10 research outputs found
Energy Spectrum of Bloch Electrons Under Checkerboard Field Modulations
Two-dimensional Bloch electrons in a uniform magnetic field exhibit complex
energy spectrum. When static electric and magnetic modulations with a
checkerboard pattern are superimposed on the uniform magnetic field, more
structures and symmetries of the spectra are found, due to the additional
adjustable parameters from the modulations. We give a comprehensive report on
these new symmetries. We have also found an electric-modulation induced energy
gap, whose magnitude is independent of the strength of either the uniform or
the modulated magnetic field. This study is applicable to experimentally
accessible systems and is related to the investigations on frustrated
antiferromagnetism.Comment: 8 pages, 6 figures (reduced in sizes), submitted to Phys. Rev.
Magnetic Barriers and their q95 dependence at DIII-D
It is well known that externally generated resonant magnetic perturbations
(RMPs) can form islands in the plasma edge. In turn, large overlapping islands
generate stochastic fields, which are believed to play a role in the avoidance
and suppression of edge localized modes (ELMs) at DIII-D. However, large
coalescing islands can also generate, in the middle of these stochastic
regions, KAM surfaces effectively acting as "barriers" against field-line
dispersion and, indirectly, particle diffusion. It was predicted in [H. Ali and
A. Punjabi, Plasma Phys. Control. Fusion 49 (2007), 1565-1582] that such
magnetic barriers can form in piecewise analytic DIII-D plasma equilibria. In
the present work, the formation of magnetic barriers at DIII-D is corroborated
by field-line tracing calculations using experimentally constrained EFIT [L.
Lao, et al., Nucl. Fusion 25, 1611 (1985)] DIII-D equilibria perturbed to
include the vacuum field from the internal coils utilized in the experiments.
According to these calculations, the occurrence and location of magnetic
barriers depends on the edge safety factor q95. It was thus suggested that
magnetic barriers might contribute to narrowing the edge stochastic layer and
play an indirect role in the RMPs failing to control ELMs for certain values of
q95. The analysis of DIII-D discharges where q95 was varied, however, does not
show anti-correlation between barrier formation and ELM suppression
Equivalent methods for quasi-linear turbulent trajectories
SIGLEAvailable from CEN Saclay, Seervice de Documentation, 91191 - Gif-sur-Yvette (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
A new kinetic description for turbulent collisions including mode-coupling
SIGLEAvailable from CEN Saclay, Service de Documentation, 91191 - Gif-sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc