99 research outputs found
Nusselt number scaling in tokamak plasma turbulence
K. Takeda et al., Physics of Plasmas 12, 052309 (2005) https://doi.org/10.1063/1.189516
Control of Transport-barrier relaxations by Resonant Magnetic Perturbations
Transport-barrier relaxation oscillations in the presence of resonant
magnetic perturbations are investigated using three-dimensional global fluid
turbulence simulations from first principles at the edge of a tokamak. It is
shown that resonant magnetic perturbations have a stabilizing effect on these
relaxation oscillations and that this effect is due mainly to a modification of
the pressure profile linked to the presence of both residual residual magnetic
island chains and a stochastic layer.Comment: 4 page
Linear study of the precessional fishbone instability
The precessional fishbone instability is an m = n = 1 internal kink mode destabilized by a population of trapped energetic particles. The linear phase of this instability is studied here, analytically and numerically, with a simplified model. This model uses the reduced magneto-hydrodynamics (MHD) equations for the bulk plasma and the Vlasov equation for a population of energetic particles with a radially decreasing density. A threshold condition for the instability is found, as well as a linear growth rate and frequency. It is shown that the mode frequency is given by the precession frequency of the deeply trapped energetic particles at the position of strongest radial gradient. The growth rate is shown to scale with the energetic particle density and particles energy while it is decreased by continuum damping
Effect of the curvature and the {\beta} parameter on the nonlinear dynamics of a drift tearing magnetic island
We present numerical simulation studies of 2D reduced MHD equations
investigating the impact of the electronic \beta parameter and of curvature
effects on the nonlinear evolution of drift tearing islands. We observe a
bifurcation phenomenon that leads to an amplification of the pressure energy,
the generation of E \times B poloidal flow and a nonlinear diamagnetic drift
that affects the rotation of the magnetic island. These dynamical modifications
arise due to quasilinear effects that generate a zonal flow at the onset point
of the bifurcation. Our simulations show that the transition point is
influenced by the \beta parameter such that the pressure gradient through a
curvature effect strongly stabilizes the transition. Regarding the modified
rotation of the island, a model for the frequency is derived in order to study
its origin and the effect of the \beta parameter. It appears that after the
transition, an E \times B poloidal flow as well as a nonlinear diamagnetic
drift are generated due to an amplification of the stresses by pressure
effects
Recommended from our members
Self-similarity and transport in the standard map
Anomalous transport is investigated for the Standard Map. A chain of exact self similar islands in the vicinity of the period 5 accelerator island is found for a particular value of the map parameter. The transport is found to be superdiffusive with an anomalous exponent related to the characteristic temporal and spatial scaling parameters of the island chain. The value of the transport exponent is compared to the theory. The escape time distribution and Poincare recurrence distribution are found to have power-like tails and the corresponding exponents are obtained and compared to the theory
Effects of a nonlinear perturbation on dynamical tunneling in cold atoms
We perform a numerical analysis of the effects of a nonlinear perturbation on
the quantum dynamics of two models describing non-interacting cold atoms in a
standing wave of light with a periodical modulated amplitude . One model
is the driven pendulum, considered in ref.\cite{raiz1}, and the other is a
variant of the well-known Kicked Rotator Model. In absence of the nonlinear
perturbation, the system is invariant under some discrete symmetries and
quantum dynamical tunnelling between symmetric classical islands is found. The
presence of nonlinearity destroys tunnelling, breaking the symmetries of the
system. Finally, further consequences of nonlinearity in the kicked rotator
case are considered.Comment: 10 pages, 15 figure
Electron Temperature Gradient Mode Transport
Anomalous electron thermal losses plays a central role in the history of the controlled fusion program being the first and most persistent form of anomalous transport across all toroidal magnetic confinement devices. In the past decade the fusion program has made analysis and simulations of electron transport a high priority with the result of a clearer understanding of the phenomenon, yet still incomplete. Electron thermal transport driven by the electron temperature gradient is examined in detail from theory, simulation and power balance studies in tokamaks with strong auxiliary heating.Physic
Quantum Breaking Time Scaling in the Superdiffusive Dynamics
We show that the breaking time of quantum-classical correspondence depends on
the type of kinetics and the dominant origin of stickiness. For sticky dynamics
of quantum kicked rotor, when the hierarchical set of islands corresponds to
the accelerator mode, we demonstrate by simulation that the breaking time
scales as with the transport exponent
that corresponds to superdiffusive dynamics. We discuss also other
possibilities for the breaking time scaling and transition to the logarithmic
one with respect to
- …