{{Short description|Type of magnetohydrodynamic instability}} 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 possess a number of solutions, including ion-acoustic solitary waves,<ref>{{Cite journal |last1=Meiss |first1=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|url-access=subscription }}</ref> and are roughly analogous to modons.<ref>{{Cite journal |last=Swaters |first=Gordon E. |date=1986-05-01 |title=Stability conditions and<i>a</i> <i>p</i><i>r</i><i>i</i><i>o</i><i>r</i><i>i</i>estimates 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|url-access=subscription }}</ref>
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.<ref>{{Cite book |last1=Goldston|first1=Robert J.|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}}</ref> Drift wave turbulence is responsible for the transport of particles, energy and momentum across magnetic field lines.<ref>{{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}}</ref>
The characteristic frequency associated with drift waves involving electron flow<ref>{{Cite book| last=Chen | first = Francis F.|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}}</ref> is given by <math display="block">\omega^* = k_\perp \left(-\frac{k_BT_e}{eB_0}\frac{\nabla n_0}{n_0}\right) ,</math> where <math>k_\perp</math> is the wavenumber perpendicular to the pressure gradient of the plasma, <math>k_B</math> is the Boltzmann constant, <math>T_e</math> is the electron temperature, <math>e</math> is the elementary charge, <math>B_0</math> is the background magnetic field and <math>\nabla n_0</math> is the number density gradient of the plasma.
== References == {{reflist}}
Category:Waves in plasmas
{{plasma-stub}}