Kinetic versus Magnetic Chaos in Toroidal Plasmas: A systematic quantitative comparison
arXiv (Cornell University)(2023)
摘要
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.
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关键词
toroidal plasmas,magnetic chaos
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