1,779 research outputs found
Impurity transport in plasma edge turbulence
The turbulent transport of minority species/impurities is investigated in 2D
drift-wave turbulence as well as in 3D toroidal drift-Alfven edge turbulence.
The full effects of perpendicular and -- in 3D -- parallel advection are kept
for the impurity species. Anomalous pinch effects are recovered and explained
in terms of Turbulent EquiPartition (TEP)Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Impurity and Trace Tritium Transport in Tokamak Edge Turbulence
The turbulent transport of impurity or minority species, as for example
Tritium, is investigated in drift-Alfv\'en edge turbulence. The full effects of
perpendicular and parallel convection are kept for the impurity species. The
impurity density develops a granular structure with steep gradients and locally
exceeds its initial values due to the compressibility of the flow. An
approximate decomposition of the impurity flux into a diffusive part and an
effective convective part (characterized by a pinch velocity) is performed and
a net inward pinch effect is recovered. The pinch velocity is explained in
terms of Turbulent Equipartition and is found to vary poloidally. The results
show that impurity transport modeling needs to be two-dimensional, considering
besides the radial direction also the strong poloidal variation in the
transport coefficients.Comment: 12 Pages, 5 Figure
On the instability of linear nonautonomous delay systems
summary:The unstable properties of the linear nonautonomous delay system , with nonconstant delay , are studied. It is assumed that the linear system is unstable, the instability being characterized by a nonstable manifold defined from a dichotomy to this linear system. The delay is assumed to be continuous and bounded. Two kinds of results are given, those concerning conditions that do not include the properties of the delay function and the results depending on the asymptotic properties of the delay function
Numerical Simulations of Intermittent Transport in Scrape-Off Layer Plasmas
Two-dimensional fluid simulations of interchange turbulence for geometry and
parameters relevant for the scrape-off layer of confined plasmas are presented.
We observe bursty ejection of particles and heat from the bulk plasma in the
form of blobs. These structures propagate far into the scrape-off layer where
they are lost due to transport along open magnetic field lines. From
single-point recordings it is shown that the blobs have asymmetric conditional
wave forms and lead to positively skewed and flat probability distribution
functions. The radial propagation velocity may reach one tenth of the sound
speed. These results are in excellent agreement with recent experimental
measurements.Comment: 8 pages, 7 figure
Intermittent transport in edge plasmas
The properties of low-frequency convective fluctuations and transport are
investigated for the boundary region of magnetized plasmas. We employ a
two-dimensional fluid model for the evolution of the global plasma quantities
in a geometry and with parameters relevant to the scrape-off layer of confined
toroidal plasmas. Strongly intermittent plasma transport is regulated by
self-consistently generated sheared poloidal flows and is mediated by bursty
ejection of particles and heat from the bulk plasma in the form of blobs.
Coarse grained probe signals reveal a highly skewed and flat distribution on
short time scales, but tends towards a normal distribution at large time
scales. Conditionally averaged signals are in perfect agreement with
experimental measurements.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Control of test particle transport in a turbulent electrostatic model of the Scrape Off Layer
The drift motion of charged test particle dynamics in
the Scrape Off Layer (SOL)is analyzed to investigate a transport control
strategy based on Hamiltonian dynamics. We model SOL turbulence using a 2D
non-linear fluid code based on interchange instability which was found to
exhibit intermittent dynamics of the particle flux. The effect of a small and
appropriate modification of the turbulent electric potential is studied with
respect to the chaotic diffusion of test particle dynamics. Over a significant
range in the magnitude of the turbulent electrostatic field, a three-fold
reduction of the test particle diffusion coefficient is achieved
Variation of constants formulae for difference equations with advanced arguments
The construction of a variation of constants formula for the
difference equation with advanced arguments
y(n+1)=A(n)y(n)+B(n)y(g(n))+f(n), g(n)â„n+1, is given for
specific sequential spaces
Collisional transport across the magnetic field in drift-fluid models
Drift ordered fluid models are widely applied in studies of low-frequency
turbulence in the edge and scrape-off layer regions of magnetically confined
plasmas. Here, we show how collisional transport across the magnetic field is
self-consistently incorporated into drift-fluid models without altering the
drift-fluid energy integral. We demonstrate that the inclusion of collisional
transport in drift-fluid models gives rise to diffusion of particle density,
momentum and pressures in drift-fluid turbulence models and thereby obviate the
customary use of artificial diffusion in turbulence simulations. We further
derive a computationally efficient, two-dimensional model which can be time
integrated for several turbulence de-correlation times using only limited
computational resources. The model describes interchange turbulence in a
two-dimensional plane perpendicular to the magnetic field located at the
outboard midplane of a tokamak. The model domain has two regions modeling open
and closed field lines. The model employs a computational expedient model for
collisional transport. Numerical simulations show good agreement between the
full and the simplified model for collisional transport
- âŠ