Microturbulence is a form of
turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
that varies over small distance scales. (Large-scale turbulence is called macroturbulence.)
Stellar
Microturbulence is one of several mechanisms that can cause
broadening of the
absorption lines in the stellar spectrum. Stellar microturbulence varies
with the effective temperature and the surface gravity.
The microturbulent velocity is defined as the microscale
non-thermal component of the gas velocity in the region of spectral
line formation.
Convection is the mechanism believed to be responsible for the observed turbulent velocity field, both in low mass stars and massive stars.
When examined by a
spectroscope
An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mate ...
, the velocity of the convective gas along the line of sight produces
Doppler shifts in the absorption bands. It is the distribution of these velocities along the line of sight that produces the microturbulence broadening of the absorption lines in low mass stars that have convective envelopes. In massive stars convection can be present only in small regions below the surface; these sub-surface convection zones can excite turbulence at the stellar surface through the emission of acoustic and gravity waves.
The strength of the microturbulence (symbolized by
ξ, in units of
km s−1) can be determined by comparing the broadening of strong lines versus weak lines.
Magnetic nuclear fusion
Microturbulence plays a critical role in energy transport during magnetic nuclear fusion experiments, such as the
Tokamak
A tokamak (; russian: токамáк; otk, 𐱃𐰸𐰢𐰴, Toḳamaḳ) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being ...
.
References
External links
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Emission spectroscopy
Physical oceanography
Stellar astronomy
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