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Corrected Freidberg
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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 name="freidberg">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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where <math>B_T</math> is the toroidal magnetic field in T, <math>a</math> is the minor radius in m, and <math>I_p</math> is the plasma current in MA. | where <math>B_T</math> is the toroidal magnetic field in T, <math>a</math> is the minor radius in m, and <math>I_p</math> is the plasma current in MA. | ||
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 | 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 name="freidberg"></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>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> | <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> | ||