524 research outputs found
Nonlinear dynamics of Shear Alfv\'en fluctuations in Divertor Tokamak Test facility plasmas
Following the analysis on linear spectra of shear Alfv\'en fluctuations
excited by energetic particles (EPs) in the Divertor Tokamak Test (DTT)
facility plasmas [T. Wang et al., Phys. Plasmas 25, 062509 (2018)], in this
work, nonlinear dynamics of the corresponding mode saturation and the
fluctuation induced EP transport is studied by hybrid
magnetohydrodynamic-gyrokinetic simulations. For the reversed shear Alfv\'en
eigenmode driven by magnetically trapped EP precession resonance in the central
core region of DTT plasmas, the saturation is mainly due to radial decoupling
of resonant trapped EPs. Consistent with the wave-EP resonance structure, EP
transport occurs in a similar scale to the mode width. On the other hand,
passing EP transport is analyzed in detail for toroidal Alfv\'en eigenmode in
the outer core region, with mode drive from both passing and trapped EPs. It is
shown that passing EPs experience only weak redistributions in the weakly
unstable case; and the transport extends to meso-scale diffusion in the
strongly unstable case, due to orbit stochasticity induced by resonance
overlap. Here, weakly/strongly unstable regime is determined by Chirikov
condition for resonance overlap. This work then further illuminates rich and
diverse nonlinear EP dynamics related to burning plasma studies, and the
capability of DTT to address these key physics.Comment: 32 pages, 20 figure
On Content-centric Wireless Delivery Networks
The flux of social media and the convenience of mobile connectivity has
created a mobile data phenomenon that is expected to overwhelm the mobile
cellular networks in the foreseeable future. Despite the advent of 4G/LTE, the
growth rate of wireless data has far exceeded the capacity increase of the
mobile networks. A fundamentally new design paradigm is required to tackle the
ever-growing wireless data challenge.
In this article, we investigate the problem of massive content delivery over
wireless networks and present a systematic view on content-centric network
design and its underlying challenges. Towards this end, we first review some of
the recent advancements in Information Centric Networking (ICN) which provides
the basis on how media contents can be labeled, distributed, and placed across
the networks. We then formulate the content delivery task into a content rate
maximization problem over a share wireless channel, which, contrasting the
conventional wisdom that attempts to increase the bit-rate of a unicast system,
maximizes the content delivery capability with a fixed amount of wireless
resources. This conceptually simple change enables us to exploit the "content
diversity" and the "network diversity" by leveraging the abundant computation
sources (through application-layer encoding, pushing and caching, etc.) within
the existing wireless networks. A network architecture that enables wireless
network crowdsourcing for content delivery is then described, followed by an
exemplary campus wireless network that encompasses the above concepts.Comment: 20 pages, 7 figures,accepted by IEEE Wireless
Communications,Sept.201
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