the present

Magnetic reconnection in fusion plasmas

This thesis is devoted to the experimental study of magnetic reconnection and the related phenomena taking place in the plasmas produced in the RFX-mod device, a flexible toroidal facility for the study of magnetic plasma confinement for nuclear fusion. Magnetic reconnection consists in a rearrangement of the magnetic field topology, which results in a conversion of magnetic energy into heat and kinetic energy of charged particles. It occurs everywhere in the universe, being observed in the evolution of solar flares, in the interaction of solar-wind with the Earth’s magnetosphere and in star accretion disks. Magnetic reconnection occurs also in laboratory plasmas, especially in the self-organization processes in current carrying fusion plasmas. In the latter, magnetic reconnection events are particularly evident during sawtooth activities in tokamaks and in the discrete relaxation events (DREs) in Reversed Field Pinchs (RFPs). They are also involved in island formation associated to the stearing instability. During these phenomena, a topology change of the magnetic field lines occurs, leading to new equilibrium configurations of lower magnetic energy. A complete and detailed understanding of magnetic reconnection is still missing, therefore this phenomenon represents an important topic to be studied for a better understanding of a large variety of astrophysical and laboratory phenomena. The research activity, here presented, is based on the analysis of the experimental RFX-mod data, coming mainly from the in-vessel system of electrostatic and magnetic probes. The experimental analyzes have been performed alongside theoretical modelling activities. The overall activity can be divided in two main parts: in the first one, a characterization of reconnection phenomena in fusion plasmas, with special emphasis on the RFP configuration, has been performed; the second one is dedicated to the study of the rotation of magnetic islands in tokamak circular discharges. The characterization of magnetic reconnection has been carried out by analyzing the DREs in RFP discharges. During these phenomena, a toroidally localized m = 0 magnetic perturbation develops, associated with the formation of a poloidal current sheet. The analysis, performed on the high frequency magnetic perturbation data, has shown that the current sheet is naturally subject to a fragmentation process, determining, in turn, a multiscale electric field structure, which has been suggested to be able to efficiently accelerate charged particles. Indeed, the acceleration of supra-thermal ions, mainly localized at the position where magnetic reconnection occurs, has been observed during the discrete relaxation events. Such particles have energies high enough to induce enhanced fusion reactivity, as evidenced by the time behavior of the detected neutron fluxes. These evidences show that magnetic reconnection can efficiently contribute to the plasma heating of RFP plasmas. The second main research activity has been devoted to the analysis of tearing mode dynamics in the RFX-mod plasmas in tokamak configuration. Tearing modes are resistive instabilities, developing both in tokamak and RFP plasmas. In the presence of resistivity, field lines can tear and reconnect, determining a change in the magnetic topology. The resulting magnetic configuration is characterized by the presence of magnetic islands, which, in turn, favor the radial transport of particles and the confinement reduction. Tearing modes are therefore a concern for magnetic confinement and their characterization is important in order to control them and achieve better confinement performances. The study of tokamak circular discharges has included both the analysis of experimental data and a theoretical modeling of mode rotation based on the two-fluid MHD equations. The comparison of experimental and theoretical results has shown that the rotation of magnetic islands in RFX-mod tokamak plasmas is driven mainly by the diamagnetic drift. The variation of the latter can determine the slowing down of tearing mode rotation, a phenomenon which is sometimes associated with the growth of the instability and the sudden loss of magnetic confinement (disruption). Finally, a characteristic quasi-cyclic oscillation of both amplitude and frequency of tearing mode, known as ‘limit cycle’, has been observed. This behavior has been found to be coupled to sawtooth activities occurring in the plasma core.Questa tesi è dedicata allo studio sperimentale della riconnessione magnetica e ai fenomeni correlati che si verificano nei plasmi generati da RFX-mod, una macchina sperimentale molto flessibile per lo studio del confinamento magnetico dei plasmi per la fusione termonucleare. La riconnessione magnetica consiste in un riarrangiamento della topologia del campo magnetico, che determina una conversione di energia magnetica in calore e energia cinetica di particelle cariche. Essa si verifica ovunque nell’universo, essendo osservata nell’evoluzione dei brillamenti solari, nella interazione del vento solare con la magnetosfera della Terra e nei dischi di accrescimento delle stelle. La riconnessione magnetica avviene anche nei plasmi di laboratorio, specialmente nei processi di auto-organizzazione che si verificano nei plasma da fusione. In quest’ultimi, gli eventi di riconnessione magnetica sono particolarmente evidenti durante le attività sawtooth dei tokamak e negli eventi di rilassamento discreti (DRE) nei reversed field pinch (RFP) e sono coinvolti nella formazione di isole magnetiche associate alle instabilità ‘tearing’. Durante questi processi si verifica un cambiamento topologico delle linee del campo magnetico, che porta a nuove configurazioni di equilibrio di energia magnetica inferiore. Una comprensione completa e dettagliata della riconnessione magnetica è ancora mancante. Tale fenomeno rappresenta un importante argomento da studiare per una migliore comprensione di una grande varietà di fenomeni astrofisici e di laboratorio. Il lavoro di analisi presentato in questa tesi è principalmente basato sull’analisi dei dati sperimentali di RFX-mod, provenienti da sistemi di sonde elettrostatiche e magnetiche, posizionate all’interno della camera da vuoto. Le analisi sperimentali sono state affiancate anche da attività di modellizazione teorica. L’attività complessiva può essere divisa in due parti principali: nella prima è stata svolta una caratterizzazione dei fenomeni di riconnessione nei plasmi in configurazione RFP; la seconda è dedicata allo studio della rotazione delle isole magnetiche in scariche tokamak circolari. La caratterizzazione della riconnessione magnetica è stata effettuata analizzando i DRE in scariche RFP. Durante questi fenomeni, la perturbazione magnetica determina la formazione di modi toroidalmente localizzati m = 0, associati alla formazione di strutture di corrente poloidale. L’analisi ha dimostrato che queste strutture sono naturalmente soggette a frammentazione, la quale determina a sua volta una struttura di campo elettrico multi-scala che, come mostrato in letteratura, è in grado di accelerare efficacemente le particelle cariche. In effetti, è stata osservata l’accelerazione di ioni sovratermici, particolarmente evidenti nelle posizioni in cui si verifica la riconnessione magnetica, durante gli eventi discreti di rilassamento. Tali particelle hanno energia abbastanza alta da indurre una reattività da fusione, come dimostrano gli andamenti temporali dei flussi neutronici. Queste evidenze sperimentali dimostrano che la riconnessione magnetica può contribuire in modo efficace al riscaldamento del plasma nei dispositivi RFP. La seconda attività di ricerca principale è stata dedicata all’analisi della dinamica dei modi tearing nei plasmi di RFX-mod in configurazione tokamak. Tali modi tearing sono instabilità resistive, che si sviluppano sia nei plasmi tokamak che in quelli RFP. In presenza di resistività, le linee di campo possono rompersi e riconnettere, determinando un cambiamento nella topologia magnetica. La configurazione magnetica risultante è caratterizzata dalla presenza di isole magnetiche che, a loro volta, favoriscono il trasporto radiale di particelle e la riduzione del confinamento magnetico. I modi tearing costituiscono quindi un problema per il confinamento magnetico e la loro caratterizzazione è importante per poter proporre metodi di controllo al fine di migliorare le prestazioni del confinamento. Lo studio delle scariche tokamak ha incluso sia l’analisi dei dati sperimentali che una modellazione teorica della rotazione dei modi tearing basata sulle equazioni MHD a due fluidi. Il confronto dei risultati sperimentali con le previsioni del modello teorico ha mostrato che la rotazione delle isole magnetiche nei plasmi tokamak di RFX-mod è guidata principalmente dalla deriva diamagnetica. La variazione di quest’ultima può determinare, associate ad una modifica dei profili di pressione, al rallentamento della rotazione di tali modi, un fenomeno talvolta associato alla crescita delle instabilità e che può portare alla disruzione. Infine, è stata osservata una caratteristica oscillazione quasi-ciclica di ampiezza e frequenza dei modi tearing, chiamata ‘ciclo limite’. Questo comportamento è dimostrato essere accoppiato alla cosiddetta attività ‘sawtooth’ che si verifica nella regione centrale del plasma

Studio dei processi di riconnessione magnetica in plasmi di interesse termonucleare

La tesi si dedica allo studio dei processi di riconnessione magnetica nel plasma di RFX-mod. Sono analizzati gli effetti magnetici e cinetici causati dai processi di riconnessione confrontandoli con gli studi dei plasmi in ambito solare e astrofisico. Particolare attenzione è rivolta al processo di frammentazione dei current sheet prodetti dalla riconnessione.ope

The Role of Thermal Effects in Plasma Medical Applications: Biological and Calorimetric Analysis

Plasma Medicine tools exploit the therapeutic effects of the exposure of living matter to plasma produced at atmospheric pressure. Since these plasmas are usually characterized by a non-thermal equilibrium (highly energetic electrons, low temperature ions), thermal effects on the substrate are usually considered negligible. Conversely, reactive oxygen and nitrogen species (RONS), UV radiation and metastables are thought to play a major role. In this contribution, we compare the presence of thermal effects in different operational regimes (corresponding to different power levels) of the Plasma Coagulation Controller (PCC), a plasma source specifically designed for accelerating blood coagulation. In particular, we analyze the application of PCC on human blood samples (in vitro) and male Wistar rats tissues (in vivo). Histological analysis points out, for the highest applied power regime, the onset of detrimental thermal effects such as red cell lysis in blood samples and tissues damages in in-vivo experiments. Calorimetric bench tests performed on metallic targets show that the current coupled by the plasma on the substrate induces most of measured thermal loads through a resistive coupling. Furthermore, the distance between the PCC nozzle and the target is found to strongly affect the total power

Studio dei processi di riconnessione magnetica in plasmi di interesse termonucleare

La tesi si dedica allo studio dei processi di riconnessione magnetica nel plasma di RFX-mod. Sono analizzati gli effetti magnetici e cinetici causati dai processi di riconnessione confrontandoli con gli studi dei plasmi in ambito solare e astrofisico. Particolare attenzione è rivolta al processo di frammentazione dei current sheet prodetti dalla riconnessione