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Beta: Difference between revisions
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Plasma performance is often expressed in terms of beta (<math>\beta</math>), defined as: | Plasma performance is often expressed in terms of beta (<math>\beta</math>), defined as: | ||
<ref>J.P. Freidberg, ''Plasma physics and fusion energy'', Cambridge University Press (2007) ISBN 0521851076</ref> | <ref>J.P. Freidberg, ''Plasma physics and fusion energy'', Cambridge University Press (2007) ISBN 0521851076</ref> | ||
:<math>\beta = \frac{\left \langle p \right \rangle}{B^2/2\mu_0}</math> | :<math>\beta = \frac{\left \langle p \right \rangle}{B^2/2\mu_0}</math> | ||
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== Normalized beta, beta limit == | == Normalized beta, beta limit == | ||
[[File:Troyon limit.png|200px|thumb|Troyon Limit<ref>ITER | [[File:Troyon limit.png|200px|thumb|Troyon Limit<ref>ITER Physics Expert Group on Disruptions, Plasma Control, and MHD, ''ITER Physics Basis Chapter 3: MHD stability, operational limits and disruptions'', [[doi:10.1088/0029-5515/39/12/303|Nucl. Fusion '''39 ''' (1999) 2251-2389]]</ref>]] | ||
<math>\beta</math> is often expressed in terms of the normalized beta (or Troyon factor)<ref> | <math>\beta</math> is often expressed in terms of the normalized beta (or Troyon factor)<ref>F. Troyon, R. Gruber, H. Saurenmann, S. Semenzato and S. Succi, ''MHD-Limits to Plasma Confinement'', [[doi:10.1088/0741-3335/26/1A/319|Plasma Phys. Control. Fusion '''26''' (1984) 209]]</ref>, an operational parameter indicating how close the plasma is to reaching the [[Greenwald limit]] or a destabilising major MHD activity. Its definition is (for tokamaks): | ||
<ref>K. Miyamoto, ''Plasma Physics and Controlled Nuclear Fusion'', Springer-Verlag (2005) ISBN 3540242171</ref> | <ref>K. Miyamoto, ''Plasma Physics and Controlled Nuclear Fusion'', Springer-Verlag (2005) ISBN 3540242171</ref> | ||
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The value of <math>\beta_N</math> has been determined numerically by Troyon to 0.028. Often <math>\beta</math> is expressed in percent, in which case <math>\beta_N = 2.8</math>. This limit results from many different numerical studies determined to find the overall <math>\beta</math> limit out of many different MHD instabilities, such as [[external kink modes]], [[ballooning kink modes]], [[internal modes]], [[localized modes]], etc. <ref>J. Freidberg, "Plasma Physics and Fusion Energy",Cambridge University Press (2007) ISBN 139780511273759</ref> <br> | The value of <math>\beta_N</math> has been determined numerically by Troyon to 0.028. Often <math>\beta</math> is expressed in percent, in which case <math>\beta_N = 2.8</math>. This limit results from many different numerical studies determined to find the overall <math>\beta</math> limit out of many different MHD instabilities, such as [[external kink modes]], [[ballooning kink modes]], [[internal modes]], [[localized modes]], etc. <ref>J. Freidberg, "Plasma Physics and Fusion Energy",Cambridge University Press (2007) ISBN 139780511273759</ref> <br> | ||
Empirical evaluation from the data of different tokamaks raises this value slightly to <math>\beta_N = 3.5</math>, although significantly higher values have been achieved. | Empirical evaluation from the data of different tokamaks raises this value slightly to <math>\beta_N = 3.5</math>, although significantly higher values have been achieved. | ||
<ref> | <ref>S.A. Sabbagh et al, ''Resistive wall stabilized operation in rotating high beta NSTX plasmas'', [[doi:10.1088/0029-5515/46/5/014|Nucl. Fusion '''46''' (2006) 635-644]]</ref> | ||
== See also == | == See also == | ||