drift waves

In plasma physics, a drift wave is a type of collective excitation that is driven by a pressure gradient within a magnetised plasma, which can be destabilised by differences between ion and electron motion (then known as drift-wave instability or drift instability). The equations which describe these waves a number of solutions, including ion-acoustic solitary waves,{{Cite journal |last=Meiss |first=J. D. |last2=Horton |first2=W. |date=1983-04-01 |title=Solitary drift waves in the presence of magnetic shear |url=https://doi.org/10.1063/1.864251 |journal=The Physics of Fluids |volume=26 |issue=4 |pages=990–997 |doi=10.1063/1.864251 |issn=0031-9171}} and are roughly analogous to modons.{{Cite journal |last=Swaters |first=Gordon E. |date=1986-05-01 |title=Stability conditions anda prioriestimates for equivalent-barotropic modons |url=https://doi.org/10.1063/1.865658 |journal=The Physics of Fluids |volume=29 |issue=5 |pages=1419–1422 |doi=10.1063/1.865658 |issn=0031-9171}}

The drift wave typically propagates across the pressure gradient and is perpendicular to the magnetic field. It can occur in relatively simple configurations such as in a column of plasma with a non-uniform density but a straight magnetic field.{{Cite book |last1=Goldston|first1=Robert J.|url=https://www.worldcat.org/oclc/33079555|title=Introduction to plasma physics|last2=Rutherford|first2=Paul H.|publisher=Institute of Physics|year=1995 | isbn=0-7503-0325-5 | location=Bristol, UK|chapter=21. Drift waves and instabilities|oclc=33079555}} Drift wave turbulence is responsible for the transport of particles, energy and momentum across magnetic field lines.{{Cite journal| last=Horton|first=W.|date=1999|title=Drift waves and transport | url=https://link.aps.org/doi/10.1103/RevModPhys.71.735|journal=Reviews of Modern Physics | language=en | volume=71 | issue=3|pages=735–778|doi=10.1103/RevModPhys.71.735 |bibcode=1999RvMP...71..735H | issn=0034-6861 | hdl=2152/61083 |s2cid=122400874 | hdl-access=free}}

The characteristic frequency associated with drift waves involving electron flow{{Cite book| last=Chen | first = Francis F.|url=https://www.worldcat.org/oclc/933392530|title=Introduction to plasma physics and controlled fusion |year=2016 | isbn=978-3-319-22309-4|edition=3rd |location=Cham |chapter=6.8 Resistive Drift Waves|oclc=933392530}} is given by

$$\backslash omega^*\; =\; k\_\backslash perp\; \backslash left(-\backslash frac\{k\_BT\_e\}\{eB\_0\}\backslash nabla\; n\_0\backslash right)\; ,$$

where $k\_\backslash perp$ is the wavenumber perpendicular to the pressure gradient of the plasma, $k\_B$ is the Boltzmann constant, $T\_e$ is the electron temperature, $e$ is the elementary charge, $B\_0$ is the background magnetic field and $\backslash nabla\; n\_0$ is the number density gradient of the plasma.