arXiv subjects

Thomas Body

Publications and source records attributed to Thomas Body.

7 recordsLinked to original sources

arXiv2026

Core-edge integrated modeling of ARC: on the effect of impurity transport and detachment conditions

Integrated modeling of ARC H-modes has been conducted to assess the feasibility of high-performance scenarios compatible with divertor detachment. The analysis incorporates self-consistent evolution of impurity radiation and density profiles, demonstrating that fusion power levels approaching a GW can be achieved while maintaining divertor temperatures below 2 eV with Ar seeding. Sensitivity studies reveal a strong dependence of fusion power on the separatrix density, with performance spanning 750-1000 MW, and a weaker dependence on enrichment factor and pedestal density. Alternative seeding strategies using Neon have also been explored. Plasmas with Argon seeding consistently access H-mode, providing the highest fusion power and detached divertor operation, whereas Neon seeding leads to lower performance (600-850 MW) and less robust H-mode access, due to excessive core impurity accumulation. A small W impurity peaking has been found, with decreasing values at higher Zeff. Further analyses incorporate reduced momentum transport modeling, and sensitivity studies of neoclassical impurity transport, confirming the robustness of the results. Overall, these findings support the viability of high-performing H-mode operation in ARC, ensuring divertor protection, enabled through Argon and Neon impurity seeding.

physics.plasm-ph↗

arXiv2025

Impurity peaking of SPARC H-modes: a sensitivity study on physics and engineering assumptions

In this paper, an overview of the impurity transport for three H-mode plasmas in the upcoming SPARC tokamak has been provided. The simulations have been performed within the ASTRA+STRAHL framework, using FACIT and TGLF-SAT2 to predict, respectively, neoclassical and turbulent core transport, while a neural network trained on EPED simulations has been employed to calculate the pedestal height and width self-consistently. A benchmark with previous simulations at constant impurity fraction has been provided for three H-modes, spanning different plasma current and magnetic field values. For a scenario, additional simulations have been performed to account for uncertainties in the modeling assumptions. The predictions are nearly insensitive to changes in the top of pedestal W concentrations. Varying the Ar pedestal concentration has shown a small effect on the impurity peaking and nearly constant fusion gain values, due to multiple effects on pedestal pressure, main ion dilution and density peaking. The inclusion of rotation in ASTRA simulations has shown minimal impact on confinement and impurity transport predictions. An exploratory study has been provided with a first set of simulations treating D and T separately, experiencing a maximum fusion power at 55-45% DT fuel composition, and an asymmetric distribution with respect to the D concentration. All the results, including sensitivity scans of toroidal velocity and ion temperature and density gradients, highlighted that turbulent impurity transport prevails on the neoclassical component, aligning with previous ITER predictions, and suggesting that next generation devices like SPARC, operating at low collisionality, will experience low W accumulation.

physics.plasm-ph↗

arXiv2025

A simple, accurate model for detachment access

In next-step fusion tokamaks such as SPARC and ITER, achieving high levels of scrape-off-layer power dissipation will be essential to protect the divertor while maintaining good core plasma performance. The Lengyel model for power dissipation is easy to interpret and fast enough to incorporate into plasma control and scoping tools, but it systematically overestimates the impurity concentration required to reach detachment by a factor of ~5 relative to experiments and higher-fidelity simulations. In this work, we extend the Lengyel model to match the semi-empirical Kallenbach scaling, which successfully describes detachment access on several operating tokamaks. We found that we can reproduce the experimental scaling by accounting for cross-field transport in the divertor, power and momentum loss due to neutral ionization close to the divertor target and turbulent broadening of the upstream heat flux channel. These corrections cause the impurity concentration required for detachment to decrease faster than $n_{e,u}^2$, reproducing the $c_z\propto 1/n_{e,u}^{2.7-3.2}$ scalings found in experiment. The model also quantitatively reproduces the impurity concentration needed to reach detachment in experiment, demonstrating that the extended Lengyel model can be used as a simple, accurate model for detachment access.

physics.plasm-ph↗

arXiv2024

The separatrix operational space of next-step fusion experiments: From ASDEX Upgrade data to SPARC scenarios

Fusion power plants require ELM-free, detached operation to prevent divertor damage and erosion. The separatrix operational space (SepOS) is proposed as a tool for identifying access to the type-I ELM-free quasi-continuous exhaust regime. In this work, we recast the SepOS framework using simple parameters and present dedicated ASDEX Upgrade discharges to demonstrate how to interpret its results. Analyzing an extended ASDEX Upgrade database consisting of 6688 individual measurements, we show that SepOS accurately describes how the H-mode boundary varies with plasma current and magnetic field strength. We then introduce a normalized SepOS framework and LH minimum scaling and show that normalized boundaries across multiple machines are nearly identical, suggesting that the normalized SepOS can be used to translate results between different machines. The LH minimum density predicted by SepOS is found to closely match an experimentally determined multi-machine scaling, which provides a further indirect validation of SepOS across multiple devices. Finally, we demonstrate how SepOS can be used predictively, identifying a viable QCE operational point for SPARC, at a separatrix density of 4e20/m3, a separatrix temperature of 156eV and an alpha-t of 0.7 - a value solidly within the QCE operational space on ASDEX Upgrade. This demonstrates how SepOS provides a concise, intuitive method for scoping ELM-free operation on next-step devices.

physics.plasm-ph↗

arXiv2024

Detachment scalings derived from 1D scrape-off-layer simulations

Fusion power plants will require detachment to mitigate sputtering and keep divertor heat fluxes at tolerable levels. Controlling detachment on these devices may require the use of real-time scrape-off-layer modeling to complement the limited set of available diagnostics. In this work, we use the configurable Hermes-3 edge modeling framework to perform time-dependent, fixed-fraction-impurity 1D detachment simulations. Although currently far from real-time, these simulations are used to investigate time-dependent effects and the minimum physics set required for control-relevant modeling. We show that these simulations reproduce the expected rollover of the target ion flux - a typical characteristic of detachment onset. We also perform scans of the input heat flux and impurity concentration and show that the steady-state results closely match the scalings predicted by the 0D time-independent Lengyel-Goedheer model. This allows us to indirectly compare to SOLPS simulations, which find a similar scaling but a lower value for the impurity concentration required for detachment for given upstream conditions. We use this result to suggest a series of improvements for the Hermes simulations, and finally show simulations demonstrating the impact of time-dependence.

physics.plasm-ph↗

arXiv2023

The SPARC Primary Reference Discharge defined by cfsPOPCON

The Primary Reference Discharge (PRD) is a design point maximizing the highest-achievable fusion power gain in a full-field (12.2T), full-current (8.7MA) DT-fueled H-mode on SPARC. The Primary Reference Discharge was defined in the SPARC Physics Basis using a precursor to the cfsPOPCON scoping tool. In this memo, we discuss modifications made to the cfsPOPCON scoping tool since the release of the SPARC Physics Basis and show that the key parameters of the PRD design point have not changed significantly.

physics.plasm-ph↗

arXiv2019

Treatment of Advanced Divertor Configurations in the Flux-Coordinate Independent turbulence code GRILLIX

Advanced divertor configurations modify the magnetic geometry of the diverter to achieve a combination of strong magnetic flux expansion, increased connection length and higher divertor volume - to improve detachment stability, neutral/impurity confinement and heat-channel broadening. In this paper, we discuss the modification of the Flux-Coordinate Independent (FCI) turbulence code GRILLIX to treat generalised magnetic geometry, to allow for the investigation of the effect of magnetic geometry on turbulent structures in the edge and SOL. The development of grids and parallel operators from numerically-defined magnetic equilibria is discussed, as is the application of boundary conditions via penalisation, with the finite-width method generalised to treat complex non-conformal boundaries. Initial testing of hyperbolic (advection) and parabolic (diffusion) test cases is presented for the Snowflake scenario.

physics.plasm-ph↗