Elevating zero dimensional global scaling predictions to self-consistent theory-based simulations

We have developed an innovative workflow, STEP-0D, within the OMFIT integrated modelling framework. Through systematic validation against the International Tokamak Physics Activity (ITPA) global H-mode confinement database, we demonstrated that STEP-0D, on average, predicts the energy confinement time with a mean relative error (MRE) of less than 19%. Moreover, this workflow showed promising potential in predicting plasmas for proposed fusion reactors such as ARC, EU-DEMO, and CFETR, indicating moderate H-factors between 0.9 and 1.2. STEP-0D allows theory-based prediction of tokamak scenarios, beginning with zero-dimensional (0D) quantities. The workflow initiates with the PRO-create module, generating physically consistent plasma profiles and equilibrium using the same 0D quantities as the IPB98(y,2) confinement scaling. This sets the starting point for the STEP (Stability, Transport, Equilibrium, and Pedestal) module, which further iterates between theory-based physics models of equilibrium, core transport, and pedestal to yield a self-consistent solution. Given these attributes, STEP-0D not only improves the accuracy of predicting plasma performance but also provides a path towards a novel fusion power plant (FPP) design workflow. When integrated with engineering and costing models within an optimization, this new approach could eliminate the iterative reconciliation between plasma models of varying fidelity. This potential for a more efficient design process underpins STEP-0D's significant contribution to future fusion power plant development.Comment: 12 pages, 13 figures, accepted by Physics of Plasmas 202

Microtearding mode study in NSTX using machine learning enhanced reduced model

This article presents a survey of NSTX cases to study the microtearing mode (MTM) stabilities using the newly developed global reduced model for Slab-Like Microtearing modes (SLiM). A trained neutral network version of SLiM enables rapid assessment (0.05s/mode) of MTM with $98\%$ accuracy providing an opportunity for systemic equilibrium reconstructions based on the matching of experimentally observed frequency bands and SLiM prediction across a wide range of parameters. Such a method finds some success in the NSTX discharges, the frequency observed in the experiment matches with what SLiM predicted. Based on the experience with SLiM analysis, a workflow to estimate the potential MTM frequency for a quick assessment based on experimental observation has been established

Gyrokinetic simulations of turbulence in the near-edge of fusion plasmas

The main purpose of this thesis is the validation of the gyrokinetic method in the near-edge region of L-mode plasmas. Our primary finding is that gyrokinetic simulations are able to match the heat-flux in the near-edge region of an L-mode plasma at ρ = 0.80 and ρ = 0.90 within the combined statistical and systematic uncertainty σ of the experiment at the 1.6σ and 1.3σ levels, respectively. At ρ = 0.95, gyrokinetic simulations are able to match the total experimental heat flux with nominal experimental parameters. In the big picture, this successful validation exercise helps push the gyrokinetic validation frontier closer to the L-mode edge region. In the course of this validation study, we make three secondary findings that may be helpful to the fusion community. First, the current heuristic rules for the relevance of multi-scale effects appear to be on the cautious side. Multi-scale simulations at ρ = 0.80 suggest that single-scale simulations can be sufficient in a scenario when multi-scale effects are expected. This is helpful, because it could increase the realm of applicability of single-scale simulations, which are computationally more affordable than multi-scale simulations. Second, the effect of edge E�B shear is found to become important already in the near-edge (at ρ = 0.90) rather than at larger radial positions. This was unexpected and is relevant for future simulations in the near-edge. Third, nonlinear simulations at ρ = 0.90 find a hybrid ion temperature gradient (ITG)/ trapped electron mode (TEM) scenario, which was not obvious from linear simulations due to the stability of ITG modes. This could also be an important result for spherical tokamaks, where ITG modes are more often linearly stable than in conventional tokamaks

Fermi Degenerate Antineutrino Star Model of Dark Energy

When the Large Hadron Collider resumes operations in 2021, several experiments will directly measure the motion of antihydrogen in free fall for the first time. Our current understanding of the universe is not yet fully prepared for the possibility that antimatter has negative gravitational mass. This paper proposes a model of cosmology, where the state of high energy density of the big bang is created by the collapse of an antineutrino star that has exceeded its Chandrasekhar limit. To allow the first neutrino stars and antineutrino stars to form naturally from an initial quantum vacuum state, it helps to assume that antimatter has negative gravitational mass. This assumption may also be helpful to identify dark energy. The degenerate remnant of an antineutrino star can today have an average mass density that is similar to the dark energy density of the ΛCDM model. When in hydrostatic equilibrium, this antineutrino star remnant can emit isothermal cosmic microwave background radiation and accelerate matter radially. This model and the ΛCDM model are in similar quantitative agreement with supernova distance measurements. Therefore, this model is useful as a purely academic exercise and as preparation for possible future discoveries