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MFE-IM Group Attends US-EU TTF Conference

The MFE-IM group travelled to Asheville, NC to participate in the US-EU Transport Task Force (TTF) conference, joining researchers from across the country and the European Union to present work related to turbulence and transport in fusion plasmas. The group delivered two talks as well as presenting six posters!

Audrey’s poster “On the effect of empirical modeling core transport assumptions in tokamak design” aimed to place future tokamak power plant design on a physics-based foundation.

She investigated the dependence of fusion power and Q factor on the shape of the profiles and physics assumptions used as inputs to POPCON empirical models. Her work advances on previous empirical modeling by randomly sampling thousands of combinations of these physics assumptions in order to find the operational point with the highest probability of success.

Her results show that the SPARC operational point with the greatest probability of success differs from the optimal point chosen from naïve deterministic optimization.

Vince presented a poster entitled “Developing a Neural Network Surrogate Model for Fast Integrated Modeling of SPARC,” showcasing his work building a machine learning surrogate model of the widely-used TGLF quasilinear turbulence code.

Vince’s work with running millions of TGLF simulations culminated in a neural network model which reproduces the correct heat and particle fluxes and is specifically trained to predict turbulent transport in SPARC. He plans to use this surrogate model to support realtime predictions of SPARC plasmas and scenario design.

Ivan’s Poster “Preliminary Analysis Towards Developing a Core to Edge Integrated Model of Impurity Transport” focused on his PhD work of creating a fully core to edge model of impurity transport, validated on experimental results from the DIII-D tokamak.

He presented TGLF and TGYRO predictions of impurity transport in the core and outlined a workflow for future simulations, in which he plans to couple the SOLPS-ITER edge transport code with the AURORA impurity source model, using optimization tools developed by MFE-IM to produce truly core-edge impurity transport predictions.

Pablo’s talk on “Predictions of Core Transport and Performance in SPARC First-Campaign Plasmas with Nonlinear CGYRO” outlined recent work done to predict the performance of L-mode breakeven and near-breakeven SPARC plasmas which will be produced at the beginning of operation.

His results predict a path to breakeven operations in the early days of SPARC, while highlighting challenges with core-edge integration. In addition, Pablo served as the Core Turbulence and Transport session chair.

Marco delivered a talk “Sensitivity Study of SPARC Full-Field H-Mode with a Quasi-Linear Transport Model,” in which he presented results from a database of integrated transport simulations of SPARC.

He investigated the effect of modeling assumptions on H-mode access, fusion gain, and fusion power and presented a workflow that can be used for scenario design in SPARC first campaign plasmas.

A key finding was that core performance depends highly on the temperature and pressure at the top of the pedestal, which is one of hardest quantities to model predictively, and was a major focus of many other presentations at the conference.

Joe’s Poster “Predictions of Pedestal Height and Integrated Modeling of Performance and Transport in ARC” outlined work done to create a neural network surrogate model of the pedestal pressure in ARC- a vital boundary condition for core transport simulations- and used this model to produce the first integrated transport simulations of ARC using the ASTRA transport code.

Joe, along with PSFC visiting student Olga Paikina (UiT The Arctic University of Norway), received student poster awards for their work. Congrats Olga and Joe!

Rachel presented on “Gyrokinetic modeling of negative triangularity plasmas in ASDEX Upgrade,” in which she analyzed the effect of changing the triangularity of the plasma on the heat flux and performance of AUG discharges.

In addition, she used a data from the CECE diagnostic to determine that the turbulence fluctuations are smaller for negative triangularity plasmas than for positive triangularity. She also demonstrated good agreement between Gyrokinetic modeling with CGYRO and quasilinear turbulence calculations with TGLF.

Nathan’s Poster entitled “Insights Into the Origin of Electron Density Peaking Obtained from Nonlinear Gyrokinetic Profile Predictions” showed progress in using showed progress in using first-principles profile predictions with PORTALS-CGYRO to explain the shape of core profiles.

His results give new physics insight on empirical relations between the plasma collisionality and the density peaking (the ratio of electron density at the center of the plasma to the volume averaged density), which is strongly related to fusion performance.

Six first-author contributions from MFE-IM members at DPP 2023!

This year’s APS-DPP conference was a special one for the MFE-IM group, as it was the first time since the formation of the group with significant MFE-IM presence. In Denver (CO), MFE-IM students, postdocs and scientists enjoyed meeting with collaborators, learning what the US fusion community is up to and getting feedback on their research. Apart from numerous co-authorships, MFE-IM members presented six first-author contributions:

Audrey presented a numerical investigation of turbulence dynamics to help validate transport models against experiments. The common assumption of incremental diffusivity (how the electron heat flux responds to variations in electron temperature gradients) being equal to heat pulse diffusivity (derived from heat pulse propagation experiments) is challenged in Audrey’s work. She talked about the importance of the evolution of ion temperature during electron heat pulse propagation experiments, the radial sensitivity of the inferred diffusivities and the effect of collisionality. Audrey’s work points towards a more careful consideration of these issues when interpreting experiments and comparing them to simulation in model validation studies.

Arsene presented results of calculations of impurity coefficients of diffusion (D) and convection (v) in DIII-D H-mode plasmas as a function of the charge state Zimp.

The results showed specific trends of D(Zimp) in ITG and TEM dominated plasmas. D(Zimp) ~ Zimp in TEM and D(Zimp) ~ 1/Zimp in ITG, consistent with previous gyrokinetic modeling results. Linear stability was calculated using the CGYRO and TGLF models and transport coefficients were obtained utilizing the TGYRO solver.

Next steps will consist of calculating the transport coefficients with non-linear CGYRO and validating results against experimental measurements in the DIII-D tokamak. This work aims at contributing to a better interpretation of impurities’ emission in future tokamak devices, which are anticipated to be mainly ITG dominated.

Nathan presented predictions of performance in SPARC, ITER and ARC-class reactors using non-linear gyrokinetic simulations and the PORTALS framework, which leverage recent advances in GPU acceleration and surrogate-optimization techniques.

The simulations predicted Q~8 burning plasma conditions in SPARC PRD with ITG dominance in the core. For the density peaking, excellent agreement was found with empirical scaling laws. ITER Baseline Scenario was also predicted to achieve its burning plasma conditions with Q~10 and 500 MW fusion power. The ITER simulations pointed to potential optimization and suggested a lack of isotope effects in the core turbulence.

Nathan also discussed results for ARC-class reactors, which show similar features to other inductive burning plasmas. These results suggest that ITER and SPARC operations should directly inform ARC operational space.

Marco had a contributed poster with various integrated modeling studies of SPARC plasmas.

Comparison between SPARC PRD performance with different antenna geometries was investigated with TRANSP+TGLF+TORIC. The results show minimal changes (below 5%) with 1 on-midplane or 2 off-midplane ICRH antennas, consequence of transport stiffness and small near-axis volume.

A comparison between TRANSP and ASTRA simulations of the SPARC PRD scenario with same heat fluxes revealed different kinetic profiles predictions, pointing to discrepancies in the transport solvers. This was further investigated with TGLF standalone simulations, building confidence in the ASTRA predictions. Furthermore, an optimal range of numerical diffusivity in ASTRA to aid convergence was found, demonstrating that the flux-matching solver is robust.

Future work includes the construction of an extensive database of SPARC predictions, including scans of impurity content, and the coupling to fast transport models, free-boundary solvers and heating modules.

Pablo delivered an invited talk on the use of first-principles turbulence simulations to help the planning of the first campaign in SPARC. This was enabled by the PORTALS framework, together with the GPU-accelerated CGYRO code to model nonlinear gyrokinetics. Pablo discussed how the reduced cost of the predictions allowed the study of a dozen core scenarios in non H-mode conditions in SPARC. The simulations results are being used to help plan how to best operate SPARC during the first campaign to achieve performance goals, i.e. breakeven (Q>1) for the first time in magnetic confinement fusion.

Audrey had double duty at this year’s DPP meeting. She presented, on behalf of her team, the Altator project, a new toroidal outreach device being designed, built and operated by PSFC graduate students. This device will serve to teach the main concepts of magnetic confinement fusion to the main public and students when visiting MIT and the PSFC. Graduate students on the Altator team, regardless of their main research (experimental, modeling or theory), are having hands-on experience in the lab, which they pursue as a side project.

MFE-IM members attend 2023 IAEA FEC conference

MFE-IM scientists Nathan Howard and Pablo Rodriguez-Fernandez attended the 2023 IAEA Fusion Energy Conference (IAEA-FEC), held in beautiful, rainy London (UK) the week of Oct 16th. Groundbreaking results from the fusion community were shared, from the new JET DT experiments to negative triangularity in DIII-D, and exciting announcements from the UK on their plans to boost commercial fusion initiatives. Around 2,000 participants from all over the world took part in this year’s FEC, for the first time in person since 2018 due to the COVID pandemic. This was the 29th edition of the conference since its inception in 1961.

Pablo and Nathan shared the results from their high-fidelity simulation work using PORTALS-CGYRO. Pablo presented a poster with an overview of the technique and summary of predictive results in SPARC, ITER and JET plasmas. Nathan delivered a plenary talk on DIII-D ITER Baseline Scenario validation of ion-scale gyrokinetics, with comprehensive turbulence and impurity measurements. Nathan’s talk also presented the first-ever core performance predictions of ITER with first-principles simulations.