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  • 1
    Electronic Resource
    Electronic Resource
    Long mean-free path collisional stability of electromagnetic modes in axisymmetric closed magnetic field configurations (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 201-211 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An axially symmetric plasma confined by a poloidal magnetic field with closed field lines is considered. A kinetic analysis of electromagnetic modes is performed for an "intermediate collisionality" ordering in which the particle collision frequency is much smaller than the transit or bounce frequency, but much larger than the mode, magnetic drift, and diamagnetic drift frequencies. A second order integrodifferential ballooning equation for electromagnetic modes is derived, which describes "high-frequency" ideal magnetohydrodynamic (MHD) and "low-frequency" entropy modes. The equation recovers the corresponding ideal MHD ballooning equation for the mode frequency greater than the magnetic drift and diamagnetic drift frequencies, and generalizes the results of an earlier electrostatic treatment of the entropy mode to arbitrary plasma beta. Ion gyrorelaxation collisional modifications to the entropy mode are also evaluated for arbitrary plasma beta and specific results are presented for both a point dipole and Z pinch. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1424309
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetic stability of electrostatic plasma modes in a dipolar magnetic field (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4414-4426 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An axially symmetric plasma immersed in a poloidal magnetic field with closed lines is considered. Low-frequency electrostatic modes are studied kinetically for an "intermediate collisionality" ordering, in which the particle collision frequency is much smaller than the transit or bounce frequency, but much larger than the mode, magnetic drift, and diamagnetic drift frequencies. This ordering is appropriate for the Levitated Dipole Experiment (LDX) [J. Kesner et al., 17th IAEA Fusion Energy Conference, Yokahama, Japan (IAEA, Vienna, 1999)] and some other closed field line devices. "High-frequency" magnetohydrodynamic-like and "low-frequency" entropy modes are found and stability boundaries are determined. Collisional effects are considered and the corresponding ion gyro-relaxation effects are evaluated. These effects introduce dissipation (or inverse dissipation) and are shown to modify the stability picture considerably, while leaving large stability regions in the d, η parametric space, where η is the ratio of the gradients of temperature and density and d is the ratio of the diamagnetic and magnetic drift frequencies. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1399058
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  • 3
    Electronic Resource
    Electronic Resource
    A rotating shell and stabilization of the tokamak resistive wall mode (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 5007-5012 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The finite resistivity of the wall that surrounds any toroidal plasma confinement device can lead to a branch of instabilities known as the resistive wall mode (RWM). Theory indicates that the RWM is potentially activated whenever the plasma equilibrium is unstable with the wall placed at infinity. In particular, advanced tokamak power plant designs require the plasma β to be above the critical value for this condition to be satisfied. Accordingly, it is important to find a method of stabilizing this mode. In this work we describe a method of stabilizing the tokamak RWM that utilizes a secondary rotating conducting shell surrounding the plasma and first wall. This scheme was first thought of for the reversed-field pinch, but must be reexamined for the tokamak as the mode involved has different characteristics. It is shown that provided the second wall is suitably positioned, RWM stabilization of a tokamak is possible even in the absence of plasma rotation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319333
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  • 4
    Electronic Resource
    Electronic Resource
    The bootstrap current in a tokamak with electron cyclotron heating (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3211-3216 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The bootstrap current in a non-Maxwellian tokamak plasma with electron cyclotron heating is calculated. The calculation is exact in the limit of highly charged ions, where pitch-angle scattering dominates over quasilinear diffusion, and shows that the current is entirely determined by the pressure of the trapped electrons. If the ion charge is finite, the current is shown to consist of two terms: one driven by collisions, and one driven by the heating and losses. The former is calculated approximately by using a model collision operator, and is found to be determined by the distribution of trapped electrons alone; the latter is discussed qualitatively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872462
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  • 5
    Electronic Resource
    Electronic Resource
    The influence of fast ions on the magnetohydrodynamic stability of negative shear profiles (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2181-2187 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of energetic ions on the stability of ideal double kink modes in a tokamak plasma with negative magnetic shear is investigated. It is found that the fast ions play a similar role as for the ordinary m=n=1 internal kink. In particular, phenomena analogous to sawtooth stabilization and fishbone excitation are possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872381
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  • 6
    Electronic Resource
    Electronic Resource
    An analytic study of the magnetohydrodynamic stability of inverse shear profiles (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3369-3374 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper reports on the ideal magnetohydrodynamic (MHD) stability of tokamak field profiles that have a non-monotonic safety factor q(r). An analytic criterion is obtained for these "inverse shear'' profiles by expanding in inverse aspect ratio and assuming that the minimum in q is slightly less than the m/n value of the mode under examination (m and n being the principal poloidal and toroidal mode numbers of the instability). Three terms are identified as controlling the stability of this "double kink''; two of them are stabilizing and due, respectively, to field line bending and the interaction of average favorable curvature with the pressure gradient. The possibility of instability comes from the third term which is due to toroidal coupling and is ballooning in character. The analytic results are compared with those from a fully toroidal stability code.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871612
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  • 7
    Electronic Resource
    Electronic Resource
    Non-uniform rotation and the resistive wall mode (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3619-3627 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Advanced Tokamak Concepts [C. Kessel, J. Manickam, G. Rewoldt, and W. M. Tang, Phys. Rev. Lett. 72, 1212 (1994)] have been designed assuming that the "Resistive Wall Mode'' (RWM) is stable. It has recently been shown that the RWM can be stabilized by a combination of strong uniform plasma rotation and visco-resistive dissipation. In this paper we examine the consequences of a sheared flow on the RWM, and contrast the results to the case of uniform flow. It is shown that, as for uniform flow, the rotation initially further destabilizes the resistive wall mode, but for higher rotation velocities the growth rate is reduced, and the presence of plasma dissipation may completely stabilize the mode. However, sheared rotation allows the possibility of the RWM coupling to and converting into a Kelvin-Helmholtz mode. It is shown that the position of the wall with respect to the critical position for stabilization of the external kink mode is of crucial importance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871954
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  • 8
    Electronic Resource
    Electronic Resource
    Threshold for neoclassical magnetic islands in a low collision frequency tokamak (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 248-265 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A kinetic theory for magnetic islands in a low collision frequency tokamak plasma is presented. Self-consistent equations for the islands' width, w, and propagation frequency, ω, are derived. These include contributions from the perturbed bootstrap current and the toroidally enhanced ion polarization drift. The bootstrap current is independent of the island propagation frequency and provides a drive for the island in tokamak plasmas when the pressure decreases with an increasing safety factor. The polarization drift is frequency dependent, and therefore its effect on the island stability cannot be deduced unless ω is known. This frequency is determined by the dominant dissipation mechanism, which for low effective collision frequency, νeff=ν/ε〈ω, is governed by the electrons close to the trapped/passing boundary. The islands are found to propagate in the electron diamagnetic direction in which case the polarization drift is stabilizing and results in a threshold width for island growth, which is of the order of the ion banana width. At larger island widths the polarization current term becomes small and the island evolution is determined by the bootstrap current drive and Δ′ alone, where Δ′ is a measure of the magnetic free energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871830
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  • 9
    Electronic Resource
    Electronic Resource
    Response to "Comment on ‘Stability of coupled tearing and twisting modes in tokamaks''' [Phys. Plasmas 1, 3308 (1994)] (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3925-3925 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The authors contend that incorrect inferences are drawn by Ding Li regarding the sources of error and of the basis function method used in the calculations of toroidally coupled tearing modes. (AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871024
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  • 10
    Electronic Resource
    Electronic Resource
    Stability criterion for edge-localized, high-n external modes in tokamaks : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2029-2032 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ideal-magnetohydrodynamics (MHD) energy principle is used to derive a necessary stability criterion for high-toroidal-number (n) external modes in axisymmetric equilibria. The corresponding trial functions are expressed in the ballooning representation, but have a finite amplitude at the plasma boundary and can apply to equilibria where the conventional, high-n internal ballooning criterion predicts stability. These trial functions are constructed by solving the standard local ballooning equation at the plasma boundary flux surface with the radial wave number parameter as a complex eigenvalue, such that the radial envelope of the mode is an exponential decaying into the plasma. The resulting stability criterion includes the surface and vacuum contributions to the MHD potential energy associated with the mode finite edge amplitude, and provides a framework for analyzing free-boundary ballooning and peeling modes. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1347038
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