The collisionality dependence of tokamak β-limits

H. R. Wilson; M. Alexander; J. W. Connor; A. M. Edwards; D. Gates; O. Grüber; R. J. Hastie; C. C. Hegna; T. C. Hender; R. J. La Haye; L. L. Lao; A. W. Morris; C. M. Roach; E. J. Strait; T. S. Taylor; M. Valovič; H. Zohm

doi:10.1088/0741-3335/38/12A/012

The collisionality dependence of tokamak β-limits

H. R. Wilson, M. Alexander, J. W. Connor, A. M. Edwards, D. Gates, O. Grüber, R. J. Hastie, C. C. Hegna, T. C. Hender, R. J. La Haye, L. L. Lao, A. W. Morris, C. M. Roach, E. J. Strait, T. S. Taylor, M. Valovič, H. Zohm

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Abstract

An interpretation of the collisionality dependence of β_N, which has been observed in many tokamaks, is presented in terms of neoclassical tearing mode theory. Magnetic islands are predicted to be driven to large saturated widths by the perturbed bootstrap current, provided their width exceeds a certain threshold value. This width is of the order of the ion banana width for low collisionality plasmas, but is substantially larger in collisional plasmas (though still within the banana regime); below this threshold value the stabilizing ion polarization current causes an island to decay. Assuming that 'background' MHD events such as ELMs or sawteeth can provide an initial 'seed' magnetic island of width w ≳ 2 cm (through toroidal coupling, for example) one can develop a model equation which retains the essential properties of neoclassical tearing mode theory and is able to reproduce many of the experimental trends associated with the reduced β-limit.

Original language	English
Pages (from-to)	A149-A163
Journal	Plasma Physics and Controlled Fusion
Volume	38
Issue number	12A
DOIs	https://doi.org/10.1088/0741-3335/38/12A/012
State	Published - 1996
Externally published	Yes

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Wilson, H. R., Alexander, M., Connor, J. W., Edwards, A. M., Gates, D., Grüber, O., Hastie, R. J., Hegna, C. C., Hender, T. C., La Haye, R. J., Lao, L. L., Morris, A. W., Roach, C. M., Strait, E. J., Taylor, T. S., Valovič, M., & Zohm, H. (1996). The collisionality dependence of tokamak β-limits. Plasma Physics and Controlled Fusion, 38(12A), A149-A163. https://doi.org/10.1088/0741-3335/38/12A/012

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title = "The collisionality dependence of tokamak β-limits",

abstract = "An interpretation of the collisionality dependence of βN, which has been observed in many tokamaks, is presented in terms of neoclassical tearing mode theory. Magnetic islands are predicted to be driven to large saturated widths by the perturbed bootstrap current, provided their width exceeds a certain threshold value. This width is of the order of the ion banana width for low collisionality plasmas, but is substantially larger in collisional plasmas (though still within the banana regime); below this threshold value the stabilizing ion polarization current causes an island to decay. Assuming that 'background' MHD events such as ELMs or sawteeth can provide an initial 'seed' magnetic island of width w ≳ 2 cm (through toroidal coupling, for example) one can develop a model equation which retains the essential properties of neoclassical tearing mode theory and is able to reproduce many of the experimental trends associated with the reduced β-limit.",

author = "Wilson, {H. R.} and M. Alexander and Connor, {J. W.} and Edwards, {A. M.} and D. Gates and O. Gr{\"u}ber and Hastie, {R. J.} and Hegna, {C. C.} and Hender, {T. C.} and {La Haye}, {R. J.} and Lao, {L. L.} and Morris, {A. W.} and Roach, {C. M.} and Strait, {E. J.} and Taylor, {T. S.} and M. Valovi{\v c} and H. Zohm",

year = "1996",

doi = "10.1088/0741-3335/38/12A/012",

language = "English",

volume = "38",

pages = "A149--A163",

journal = "Plasma Physics and Controlled Fusion",

issn = "0741-3335",

publisher = "IOP Publishing",

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Wilson, HR, Alexander, M, Connor, JW, Edwards, AM, Gates, D, Grüber, O, Hastie, RJ, Hegna, CC, Hender, TC, La Haye, RJ, Lao, LL, Morris, AW, Roach, CM, Strait, EJ, Taylor, TS, Valovič, M & Zohm, H 1996, 'The collisionality dependence of tokamak β-limits', Plasma Physics and Controlled Fusion, vol. 38, no. 12A, pp. A149-A163. https://doi.org/10.1088/0741-3335/38/12A/012

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T1 - The collisionality dependence of tokamak β-limits

AU - Wilson, H. R.

AU - Alexander, M.

AU - Connor, J. W.

AU - Edwards, A. M.

AU - Gates, D.

AU - Grüber, O.

AU - Hastie, R. J.

AU - Hegna, C. C.

AU - Hender, T. C.

AU - La Haye, R. J.

AU - Lao, L. L.

AU - Morris, A. W.

AU - Roach, C. M.

AU - Strait, E. J.

AU - Taylor, T. S.

AU - Valovič, M.

AU - Zohm, H.

PY - 1996

Y1 - 1996

N2 - An interpretation of the collisionality dependence of βN, which has been observed in many tokamaks, is presented in terms of neoclassical tearing mode theory. Magnetic islands are predicted to be driven to large saturated widths by the perturbed bootstrap current, provided their width exceeds a certain threshold value. This width is of the order of the ion banana width for low collisionality plasmas, but is substantially larger in collisional plasmas (though still within the banana regime); below this threshold value the stabilizing ion polarization current causes an island to decay. Assuming that 'background' MHD events such as ELMs or sawteeth can provide an initial 'seed' magnetic island of width w ≳ 2 cm (through toroidal coupling, for example) one can develop a model equation which retains the essential properties of neoclassical tearing mode theory and is able to reproduce many of the experimental trends associated with the reduced β-limit.

AB - An interpretation of the collisionality dependence of βN, which has been observed in many tokamaks, is presented in terms of neoclassical tearing mode theory. Magnetic islands are predicted to be driven to large saturated widths by the perturbed bootstrap current, provided their width exceeds a certain threshold value. This width is of the order of the ion banana width for low collisionality plasmas, but is substantially larger in collisional plasmas (though still within the banana regime); below this threshold value the stabilizing ion polarization current causes an island to decay. Assuming that 'background' MHD events such as ELMs or sawteeth can provide an initial 'seed' magnetic island of width w ≳ 2 cm (through toroidal coupling, for example) one can develop a model equation which retains the essential properties of neoclassical tearing mode theory and is able to reproduce many of the experimental trends associated with the reduced β-limit.

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VL - 38

SP - A149-A163

JO - Plasma Physics and Controlled Fusion

JF - Plasma Physics and Controlled Fusion

IS - 12A

ER -

The collisionality dependence of tokamak β-limits

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