1,987 research outputs found
The effect of magnetic islands on ITG turbulence driven transport
In this work, we address the question of the influence of magnetic islands on
the perpendicular transport due to steady-state ITG turbulence on the energy
transport time scale. We demonstrate that turbulence can cross the separatrix
and enhance the perpendicular transport across magnetic islands. As the
perpendicular transport in the interior of the island sets the critical island
size needed for growth of neoclassical tearing modes, this increased transport
leads to a critical island size larger than that predicted from considering
collisional conductivities, but smaller than that using anomalous effective
conductivities.
We find that on Bohm time scales, the turbulence is able to re-establish the
temperature gradient across the island for islands widths , the turbulence correlation length. The reduction in the island
flattening is estimated by comparison with simulations retaining only the
perpendicular temperature and no turbulence. At intermediate island widths,
comparable to , turbulence is able to maintain finite
temperature gradients across the island
Plasma turbulence simulations with X-points using the flux-coordinate independent approach
In this work, the Flux-Coordinate Independent (FCI) approach to plasma
turbulence simulations is formulated for the case of generic, static magnetic
fields, including those possessing stochastic field lines. It is then
demonstrated that FCI is applicable to nonlinear turbulent problems with and
without X-point geometry. In particular, by means of simulations with the
FENICIA code, it is shown that the standard features of ITG modes are recovered
with reduced toroidal resolution. Finally, ITG turbulence under the influence
of a static island is studied on the transport timescale with ITER-like
parameters, showing the wide range of applicability of the method
Cross phase modulation in a five--level atomic medium: Semiclassical theory
The interaction of a five-level atomic system involving electromagnetically
induced transparency with four light fields is investigated. Two different
light-atom configurations are considered, and their efficiency in generating
large nonlinear cross-phase shifts compared. The dispersive properties of those
schemes are analyzed in detail, and the conditions leading to group velocity
matching for two of the light fields identified. An analytical treatment based
on amplitude equations is used in order to obtain approximate solutions for the
susceptibilities, ehich are shown to fit well with the numerical simulations of
the full Bloch equations in a large parameter region.Comment: New version: section on pulse propagation added, reference list
expanded; 17 pages, 15 figure
Implementation of a three-qubit quantum error correction code in a cavity-QED setup
The correction of errors is of fundamental importance for the development of
contemporary computing devices and of robust communication protocols. In this
paper we propose a scheme for the implementation of the three-qubit quantum
repetition code, exploiting the interaction of Rydberg atoms with the quantized
mode of a microwave cavity field. Quantum information is encoded within two
circular Rydberg states of the atoms and encoding and decoding process are
realized within two separate microwave cavities. We show that errors due to
phase noise fluctuations could be efficiently corrected using a
state-of-the-art apparatus.Comment: 9 pages, 5 figures. This is v2. Some misprints corrected, conclusions
section extended, refs added. Accepted for publication on PR
Quantum theory of a polarization phase-gate in an atomic tripod configuration
We present the quantum theory of a polarization phase-gate that can be
realized in a sample of ultracold rubidium atoms driven into a tripod
configuration. The main advantages of this scheme are in its relative
simplicity and inherent symmetry. It is shown that the conditional phase shifts
of order can be attained.Comment: X International Conference on Quantum Optics, Minsk, Belaru
Deep Saturated Free Electron Laser Oscillators and Frozen Spikes
We analyze the behavior of Free Electron Laser (FEL) oscillators operating in
the deep saturated regime and point out the formation of sub-peaks of the
optical pulse. They are very stable configurations, having a width
corresponding to a coherence length. We speculate on the physical mechanisms
underlying their growth and attempt an identification with FEL mode locked
structures associated with Super Modes. Their impact on the intra-cavity
nonlinear harmonic generation is also discussed along with the possibility of
exploiting them as cavity out-coupler.Comment: 28 page
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