Abstract
The main research on the energy from thermonuclear fusion uses deuterium plasmas magnetically trapped in toroidal devices. To suppress the turbulent eddies that impair thermal insulation and pressure tight of the plasma, current drive (CD) is necessary, but tools envisaged so far are unable accomplishing this task while efficiently and flexibly matching the natural current profiles self-generated at large radii of the plasma column [1–5]. The lower hybrid current drive (LHCD) [6] can satisfy this important need of a reactor [1], but the LHCD system has been unexpectedly mothballed on JET. The problematic extrapolation of the LHCD tool at reactor graded high values of, respectively, density and temperatures of plasma has been now solved. The high density problem is solved by the FTU (Frascati Tokamak Upgrade) method [7], and solution of the high temperature one is presented here. Model results based on quasi-linear (QL) theory evidence the capability, w.r.t linear theory, of suitable operating parameters of reducing the wave damping in hot reactor plasmas. Namely, using higher RF power densities [8], or a narrower antenna power spectrum in refractive index [9,10], the obstacle for LHCD represented by too high temperature of reactor plasmas should be overcome. The former method cannot be used for routinely, safe antenna operations, Thus, only the latter key is really exploitable in a reactor. The proposed solutions are ultimately necessary for viability of an economic reactor.
Highlights
The main research on fusion energy utilises toroidal plasmas magnetically trapped in toroidal machines
The lower hybrid current drive (LHCD) [6] can satisfy this important need of a reactor [1], but the LHCD system has been unexpectedly mothballed on JET
Using higher RF power densities [8], or a narrower antenna power spectrum in refractive index [9,10], the obstacle for LHCD represented by too high temperature of reactor plasmas should be overcome
Summary
The main research on fusion energy utilises toroidal plasmas magnetically trapped in toroidal machines (tokamaks). As major scientific problem for an economic reactor, we must understand how to lead strongly heated plasma to sustain a high fusion gain, while a large fraction of current is self-produced via pressure gradient naturally present especially at large radii of the plasma column. The pressure profile should be mandatorily controlled (for at least several hours for enabling energy production) by properly shaping the plasma current density radial profile, j(r). This allows suppressing turbulence that impairs thermal insulation and pressure tight of the plasma column, which in turn enables sustaining the plasma current
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