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  • 1
    Electronic Resource
    Electronic Resource
    J* optimization of small aspect ratio stellarator/tokamak hybrid devices : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1752-1758 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new class of low aspect ratio toroidal hybrid stellarators is found using a more general plasma confinement optimization criterion than quasisymmetrization. The plasma current profile and shape of the outer magnetic flux surface are used as control variables to achieve near constancy of the longitudinal invariant J* on internal flux surfaces (quasiomnigeneity), in addition to a number of other desirable physics target properties. A range of compact (small aspect ratio A), low plasma current devices have been found with significantly improved confinement, both for thermal as well as energetic (collisionless) particle components. With reasonable increases in magnetic field and geometric size, such devices can also be scaled to confine 3.5 MeV alpha particle orbits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872844
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  • 2
    Electronic Resource
    Electronic Resource
    Physics of compact stellarators : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1858-1864 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent progress in the theoretical understanding and design of compact stellarators is described. Hybrid devices, which depart from canonical stellarators by deriving benefits from the bootstrap current which flows at finite beta, comprise a class of low aspect ratio A〈4 stellarators. They possess external kink stability (at moderate beta) in the absence of a conducting wall, possible immunity to disruptions through external control of the transform and magnetic shear, and they achieve volume-averaged ballooning beta limits (4%–6%) similar to those in tokamaks. In addition, bootstrap currents can reduce the effects of magnetic islands (self-healing effect) and lead to simpler stellarator coils by reducing the required external transform. Powerful physics and coil optimization codes have been developed and integrated to design experiments aimed at exploring compact stellarators. The physics basis for designing the national compact stellarator will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873489
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  • 3
    Electronic Resource
    Electronic Resource
    Equilibrium reconstruction of the safety factor profile in tokamaks from motional Stark effect data (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2277-2290 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The motional Stark effect (MSE) diagnostic has been used to obtain accurate measurements of the internal magnetic pitch angle tan−1(BZ/BT) in finite-pressure tokamaks. The MSE data, together with external magnetic probe data, are used to reconstruct self-consistently the equilibrium safety factor (q) profile and, hence, the plasma current density, in the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Nucl. Fusion Res. 1, 51 (1986)] and the Princeton Beta Experiment-Modified (PBX-M) tokamak [Phys. Fluids B 2, 1271 (1990)]. An efficient computational scheme, based on an inverse coordinate representation of the magnetic field, has been developed to solve the coupled nonlinear equations describing both the magnetohydrodynamic (MHD) equilibrium and the q profile, which best match all the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870625
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  • 4
    Electronic Resource
    Electronic Resource
    Explicit spectrally optimized Fourier series for nested magnetic surfaces (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2664-2675 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonuniqueness of the poloidal angle θ in the parametric representation of a space curve x(θ)=[R(θ),Z(θ)] can be exploited to condense the Fourier spectra of R and Z. The nonlinear equation describing this spectral condensation was previously derived and solved numerically using Lagrange multipliers. Here a special case of the condensation equation is shown to be exactly solvable, leading to an explicit representation for x. A family of such representations is generated that possesses increasingly condensed spectra as a parameter is varied. Applications to a variety of curves are considered as models for three-dimensional magnetohydrodynamic (MHD) equilibria with nested flux surfaces. A substantial improvement occurs in spectral convergence compared with a polar representation, while retaining the numerical simplicity of the polar constraint. The asymptotic behavior for the R and Z spectral coefficients near a magnetic axis is analyzed. Implications for improvements of MHD equilibrium calculations are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872954
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  • 5
    Electronic Resource
    Electronic Resource
    Relaxation rate of poloidal rotation in the banana regime in tokamaks (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 705-707 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The relaxation rate νp of poloidal rotation in the banana regime in tokamaks is calculated using a time-dependent parallel viscosity. It is found that νp is on the order of νii, the ion–ion collision frequency, with no geometric enhancement factor associated with toroidicity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859134
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  • 6
    Electronic Resource
    Electronic Resource
    Finite-aspect-ratio effects on the bootstrap current in tokamaks (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3150-3152 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The bootstrap current in tokamaks is determined in the low collision frequency regime for arbitrary values of the aspect ratio and effect charge. The resulting expression should be useful for a quantitative analysis of currents in tokamaks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866973
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  • 7
    Electronic Resource
    Electronic Resource
    Transport scaling in the collisionless-detrapping regime in stellarators (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 11-14 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stellarator transport scalings with electric field, geometry, and collision frequency in the reactor-relevant collisionless-detrapping regime are determined from numerical solutions of the drift kinetic equation. A new geometrical scaling, proportional to ε3/2t rather than εtε1/2h, is found, where εt is the inverse aspect ratio and εh is the helical ripple. With the new scaling, no reduction in energy confinement time is associated with large helical ripple, which provides design flexibility. Integral expressions for the particle and heat fluxes that are useful for transport simulations are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866559
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  • 8
    Electronic Resource
    Electronic Resource
    External inductance of an axisymmetric plasma (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 790-793 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The external inductance of an axisymmetric toroidal plasma with an arbitrary aspect ratio and cross section is obtained using a Green's function method. By varying an equivalent skin current density over the plasma surface, while keeping the total toroidal current fixed, the plasma boundary is made to coincide with a magnetic surface. Numerical computations of the self-inductance and mutual inductance as functions of aspect ratio and elongation are fitted to simple analytic formulas. The effect of distributed plasma current on the volt-seconds required to reach a prescribed net current is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865934
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  • 9
    Electronic Resource
    Electronic Resource
    Neoclassical transport fluxes in the plateau regime in nonaxisymmetric toroidal plasmas (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 521-526 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The neoclassical fluxes in the plateau regime in an arbitrary large aspect ratio nonaxisymmetric toroidal system are calculated using fluid equations. The results are evaluated explicitly for a stellarator and for a rippled tokamak. For typical stellarator parameters, the helical magnetic field contribution to the particle and heat fluxes is comparable to the toroidicity contribution, and therefore, cannot be neglected. In addition, the helical magnetic field contribution to the parallel viscosity is capable of reversing the directions of the bootstrap current and Ware pinch flux in the plateau regime. In contrast, the neoclassical particle and heat fluxes in a rippled tokamak are comparable to those in an axisymmetric tokamak after the radial electric field and parallel flow velocity are determined (without external sources).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865439
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  • 10
    Electronic Resource
    Electronic Resource
    Ballooning stability boundaries with plasma compression (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2813-2815 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Level curves for the resistive compressible ballooning growth rates and the ideal ballooning stability boundaries with incompressibility and perpendicular compressibility are determined in the parameter space of shear-versus-pressure gradient for realistic tokamak equilibria. The trajectories of these level curves differ from the ideal incompressible stability boundary in this space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865242
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