Coils and power supplies design for the SMART tokamak

Agredano-Torres, M., et al.A new spherical tokamak, the SMall Aspect Ratio Tokamak (SMART), is currently being designed at the University of Seville. The goal of the machine is to achieve a toroidal field of 1 T, a plasma current of 500 kA and a pulse length of 500 ms for a plasma with a major radius of 0.4 m and minor radius of 0.25 m. This contribution presents the design of the coils and power supplies of the machine. The design foresees a central solenoid, 12 toroidal field coils and 8 poloidal field coils. Taking the current waveforms for these set of coils as starting point, each of them has been designed to withstand the Joule heating during the tokamak operation time. An analytical thermal model is employed to obtain the cross sections of each coil and, finally, their dimensions and parameters. The design of flexible and modular power supplies, based on IGBTs and supercapacitors, is presented. The topologies and control strategy of the power supplies are explained, together with a model in MATLAB Simulink to simulate the power supplies performance, proving their feasibility before the construction of the system.This work received funding from the Fondo Europeo de Desarollo Regional (FEDER) by the European Commission under grant agreement numbers IE17-5670 and US-15570. Furthermore, it has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under grant agreement no. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission

Mechanical and electromagnetic design of the vacuum vessel of the SMART tokamak

The SMall Aspect Ratio Tokamak (SMART) is a new spherical device that is currently being designed at the University of Seville. SMART is a compact machine with a plasma major radius (R) greater than 0.4 m, plasma minor radius (a) greater than 0.2 m, an aspect ratio (A) over than 1.7 and an elongation (k) of more than 2. It will be equipped with 4 poloidal field coils, 4 divertor field coils, 12 toroidal field coils and a central solenoid. The heating system comprises of a Neutral Beam Injector (NBI) of 600 kW and an Electron Cyclotron Resonance Heating (ECRH) of 6 kW for pre-ionization. SMART has been designed for a plasma current (I) of 500 kA, a toroidal magnetic field (B) of 1 T and a pulse length of 500 ms preserving the compactness of the machine. The free boundary equilibrium solver code FIESTA [1] coupled to the linear time independent, rigid plasma model RZIP [2] has been used to calculate the target equilibria taking into account the physics goals, the required plasma parameters, vacuum vessel structures and power supply requirements. We present here the final design of the SMART vacuum vessel together with the Finite Element Model (FEM) analysis carried out to ensure that the tokamak vessel provides high quality vacuum and plasma performance withstanding the electromagnetic j×B loads caused by the interaction between the eddy currents induced in the vessel itself and the surrounding magnetic fields. A parametric model has been set up for the topological optimization of the vessel where the thickness of the wall has been locally adapted to the expected forces. An overview of the new machine is presented here.This work received funding from the Fondo Europeo de Desarollo Regional (FEDER) by the European Commission under grant agreement numbers IE17-5670 and US-15570. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission

Predictive simulations for plasma scenarios in the SMART tokamak

The SMall Aspect Ratio Tokamak (SMART) is a new spherical machine that is currently being constructed at the University of Seville (Mancini et al., 2021; Agredano-Torres et al., 2021). The operation of SMART will cover three different phases reaching an inductive plasma current (IP) of more than 500 kA, a toroidal magnetic field (BT) of 1 T and a pulse length of 500 ms (Mancini et al., 2021; Agredano-Torres et al., 2021). The main goal of the SMART tokamak is to study high plasma confinement regimes in a broad triangularity range (-0.5≤δ≤0.5) (Doyle et al., 2021; Doyle et al., 2021). While in phase 1 the ohmic heating alone is expected to provide enough power to access the H-mode, in phase 2 and phase 3 the access to the H-mode will be ensured by applying Neutral Beam Injection (NBI) as external heating system. The NBI will consist of one injector at 25 keV and 1 MW of power. The overall design of the NBI, including injection geometry, energy and power have been optimized using the ASCOT5 code (Hirvijoki et al., 2021). The SMART scenarios have been developed with the help of the free boundary equilibrium solver code FIESTA (Cunningham, 2013) coupled to the linear time independent, rigid plasma model RZIP (Lazarus et al., 1990) to calculate the target equilibria for all the different operational phases. To assess the feasibility of those scenarios, predictive modelling needs to be included to evaluate properly the evolution of the temperatures, density profiles for both electrons and ions. To this extent, the 1.5D transport code ASTRA (Pereverzev and Yushmanov, 2002) has been used including models for the ohmic current, bootstrap current and current driven by NBI. This contribution discusses the electron and ion density and temperature profiles obtained for various scenarios for phase 1 and 2 and presents the design study of the NBI.his work received funding from the Fondo Europeo de Desarollo Regional (FEDER) by the European Commission under grant agreement numbers IE17-5670 and US-15570. The authors gratefully acknowledge the financial support of the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 805162).Peer reviewe

Analysis of supercritical carbon dioxide Brayton cycles for a helium-cooled pebble bed blanket DEMO-like fusion power plant

Nuclear fusion is expected to be a clean and almost-unlimited power source in the near future. The first net power demonstration plant (DEMO) is planned to start operation in 2050. The supercritical carbon dioxide (S-CO) Brayton cycle is an excellent candidate for integration with a fusion power plant, such as DEMO, because of its high efficiency at intermediate temperatures and low interaction of coolant with tritium. This work analyses a set of S-CO Brayton cycle layouts for its integration in a DEMO-like fusion power plant, considering the specific requirements and heat availability characteristics. A framework has been developed to integrate the PROCESS code and the numerical solver EES to study the thermal and economic aspects of integrating the different S-CO cycle layouts. In total, 14 layouts have been studied and grouped into a more conservative (DEMO1, pulsed operation) and more advanced (DEMO2, steady-state operation) fusion reactors. The PROCESS code has been used to obtain the DEMO 2018 Baseline, which defines the available power from each heat source and their boundary conditions. This code has also been used to assess the cost of the optimal layout. Thermal storage has been added to the DEMO1 scenario to avoid standby times that could negatively affect the cycle equipment lifetime and efficiency. Besides, these boundary conditions have been extended to account for possible technical improvements by the time of its construction in the DEMO2 scenario. A sensitivity analysis of the most characteristic parameters of the cycles shows a strong dependence on the turbine inlet temperature for all layouts, which is constrained by the reactor material limits. The cycle efficiency (electric power produced before consumptions non-related to the cycle) has been selected as the figure of merit for the optimisation. The results show a 38% cycle efficiency for DEMO1 and 56% for DEMO2 scenarios. These efficiencies drop to 20% and 38% values, respectively, when the reactor and cooling loop power consumptions are considered. These values are obtained for current fusion reactor conceptual designs. The economic analysis shows the economic viability of DEMO2 scenarios.The authors would like to thank J. Morris, M. Kovari and the rest of the PROCESS team of UKAEA for discussion and guidance on using the UKAEA systems code PROCESS for this work. The authors gratefully acknowledge the financial support of the Spanish Ministry of Science, Innovation and Universities (grant FPU17/06273), the H2020 Marie-Sklodowska Curie programme (grant agreement No. 708257) and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 805162)