118,307 research outputs found
Prediction and analysis of JET fusion performance based on reduced first principle transport models
No full textThe design of a Tokamak device is carried out initially with a 0D approach aiming at defining the plasma engineering parameters estimated with the help of empirical scaling laws, and the technological limits of the device components. The assessment of local parameters (1D) is then required to define the optimal plasma performance during the entire time evolution of the discharge. In this contest, the transport of energy and particles in fusion plasmas is one of the main actor in determining the evolution of a plasma scenario both in present experiments and in future reactors.
The Joint European Torus (JET) experiment has operated in deuterium (D) and tritium (T) main ion plasma composition in 1997 (DTE1) and in 2021 (DTE2). The most important differences between the two experimental campaigns are related to the plasma facing components, carbon (C) in DTE1 and Be/W in DTE2, the increased additional heating power, and the presence of improved diagnostics, especially at the plasma edge which is determinant in the global plasma performance. After DTE1 the high levels of T retention in the C-wall have been considered unacceptable for a reactor, leading to the substitution of the C-wall with a metallic wall in the design of the International Tokamak Experimental Reactor (ITER). DTE2 campaign at JET aimed at studying D-T plasmas in the closest conditions to ITER operations. Differently from DTE1, the recent campaign focused on the stationarity of the performance and on addressing ITER-relevant aspects such as α-particles physics, plasma wall interactions and plasma heating schemes. In preparation to D-T operations, a wide experimental and modelling activity has been performed at JET in order to optimise the plasma scenarios.
The focus of this thesis is the extrapolation in D-T main ion plasma composition of the JET baseline scenario. The latter is a high confinement mode (H-mode) plasma, characterized by the presence of Edge Localized Modes (ELMs), where the confinement relies on high plasma current. In ITER D-T operations, the baseline scenario is envisaged to achieve a gain factor, defined as the ratio between the fusion power and the input power, Q = Pfus/Pin ≈ 10. The objective of the thesis has been achieved through extensive integrated modelling, based on the reduced first principles transport models QuaLiKiz and TGLF employing different assumptions, and in a wide range of plasma operating conditions. QuaLiKiz and TGLF transport models have been validated in reference D plasmas, and their extrapolation capability with different plasma parameters has been tested by performing blind predictions. The results of the predictive modelling have been compared with the experimental data and analysed in order to address the sensitivity of the plasma scenario to the experimental boundary conditions. The QuaLiKiz transport model has also been validated against the experimental results produced at JET in DTE1.
Before the start of the DTE2 campaign, an estimate of the particle sources required to sustain a 50-50 D-T baseline plasma has been obtained. This result has provided inputs to the JET control team in the preparation phase of the baseline fuelling scheme. This contribution boosted JET D-T operations without spending experimental time, neutron and T budget.
The results of the predictive modelling performed in preparation to DTE2 are presented and discussed. The sensitivity of the predictions to plasma parameters
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such as current, toroidal magnetic field, pedestal confinement and impurity content are analysed together with the sensitivity to the available amount of auxiliary heating power.
The experimental results obtained in DTE2 by the baseline scenario are also presented and discussed. In the last part of this thesis, the implications of the modelling assumptions performed on D pulses will be compared with the assumptions done on D-T discharges with the experimental boundary conditions. The key parameters needed for reliable predictions of future experiments are discussed both in D and D-T main ion plasma composition. The estimate of particle sources obtained before the DTE2 campaign are adjusted to reproduce the experimental conditions, leading to an estimate of the different fuelling channels and an evaluation of the wall sources.
The thesis is organised as follows:
• In Chapter 1 we introduce fusion as a potential energy source.
• In Chapter 2 we describe the Tokamak configuration and the JET experi- mental device, and we present a first comparison between the different D-T experimental campaign, and between the different scenarios prepared for DTE2.
• In Chapter 3 we introduce the issue of energy and particle transport in Tokamaks, we present the theoretical background and the state of the art of transport analysis. The models used in this work are presented together with the different assumptions implemented in JINTRAC.
• In Chapter 4 we present and discuss the validation of the reduced first principle transport models performed on D pulses. The extrapolations in D-T plasma mixture are presented with their sensitivity to the operating conditions.
• In Chapter 5 we present and discuss the baseline results obtained in DTE2. The predictive simulations are improved by adopting the actual boundary conditions of the D-T experiments, and we discuss the impact of the different assumptions on the modelling of D plasmas extrapolated to D-T plasma mixture. We show the limits of predictive simulations in integrated modelling, and we use the predictive simulations to obtain an estimate of the different fuelling sources in the D-T experiments
Impurity behaviour in JET high-current baseline scenario for Deuterium, Tritium and Deuterium-Tritium plasmas
No full textTo support future ITER operation, experimental campaigns at the Joint European Torus (JET) with an ITER-like wall (tungsten divertor and beryllium main chamber) in pure deuterium (D), tritium (T) and Deuterium-Tritium (D-T) were performed. One of the most important challenges in recent years was the development of two main scenarios that investigated different approaches to achieve the high fusion power as well as good plasma confinement (Garzotti et al., 2023). The first one, so-called baseline scenario is relying on high plasma current (Ip≈3.5 MA), normalized beta βN < 2 and safety factor q95 ≈ 3 (Garzotti et al., 2023). On the other hand, the second one, so-called Hybrid scenario is operating at lower plasma current (flat-top Ip ≤ 2.6 MA) and density with respect to the baseline, higher normalized beta βN > 2 and safety factor q95 ≈ 4.8 (Hobirk et al., 2023). In this paper we focus on the impurity behaviour analysis for the baseline discharges at Ip = 3.5 MA and BT = 3.3 T with D, T and DT plasmas, in which the gas and power waveform were optimized to achieve the best possible performance. In particular, we study the impact of total heating power (Ptot + Palpha), flat-top gas flow and ELM (edge localized modes) frequency on mid-Z (Nickel (Ni), Copper (Cu)) and high-Z (Tungsten (W)) impurities. In addition, we compared the two best performing pulses of the baseline scenario (Ip = 3.5MA, BT = 3.3 T and Pin ≈ 35 MW) in D and DT in order to identify the causes responsible for the increase in radiation during the DT pulse, which led to an early plasma termination. All presented results rely on the data collected by the VUV as well as the bolometry system. Detailed analysis indicates that in the baseline scenario, higher radiation, which is most likely due to the tungsten (W), is observed for T and DT plasmas in comparison to D. Moreover, for the two best performing baseline pulses, tomographic reconstructions show that the radiated power density is mainly emitted from the low field side (LFS) of the plasma and W does not accumulate in the plasma center (Telesca et al., 2024)
Integrated modelling of the ramp-up phase of the hybrid scenario for the JT-60SA tokamak
No full textJT-60SA is a large superconducting tokamak built and operated by Europe and Japan under the Broader Approach Satellite Tokamak Program. The machine is designed to support the exploitation of ITER and the investigation of key physics and engineering issues for future demonstration power plants. The main operational parameters of the plasma scenarios, envisaged for the Integrated Research Phase and described in the JT-60SA Research Plan [1], were simulated using the 0.5-dimensional code METIS and the 2-dimensional equilibrium code ACCOME, as reported in [2]. Moreover, the feasibility of the flat-top phase of these scenarios was confirmed by means of 1.5-dimensional transport codes [3, 4]. However, it is of primary importance to simulate the ramp-up in order to assess whether the main plasma parameters foreseen for the scenario are achievable and under which range of assumptions.
The goal of this study is to model the ramp-up phase of the scenario 4-2 (hybrid) (3.5 MA/2.28 T, q95=4.4, βN =3.0) with the JINTRAC [5] suite of codes and the Bohm/gyro-Bohm [6] semi-empirical transport model, taking as starting point the modelling performed with the METIS code. We are predicting the current density, ion density, ion temperature and electron temperature, self-consistently with the plasma equilibrium. The speed of the current ramp-up is imposed, while a feedback loop acting on the gas puff rate is controlling the density in order to follow the target volume averaged density. The heating power deposition profiles and current densities of ECRH and NBI are modelled with the GRAY [7] and PENCIL [8] codes respectively, injecting the power of 37 MW (7 MW of ECRH and 30 MW of NBI).
The results of the modelling in terms of plasma kinetic profiles evolution, L-H transition, flux consumption and neutral beam shine-through are presented for different levels of ECRH power and different NBI switching on times. JINTRAC results are fairly close to the ones predicted by METIS, however the L-H transition, predicted by Martin scaling, is found earlier in JINTRAC. The electron temperature profiles are also very sensitive to the different shape of the ECRH power deposition computed by GRAY, with respect to the Gaussian-like profiles imposed by METIS.
References
[1] JT-60SA Research Plan, version 4.0 www.jt60sa.org/pdfs/JT-60SA_Res_Plan.pdf (September 2018)
[2] G. Giruzzi et al 2020 Plasma Phys. Control. Fusion 62 014009
[3] L. Garzotti et al 2018 Nucl. Fusion 58 026029
[4] J. Garcia et al 2014 Nucl. Fusion 54 093010
[5] Romanelli M. et al 2014 Plasma and Fusion Research 9 3403023
[6] M Erba et al 1997 Plasma Phys. Control. Fusion 39 261
[7] D. Farina, Fusion Science and Technology 154, 52 (2007)
[8] C.D. Challis et al 1989 Nucl. Fusion 29 5
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Impurity behaviour in JET high-current baseline scenario for Deuterium, Tritium and Deuterium-Tritium plasmas
No full textTo support future ITER operation, experimental campaigns at the Joint European Torus (JET) with an ITER-like wall (tungsten divertor and beryllium main chamber) in pure deuterium (D), tritium (T) and Deuterium-Tritium (D-T) were performed. One of the most important challenges in recent years was the development of two main scenarios that investigated different approaches to achieve the high fusion power as well as good plasma confinement (Garzotti et al., 2023). The first one, so-called baseline scenario is relying on high plasma current (Ip≈3.5 MA), normalized beta βN < 2 and safety factor q95 ≈ 3 (Garzotti et al., 2023). On the other hand, the second one, so-called Hybrid scenario is operating at lower plasma current (flat-top Ip ≤ 2.6 MA) and density with respect to the baseline, higher normalized beta βN > 2 and safety factor q95 ≈ 4.8 (Hobirk et al., 2023).
In this paper we focus on the impurity behaviour analysis for the baseline discharges at Ip = 3.5 MA and BT = 3.3 T with D, T and DT plasmas, in which the gas and power waveform were optimized to achieve the best possible performance. In particular, we study the impact of total heating power (Ptot + Palpha), flat-top gas flow and ELM (edge localized modes) frequency on mid-Z (Nickel (Ni), Copper (Cu)) and high-Z (Tungsten (W)) impurities. In addition, we compared the two best performing pulses of the baseline scenario (Ip = 3.5MA, BT = 3.3 T and Pin ≈ 35 MW) in D and DT in order to identify the causes responsible for the increase in radiation during the DT pulse, which led to an early plasma termination. All presented results rely on the data collected by the VUV as well as the bolometry system. Detailed analysis indicates that in the baseline scenario, higher ra- diation, which is most likely due to the tungsten (W), is observed for T and DT plasmas in comparison to D. Moreover, for the two best performing baseline pulses, tomographic reconstructions show that the radiated power density is mainly emitted from the low field side (LFS) of the plasma and W does not accumulate in the plasma center (Telesca et al., 2024)
Square Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Letter from unknown writer to Jesse L. Boyce
No full textLetter to Jesse L. Boyce from unknown author (possibly Jack) about the investigation into the powder magazine located in the Grand Canyon. Some personal news is included in the letter such as the writer's marriage to the daughter of C.A. Taylor, former Supervisor of Cochise County
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Particle balance during edge biasing experiments in the reversed field pinch RFX
No full textThe results of an edge biasing experiment in RFX are reported. The particle balance has been interpreted by a zero-dimensional model which allows the particle confinement time to be adjusted in order to reproduce the experimental behaviour of the plasma density. It is found that, despite the substantial reduction of the electrostatic transport by a factor of three, the particle confinement time does not increase by more than 35%. This behaviour has been interpreted as an indication that another loss channel must be considered which is responsible for a particle flux twice as large as that carried by electrostatic fluctuations and it has been identified in the pertubation due to the locked mode
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