Phase effects on turbulent transport in the magnetic confinement of plasmas for nuclear fusion

Abstract

With climate change effects on the rise, the global energy infrastructure requires revision. We first provide a brief review of common energy resources as well as their safety and climate effects. We then compare and contrast nuclear fission and fusion based energy schemes. Difficulties based on the requirements of the fusion triple product, as well as the fast neutrons from the deuterium and tritium reaction are also discussed. The lack of sufficient experimental controls in enhanced confinement modes like the I-mode and the H-mode, lead to difficulties satisfying the restrictions imposed by the Greenwald density limit. These combined with several operational needs like ash and impurity removal, enhanced density control, the ability to access other confinement modes at reduced energy thresholds, motivates the search for a barrier capable of variable energy and density confinement. Self consistent models suggest that unique phase relationships exist between different turbulent instabilities and plasma profiles like temperature and density, that determine the turbulent transport of the quantity. Two common instabilities, driven by the electron and ion temperature gradient, and their unique phase relations are used to arrive at a net phase relation for temperature and for density. Then, using electron and ion radio frequency heating, the difference in phase of the turbulent transport may be locally changed, altering transport dynamics. Methods to increase core temperature while simultaneously increasing density transport, thereby avoiding the Greenwald limit, are discussed. The proposed transport controls are based upon characteristics of the localized radio frequency heating including amplitude, location, and duration. These parameters determine the power deposited in the plasma, and therefore the local ratios of the electron and ion temperature driven instabilities. Aspects of each parameter's effect on radial transport are summarized, with the strongest phase barrier allowing for a ∼ 15% increase of core ion temperature and ∼ 30% decrease of core density.