Overview of interpretive modelling of fusion performance in JET DTE2 discharges with TRANSP

In the paper we present an overview of interpretive modelling of a database of JET-ILW 2021 D-T discharges using the TRANSP code. The main aim is to assess our capability of computationally reproducing the fusion performance of various D-T plasma scenarios using different external heating and D-T mixtures, and to understand the performance driving mechanisms. We find that interpretive simulations confirm a general power-law relationship between increasing external heating power and fusion output, which is supported by absolutely calibrated neutron yield measurements. A comparison of measured and computed D-T neutron rates shows that the calculations' discrepancy depends on the absolute neutron yield. The calculations are found to agree well with measurements for higher performing discharges with external heating power above ∼20 $\mathrm{MW}$, while low-neutron shots display an average discrepancy of around +40% compared to measured neutron yields. A similar trend is found for the ratio between thermal and beam-target fusion, where larger discrepancies are seen in shots with dominant beam-driven performance. We compare the observations to studies of JET-ILW D discharges, to find that on average the fusion performance is well modelled over a range of heating power, although an increased unsystematic deviation for lower-performing shots is observed. The ratio between thermal and beam-induced D-T fusion is found to be increasing weakly with growing external heating power, with a maximum value of $\gtrsim$1 achieved in a baseline scenario experiment. An evaluation of the fusion power computational uncertainty shows a strong dependence on the plasma scenario type and fusion drive characteristics, varying between ±25% and 35%. D-T fusion alpha simulations show that the ratio between volume-integrated electron and ion heating from alphas is $\lesssim$10 for the majority of analysed discharges. Alphas are computed to contribute between ∼15% and 40% to the total electron heating in the core of highest performing D-T discharges. An alternative workflow to TRANSP was employed to model JET D-T plasmas with the highest fusion yield and dominant non-thermal fusion component because of the use of fundamental radio-frequency heating of a large minority in the scenario, which is calculated to have provided ∼10% to the total fusion power.This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No. 101052200—EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. This work has been part-funded by the EPSRC Energy Programme with grant number EP/W006839/1. The Barcelona Supercomputing Center part of this work has contributed through the Spanish National R&D Project PID2019-110854RB-I00 funded through MCIN/AEI/10.13039/501100011033. In addition BSC are grateful for the support received from the Departament de Recerca i Universitats de la Generalitat de Catalunya via the Research Group Fusion Group with code: 2021 SGR 00908. The Laboratorio Nacional de Fusión contribution was funded in part via the Spanish National R&D Project PID2021-127727OB-I00 funded through MCIN/AEI /10.13039/501100011033.Peer Reviewed"Article signat per 43 autors/es: Ž. Štancar, K.K. Kirov, F. Auriemma, H.-T. Kim, M. Poradziński, R. Sharma, R. Lorenzini, Z. Ghani, M. Gorelenkova, F. Poli, A. Boboc, S. Brezinsek, P. Carvalho, F.J. Casson, C.D. Challis, E. Delabie, D. Van Eester, M. Fitzgerald, J.M. Fontdecaba, D. Gallart, J. Garcia, L. Garzotti, C. Giroud, A. Kappatou, Ye.O. Kazakov, D.B. King, V.G. Kiptily, D. Kos, E. Lerche, E. Litherland-Smith, C.F. Maggi, P. Mantica, M.J. Mantsinen, M. Maslov, S. Menmuir, M. Nocente, H.J.C. Oliver, S.E. Sharapov, P. Sirén, E.R. Solano, H.J. Sun, G. Szepesi and JET Contributors"Postprint (published version

Effect of the relative shift between the electron density and temperature pedestal position on the pedestal stability in JET-ILW and comparison with JET-C

The electron temperature and density pedestals tend to vary in their relative radial positions, as observed in DIII-D (Beurskens et al 2011 Phys. Plasmas 18 056120) and ASDEX Upgrade (Dunne et al 2017 Plasma Phys. Control. Fusion 59 14017). This so-called relative shift has an impact on the pedestal magnetohydrodynamic (MHD) stability and hence on the pedestal height (Osborne et al 2015 Nucl. Fusion 55 063018). The present work studies the effect of the relative shift on pedestal stability of JET ITER-like wall (JET-ILW) baseline low triangularity (\u3b4) unseeded plasmas, and similar JET-C discharges. As shown in this paper, the increase of the pedestal relative shift is correlated with the reduction of the normalized pressure gradient, therefore playing a strong role in pedestal stability. Furthermore, JET-ILW tends to have a larger relative shift compared to JET carbon wall (JET-C), suggesting a possible role of the plasma facing materials in affecting the density profile location. Experimental results are then compared with stability analysis performed in terms of the peeling-ballooning model and with pedestal predictive model EUROPED (Saarelma et al 2017 Plasma Phys. Control. Fusion). Stability analysis is consistent with the experimental findings, showing an improvement of the pedestal stability, when the relative shift is reduced. This has been ascribed mainly to the increase of the edge bootstrap current, and to minor effects related to the increase of the pedestal pressure gradient and narrowing of the pedestal pressure width. Pedestal predictive model EUROPED shows a qualitative agreement with experiment, especially for low values of the relative shift

Particle transport in Reversed Field Pinch plasmas

This thesis is aimed at studying the transport of particles in magnetically confined thermonuclear plasma. The understanding of the transport properties in devices for fusion plasmas is one of the key factor to keep the correct operating conditions in a future fusion reactor. Indeed one of the open issues in magnetic fusion studies, which prevents the realization of an efficient thermonuclear reactor, is the high level of energy and particle transport in the direction perpendicular to the confining magnetic field. This phenomenon reduces confinement properties and has to be solved in order to obtain energy from thermonuclear fusion processes. The amount of particle and energy transport experimentally observed cannot be interpreted in the framework of the classical theory. Understanding the underlying physics of this anomalous transport remains the outstanding critical physical issue in fusion research. Nowadays it is generally accepted that anomalous transport is partially due to magnetic chaos owing to the magnetic perturbations of the equilibrium magnetic fields. The Reversed Field Pinch (RFP) configuration, with its wide spectrum of magnetic perturbations, offers a suitable testbed to verify the theory and to reveal the inner mechanism underlying the transport in fusion magnetic devices. The magnetic perturbations, also dubbed dynamo or MagnetoHydroDynamic (MHD) modes, sustain the RFP configuration against the resistive magnetic diffusion. Unfortunately they have global negative effects: as already stated they lead to the stochastization of the equilibrium magnetic field over a large part of the plasma core and moreover their phase locking generates an interference pattern that results in a global distortion of the plasma column: the so-called Locked Mode (LM) that has its maximum effect at a well defined toroidal position. Many techniques have been tested with the aim of reducing the MHD modes. The most effective are the Pulsed Poloidal Current Drive (PPCD) that modifies the internal current profile and the active control of the radial field at the edge by means of a system of active coils, the so-called Virtual Shell (VS). All the transport mechanisms acting inside the plasma modify the shape of the density profile. The density is measured by means of interferometer: a non-perturbative diagnostic that utilizes electromagnetic waves to probe the plasma. A part of this thesis will be addressed to determine the global particle diffusion coefficients in relation to the magnetic perturbations amplitude. This analysis has been carried on TPE-RX device: a large RFP machine sited in Tsukuba (Jp). In order to study the global confinement properties, the transport analysis has been carried out analyzing data collected far from to the LM, where its local effect could be neglected. A transport code (in our case TED, acronym of TEmperature and Density) computes the density profile according to transport parameters supplied by the user. The computed profile is compared to the experimental one, determining the correctness of the model assumed to provide the transport coefficients. With this analysis it has been confirmed that damping the MHD modes amplitude by means of the PPCD the particle confinement globally improves and the diffusion coefficient is strongly reduced in the central zone of the plasma. This result has been further confirmed by the density behaviour during pellet injection experiments, where the particles released by the pellet in PPCD discharges are better confined inside the plasma than in plasmas with standard magnetic perturbations. The dynamo modes, as already stated, generate a global distortion of the Last Close Flux Surface (LCFS) of the plasma: the LM. The plasma cross section results shrunk in a wide toroidal region of about 100° and bulging in another region of the similar toroidal range. Moreover an helical distortion of the column with magnetic lines that directly hit the wall is present. The VS system installed at RFX-mod (the largest RFP device in the world with design maximum plasma current of 2 MA, located in Padova) provides an important reduction of the helical perturbation but is less effective on healing the shrinking of the LCFS, highlighting for the first time its effects on plasma confinement. The two toroidal regions with different cross section have been characterized studying the density profile, the density fluctuations and the magnetic fluctuations: the shrunk region shows an improved transport, providing the first experimental evidence of toroidal asymmetric confinement properties in an RFP plasma. Moreover the RFX-mod pulses are affected by spontaneous reorganization of the internal current and magnetic profiles, the so-called Dynamo Relaxation Events (DREs). The density behaviour and the magnetic topology during the DREs have been analyzed, confirming the different nature of the shrunk and the bulging region of the plasma

Economic assessment of different operational reactor cycle structures in a pulsed DEMO-like power plant

Abstract The operative cycle of a pulsed fusion power plant is composed by a sequence of phases whose duration cannot be arbitrarily chosen due to both technical and physical constraints. A pulsed DEMO-like power plant is modeled with the FRESCO code and the optimization of the operative cycle structure is carried out with a genetic algorithm in order to find the economic optimal solution. Specifically, the duration of each cycle phase (current ramp up and ramp down, plasma heating, burn, central solenoid recharge) is changed randomly in order to identify the set of phase durations that minimizes the cost of electricity. The results show that the cheapest electricity is generated when the phases composing the dwell time are minimized. Furthermore room exists to extend the burn time and reduce the number of cycles over the plant lifetime by up to 35% with negligible effects on the COE. It also emerges that the power plant under study generates cheaper electricity when operating in partially inductive mode. Moreover the optimum flat top duration is a function of the heating and current drive costs

An Application of SOL 400 to Support the Design of Damaged CFRP Stiffened Panels

The aim of this work is to show an application of the SOL 400 of MSC Nastran® in order to investigate the final failure response of damaged composite stiffened panels in post buckling regime, by using progressive failure analysis (PFA) methodology. This methodology has been applied in order to support the design of composite stiffened panels by predicting the initiation of the local failure and its propagation up to the final collapse of the panel, in presence of local damage (barely visible impact damage, BVID) and in post-buckling regime. Discrete damages have been considered in the skin of the panel. According to the indications enclosed in many guidelines for the preliminary design of composite structures, a simplified model of BVID has been considered in this work, in particular by simulating this kind of damage with a hole of 1/4 inches in diameter. The collapse load of the panel has been evaluated both for different locations of a single damage and for multi-damage scenarios. The results of the analyses illustrate the combined effect of the reduction of the panel stiffness and of the damage propagation, and also the sensitivity of the residual strength of the panel with respect to different damage locations and damage density

First measurements of the multichannel far-infrared polarimeter on RFX-mod

A multichannel far-infrared (FIR) polarimeter has been recently installed and improved in RFX-mod to measure the Faraday rotation angle along vertical chords on a poloidal plasma section. Polarimetric data, associated with measurements of the electron density, permit the reconstruction of the poloidal magnetic field profile, Bp . The entire diagnostic is described and its main sections outlined. Emphasis is placed on the work performed on the polarimeter to reduce the fluctuations affecting the old diagnostic signals and to increase the S/N ratio. In the recent installation of the polarimeter the optical line was more carefully designed and the mirror holders have been made in insulating material to avoid any interaction with the variable magnetic fields. Moreover all the optics have been fixed on an inertial granite platform. Examples of the first Faraday angle measurements performed on five chords are presented and discussed. The measured Faraday rotation angles are compared to a theoretically calculated value, based on the mu-and-p model, showing a good agreement between experimental and predicted data in the central region of the plasma. The comparison between experimental and predicted data is reported and discussed in the present work

Study of the sloshing In a fuel tank using CFD and EFD approaches

This paper is focused on the study of the sloshing in the fuel tank of vehicles. As well known, fluid dynamic in an automotive fuel tank have to be studied and optimized to allow the correct fuel suction in all driving conditions, prevent undesired slosh noise and limit its influence on fuel vapor formation and management. Experimentation to predict the sloshing with a good accuracy depends on the ability to replace real working parameters and conditions like accelerations, decelerations, slope variations and rotations. This paper shows results obtained studying the sloshing inside a reference tank with computational fluid-dynamic and experimental approaches. The test bench for automotive fuel tank, employed in this analysis, has been designed by Moog Inc. on specification from Fiat Chrysler Automobiles and it is aimed at covering the wider possible range of dynamic conditions. It basically consists of a hexapod, which uses six independent actuators arranged in three triangles and connecting a base and a top platform, thus allowing all six DOFs. Above the top platform is mounted a tilt table with two additional actuators, to extend pitch and roll envelope, thus the name of “8-DOF bench”. A dedicated CFD model has been built up using a CFD commercial code. The model has been integrated with the multiphase tool in order to correctly reply the real free surface. Results, numerical and experimental, have been post-processed with Matlab® comparing percentage gaps of the free surfaces each other. The comparison has shown a good agreement. This research is the result of a scientific collaboration between the Industrial Engineering Department of University of Naples Federico II and FCA Fiat Chrysler Automobiles