Particle transport through density modulation studies in helical devices*

Helical devices like stellarators and heliotrons pose a strong candidate for future fusion reactors given their ability to operate in steady state. Quasisymmetric stellarators like the Helically Symmetric eXperiment (HSX) have the added benefit of reducing plasma neoclassical transport to a level comparable or better than conventional tokamaks[1, 2]. These future reactors, however, will require peaked density profiles to maximize fusion products, which are ultimately governed by particle transport. While optimized stellarator configurations can now virtually eliminate neoclassical losses, anomalous transport still dominates a majority of total experimental transport observed [3].

This work utilizes density modulation experiments to determine diffusion and convection coefficients of particle transport in the HSX and the Large Helical Device (LHD) heliotron for both neoclassical and anomalous components. Interferometry measurements and the pySTRAHL code will utilize Bayesian Inference parameter estimation to determine experimental transport coefficients while neoclassical transport coefficients will be determined with the code PENTA [4-6]. Anomalous transport will be elucidated for both HSX and LHD in examining the difference between experimental and neoclassical transport.

contact: dionysi.damaskopoulos@wisc.edu

US DOE Grant No. DE-FG02-93ER54222.

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[2] M. Landreman and E. Paul, Magnetic Fields with Precise Quasisymmetry for Plasma Confinement, Phys. Rev. Lett. 128, 035001 (2022).

[3] F. Warmer et al. Impact of Magnetic Field Configuration on Heat Transport in Stellarators and Heliotrons, Phys. Rev. Lett. 127, 225001 (2021).

[4] C. Swee, et al. Impurity Transport Studies at the HSX Stellarator Using Active and Passive CVI Spectroscopy, Plasma Phys. Control. Fusion 64, 015008 (2021).

[5] U. von Toussaint, Bayesian Inference in Physics, Rev. Mod. Phys. 83, 943 (2011).

[6] A. Briesemeister, et al. Comparison of the Flows and Radial Electric Field in the HSX Stellarator to Neoclassical Calculations, Plasma Phys. Control. Fusion 55, 014002 (2012).