Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session W16: Sherwood IV |
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Sponsoring Units: DPP Chair: Eric Held, Utah State University Room: Hyatt Regency Dallas Landmark D |
Tuesday, April 25, 2006 10:45AM - 11:15AM |
W16.00001: Nonlinear Evolution of Nonthermal Ion Distributions in the Presence of High Power Ion Cyclotron Resonance Heating Invited Speaker: The nonlinear evolution of nonthermal ion distribution functions in the presence of high power ICRF waves is of great interest in both present day tokamaks and in future burning plasmas. Wave-particle interactions of special interest include evolution of the ion distribution due to wave-driven velocity space diffusion, as well as ICRF wave interaction with nonthermal distributions of fast neutral beam ions and fusion generated alpha-particles. In order to accurately simulate these interactions a full-wave field solver has been developed to compute the wave propagation using a plasma response that is valid to all orders in the ion Larmor radius and is valid for arbitrary ion particle distributions. A novel re-formulation of the quasilinear diffusion coefficient has made it possible to couple electric field predictions from this field solver to a bounce averaged Fokker Planck code. The combined model is then iterated until a self-consistent ion particle distribution is achieved. We have also coupled a Monte Carlo orbit code to a full-wave field solver in order to explore situations where finite orbit effects may be important. Results and implications from these combined models will be discussed for experiments in the DIII-D, NSTX, and Alcator C-Mod devices. [Preview Abstract] |
Tuesday, April 25, 2006 11:15AM - 11:45AM |
W16.00002: How Good is a Quasilinear ICRH Operator? A New Method for ICRH Simulation in a Guiding Center Code Invited Speaker: The widely used form of conventional quasilinear cyclotron resonance heating operator was derived in a homogeneous system, and then extended to an inhomogeneous system assuming that the resonance layer is thin enough to ignore the inhomogeneity effects and the resonance time is short enough to neglect the nonlinear interactions. It is also assumed that the Coulomb collisions are weak enough not to interfere with the quasilinear wave-particle interaction process within a resonance layer, but strong enough to decorrelate the consecutive resonance layers (in addition to the multi-mode decorrelation). However, a six dimensional numerical Lorentz-force simulation reveals that these assumptions break down in many physical situations and can yield incorrect estimate of quasilinear heating rate. Detailed description on the validity of the quasilinear theory will be presented, in comparison with the six dimensional numerical results, under assumed rf field profiles of practical interest. Based upon the six dimensional study, we also report a new reduced method to evaluate the ion cyclotron resonance interaction in a guiding center kinetic code, which can accurately include the effects of nonlinear orbit distortion, wave inhomogeneity, magnetic field inhomogeneity (trapped-passing particles), multiple wave numbers, and Coulomb collisions. \newline \newline In collaboration with Gunyoung Park, Dept. of Physics, KAIST, Daejon, 305-701, Korea. [Preview Abstract] |
Tuesday, April 25, 2006 11:45AM - 12:15PM |
W16.00003: Ion acceleration in laser-irradiated micro-clusters Invited Speaker: A theory has been developed to describe ion acceleration in dense laser-irradiated clusters that are smaller than the laser wave-length [1]. The theory reveals that the breakdown of quasineutrality affects cluster dynamics in a dramatic way: the laser can create a positively charged ion shell that expands due to its own space-charge much faster than the central part of the cluster. The theory also shows a trend for the electrons to have a two-component distribution: a cold core that responds to the laser field coherently and a hot halo that undergoes stochastic heating. The hot electrons expand together with the equal number of ions accelerated to supersonic velocities in a double layer at the cluster edge. The mechanism produces ions with energies grater than the ponderomotive potential. A spectrum of ions produced by large clusters is found from a kinetic model of the hot-electron halo that takes into account electron cooling due to the cluster expansion. The halo makes ion spectrum anisotropic, which is consistent with recent experimental results. The theory of ion acceleration suggests that larger deuterium clusters can significantly enhance the neutron yield in laser-cluster experiments. \newline \newline [1] B.N. Breizman and A.V. Arefiev, Phys. Plasmas 12, 056706 (2005). [Preview Abstract] |
Tuesday, April 25, 2006 12:15PM - 12:45PM |
W16.00004: Nonadiabatic Ponderomotive Barriers Invited Speaker: A ponderomotive potential is an effective potential seen by a particle in ac field in average over the fast oscillations. It is not a true potential though, and, if the ac field is in resonance with particle natural oscillations, the particle can exhibit irreversible drift motion [1-3]. A new ponderomotive potential is found for this case that can capture nonadiabatic dynamics [4]. The particle drift in this new potential resembles the motion of a quantum object in a conservative field [5]. Among other applications, these nonadiabatic potentials can perform selective separation and cooling of plasma species or drive electric current by asymmetrically transmitting thermal particles in a preferential direction [1, 2, 6].\newline [1] N.J. Fisch, J.M. Rax, and I.Y. Dodin, Phys. Rev. Lett. {\bf 91}, 205004 (2003).\newline [2] I.Y. Dodin, N.J. Fisch, and J.M. Rax, Phys. Plasmas {\bf 11}, 5046 (2004).\newline [3] I.Y. Dodin and N.J. Fisch, J. Plasma Phys. {\bf 71}, 289 (2005).\newline [4] I.Y. Dodin and N.J. Fisch, Phys. Lett. A {\bf 349}, 356 (2006).\newline [5] I.Y. Dodin and N.J. Fisch, Phys. Rev. Lett. {\bf 95}, 115001 (2005).\newline [6] I.Y. Dodin and N.J. Fisch, Phys. Rev. E {\bf 72}, 046602 (2005). [Preview Abstract] |
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