Transport Barriers in Magnetized Plasmas -- General Theory with Dynamical Constraints

TL;DR

This paper introduces a fundamental dynamical constraint in magnetized plasmas that influences the formation of transport barriers, potentially enabling high confinement states without the need for velocity shear, supported by analytic and gyrokinetic simulation methods.

Contribution

It presents a new theoretical framework based on a dynamical constraint that explains transport barrier formation independently of velocity shear, supported by analytic and simulation results.

Findings

Density gradients exceeding a threshold violate the constraint, stabilizing the plasma.

The constraint broadens the conditions for forming high confinement states.

Analytic methods and gyrokinetic simulations validate the theoretical predictions.

Abstract

A fundamental dynamical constraint -- that fluctuation induced charge-weighted particle flux must vanish -- can prevent instabilities from accessing the free energy in the strong gradients characteristic of Transport Barriers (TBs). Density gradients, when larger than a certain threshold, lead to a violation of the constraint and emerge as a stabilizing force. This mechanism, then, broadens the class of configurations (in magnetized plasmas) where these high confinement states can be formed and sustained. The need for velocity shear, the conventional agent for TB formation, is obviated. The most important ramifications of the constraint is to permit a charting out of the domains conducive to TB formation and hence to optimally confined fusion worthy states; the detailed investigation is conducted through new analytic methods and extensive gyrokinetic simulations.