219 research outputs found
Irreversible energy flow in forced Vlasov dynamics
No full textThe recent paper of Plunk [G.G. Plunk, Phys. Plasmas 20, 032304 (2013)]
considered the forced linear Vlasov equation as a model for the quasi-steady state of a
single stable plasma wavenumber interacting with a bath of turbulent fluctuations. This
approach gives some insight into possible energy flows without solving for nonlinear
dynamics. The central result of the present work is that the forced linear Vlasov equation
exhibits asymptotically zero (irreversible) dissipation to all orders under a detuning of
the forcing frequency and the characteristic frequency associated with particle streaming.
We first prove this by direct calculation, tracking energy flow in terms of certain exact
conservation laws of the linear (collisionless) Vlasov equation. Then we analyze the
steady-state solutions in detail using a weakly collisional Hermite-moment formulation,
and compare with numerical solution. This leads to a detailed description of the Hermite
energy spectrum, and a proof of no dissipation at all orders, complementing the
collisionless Vlasov result
Direct construction of stellarator-symmetric quasi-isodynamic magnetic configurations
No full textWe develop the formalism of the first order near-axis expansion of the MHD
equilibrium equations described in Garren & Boozer (1991), Plunk et al. (2019)
and Plunk et al. (2021), for the case of a quasi-isodynamic, N-field period,
stellarator symmetric, single-well magnetic field equilibrium. The importance
of the magnetic axis shape is investigated, and we conclude that control of the
curvature and torsion is crucial to obtain omnigenous configurations with
finite aspect ratio and low effective ripple, especially for a higher number of
field periods. For this reason a method is derived to construct classes of axis
shapes with favourable curvature and torsion. Solutions are presented,
including a three-field-period configuration constructed at an aspect ratio of
A=20, with a maximum elongation of e=3.2 and an effective ripple under 1%,
which demonstrates that high elongation is not a necessary feature of QI
stellarators.Comment: 28 pages, 19 figure
Irreversible energy flow in forced Vlasov dynamics
No full text© EDP Sciences, Società Italiana di Fisica, Springer-Verlag. The recent paper of Plunk [G.G. Plunk, Phys. Plasmas 20, 032304 (2013)] considered the forced linear Vlasov equation as a model for the quasi-steady state of a single stable plasma wavenumber interacting with a bath of turbulent fluctuations. This approach gives some insight into possible energy flows without solving for nonlinear dynamics. The central result of the present work is that the forced linear Vlasov equation exhibits asymptotically zero (irreversible) dissipation to all orders under a detuning of the forcing frequency and the characteristic frequency associated with particle streaming. We first prove this by direct calculation, tracking energy flow in terms of certain exact conservation laws of the linear (collisionless) Vlasov equation. Then we analyze the steady-state solutions in detail using a weakly collisional Hermite-moment formulation, and compare with numerical solution. This leads to a detailed description of the Hermite energy spectrum, and a proof of no dissipation at all orders, complementing the collisionless Vlasov result.This work was supported by the UK Engineering and Phys-ical Sciences Research Council through a Doctoral TrainingGrant award to J.T.P., with additional support from AwardNo KUK-C1-013-04 made by King Abdullah University of Sci-ence and Technology (KAUST). G.G.P. acknowledges supportfrom the Max-Planck/Princeton Research Center for PlasmaPhysics. This project has received funding from the EuropeanUnion’s Horizon 2020 research and innovation programme un-der Grant agreement No. 633053. The views and opinions ex-pressed herein do not necessarily reflect those of the EuropeanCommission
Perturbing an axisymmetric magnetic equilibrium to obtain a quasi-axisymmetric stellarator
No full textIt is demonstrated that finite-pressure, approximately quasi-axisymmetric
stellarator equilibria can be directly constructed (without numerical
optimization) via perturbations of given axisymmetric equilibria. The size of
such perturbations is measured in two ways, via the fractional external
rotation and, alternatively, via the relative magnetic field strength, i.e. the
average size of the perturbed magnetic field, divided by the unperturbed field
strength. It is found that significant fractional external rotational transform
can be generated by quasi-axisymmetric perturbations, with a similar value of
the relative field strength, despite the fact that the former scales more
weakly with the perturbation size. High mode number perturbations are
identified as a candidate for generating such transform with local current
distributions. Implications for the development of a general non-perturbative
solver for optimal stellarator equilibria is discussed
On the scaling of ion and electron temperature gradient driven turbulence in slab geometry
No full textOn the nonlinear stability of a quasi-two-dimensional drift kinetic model for ion temperature gradient turbulence
No full text
Enstrophy non-conservation and the forward cascade of energy in two-dimensional electrostatic magnetized plasma turbulence
No full text
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