Abstract:The gap between a recently developed dynamical version of relaxed magnetohydrodynamics (RxMHD) and ideal MHD (IMHD) is bridged by approximating the zero-resistivity ‘ideal’ Ohm's law (IOL) constraint using an augmented Lagrangian method borrowed from optimization theory. The augmentation combines a pointwise vector Lagrange multiplier method and global penalty function method and can be used either for iterative enforcement of the IOL to arbitrary accuracy, or for constructing a continuous sequence of magnetof… Show more
“…Recent work by Dewar et al. (2020) and Dewar & Qu (2022) developed variational principles to describe time- dependent relaxed MHD using a global cross-helicity constraint with a phase space Lagrangian action principle (PSL) as opposed to a configuration space Lagrangian (CSL) action. The theory has been used to describe multi-region, extended MHD (RxMHD) in fusion plasma devices.…”
The ideal Chew–Goldberger–Low (CGL) plasma equations, including the double adiabatic conservation laws for the parallel (
$p_\parallel$
) and perpendicular pressure (
$p_\perp$
), are investigated using a Lagrangian variational principle. An Euler–Poincaré variational principle is developed and the non-canonical Poisson bracket is obtained, in which the non-canonical variables consist of the mass flux
${\boldsymbol {M}}$
, the density
$\rho$
, the entropy variable
$\sigma =\rho S$
and the magnetic induction
${\boldsymbol {B}}$
. Conservation laws of the CGL plasma equations are derived via Noether's theorem. The Galilean group leads to conservation of energy, momentum, centre of mass and angular momentum. Cross-helicity conservation arises from a fluid relabelling symmetry, and is local or non-local depending on whether the gradient of
$S$
is perpendicular to
${\boldsymbol {B}}$
or otherwise. The point Lie symmetries of the CGL system are shown to comprise the Galilean transformations and scalings.
“…Recent work by Dewar et al. (2020) and Dewar & Qu (2022) developed variational principles to describe time- dependent relaxed MHD using a global cross-helicity constraint with a phase space Lagrangian action principle (PSL) as opposed to a configuration space Lagrangian (CSL) action. The theory has been used to describe multi-region, extended MHD (RxMHD) in fusion plasma devices.…”
The ideal Chew–Goldberger–Low (CGL) plasma equations, including the double adiabatic conservation laws for the parallel (
$p_\parallel$
) and perpendicular pressure (
$p_\perp$
), are investigated using a Lagrangian variational principle. An Euler–Poincaré variational principle is developed and the non-canonical Poisson bracket is obtained, in which the non-canonical variables consist of the mass flux
${\boldsymbol {M}}$
, the density
$\rho$
, the entropy variable
$\sigma =\rho S$
and the magnetic induction
${\boldsymbol {B}}$
. Conservation laws of the CGL plasma equations are derived via Noether's theorem. The Galilean group leads to conservation of energy, momentum, centre of mass and angular momentum. Cross-helicity conservation arises from a fluid relabelling symmetry, and is local or non-local depending on whether the gradient of
$S$
is perpendicular to
${\boldsymbol {B}}$
or otherwise. The point Lie symmetries of the CGL system are shown to comprise the Galilean transformations and scalings.
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