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343 results on '"Ragona, Riccardo"'

1. Conceptual Study of a Collective Thomson Scattering Diagnostic for SPARC

Author

Mentz-Jørgensen, Mads, Ragona, Riccardo, Korsholm, Søren B., and Rasmussen, Jesper

Subjects
Physics - Plasma Physics
Abstract

The SPARC tokamak is a compact high-field device that will operate at high plasma density with the aim to demonstrate net fusion energy. The experimentally unexplored plasma conditions in SPARC will require a carefully selected set of diagnostics for plasma monitoring and control. Here we explore conceptual design options and potential measurement capabilities of a collective Thomson scattering diagnostic at SPARC. We show that a 140 GHz X-mode CTS system is the most attractive option in terms of optimizing the signal-to-noise ratio and limiting sensitivity to refraction, as well as from a technological readiness perspective. Such a setup can provide core-localized measurements of the fusion -born alpha distribution function, main-ion temperature and toroidal rotation, fuel-ion ratio, and 3He content with relevant spatio-temporal resolution. Our proposed diagnostic layout can in principle be integrated into SPARC and could provide a valuable addition to its diagnostic suite at limited development costs and time., Comment: 26 pages, 10 figures, submitted to Nuclear Fusion

Published
2024

2. Two-plasmon decay of microwaves in low temperature magnetized laboratory plasmas.

Author

Kølsen de Wit, Johan, Senstius, Mads Givskov, Pedersen, Asbjørn Clod, Ragona, Riccardo, and Nielsen, Stefan Kragh

Subjects
MICROWAVES, PLASMONS (Physics), LOW temperature plasmas, SIMULATION methods & models, MAGNETIC confinement
Abstract

Observations from magnetically confined fusion experiments have in the past decades revealed instances of two-plasmon decay instabilities (TPDIs) between injected 2nd harmonic X-mode waves and trapped upper hybrid (UH) waves near half frequency of the injected wave. We present and compare growth rates of TPDIs computed from reduced analytical models and particle-in-cell (PIC) simulations in low-temperature plasmas, emulating conditions found in more accessible controllable laboratory devices. The growth rates obtained from simulations agree with our modeling, confirming that we can model TPDIs using both analytical models and PIC simulations in low-temperature plasmas. Furthermore, the growth rates are on the order of 0.01 ns−1 to 0.1 ns−1 for injected waves with intensity of 103 W/cm2, which indicates that we can expect to see signals of TPDIs in controllable laboratory plasma devices. [ABSTRACT FROM AUTHOR]

Published
2024
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5. Variability of clinical target volume delineation for rectal cancer patients planned for neoadjuvant radiotherapy with the aid of the platform Anatom-e

Author

Franco, Pierfrancesco, Arcadipane, Francesca, Trino, Elisabetta, Gallio, Elena, Martini, Stefania, Iorio, Giuseppe Carlo, Piva, Cristina, Moretto, Francesco, Ruo Redda, Maria Grazia, Verna, Roberta, Tseroni, Vassiliki, Bona, Cristina, Pozzi, Gabriele, Fiandra, Christian, Ragona, Riccardo, Bertetto, Oscar, and Ricardi, Umberto

Published
2018
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11. Lung stereotactic ablative body radiotherapy: A large scale multi-institutional planning comparison for interpreting results of multi-institutional studies

Author

Giglioli, Francesca Romana, Strigari, Lidia, Ragona, Riccardo, Borzì, Giuseppina R., Cagni, Elisabetta, Carbonini, Claudia, Clemente, Stefania, Consorti, Rita, El Gawhary, Randa, Esposito, Marco, Falco, Maria Daniela, Fedele, David, Fiandra, Christian, Frassanito, Maria Cristina, Landoni, Valeria, Loi, Gianfranco, Lorenzini, Elena, Malisan, Maria Rosa, Marino, Carmelo, Menghi, Enrico, Nardiello, Barbara, Nigro, Roberta, Oliviero, Caterina, Pastore, Gabriella, Quattrocchi, Mariagrazia, Ruggieri, Ruggero, Redaelli, Irene, Reggiori, Giacomo, Russo, Serenella, Villaggi, Elena, Casati, Marta, and Mancosu, Pietro

Published
2016
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12. Characterisation of Electron Cyclotron Wall Conditioning plasma in ASDEX Upgrade

Author

Wauters, Tom, primary, Buermans, Johan, additional, Cavalier, Jordan, additional, Huett, Emanuel, additional, Ragona, Riccardo, additional, Svoboda, Jakub, additional, Bobkov, Volodymyr V, additional, Griener, Michael, additional, Jacobsen, Asger Schou, additional, Kallenbach, Arne, additional, Likonen, Jari, additional, Loarer, Thierry, additional, Lunt, Tilmann, additional, Nielsen, S Kragh, additional, Pitts, Richard A, additional, Ricci, Daria, additional, Rohde, Volker, additional, Stober, Joerg, additional, Schneider, Philip Adrian, additional, and Usoltceva, Mari, additional

Published
2023
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23. Development and applications of an ICRH antenna design & performance analysis tool accounting for the edge plasma. Comparison of an in-port and travelling wave array solution for fusion reactors.

Author

Louis, Yves, Ongena, Jef, Van Schoor, Michael, Haelterman, Marc, Knaepen, Bernard, Vergote, Maarten, Ragona, Riccardo, Van Eester, Dirk, Crombe, Kristel, Louche, Fabrice, Maquet, Vincent, Louis, Yves, Ongena, Jef, Van Schoor, Michael, Haelterman, Marc, Knaepen, Bernard, Vergote, Maarten, Ragona, Riccardo, Van Eester, Dirk, Crombe, Kristel, Louche, Fabrice, and Maquet, Vincent

Abstract

While far from being technologically mature, fusion is an attractive low-carbon source ofenergy that could play an important role in the future world electricity and heat productionmix. Following this target, the next step after demonstrating a net energy gain in fusion willbe the construction of a demonstration fusion reactor to produce heat or electricity.To reach a burning state, where the energy of the fusion products is sufficient to sustainthe fusion reaction, one first needs to bring the fusion fuel above an energy threshold. Oneof the experimentally proven techniques used in present day tokamaks to heat the plasmafuel launches microwaves in the Ion Cyclotron Range of Frequencies (ICRF) in the low temperatureand density edge of fusion devices using an antenna. This heating method, calledIon Cyclotron Resonance Heating (ICRH), is cost effective, has a mature radio-frequencysource technology and comes with highly flexible and efficient heating scenarios. ICRH alsocovers other important fusion applications like current drive, turbulence stabilization in theplasma, wall conditioning, etc.For these reasons, the installation of an ICRH system is considered for future fusiondemonstration power plants like DEMO or ARC. However, future fusion reactor conditionsare quite challenging for ICRH. The two most stringent aspects of a reactor lies (i) in theexpected low density profile in the edge leading to a low coupling of power to the plasma(ii) the restricted space available for auxiliary components inside the reactor’s chamber andsurrounding wall structures. The other challenges faced are the installation, availability andmaintainability of these components in a reactor environment. On top of these challenges theICRH system should minimize the plasma wall interactions and the impurity release inducedduring its operation.Two very different ICRH systems are proposed for the next reactor generation. One relieson high power high density antennas inserted in a port of the fu, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

Published
2022

34. Modeling of the Traveling Wave Antenna in view of the ICRF heating of DEMO

Author

Messiaen Andre and Ragona Riccardo

Subjects
Physics, QC1-999
Abstract

An upgraded version of the fast semi-analytical code ANTITER is used to model the refueled TWA sections of any arbitrary number of straps facing a low coupling plasma profile. The code computes the Y, Z and S matrices of the antenna array from which the performances of the TWA sections and of their feeding system are deduced as a function of the geometry of the TWA. The model incorporates the feeding of the section by a resonant ring circuit recirculating the output power of each section. Approximate scaling laws guiding the design are derived for the antenna main parameters. A first optimization of the design for the DEMO antenna section is made and the resulting power capability of a DEMO system evaluated.

Published
2017
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35. Advanced ponderomotive description of electron acceleration in ICRF discharge initiation

Author

Wauters Tom, Tripský Matej, Lyssoivan Anatoli, Louche Fabrice, Möller Sören, Ragona Riccardo, and Van Eester Dirk

Subjects
Physics, QC1-999
Abstract

This contribution proposes a new approach for the ponderomotive description of electron acceleration in ICRF discharge initiation. The motion of electrons in the parallel electric field Ez is separated into a fast oscillation and a slower drift around the oscillation centre. Three terms are maintained in the Taylor expansion of the electric field (0th , 1st and 2nd order). The efficiency for electron acceleration by Ez (z, t) is then assessed by comparing the values of these terms at the slow varying coordinate z0 . When (i) the 0th order term is not significantly larger than 1st order term at the reflection point, or when (ii) the 2nd order term is negative and not sufficiently small compared to the 1st order term at the reflection point, then the electron will gain energy in the reflection. An example for plasma production by the TOMAS ICRF system is given. Following the described conditions it can be derived that plasma production is (i) most efficient close to the antenna straps (few cm's) where the field gradient and amplitude are large, and (ii) that the lower frequency field accelerates electrons more easily for a given antenna voltage.

Published
2017
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36. Study of a distributed ICRF antenna system in DEMO

Author

Ragona Riccardo and Messiaen André

Subjects
Physics, QC1-999
Abstract

Different feeding options for distributed ICRF antenna systems in DEMO are analysed and compared, based on detailed circuit modelling. Voltages and currents (amplitude and phase) are computed for each element of the array. The power delivered by the feeding networks is evaluated characterizing each system. Although the results presented are for a small number of radiating elements, the procedure can be scaled to any arbitrary number of straps and feeding connections. Among the three options analysed (i.e. allfed; distributed; resonant ring) the resonant ring feeding appears to be the most suitable configuration for a traveling wave array distributed antenna system in the DEMO reactor.

Published
2017
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37. Characterization of neutral particle fluxes from ICWC and ECWC plasmas in the TOMAS facility

Author

Moon, Sunwoo, Petersson, Per, Brunsell, Per R., Rubel, Marek, Goriaev, Andrei, Ragona, Riccardo, Moeller, Soren, Brezinsek, Sebastijan, Nicolai, Dirk, Linsmeier, Christian, Kovtun, Yurii, Wauters, Tom, Moon, Sunwoo, Petersson, Per, Brunsell, Per R., Rubel, Marek, Goriaev, Andrei, Ragona, Riccardo, Moeller, Soren, Brezinsek, Sebastijan, Nicolai, Dirk, Linsmeier, Christian, Kovtun, Yurii, and Wauters, Tom

Abstract

Electron- (ECWC) and ion- (ICWC) cyclotron wall conditioning are essential means for controlled fusion to modify the surface state of plasma-facing components in order to reduce impurity generation and fuel accumulation in the wall. Development of ECWC and ICWC requires characterization of neutral particle fluxes generated in discharges, because neutrals enhance the homogeneity of the conditioning, which may contribute to remote or shadowed areas, especially in the presence of a permanent magnetic field (e.g. W7-X, ITER). A time-of-flight neutral particle analyzer (ToF-NPA) with 4.07 m flight distance is employed to measure time- and energy-resolved low energetic (<1 keV) neutral particle distributions. The ToF-NPA setup tested at the EXTRAP T2R reversed field pinch was installed at the TOMAS toroidal plasma facility to determine low energy neutral particle fluxes while investigating the impact of the gas pressure in the instrument and compatibility with low count rates during EC- and ICWC discharges. TOMAS has a major radius of 0.78 m and provides various plasma operation conditions: toroidal magnetic field up to 0.12 T, EC frequency 2.45 GHz with the power of 0.6-6 kW, IC frequency of 10-50 MHz with the power of up to 6 kW. Early results on the characterization of three phases (EC only, EC + IC, and IC only) of hydrogen discharges demonstrate: (i) the low energy (10-725 eV) neutrals distribution has been determined by the NPA system, (ii) the mixed EC + IC phase produces the highest population of neutral particles, while the EC only provides one order of magnitude lower rate, (iii) the neutrals produced in IC only have higher average energy (28 eV) than EC only (7 eV) and EC + IC (16 eV)., QC 20211004

Published
2021
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38. Ragona, Riccardo

Author

Ragona, Riccardo and Ragona, Riccardo

Published
2021

41. Dose prescription in SBRT for early-stage non-small cell lung cancer: are we all speaking the same language?

Author

Merlotti, Anna, primary, Bonomo, Pierluigi, additional, Ragona, Riccardo, additional, Trovò, Marco, additional, Alongi, Filippo, additional, Mazzola, Rosario, additional, Vigna Taglianti, Riccardo, additional, Gianello, Luca, additional, Reali, Alessia, additional, Bergesio, Fabrizio, additional, Lucio, Francesco, additional, Boriano, Alberto, additional, De Maggi, Adriano, additional, and Russi, Elvio, additional

Published
2020
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42. Supplementary_Materials – Supplemental material for Dose prescription in SBRT for early-stage non-small cell lung cancer: are we all speaking the same language?

Author

Merlotti, Anna, Bonomo, Pierluigi, Ragona, Riccardo, Trovò, Marco, Alongi, Filippo, Mazzola, Rosario, Taglianti, Riccardo Vigna, Gianello, Luca, Reali, Alessia, Bergesio, Fabrizio, Lucio, Francesco, Boriano, Alberto, Maggi, Adriano De, and Russi, Elvio

Subjects
Medicine
Abstract

Supplemental material, Supplementary_Materials for Dose prescription in SBRT for early-stage non-small cell lung cancer: are we all speaking the same language? by Anna Merlotti, Pierluigi Bonomo, Riccardo Ragona, Marco Trovò, Filippo Alongi, Rosario Mazzola, Riccardo Vigna Taglianti, Luca Gianello, Alessia Reali, Fabrizio Bergesio, Francesco Lucio, Alberto Boriano, Adriano De Maggi and Elvio Russi in Tumori Journal

Published
2020
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46. Study of the ohmic losses of a traveling wave antenna section in view of application on DEMO

Author

Maquet, Vincent, Messiaen, André A.M., Ragona, Riccardo, Maquet, Vincent, Messiaen, André A.M., and Ragona, Riccardo

Abstract

A multi-section Traveling Wave Antenna (TWA) is one of the presently proposed options for Ion Cyclotron Resonance Heating (ICRH) of DEMO. This option would reduce the antenna power density while enabling sufficient heating in low coupling situations by increasing the number of radiating straps. Such an antenna consists of several sections each fed in a resonant ring configuration. In order to guide future engineering requirements, a detailed computation of the ohmic losses due to finite conductivity of the antenna components of one TWA section is performed for different loading conditions. The geometry of the TWA section is compatible with the presently proposed layout of DEMO and is modeled by the finite element code Microwave Studio (MWS) taking into account the finite resistivity of its constituent materials. As MWS cannot handle plasma loading, it has been implemented in the code by a layer in front of the antenna with the real part of the permittivity of water and open boundary conditions to reproduce single-pass absorption conditions and capture the main antenna loading characteristics of a plasma. The loading conditions are then varied changing the distance between the antenna and this layer. An equivalent antenna resistance characterizing those ohmic losses as a function of frequency, material resistivity and loading has been computed. This resistance can be linked to the skin depth resistance and compared to the radiation resistance in order to assess the performance of the antenna for a given choice of material. These results are then extrapolated to a real plasma loading based on ANTITER results for different plasma profiles and water dielectric load distance., SCOPUS: cp.p, DecretOANoAutActif, info:eu-repo/semantics/published

Published
2020

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