Magnetic equilibrium design for the SMART tokamak

Self Cite

In this work, we study the impact of aspect ratio A = R0/r (the ratio of major radius R0 to minor radius r) on the confinement benefits of Negative Triangularity (NT) plasma shaping. We use high-fidelity flux tube gyrokinetic GENE simulations and consider several different scenarios: four of them inspired by TCV experimental data, a scenario inspired by DIII-D experimental data and a scenario expected in the new SMART spherical tokamak. The present study reveals a surprising and non-trivial dependence. NT improves confinement at any value of A for ITG turbulence, while for TEM turbulence confinement is improved only in the case of large and conventional aspect ratios. Additionally, through a detailed study of a large aspect ratio case with pure ITG drive, we develop an intuitive physical picture that explains the beneficial effect of NT at large and conventional aspect ratios. This picture does not hold in TEM-dominated regimes, where a complex synergistic effect of many factors is found. Finally, we performed the first linear gyrokinetic simulations of SMART, finding that both NT and PT scenarios are dominated by micro-tearing-mode (MTM) turbulence and that NT is more susceptible to MTMs at tight aspect ratio. However, we found that a regime where ITGs dominate in SMART can be found, and in this regime NT is more linearly stable.

“…Both single-null and double-null configurations can be produced. For more technical details, the interested reader is referred to [14][15][16][17].…”

Section: Smartmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Physical insights from the aspect ratio dependence of turbulence in negative triangularity plasmas

Balestri,

Ball,

Coda

et al. 2024

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“…Several devices have recently been built or upgraded, such as NSTX-U [5], ST40 [6] and MAST-U [7]. Others are currently being designed or built, such as SMART [8] and STEP [9]. However, reactor-relevant equilibria must have sufficiently low turbulent transport to provide sufficient confinement time to maintain density and temperature profiles with modest heating power.…”

Section: Introductionmentioning

confidence: 99%

Kinetic ballooning modes as a constraint on plasma triangularity in commercial spherical tokamaks

Davies

Dickinson

Wilson

2022

To be economically competitive, spherical tokamak (ST) power plant designs require a high β (plasma pressure/magnetic pressure) and suﬃciently low turbulent transport to enable steady-state operation. A novel approach to tokamak optimisation is for the plasma to have negative triangularity, with experimental results indicating this reduces transport. However, negative triangularity is known to close access to the “second stability” region for ballooning modes, and thus impose a hard β limit. Second stability access is particularly important in ST power plant design, and this raises the question as to whether negative triangularity is feasible. A linear gyrokinetic study of three hypothetical high β ST equilibria is performed, with similar size and fusion power in the range 500-800MW. By closing the second stability window, the negative triangularity case becomes strongly unstable to long-wavelength kinetic ballooning modes (KBMs) across the plasma, likely driving unacceptably high transport. By contrast, positive triangularity can completely avoid the ideal ballooning unstable region whilst having reactor-relevant β, provided the on-axis safety factor is suﬃciently high. Nevertheless, the dominant instability at long wavelength still appears to be the KBM, though it could be stabilised by ﬂow shear.

“…Three pairs of in-vessel poloidal field (PF) coils complement two out-vessel coils to provide the required flexibility in the achievable magnetic configurations [7,8,20]. According to initial modeling, a triangularity in the range δ = −0.6 → +0.6 can be achieved.…”

Section: The Smart Devicementioning

confidence: 99%

“…To that end, the SMall Aspect Ratio Tokamak (SMART [6]) device is being commissioned at the University of Seville (Spain). The main goal of SMART is to test experimentally the potential advantages of negative triangularity scenarios in a ST configuration [6][7][8][9][10], and contribute to the overall understanding of the physics and transport scaling of ST-based fusion devices in terms of plasma confinement [11]. Experimental data will also provide valuable information for further development and validation of predictive transport models.…”

Section: Introductionmentioning

confidence: 99%

NBI optimization on SMART and implications for scenario development

Podestà,

Cruz-Zabala,

Poli

et al. 2024

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The SMall Aspect Ratio Tokamak (SMART) under commissioning at the University of Seville, Spain, aims to explore confinement properties and possible advantages in confinement for compact/spherical tokamaks operating at negative vs. positive triangularity. This work explores the benefits of auxiliary heating through Neutral Beam Injection (NBI) for SMART scenarios beyond the initial Ohmic phase of operations, in support of the device’s mission. Expected values of electron and ion temperature achievable with NBI heating are first predicted for the current flat-top phase, including modeling to optimize the NBI injection geometry to maximize NBI absorption and minimize losses for a given equilibrium. Simulations are then extended for a selected case to cover the current ramp-up phase. Differences with results obtained for the flat-top phase indicate the importance of determining the plasma evolution over time, as well as self-consistently determining the edge plasma parameters for reliable time-dependent simulations. Initial simulation results indicate the advantage of auxiliary NBI heating to achieve nearly double values of pressure and stored energy compared to Ohmic discharges, thus significantly increasing the device’s performance. The scenarios developed in this work will also contribute to diagnostic development and optimization for SMART, as well as providing test cases for initial predictions of macro- and micro-instabilities.