Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Zero Turbulence Manifold in Fusion Plasmas   The transport of heat that results from turbulence is a major factor limiting
the temperature gradient, and thus the performance, of fusion devices. We use
nonlinear simulations to show that a toroidal equilibrium scale sheared flow
can completely suppress the turbulence across a wide range of flow gradient and
temperature gradient values. We demonstrate the existence of a bifurcation
across this range whereby the plasma may transition from a low flow gradient
and temperature gradient state to a higher flow gradient and temperature gra-
dient state. We show further that the maximum temperature gradient that can be
reached by such a transition is limited by the existence, at high flow
gradient, of subcritical turbulence driven by the parallel velocity gradient
(PVG). We use linear simulations and analytic calculations to examine the
properties of the transiently growing modes which give rise to this subcritical
turbulence, and conclude that there may be a critical value of the ratio of the
PVG to the suppressing perpendicular gradient of the velocity (in a tokamak
this ratio is equal to q/{\epsilon} where q is the magnetic safety factor and
{\epsilon} the inverse aspect ratio) below which the PVG is unable to drive
subcritical turbulence. In light of this, we use nonlinear simulations to
calculate, as a function of three parameters (the perpendicular flow shear,
q/{\epsilon} and the temperature gradient), the surface within that parameter
space which divides the regions where turbulence can and cannot be sustained:
the zero- turbulence manifold. We are unable to conclude that there is in fact
a critical value of q/{\epsilon} below which PVG-driven turbulence is
eliminated. Nevertheless, we demonstrate that at low values of q/{\epsilon},
the maximum critical temperature gradient that can be reached without
generating turbulence is dramatically increased.

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The categories of this paper are: atom-ph
4
The categories of this paper are: cond-mat
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The categories of this paper are: supr-con
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The categories of this paper are: dg-ga
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The categories of this paper are: quant-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: q-fin
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The categories of this paper are: hep-lat
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The categories of this paper are: mtrl-th
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The categories of this paper are: econ
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The categories of this paper are: cmp-lg
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The categories of this paper are: eess
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The categories of this paper are: astro-ph