59 research outputs found
Reduced magnetohydrodynamic theory of oblique plasmoid instabilities
The three-dimensional nature of plasmoid instabilities is studied using the
reduced magnetohydrodynamic equations. For a Harris equilibrium with guide
field, represented by \vc{B}_o = B_{po} \tanh (x/\lambda) \hat{y} + B_{zo}
\hat{z}, a spectrum of modes are unstable at multiple resonant surfaces in the
current sheet, rather than just the null surface of the polodial field , which is the only resonant surface in 2D or in
the absence of a guide field. Here is the asymptotic value of the
equilibrium poloidal field, is the constant equilibrium guide field,
and is the current sheet width. Plasmoids on each resonant surface
have a unique angle of obliquity . The resonant
surface location for angle is x_s = - \lambda \arctanh (\tan \theta
B_{zo}/B_{po}), and the existence of a resonant surface requires . The most unstable angle is oblique, i.e. and , in the constant- regime, but parallel, i.e.
and , in the nonconstant- regime. For a fixed angle
of obliquity, the most unstable wavenumber lies at the intersection of the
constant- and nonconstant- regimes. The growth rate of this mode is
, in which
, is the Alfv\'{e}n speed, is the current sheet
length, and is the Lundquist number. The number of plasmoids scales as .Comment: 9 pages, 8 figures, to be published in Physics of Plasma
Particle-in-cell simulations of a current-free double layer
Current-free double layers of the type reported in plasmas in the presence of
an expanding magnetic field [C. Charles and R. W. Boswell, Appl. Phys. Lett.
82, 1356 (2003)] are modeled theoretically and with particle-in-cell/Monte
Carlo simulations. Emphasis is placed on determining what mechanisms affect the
electron velocity distribution function (EVDF) and how the EVDF influences the
double layer. A theoretical model is developed based on depletion of electrons
in certain velocity intervals due to wall losses and repletion of these
intervals due to ionization and elastic electron scattering. This model is used
to predict the range of neutral pressures over which a double layer can form
and the electrostatic potential drop of the double layer. These predictions are
shown to compare well with simulation results.This
work was supported by the United States National Science
Foundation and the Australian Academy of Sciences under
East Asia and Pacific Summer Institute (EAPSI) award number
1015362
The 2017 Plasma Roadmap: Low temperature plasma science and technology
Journal of Physics D: Applied Physics published the first Plasma Roadmap in 2012 consisting of the individual perspectives of 16 leading experts in the various sub-fields of low temperature plasma science and technology. The 2017 Plasma Roadmap is the first update of a planned series of periodic updates of the Plasma Roadmap. The continuously growing interdisciplinary nature of the low temperature plasma field and its equally broad range of applications are making it increasingly difficult to identify major challenges that encompass all of the many sub-fields and applications. This intellectual diversity is ultimately a strength of the field. The current state of the art for the 19 sub-fields addressed in this roadmap demonstrates the enviable track record of the low temperature plasma field in the development of plasmas as an enabling technology for a vast range of technologies that underpin our modern society. At the same time, the many important scientific and technological challenges shared in this roadmap show that the path forward is not only scientifically rich but has the potential to make wide and far reaching contributions to many societal challenges.I Adamovich et al 2017 J. Phys. D: Appl. Phys. 50 32300
Electron-ion temperature relaxation in warm dense hydrogen observed with picosecond resolved X-Ray scattering
Angularly resolved X-ray scattering measurements from fs-laser heated hydrogen have been used to determine the equilibration of electron and ion temperatures in the warm dense matter regime. The relaxation of rapidly heated cryogenic hydrogen is visualized using 5.5 keV X-ray pulses from the Linac Coherent Light (LCLS) source in a 1 Hz repetition rate pump-probe setting. We demonstrate that the electron-ion energy transfer is faster than quasi-classical Landau-Spitzer models that use ad hoc cutoffs in the Coulomb logarithm
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