Ion Temperature Gradient instability: Difference between revisions
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The ion temperature gradient (ITG) instability is a microinstability in | The ion temperature gradient (ITG) instability is a microinstability in [[tokamak]]s relevant to turbulence and the associated [[anomalous transport]]. | ||
The instability occurs due to the nature of Grad-B drift. The Grad-B drift velocity of a particle (caused by a gradient in the magnetic field) is proportional to the particle's kinetic energy. Hotter particles drift further than colder particles. | The instability occurs due to the nature of Grad-B drift. The Grad-B drift velocity of a particle (caused by a gradient in the magnetic field) is proportional to the particle's kinetic energy. Hotter particles drift further than colder particles. | ||
Hence, if a temperature gradient is aligned with a magnetic field gradient (as occurs in a tokamak), particles in the hotter region will drift further. If there is a perturbation in the temperature gradient, then the difference in drift velocities will create charge separation. The charge separation creates a electric field. This electric field creates an | Hence, if a temperature gradient is aligned with a magnetic field gradient (as occurs in a tokamak), particles in the hotter region will drift further. If there is a perturbation in the temperature gradient, then the difference in drift velocities will create charge separation. The charge separation creates a electric field. This electric field creates an <math>E\times B</math> drift which increases the perturbation's amplitude. The positive-feedback nature of this loop leads to exponential growth of the instability. | ||
Note that if the temperature gradient is anti-parallel to the magnetic field gradient, the | Note that if the temperature gradient is anti-parallel to the magnetic field gradient, the <math>E\times B</math> drift will suppress the perturbation rather than increase it. This situation occurs on the inner, "good-curvature" side of the tokamak. | ||
See the figure for a graphical explanation. | See the figure for a graphical explanation. | ||
[[File:ITG.png]] | [[File:ITG.png|600px|thumb|center|ITG mechanism]] | ||
== See also == | |||
* [[Plasma instability]] | |||
Revision as of 15:16, 19 October 2016
The ion temperature gradient (ITG) instability is a microinstability in tokamaks relevant to turbulence and the associated anomalous transport.
The instability occurs due to the nature of Grad-B drift. The Grad-B drift velocity of a particle (caused by a gradient in the magnetic field) is proportional to the particle's kinetic energy. Hotter particles drift further than colder particles.
Hence, if a temperature gradient is aligned with a magnetic field gradient (as occurs in a tokamak), particles in the hotter region will drift further. If there is a perturbation in the temperature gradient, then the difference in drift velocities will create charge separation. The charge separation creates a electric field. This electric field creates an drift which increases the perturbation's amplitude. The positive-feedback nature of this loop leads to exponential growth of the instability.
Note that if the temperature gradient is anti-parallel to the magnetic field gradient, the drift will suppress the perturbation rather than increase it. This situation occurs on the inner, "good-curvature" side of the tokamak.
See the figure for a graphical explanation.
