1,720,993 research outputs found
Analysis of activation and damage of ITER material samples expected from DD/DT campaign at JET
No full textActivation inventories, decay heat, contact dose rate and radiation induced damage are important nuclear quantities which need to be assessed on a reliable basis for the safe operation of a fusion nuclear power reactor and its decommissioning. This paper describes the calculations performed in the frame of the EUROfusion JETS programme of the activation and dose rate of materials irradiated in the Inner/Outer Long Term Irradiation Station ((I-O)LTIS) during DD and DTE2 campaigns. In the frame of JET3, samples of real ITER materials used in the manufacturing of several different, mainly in-vessel and vessel, components will be irradiated at JET during DTE2 such as ITER-grade W, Be, CuCrZr,316L(N), and also functional materials used in diagnostics and heating systems for radiation damage studies. Neutron induced activities and contact dose rates at shutdown are calculated by means of the FISPACT code using the irradiation scenario specified for JET, with the neutron flux densities and spectra provided by the preceding MCNP neutron transport calculation for (I-O)LTIS box. (C) 2017 EURATOM. Published by Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Analiza in modeliranje emisije žarkov gama v plazmah velikih tokamakov
No full textUnderstanding the physics of fast ions in a fusion plasma is widely regarded as one of the crucial tasks for the reliable operation of fusion tokamak reactors. Measurements on tokamaks have shown that gamma rays are produced when fast ions react either with the plasma fuel ions or with main plasma impurities such as beryllium, carbon, oxygen and nitrogen. Spectroscopy of these gamma rays can be used to measure fusion rates in the plasma or to determine the behaviour and confinement of fusion reaction products, such as alpha particles.
The dissertation focuses on the development of a modelling methodology for the creation of a realistic plasma gamma ray source for Monte Carlo transport simulations in large tokamaks. The methodology consists of several steps. First step is the generation of validated plasma parameters using the code TRANSP based on experimental measurements. Second step is the generation of sampling distribution functions from the calculated plasma parameters, such as the calculation of the source position distribution function based on the reaction rate densities for the gamma ray emitting reaction. Third step is the creation of a realistic plasma gamma ray source for the code MCNP to simulate gamma ray transport. The validation of the developed methodology is performed using gamma ray spectra measured with the tangential gamma ray spectrometer during two JET three-ion radio frequency heating scenario discharges performed in the JET 2019 Deuterium experimental campaign. For validation, the calculated plasma gamma ray spectrum was combined with the neutron induced prompt gamma ray background originating in the vacuum vessel and scaled to absolute values by calculating the total number of plasma gamma ray and neutron emitting reactions. The comparison shows good agreement between the shape and absolute values of the spectra at the end of a long detector line of sight. An analysis of a deuterium-tritium neutron commissioning discharge is also performed to test and prepare the developed methodology for the deuterium-tritium experimental campaign at JET. Validation and testing of the developed methodology for the plasma gamma ray source at JET provides a basis for using the developed methodology to support the development of future tokamaks such as ITER and DEMO.Zadrževanje plazemskih ionov ter razumevanje njihovih fizikalnih principov velja za eno ključnih nalog za zanesljivo delovanje fuzijskih tokamak reaktorjev. Pretekle meritve na tokamakih so pokazale, da pri reakcijah hitrih ionov bodisi s plazemskimi ioni ali z nečistočami v plazmi, kot so berilij, ogljik, kisik in dušik, nastanejo žarki gama. Spektroskopija teh žarkov gama omogoča merjenje hitrosti fuzijskih reakcij v plazmi ali določitev zadrževanja fuzijskih reakcijskih produktov, kot so alfa delci v plazmi.
Doktorska disertacija se osredotoča na razvoj metodologije modeliranja realističnega plazemskega izvora žarkov gama v velikih tokamakih za transportne simulacije z metodo Monte Carlo. Metodologija je sestavljena iz številnih korakov. Prvi korak je izračun realističnih plazemskih parametrov na osnovi eksperimentalnih meritev z uporabo kode TRANSP. Drugi korak je generiranje verjetnostnih porazdelitev za Monte Carlo metodo na podlagi izračunanih plazemskih parametrov, kot je na primer izračun verjetnostne porazdelitve za določitev položaja izvora žarkov gama na podlagi gostote reakcijske hitrosti za reakcije, ki izsevajo te žarke gama. Tretji korak je generiranje realističnega izvora plazemskih žarkov gama za transportno simulacijo žarkov gama s programom MCNP. Validacija razvite metodologije je bila izvedena s pomočjo meritev spektrov žarkov gama v JET tangencialnem spektrometru, opravljanih med dvema JET pulzoma v devterijevi eksperimentalni kampanji leta 2019. Izračunani spekter plazemskih žarkov gama so bili za validacijo združeni z žarki gama nastalih pri nevtronskih reakcijah s tokamak komponentami in normalizirani na absolutne vrednosti z izračunom števila reakcij, ki oddajajo plazemske žarke gama in številom proizvedenih nevtronov. Primerjava je pokazala dobro ujemanje tako v obliki spektra kot tudi v absolutnih vrednostih v tangencialnem detektorju, ki se nahaja na koncu dolgega vidnega polja v biološkem ščitu tokamaka JET. V nalogi je bila izvedena tudi primerjava z meritvami žarkov gama sproščenih pri zlivanju devterija in tritija za pripravo razvite metodologije na JET devterij-tritij eksperimentalno kampanjo. Validacija in analiza razvite metodologije izvora plazemskih žarkov gama na tokamaku JET predstavlja osnovo za bodočo uporabo razvite metodologije pri podpori razvoja bodočih tokamakov, kot sta tokamaka ITER in DEMO
Analiza aktivacije vode po obsevanju z nevtroni
No full textWater as a primary coolant will play an important role in the performance of fusion reactors, as after being irradiated and activated, it causes an ionising radiation field throughout the facility. Therefore, additional protection and shielding for the instruments and personnel must be adequately considered. As part of this dissertation and in direct support of ITER, the KATANA irradiation facility, which utilises a closed-water activation loop, was designed, constructed, experimentally evaluated and studied, and successfully commissioned in 2024 at the TRIGA Mark II research reactor at the Jožef Stefan Institute in Slovenia. In this dissertation, a comprehensive overview of the KATANA, which serves as a well-defined and stable high-energy (6 MeV - 7 MeV) gamma and ∼1 MeV neutron source, is given, including the design optimisation analysis, final design, experimental set-up, detector systems. The physical characteristics of KATANA were assessed by analyses of neutron transport simulations leading to activity calculations in connection with a conventional analytical approach, without using CFD calculations. To complement the computational analyses, a series of first experiments was performed to determine the operational characteristics of the KATANA, i.e. characterisation of the neutron flux within the irradiation component, dose rate measurements, spectrum characterisation of the activated water, and response to a change in reactor power and flow rate. Since the performance of the pump and thus the flow rate was gradually improved several times during the commissioning phase, not all experiments were carried out under the same conditions. KATANA facility demonstrated the desired operational characteristics in terms of high and stable water flow rates and high activity values of the observed isotopes 16N, 17N and 19O, which is essential for minimising the experimental uncertainties. The calculations and first experiments performed at KATANA provided in-depth knowledge into the operation and capabilities of the facility and essential data to serve as a basis for further, more detailed experiments. The ultimate goal of KATANA is to perform benchmark-quality experiments, e.g. validation of fluid activation codes, and to establish itself as a reference facility for the calibration of high-energy gamma-ray detectors, which will significantly support the operation of ITER and other future water-cooled fusion reactors. The work has also been done within the framework of EUROfusion as part of the work package Preparation of ITER Operation.Voda kot primarno hladilno sredstvo bo imela pomembno vlogo pri delovanju fuzijskih reaktorjev, imenovanih tokamakih, saj se po obsevanju z nevtroni aktivira, tj. postane radioaktivna, pri čemer se izsevajo žarki gama visokih energij in nevtroni. Tako povzroča ionizirajoče sevanje okoli vodnega hladilnega sistema. To lahko segreje superprevodne tuljave, poškoduje elektroniko ali izpostavi ljudi sevanju. To sevanje je eden glavnih virov ionizirajočega sevanja izven biološkega ščita med delovanjem tokamaka, zato je ključnega pomena dobro poznavanje tega pojava, pri čemer je omenjena orodja za simulacijo in izračun ravni sevanja okoli aktivirane vode nujno treba validirati (preveriti) z eksperimenti. V okviru doktorske disertacije in neposredne podpore fuzijskemu reaktorju ITER je bila na reaktorju TRIGA na Inštitutu Jožef Stefan zasnovana, proučena, zgrajena, eksperimentalno preverjena in in proti koncu leta 2023 uspešno zagnana nova naprava, imenovana KATANA, z zaprto vodno zanko za aktivacijo vode. Obsevalna naprava KATANA služi kot dobro definiran in stabilen vir žarkov gama visokih energij (6 MeV – 7 MeV) ter nevtronov in omogoča izvajanje številnih eksperimentov, povezanih z aktivirano vodo. V disertaciji je podan celovit pregled obsevalne naprave KATANA, ki vključuje predanalize za optimizacijo zasnove, podroben opis končne zasnove, eksperimentalno postavitev ter sisteme detektorjev. Fizikalne lastnosti KATANE so bile ocenjene z analizami simulacij transporta nevtronov, ki so vodile do izračunov aktivnosti. V izračunih je bil uporabljen konvencionalni analitični pristop brez upoštevanjem izračunov dinamike tekočin (CFD). Kot podpora računskim analizam in za določitev operativnih značilnosti KATANE je bila izvedena serija prvih eksperimentov, tj. karakterizacija nevtronskega fluksa znotraj notranjega obsevalnega Polža, meritve hitrosti doznih polj v okolici naprave, karakterizacija spektra aktivirane vode in odziv KATANE na spremembo moči reaktorja ter odziv na spremembo pretoka. Ker se je zmogljivost črpalke in s tem maksimalni dosežen pretok med fazo zagona postopoma izboljševal, vsi eksperimenti niso bili izvedeni pod enakimi pogoji. KATANA je pokazala želene operativne značilnosti v smislu visokih in stabilnih pretokov vode ter visokih aktivnosti opazovanih izotopov 16N, 17N in 19O, kar je bistveno za zmanjšanje eksperimentalnih negotovosti. Izračuni in prvi eksperimenti, izvedeni na KATANI, so zagotovili poglobljeno znanje o delovanju in zmogljivostih obsevalne naprave ter bistvene podatke, ki služijo kot osnova za nadaljnje, podrobnejše eksperimente. Končni cilj KATANE je izvajanje referenčnih eksperimentov, tj. eksperimentalna validacija računskih orodij za izračun sevalnega polja v okolici hladilnega sistema, in uveljavitev kot referenčni objekt za kalibracijo detektorjev žarkov gama pri visokih energijah, kar bo znatno podprlo obratovanje ITER in DEMO ter drugih prihodnjih fuzijskih reaktorjev, hlajenih z vodo
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Evalvacija metod za kalibracijo moči velikih tokamakov
Get PDFFusion reactors based on the fusion of deuterium (D) and tritium (T) emit large amounts of 14 MeV neutrons. As exactly one neutron is emitted per such fusion reaction, neutron yield measurements are the most direct way for the determination of the released energy. Accurate measurements of neutron output will be important in fusion power plants for the determination of a reactor’s power output, tritium accountability in the system, the assessment of neutron damage of components, and for the assessments of the dose rates in the humanaccessible parts of the machine. Additionally, reliable information on a reactor’s neutron emission is important for fusion plasma analyses.
The dissertation consists of an introduction and three chapters describing the author’s work related to the calibration of neutron yield detectors at Joint European Torus (JET). Whereas most of the work was performed for the DD and DT calibrations of the tokamak JET, the lessons learned are relevant for other machines as well. The focus of the work are thus the calculations performed in support of the absolute calibrations of the neutron detectors in large fusion reactors. The details of the neutron source properties of the neutron generator used in the calibration of JET’s neutron detectors to 14 MeV neutrons were simulated. This neutron source description of the neutron generator was then used in calculations in support of the calibration experiments. Together with measurements, these calculations resulted in the calibration factors for JET’s main neutron detectors. Additionally, the use of a newly released variance reduction tool ADVANTG was tested for the speed-up of the simulations of the fission chamber responses in JET-relevant geometry. These analyses showed that the computational intensity of these simulations can be significantly reduced. The author’s main contributions presented in this dissertation are the detailed reproduction of the neutron emission properties of a neutron generator, computational quantification of corrections applied to the measured calibration factors, and one of the first independent tests of the ADVANTG code on the model of the tokamak.Fuzijski reaktorji, ki delujejo na osnovi zlivanja jeder devterija (D) in tritija (T), sprostijo velike količine nevtronov z energijo 14 MeV. Pri vsaki reakciji zlivanja devterija in tritija se sprosti en nevtron, zato so meritve števila sproščenih nevtronov, oziroma meritve pridelka nevtronov, najbolj neposreden način za merjenje sproščene energije. V bodočih fuzijskih elektrarnah bodo meritve izseva nevtronov pomembne za meritve fuzijske moči med obratovanjem, spremljanje in nadzor količine tritija v sistemu, ocene poškodb komponent kot posledice interakcije z nevtroni ter ocene hitrosti doz v delih naprave, kjer je predviden dostop delavcev. Poleg tega je natančno poznavanje nevtronskega izseva pomembno tudi pri analizi fuzijske plazme.
Disertacija vsebuje uvod v problematiko in tri poglavja, ki opisujejo avtorjevo delo povezano s kalibracijo detektorjev nevtronov tokamaka JET. Čeprav je bila večina dela opravljenega v podporo kalibraciji detektorjev nevtronov tokamaka JET na nevtrone sproščene v DD in DT fuzijskih reakcijah, so rezultati in izkušnje relevantne tudi za druge velike fuzijske reaktorje. Delo se tako osredotoča na izračune v podporo kalibracijam detektorjev nevtronov velikih fuzijskih naprav. Predstavljeno je simuliranje produkcije nevtronov v generatorju DT nevtronov, izračuni v podporo kalibracijskim eksperimentom in testiranje relativno novega programa ADVANTG za pospeševanje simulacij Monte Carlo na geometrijah relevantnih za JET, ki lahko bistveno zmanjša računsko zahtevnost simulacij v podporo kalibraciji detektorjev nevtronov. Avtorjevi glavni prispevki, predstavljeni v disertaciji, pa so reprodukcija lastnosti generatorja nevtronov v nevtronskih simulacijah, računska kvantifikacija popravkov izmerjenih kalibracijskih faktorjev in eno od prvih neodvisnih testiranj programa ADVANTG na modelu tokamaka
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