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We study the stability and instability of Langmuir waves propagating in a hot, unmagnetized plasma modeled by the Vlasov–Poisson system and encompassing a variety of velocity distributions, including perturbations of Lorentzian, Kappa, and incomplete Maxwellian steady states. The influence of both high-frequency spatial perturbations and physical parameters on the rate of growth or decay of the plasma response to the initial perturbation is elucidated. Our methods do not rely upon analytic approximation, but instead feature a numerical approximation of the roots of the associated dielectric function that can be accurately quantified without the need for prior assumptions on the parameter regimes under consideration. In this way, the computational discovery of so-called “active” subspaces in the parameter space allows one to identify and quantify the uncertainty generated by physical parameters on the stability properties of wave-like perturbations in a collisionless plasma.
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Theory of the magnetothermal instability in coronal plasma flows
The theory of the magnetothermal instability (MTI) [D. A. Tidman and R. A. Shanny, Phys. Fluids 17, 1207 (1974)] is revisited through the lens of the stability of uniform systems. The linear stability analysis includes flow advection and Nernst transport. The instability criteria derived distinguish between the convective and the absolute nature of the perturbation growth. It is proven that, in the region where the Nernst and plasma blowoff velocities cancel, the MTI can be absolute and wave-packet perturbations grow in situ. This instability is mediated by the internal feedback between the Biermann battery and Righi–Leduc terms. The analysis is extended to derive the dispersion relation for short-wavelength perturbations developing in nonuniform profiles with the application to coronal plasmas. It is found that the condition for MTI requires the net B-field convection velocity to be small at the isothermal sonic section, and the plasma conditions in this section govern the dynamics of the instability. Analysis of hydro-equivalent implosions suggests that unstable perturbations undergo more e-foldings of growth in larger-size targets.
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- Award ID(s):
- 2123496
- PAR ID:
- 10371889
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Physics of Plasmas
- Volume:
- 29
- Issue:
- 9
- ISSN:
- 1070-664X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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