kink instability

{{Short description|Current-driven plasma instability}}

File:Kink instability at Aldermaston.jpg

A kink instability (also known as a kink oscillation or kink mode) is a current-driven plasma instability characterized by transverse displacements of a plasma column's cross-section from its center of mass without any change in the characteristics of the plasma. It typically develops in a thin plasma column carrying a strong axial current which exceeds the Kruskal–Shafranov limit{{Cite journal

|last1=Ryutov|first1=D. D.

|last2=Furno|first2=I.

|last3=Intrator|first3=T. P.

|last4=Abbate|first4=S.

|last5=Madziwa-Nussinov|first5=T.

|date=2006

|title=Phenomenological theory of the kink instability in a slender plasma column

|journal=Physics of Plasmas|language=en

|volume=13|issue=3|pages=032105|doi=10.1063/1.2180667|issn=1070-664X|bibcode=2006PhPl...13c2105R

|url=https://digital.library.unt.edu/ark:/67531/metadc881368/}}{{Cite journal

|last1=DeHaas|first1=Timothy

|last2=Gekelman|first2=Walter

|last3=Van Compernolle|first3=Bart

|date=2015

|title=Experimental study of a linear/non-linear flux rope

|journal=Physics of Plasmas

|language=en|volume=22|issue=8|pages=082118

|doi=10.1063/1.4928888|issn=1070-664X|bibcode=2015PhPl...22h2118D|doi-access=free}}{{Cite journal

|last1=Oz|first1=E.

|last2=Myers|first2=C. E.

|last3=Yamada|first3=M.

|last4=Ji|first4=H.

|last5=Kulsrud|first5=R. M.

|last6=Xie|first6=J.

|date=2011

|title=Experimental verification of the Kruskal-Shafranov stability limit in line-tied partial-toroidal plasmas

|journal=Physics of Plasmas|language=en|volume=18|issue=10|pages=102107

|doi=10.1063/1.3647567|issn=1070-664X|bibcode=2011PhPl...18j2107O|url=https://digital.library.unt.edu/ark:/67531/metadc830825/}} and is sometimes known as the Kruskal–Shafranov (kink) instability,{{Cite book

|url=https://books.google.com/books?id=Jc43BQAAQBAJ&q=%22Kruskal%E2%80%93Shafranov+instability%22

|title=Handbook on Plasma Instabilities

|last=Cap|first=Ferdinand F.|date=2013-09-11|publisher=Academic Press|isbn=9781483271057|language=en}}{{Cite book

|url=https://books.google.com/books?id=0CHqCAAAQBAJ&q=%22Kruskal%E2%80%93Shafranov+instability%22|title=Plasma Instabilities and Nonlinear Effects|last=Hasegawa|first=A.|date=2012-12-06|publisher=Springer Science & Business Media|isbn=9783642659805|language=en}} named after Martin David Kruskal and Vitaly Shafranov.

The kink instability was first widely explored in fusion power machines with Z-pinch configurations in the 1950s.{{Cite book|url=https://books.google.com/books?id=Aj02DgAAQBAJ&dq=%22absolute+plasma+instabilities%22%2C+as+opposed+to+convective+processes&pg=PA46|title=Magnetic Confinement Fusion Driven Thermonuclear Energy|last=Zohuri|first=Bahman|date=2017-02-23|publisher=Springer|isbn=9783319511771|pages=46–48|language=en}} It is one of the common magnetohydrodynamic instability modes which can develop in a pinch plasma and is sometimes referred to as the $m=1$ mode. (The other is the $m=0$ mode known as the sausage instability.)

If a "kink" begins to develop in a column the magnetic forces on the inside of the kink become larger than those on the outside, which leads to growth of the perturbation.[http://plasmadictionary.llnl.gov/terms.lasso?-MaxRecords=1&-SkipRecords=1&-SortField=Term&-SortOrder=ascending&ABC=K&page=detail Plasma Dictionary] {{webarchive|url=https://web.archive.org/web/20060929192916/http://plasmadictionary.llnl.gov/terms.lasso?-MaxRecords=1&-SkipRecords=1&-SortField=Term&-SortOrder=ascending&ABC=K&page=detail |date=2006-09-29 }} As it develops at fixed areas in the plasma, kinks belong to the class of "absolute plasma instabilities", as opposed to convective processes.