41 Search Results

ParameterSpace Survey of Linear Gmode and Interchange in Extended Magnetohydrodynamics
The extended magnetohydrodynamic stability of interchange modes is studied in two configurations. In slab geometry, a local dispersion relation for the gravitational interchange mode (gmode) with three different extensions of the MHD model [P. Zhu, et al., Phys. Rev. Lett. 101, 085005 (2008)] is analyzed. Our results delineate where drifts stablize the gmode with gyroviscosity alone and with a twofluid Ohm’s law alone. Including the twofluid Ohm’s law produces an ion drift wave that interacts with the gmode. This interaction then gives rise to a second instability at finite k _{y}. A second instability is also observed in numerical extended MHD computations of linear interchange in cylindrical screwpinch equilibria, the second configuration. Particularly with incomplete models, this mode limits the regions of stability for physically realistic conditions. But, applying a consistent twotemperature extended MHD model that includes the diamagnetic heat flux density (more » 
A currentdriven resistive instability and its nonlinear effects in simulations of coaxial helicity injection in a tokamak
An instability observed in wholedevice, resistive magnetohydrodynamic simulations of the driven phase of coaxial helicity injection in the National Spherical Torus eXperiment is identified as a currentdriven resistive mode in an unusual geometry that transiently generates a current sheet. The mode consists of plasma flow velocity and magnetic field eddies in a tube aligned with the magnetic field at the surface of the injected magnetic flux. At low plasma temperatures (~10–20 eV), the mode is benign, but at high temperatures (~100 eV) its amplitude undergoes relaxation oscillations, broadening the layer of injected current and flow at the surface of themore »Cited by 1 
Analytical and numerical treatment of resistive drift instability in a plasma slab
An analytic approach combining the effect of equilibrium diamagnetic flows and the finite ionsound gyroradius associated with electron−ion decoupling and kinetic Alfvén wave dispersion is derived to study resistive drift instabilities in a plasma slab. Linear numerical computations using the NIMROD code are performed with cold ions and hot electrons in a plasma slab with a doubly periodic box bounded by two perfectly conducting walls. A linearly unstable resistive drift mode is observed in computations with a growth rate that is consistent with the analytic dispersion relation. The resistive drift mode is expected to be suppressed by magnetic shear inmore » 
Twofluid and finite Larmor radius effects on helicity evolution in a plasma pinch
The evolution of magnetic energy, helicity, and hybrid helicity during nonlinear relaxation of a drivendamped plasma pinch is compared in viscoresistive magnetohydrodynamics and twofluid models with and without the ion gyroviscous stress tensor. Magnetic energy and helicity are supplied via a boundary electric field which initially balances the resistive dissipation, and the plasma undergoes multiple relaxation events during the nonlinear evolution. The magnetic helicity is well conserved relative to the magnetic energy over each event, which is short compared with the global resistive diffusion time. The magnetic energy decreases by roughly 1.5% of its initial value over a relaxation event,more » 
The formation of blobs from a pure interchange process
In this work, we focus on examining a pure interchange process in a shearless slab configuration as a prototype mechanism for blob formation. We employ full magnetohydrodynamic simulations to demonstrate that the bloblike structures can emerge through the nonlinear development of a pure interchange instability originating from a pedestallike transition region. In the early nonlinear stage, filamentary structures develop and extend in the direction of the effective gravity. The bloblike structures appear when the radially extending filaments break off and disconnect from the core plasma. The morphology and the dynamics of these filaments and blobs vary dramatically with a sensitivemore » 
Fusion Energy Sciences Exascale Requirements Review. An Office of Science review sponsored jointly by Advanced Scientific Computing Research and Fusion Energy Sciences, January 2729, 2016, Gaithersburg, Maryland
The additional computing power offered by the planned exascale facilities could be transformational across the spectrum of plasma and fusion research — provided that the new architectures can be efficiently applied to our problem space. The collaboration that will be required to succeed should be viewed as an opportunity to identify and exploit crossdisciplinary synergies. To assess the opportunities and requirements as part of the development of an overall strategy for computing in the exascale era, the Exascale Requirements Review meeting of the Fusion Energy Sciences (FES) community was convened January 27–29, 2016, with participation from a broad range ofmore »