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Whether studying the core of our sun or the inside of a fusion reactor, scientists need to determine how energy flows in plasma. Scientists use simulations to calculate the flow. The simulations rely on the classical thermal transport model. Despite over 50 years of research, an ad hoc multiplier is often required. Without it, the simulation doesn't match real-world observations. Now, a team devised a way to measure energy flow and determined why the models need the multiplier. Further, the team's new approach lets them quantitatively test simulations.
The team's measurements show that the most sophisticated models over-predict the heat flux for all conditions tested. Now, researchers can further develop thermal transport models. Also, they can more readily study and definitively test models.
Fields - Plasma - Physics - Astrophysics - Confinement
In diverse fields of plasma physics including astrophysics, inertial confinement fusion, and magnetohydrodynamics, classical thermal transport (for example, Spitzer-Harm and Brajinskii) provides the foundation for calculating heat flux (energy flow). Despite over 50 years of research, an ad hoc multiplier is often required to account for anomalous physics (for example, nonlocal effects, turbulence, or instabilities) and to match global experimental observables. Motivated by the need to quantitatively address this topic, this research developed a novel collective Thomson-scattering technique that directly probes modifications to the electron distribution function resulting from heat flux [R.J. Henchen et al., Physical Review Letters (2018)]. Using this technique, the validity of classical transport theory when the electron-ion mean free path is sufficiently shorter than the electron...
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