Improving Predictions for Fusion Device Transport

The Science

In a fusion energy plasma, transport describes how particles and energy within the plasma move. Understanding this behavior is crucial for controlling and optimizing the fusion process. Researchers use transport models in current tokamak experiments and simulations of future fusion devices. These models help to optimize safety, efficiency, and sustainability in a fusion device. To ensure accuracy, researchers validate transport models with real-world experiments. The General Atomics theory group has developed and confirmed a new transport model. The model resolves discrepancies found in plasmas in the Joint European Torus (JET).

The Impact

The new model is a state-of-the-art tool for predicting plasma transport in deuterium-tritium (D-T) plasmas with confirmed reliability. It has consistent predictions for both D-T and deuterium-only plasmas. This boosts researchers’ confidence in extrapolating from data on deuterium plasma to future applications involving D-T plasma. Researchers validated the new model with D-T experimental data. They also identified limitations that will help apply the model’s results in the future. These insights will help predict D-T operations in future fusion power plants. The result will aid researchers in designing future fusion power devices.

Summary

The JET DTE2 experiments achieved the highest-ever fusion energy production. To forecast transport dynamics within these discharges, researchers used the TGLF and NEO models within the TGYRO transport code. In this study, scientists developed a new quasilinear transport model, TGLF-SAT2, to resolve discrepancies in JET D-T discharges. Initially, the original TGLF model was tested on deuterium discharges to prepare for D-T scenarios, but observed discrepancies led to the creation of TGLF-SAT2. Validation against JET DTE2 discharges in two primary scenarios showed the TGYRO code with the newly developed model effectively predicted temperature profiles within a broad radial window, with minor ion temperature discrepancies near the core. However, the researchers noted a consistent 20 percent underprediction of electron density profiles, indicating areas for future refinement.

To achieve a self-consistent steady-state solution based on JET DTE2 discharges, the researchers introduced an integrated modeling workflow, TGYRO-STEP. This workflow iterates among the core transport code TGYRO with the new TGLF-SAT2 model, pedestal pressure model EPED, and MHD equilibrium model EFIT, yielding a converged solution that reduces dependence on experimental boundary conditions for temperature and density profiles. While deviations from experimental data observed in standard TGYRO simulations also appear in TGYRO-STEP simulations, the key advantage of TGYRO-STEP lies in expanding the core transport boundary to the plasma edge. The utilization of the TGYRO-STEP workflow in analyzing JET DTE2 discharges plays a pivotal role in assessing its robustness and identifying its limitations, offering valuable insights for its potential future utilization in modeling D-T predictions for future fusion power plants.

Contact

Nan Shi
General Atomics
shinan@fusion.gat.com

Funding

This work was supported by the U.S. Department of Energy Office of Science.

Publications

Shi, N., et al., Prediction of transport in the JET DTE2 discharges with TGLF and NEO models using the TGYRO transport code. Nuclear Fusion 64, 076062 (2024). [DOI: 10.1088/1741-4326/ad53e3]