41,484 research outputs found
On the inward drift of runaway electrons during the plateau phase of runaway current
The well observed inward drift of current carrying runaway electrons during
runaway plateau regime after disruption is studied by considering the phase
space dynamic of runaways in a large aspect ratio toroidal system. We consider
the case where the toroidal field is unperturbed and the toroidal symmetry of
the system is preserved. The balance between the change in canonical angular
momentum and the input of mechanical angular momentum in such system requires
runaways to drift horizontally in configuration space for any given change in
momentum space. The dynamic of this drift can be obtained by taking the
variation of canonical angular momentum. It is then found that runaway
electrons will always drift inward as long as they are decelerating. This drift
motion is essentially non-linear, since the current is carried by runaways
themselves, and any runaway drift relative to the magnetic axis will cause
further displacement of the axis itself. A simplified analytical model is
constructed to describe such inward drift both in ideal wall case and no wall
case, and the runaway current center displacement as a function of parallel
momentum variation is obtained. The time scale of such displacement is
estimated by considering effective radiation drag, which shows reasonable
agreement with observed displacement time scale. This indicates that the phase
space dynamic studied here plays a major role in the horizontal displacement of
runaway electrons during plateau regime.Comment: 25 pages, 9 figures, submitted to Physics of Plasma
Coordination for a Group of Autonomous Mobile Agents with Multiple Leaders
In this paper, we consider the coordination control of a group of autonomous
mobile agents with multiple leaders. Different interconnection topologies are
investigated. At first, a necessary and sufficient condition is proved in the
case of fixed interconnection topology. Then a sufficient condition is proposed
when the interconnection topology is switched. With a simple first-order
dynamics model by using the neighborhood rule, both results show that the group
behavior of the agents will converge to the polytope formed by the leaders.Comment: 5 pages,7 figure
Double occupancies in confined attractive fermions on optical lattices
We perform a numerical study of a one-dimensional Fermion-Hubbard model in
harmonic traps within the Thomas-Fermi approximation based on the exact
Bethe-ansatz solution. The phase diagram is shown for the systems of
attractive interactions ( is the characteristic density and the
interaction strength scaled in units of the hopping parameter.). We study the
double occupancy, the local central density and their derivatives. Their roles
are discussed in details in detecting the composite phases induced by the
trapping potential.Comment: 4 pages, 4 figures, submitte
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