A model for ideal {ital m}=1 internal kink stabilization by minority ion cyclotron resonant heating
- UKAEA Government Division, Fusion, Culham Laboratory (Euratom/UKAEA Fusion Association), Abingdon, Oxfordshire, OX14 3DB (United Kingdom)
A generalized energy principle is used to determine the effect of ion cyclotron resonant heating (ICRH) on the stability of {ital m}=1 internal kink displacements in the low-frequency limit: such displacements are associated with sawtooth oscillations. An integral expression is obtained for the contribution to the plasma energy of an ICRH-heated minority ion population with strong temperature anisotropy, which relates the former to the ICRH power input and its deposition profile. The link is provided by a realistic, but analytically tractable, new model for the distribution function of the heated ions, which is based on the approach of Stix [Nucl. Fusion {bold 15}, 737 (1975)]. Numerical evaluation of the integral expression is carried out using parameters inferred from ICRH experiments in the Joint European Torus (JET) [Campbell {ital et} {ital al}., Phys. Rev. Lett. {bold 60}, 2148 (1988)]. It is shown that the ideal {ital m}=1 internal kink is stable at values of the poloidal plasma beta {beta}{sub {ital p}} which typically lie in the range 0.4--1, depending on the radio-frequency power input and the radius {ital r}{sub 1} of the {ital q}=1 surface. Stability is thus possible at values of {beta}{sub {ital p}} lying significantly above the magnetohydrodynamic instability threshold ({congruent}0.3). If the perpendicular temperature {ital T}{sub {perpendicular}} of the hot ions exceeds the parallel temperature by a factor of 10 or more, and {ital r}{sub 1} is greater than about one-third of the plasma minor radius, trapped ions have a greater stabilizing effect than passing ions. Stabilization is most easily achieved, however, if {ital r}{sub 1} is small. The hot-ion plasma energy depends strongly on the value of {ital T}{sub {perpendicular}}, but for fixed {ital T}{sub {perpendicular}} is insensitive to the degree of anisotropy.
- OSTI ID:
- 165182
- Journal Information:
- Physics of Plasmas, Vol. 2, Issue 5; Other Information: PBD: May 1995
- Country of Publication:
- United States
- Language:
- English
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