2 research outputs found
Kinetic versus Magnetic Chaos in Toroidal Plasmas: A systematic quantitative comparison
Magnetic field line chaos occurs under the presence of non-axisymmetric
perturbations of an axisymmetric equilibrium and is manifested by the
destruction of smooth flux surfaces formed by the field lines. These
perturbations also render the particle motion, as described by the guiding
center dynamics, non-integrable and, therefore, chaotic. However, the
chaoticities of the magnetic field lines and the particle orbits significantly
differ both in strength and radial location in a toroidal configuration, except
for the case of very low-energy particles whose orbits closely follow the
magnetic field lines. The chaoticity of more energetic particles, undergoing
large drifts with respect to the magnetic field lines, crucially determines the
confinement properties of a toroidal device but cannot be inferred from that of
the underlying magnetic field. In this work, we implement the Smaller ALignment
Index (SALI) method for detecting and quantifying chaos, allowing for a
systematic comparison between magnetic and kinetic chaos. The efficient
quantification of chaos enables the assignment of a value characterizing the
chaoticity of each orbit in the space of the three constants of the motion,
namely energy, magnetic moment and toroidal momentum. The respective diagrams
provide a unique overview of the different effects of a specific set of
perturbations on the entire range of trapped and passing particles, as well as
the radial location of the chaotic regions, offering a valuable tool for the
study of particle energy and momentum transport and confinement properties of a
toroidal fusion device.Comment: 27 pages, 7 figure
Role of the edge electric field in the resonant mode-particle interactions and the formation of transport barriers in toroidal plasmas
The impact of an edge radial electric field on the particle orbits and the
orbital spectrum in an axisymmetric toroidal magnetic equilibrium is
investigated using a guiding center canonical formalism. Poloidal and
bounce/transit-averaged toroidal precession frequencies are calculated,
highlighting the role of the radial electric field. The radial electric field
is shown to drastically modify the resonance conditions between particles with
certain kinetic characteristics and specific perturbative non-axisymmetric
modes and to enable the formation of transport barriers. The locations of the
resonances and the transport barriers, that determine the particle, energy and
momentum transport are shown to be accurately pinpointed in the phase space, by
employing the calculated orbital frequencies.Comment: 23 pages, 8 figure