Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A low-frequency variational model for energetic particle effects in the
  pressure-coupling scheme   Energetic particle effects in magnetic confinement fusion devices are
commonly studied by hybrid kinetic-fluid simulation codes whose underlying
continuum evolution equations often lack the correct energy balance. While two
different kinetic-fluid coupling options are available (current-coupling and
pressure-coupling), this paper applies the Euler-Poincar\'e variational
approach to formulate a new conservative hybrid model in the pressure-coupling
scheme. In our case the kinetics of the energetic particles are described by
guiding center theory. The interplay between the Lagrangian fluid paths with
phase space particle trajectories reflects an intricate variational structure
which can be approached by letting the 4-dimensional guiding center
trajectories evolve in the full 6-dimensional phase space. Then, the redundant
perpendicular velocity is integrated out to recover a four-dimensional
description. A second equivalent variational approach is also reported, which
involves the use of phase space Lagrangians. Not only do these variational
structures confer on the new model a correct energy balance, but also they
produce a cross-helicity invariant which is lost in the other pressure-coupling
schemes reported in the literature.

11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph