Browsing by Subject "Kinetic equation"

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Characteristic relaxation rates of a Bose gas in the classical, quantum and condensed regimes
(2011-08) Gust, Erich D.; Reichl, L. E.; Raizen, Mark G.; Gamba, Irene M.; Bohm, Arno; Gleeson, Austin; Niu, Qian
We obtain the characteristic relaxation rates and relaxation modes of a Bose gas in three regimes. The classical regime corresponds to a classical gas of hard spheres and the quantum regime corresponds to an interacting quantum Bose gas with no Bose-Einstein condensate present. In the condensed regime a Bose-Einstein condensate is present and modifies the behavior of the gas. In each regime there is a different kinetic equation that describes the evolution of the relevant distribution function. The classical kinetic equation is the Boltzmann equation and the quantum kinetic equation with no condensate present is the Uehling-Uhlenbeck equation. When a condensate is present, we derive a new kinetic equation that describes the evolution of the momentum distribution of Bogoliubov excitations or bogolons. For each of the three kinetic equations, we linearize the collision integral and use it to generate the elements of a collision matrix. The eigenvalues of this matrix give us the characteristic relaxation rates and the eigenvectors give us the relaxation modes. We report numerical results for the eigenvalues in each regime as the particle species, density and temperature of the gas are varied.
Tokamak disruptions : investigations of symptoms and treatments
(2019-09-16) Fontanilla, Adrian Kristopher; Breizman, Boris N.; Hazeltine, Richard D; Morrison, Philip J; Gentle, Kenneth W; Raja, Laxminarayan L
Plasma disruptions are a catastrophic loss of confinement that ultimately concludes with the release of the thermal and magnetic energy stored in the vessel containing the plasma. The threat of disruptions therefore factor into the development of fusion-grade tokamak reactors such as ITER. This work discusses the deleterious effects of disruption, particularly runaway electrons. Tokamaks are especially susceptible to runaway electrons because of their highly inductive nature. The lifetime of seed runaways are calculated and the likelihood for them to exponentiate is discussed. Strategies for alleviating the danger posed by disruptions are considered. The basic strategy, assuming a disruption is imminent, is to preemptively cool the plasma. ITER currently plans on deploying impurity pellets to safely radiate away the energy, so investigations of pellet heating and ablation are conducted.