Engineering topics

Kim, J -H

Publications and source records attributed to Kim, J -H.

4 records

DOE OSTI2012

Magnetic turbulence suppression by a helical mode in a cylindrical geometry

To study processes involved in a helical structure formation in reversed field pinch devices, the scaling of a turbulent boundary layer width associated with a vortex structure having large shears of magnetic field and flow is obtained for reduced magnetohydrodynamics. The coherent vortex, with its flow and magnetic shears, interacts with Alfven turbulence, forming a turbulent boundary layer at the edge of the vortex. The layer arises from the balance between turbulence diffusion rates and shearing rates and suppresses the turbulence in the structure. The suppression of turbulence impedes relaxation of the coherent vortex profiles, leading to long coherence times. The scaling of the boundary layer width reveals that both magnetic shear and flow shear can effectively suppress magnetic turbulence.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2012

Role of stable modes in zonal flow regulated turbulence

Zonal flows are shown to regulate ion temperature gradient turbulence by enabling efficient energy transfer from the instability to a damped eigenmode in the unstable wavenumber range. The damped mode also saturates turbulence when zonal flows are not active in saturation dynamics, for example, in electron temperature gradient turbulence, but the transfer from unstable to stable mode is less efficient and requires a larger amplitude to balance the instability drive. From numerical solutions of a fluid model with a single damped eigenmode, an eigenmode decomposition of the nonlinear evolution shows that the dominant energy transfer involves the triplet correlation of the unstable mode, the zonal flow, and the stable mode at three wavenumbers satisfying k=k Prime +k Double-Prime . In this triplet, nearly all of the energy from the instability goes to the damped mode. The very small fraction going to the zonal flow is balanced by small zonal flow damping. This combination of unstable mode, zonal flow, and stable mode minimizes the nonlinear frequency mismatch and avails itself of large coupling strengths associated with the zonal flow.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2011

A self-consistent three-wave coupling model with complex linear frequencies

A three-wave coupling model with complex linear frequencies is investigated for the nonlinear interaction in a triad that has linearly unstable and stable modes. Time scales associated with linear and nonlinear physics are identified and compared with features of the frequency spectrum. From appropriate time scales, the frequency spectra are well characterized even in the transition to the steady state. The nonlinear time scales that best match spectral features are the nonlinear frequency of the fixed point and a frequency that depends on the amplitude displacement from the fixed point through the large-amplitude Jacobian elliptic solution. Two limited efforts to model the effect of other triads suggest robustness in the single triad results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2011

ULTRAVIOLET PHOTON-INDUCED SYNTHESIS AND TRAPPING OF H{sub 2}O{sub 2} AND O{sub 3} IN POROUS WATER ICE FILMS IN THE PRESENCE OF AMBIENT O{sub 2}: IMPLICATIONS FOR EXTRATERRESTRIAL ICE

The mass uptake of ambient oxygen in nanoporous ice is enhanced by irradiation with 193 nm photons, due to conversion of O{sub 2} into H{sub 2}O{sub 2} and O{sub 3}, with an efficiency that increases with decreasing temperature. These findings show a new way to form H{sub 2}O{sub 2} and O{sub 3} on icy surfaces in the outer solar system at depths much larger than are accessible by typical ionizing radiation, with possible astrobiological implications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗