| 1. |
- Labit, B., et al.
(author)
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Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade
- 2019
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:8
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Journal article (peer-reviewed)abstract
- © 2019 Institute of Physics Publishing. All rights reserved. Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (ne,sep/nG ∼ 0.3), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened.
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| 2. |
- Coda, S., et al.
(author)
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Physics research on the TCV tokamak facility: From conventional to alternative scenarios and beyond
- 2019
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Journal article (peer-reviewed)abstract
- The research program of the TCV tokamak ranges from conventional to advanced-tokamak scenarios and alternative divertor configurations, to exploratory plasmas driven by theoretical insight, exploiting the device's unique shaping capabilities. Disruption avoidance by real-time locked mode prevention or unlocking with electron-cyclotron resonance heating (ECRH) was thoroughly documented, using magnetic and radiation triggers. Runaway generation with high-Z noble-gas injection and runaway dissipation by subsequent Ne or Ar injection were studied for model validation. The new 1 MW neutral beam injector has expanded the parameter range, now encompassing ELMy H-modes in an ITER-like shape and nearly non-inductive H-mode discharges sustained by electron cyclotron and neutral beam current drive. In the H-mode, the pedestal pressure increases modestly with nitrogen seeding while fueling moves the density pedestal outwards, but the plasma stored energy is largely uncorrelated to either seeding or fueling. High fueling at high triangularity is key to accessing the attractive small edge-localized mode (type-II) regime. Turbulence is reduced in the core at negative triangularity, consistent with increased confinement and in accord with global gyrokinetic simulations. The geodesic acoustic mode, possibly coupled with avalanche events, has been linked with particle flow to the wall in diverted plasmas. Detachment, scrape-off layer transport, and turbulence were studied in L- and H-modes in both standard and alternative configurations (snowflake, super-X, and beyond). The detachment process is caused by power 'starvation' reducing the ionization source, with volume recombination playing only a minor role. Partial detachment in the H-mode is obtained with impurity seeding and has shown little dependence on flux expansion in standard single-null geometry. In the attached L-mode phase, increasing the outer connection length reduces the in-out heat-flow asymmetry. A doublet plasma, featuring an internal X-point, was achieved successfully, and a transport barrier was observed in the mantle just outside the internal separatrix. In the near future variable-configuration baffles and possibly divertor pumping will be introduced to investigate the effect of divertor closure on exhaust and performance, and 3.5 MW ECRH and 1 MW neutral beam injection heating will be added.
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| 3. |
- Chellaï, O., et al.
(author)
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Millimeter-wave beam scattering and induced broadening by plasma turbulence in the TCV tokamak
- 2021
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 61:6
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Journal article (peer-reviewed)abstract
- The scattering of millimeter-wave beams from electron density fluctuations and the associated beam broadening are experimentally demonstrated. Using a dedicated setup, instantaneous deflection and (de-)focusing of the beam due to density blobs on the beam path are shown to agree with full-wave simulations. The detected time-averaged wave power transmitted through the turbulent plasma is reproduced by the radiative-transfer model implemented in the WKBeam code, which predicts a ∼50% turbulence-induced broadening of the beam cross-section. The role of core turbulence for the considered geometry is highlighted.
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| 4. |
- Agredano Torres, Manuel, et al.
(author)
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Coils and power supplies design for the SMART tokamak
- 2021
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In: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 168, s. 112683-112683
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Journal article (peer-reviewed)abstract
- 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.
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| 5. |
- Mancini, A., et al.
(author)
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Mechanical and electromagnetic design of the vacuum vessel of the SMART tokamak
- 2021
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In: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 171
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Journal article (peer-reviewed)abstract
- 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 () greater than 0.4 m, plasma minor radius () greater than 0.2 m, an aspect ratio () over than 1.7 and an elongation () 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 () of 500 kA, a toroidal magnetic field () 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 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.
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| 6. |
- Doyle, S.J., et al.
(author)
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Magnetic equilibrium design for the SMART tokamak
- 2021
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In: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 171, s. 112706-112706
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Journal article (peer-reviewed)abstract
- The SMall Aspect Ratio Tokamak (SMART) device is a new compact (plasma major radius Rgeo≥0.40 m, minor radius a≥0.20 m, aspect ratio A≥1.7) spherical tokamak, currently in development at the University of Seville. The SMART device has been designed to achieve a magnetic field at the plasma center of up to Bϕ=1.0 T with plasma currents up to Ip=500 kA and a pulse length up to τft=500 ms. A wide range of plasma shaping configurations are envisaged, including triangularities between −0.50≤δ≤0.50 and elongations of κ≤2.25. Control of plasma shaping is achieved through four axially variable poloidal field coils (PF), and four fixed divertor (Div) coils, nominally allowing operation in lower-single null, upper-single null and double-null configurations. This work examines phase 2 of the SMART device, presenting a baseline reference equilibrium and two highly-shaped triangular equilibria. The relevant PF and Div coil current waveforms are also presented. Equilibria are obtained via an axisymmetric Grad-Shafranov force balance solver (Fiesta), in combination with a circuit equation rigid current displacement model (RZIp) to obtain time-resolved vessel and plasma currents.
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| 7. |
- Doyle, S J, et al.
(author)
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Single and double null equilibria in the SMART Tokamak
- 2021
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In: Plasma Research Express. - : IOP Publishing. - 2516-1067. ; 3:4
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Journal article (peer-reviewed)abstract
- The SMall Aspect Ratio Tokamak (SMART) device is a novel, compact (Rgeo = 0.42 m, a = 0.22 m, A 1.70) spherical tokamak, currently under development at the University of Seville. The SMART device is being developed over 3 phases, with target on-axis toroidal magnetic fields between 0.1 ≼ Bf ≼ 1.0 T, and target plasma currents of between 35 ≼ Ip ≼ 400 kA; with phases 2 and 3 enabling access to a wide range of elongations (κ ≼ 2.30) and triangularities (− 0.50 ≼ δ ≼ 0.50). SMART employs four internal divertor coils with two internal and two external poloidal field coils, enabling operation in lower-single, upper-single and double-null configurations. This work examines phase 3 of the SMART device, presenting a prospective L-mode discharge scenario without external heating, before examining five highly-shaped equilibria, including: two double null triangular configurations, two single null triangular configurations and a baseline double null configuration. All equilibria are obtained via an axisymmetric Grad-Shafranov force balance solver (Fiesta), in combination with a circuit equation rigid current displacement model (RZIp) to obtain time-resolved vessel and plasma currents.
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| 8. |
- Segado-Fernandez, J., et al.
(author)
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Analysis and design of the central stack for the SMART tokamak
- 2023
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In: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 193
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Journal article (peer-reviewed)abstract
- The SMall Aspect Ratio Tokamak (SMART) is a new spherical machine that is currently under construction at the University of Seville aimed at exploring negative vs positive triangularity prospects in Spherical Tokamaks (ST). The operation of SMART will cover three phases, with toroidal fields Bϕ≤ 1 T, inductive plasma currents up to Ip= 500 kA and a pulse length up to 500 ms, for a plasma with R = 0.4 m, a = 0.25 m and a wide range of shaping configurations (aspect ratio, 1.4 < R/a < 3, elongation, κ≤ 3, and average triangularity, -0.6 ≤δ≤ 0.6). The magnet system of the tokamak is composed by 12 Toroidal Field Coils (TFC), 8 Poloidal Field Coils (PFC) and a Central Solenoid (CS). With such operating conditions, the design of the central stack, usually a critical part in spherical tokamaks due to space limitations, presents notable challenges. The current SMART central stack has been designed to operate up to phase 2 and it comprises the inner legs of the TFC, surrounded by the CS, two supporting rings, a central pole and a pedestal. To achieve the plasma parameters of this phase (Bϕ=0.4 T with inductive Ipup to 200 kA), the high currents required, combined with the low aspect-ratio of the machine lead to high forces on the conductors that represent an engineering challenge. The loads expected in the central stack are a centring force up to 1.5 MN and a twisting torque up to 7.4 kNm. This work describes the design of the central stack and its mechanical validation with a multiphysics finite element assessment. Using a combined electromagnetic and mechanical assessment, it is shown that the SMART central stack will meet the physics requirements in phase 2.
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