Effects of an Alpha Particle Slowing-down Distribution on Tokamak Ballooning Modes PDF Download
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Languages : en
Pages : 20
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Languages : en
Pages : 20
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Languages : en
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Hot .cap alpha.-particles and thermalized helium ash particles in tokamaks can have significant effects on high toroidal mode number instabilities such as the trapped-electron drift mode and the kinetically calculated magnetohydrodynamic ballooning mode. In particular, the effects can be stabilizing, destabilizing, or negligible, depending on the parameters involved. In high-temperature tokamaks capable of producing significant numbers of hot .cap alpha.-particles, the predominant interaction of the mode with the .cap alpha.-particles is through resonances of various sorts. In turn, the modes can cause significant anomalous transport of the .cap alpha.-particles and the helium ash. Here, results of comprehensive linear eigenfrequency-eigenfunction calculations are presented for relevant realistic cases to show these effects. 24 refs., 12 figs., 6 tabs.
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Languages : en
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The effects of a trapped, precessing alpha particle population on ballooning modes are examined for a large-aspect-ratio, shifted circular flux surface tokamak equilibrium. The alphas are modeled in the deeply trapped limit and with a Maxwellian distribution in energy. The resulting kinetic ballooning equation is solved numerically, and the dependence of the eigenvalues and stability boundaries on shear, background pressure gradient, and ratio of hot to background temperatures and densities is investigated. In the low-frequency regime (.omega. “.omega./sub dH/ = alpha precessional drift frequency), the alpha component has a stabilizing influence, while in the intermediate-frequency range (.omega. less than or equal to .omega./sub dH/) the alphas destabilize ballooning modes through interaction with the trapped particle precessional drift resonance. Parameter ranges that should be typical of alpha production in near-term tokamak devices such as the Tokamak Fusion Test Reactor (TFTR) are considered.
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Languages : en
Pages : 22
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Alpha particle populations can significantly alter existing MHD in stabilities in tokamaks through kinetic effects and coupling to otherwise stable shear Alfven waves. Here we consider resonances of the trapped alpha precessional drift with both the usual ballooning mode diamagnetic frequency ([omega]{sub *i}/2) and the toroidicity induced Alfven eigenmode (TAE). This is examined for noncircular tokamaks in the high-n ballooning limit using an isotropic alpha slowing down distribution and retaining the full energy and pitch angle dispersion in the alpha drift frequency. Applying this to CIT and ITER indicates that ballooning instabilities can persist at [Beta]'s below the ideal MHD threshold. These are especially dominated by the destabilization of the TAE mode. In addition, a hybrid fluid-particle approach for simulating alpha effects on pressure-gradient driven instabilities is described. 13 refs., 6 figs.
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Languages : en
Pages : 19
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We have analyzed theoretically the resonant excitations of kinetic ballooning modes (KBM) by the energetic ions/alpha particles in tokamaks. Our theory includes finite-size orbit effects of both circulating and trapped particles. With energetic-particle contributions suppressed in the singular inertial layer, an analytic.dispersion relation can then be derived via an asymptotic matching analysis. The dispersion relation, in particular, demonstrates the existence of two types of modes; that is, the magnetohydrodynamic (MHD) gap mode and the energetic-particle continuum mode. Specific expressions for real frequencies, growth rates and threshold conditions are also derived for a model slowing-down beam ion distribution function.
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Languages : en
Pages : 16
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This report describes the work done by Science Applications International Corporation to study the effects of energetic particles on the microstability of a high temperature tokamak. The effects of an energetic population on ballooning modes in a large aspect ratio, shifted circular flux surface tokamak equilibrium are investigated with the newly developed gryokinetic numerical technique. The gryokinetic equations for the background ion and electron, as well as that of the energetic population are solved directly as an initial problem. The energetic particles are modeled with a slow-down distribution in energy. It is found that the ballooning mode stability of the plasma with an energetic species of increasing concentration does not differ much from an increase in the background plasma beta, except for possible energetic particle drift resonances. This result is encouraging to the idea that energetic particles such as alphas may be used to stabilize the ballooning modes in a fusion reactor.
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Languages : en
Pages : 16
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Book Description
This report describes the work done by Science Applications International Corporation to study the effects of energetic particles on the microstability of a high temperature tokamak. The effects of an energetic population on ballooning modes in a large aspect ratio, shifted circular flux surface tokamak equilibrium are investigated with the newly developed gryokinetic numerical technique. The gryokinetic equations for the background ion and electron, as well as that of the energetic population are solved directly as an initial problem. The energetic particles are modeled with a slow-down distribution in energy. It is found that the ballooning mode stability of the plasma with an energetic species of increasing concentration does not differ much from an increase in the background plasma beta, except for possible energetic particle drift resonances. This result is encouraging to the idea that energetic particles such as alphas may be used to stabilize the ballooning modes in a fusion reactor.
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Category : Controlled fusion
Languages : en
Pages : 294
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Category : Aeronautics
Languages : en
Pages : 740
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Category : Power resources
Languages : en
Pages : 806
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Semiannual, with semiannual and annual indexes. References to all scientific and technical literature coming from DOE, its laboratories, energy centers, and contractors. Includes all works deriving from DOE, other related government-sponsored information, and foreign nonnuclear information. Arranged under 39 categories, e.g., Biomedical sciences, basic studies; Biomedical sciences, applied studies; Health and safety; and Fusion energy. Entry gives bibliographical information and abstract. Corporate, author, subject, report number indexes.
