Biomedical subjects

B N Rogers

Publications and source records attributed to B N Rogers.

4 recordsLinked to original sources

PubMed2003

Formation of electron holes and particle energization during magnetic reconnection.

Three-dimensional particle simulations of magnetic reconnection reveal the development of turbulence driven by intense electron beams that form near the magnetic x-line and separatrices. The turbulence collapses into localized three-dimensional nonlinear structures in which the electron density is depleted. The predicted structure of these electron holes compares favorably with satellite observations at Earth's magnetopause. The birth and death of these electron holes and their associated intense electric fields lead to strong electron scattering and energization, whose understanding is critical to explaining why magnetic explosions in space release energy so quickly and produce such a large number of energetic electrons.

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PubMed2001

Role of dispersive waves in collisionless magnetic reconnection.

Simulations of collisionless magnetic reconnection show a dramatic enhancement of the nonlinear reconnection rate due to the formation of an open outflow region. We link the formation of this open configuration to dispersive whistler and kinetic Alfvén wave dynamics at small scales. The roles of these two waves are controlled by two dimensionless parameters, which allow us to identify regions of fast and slow reconnection.

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PubMed2000

Electron temperature gradient turbulence.

The first toroidal, gyrokinetic, electromagnetic simulations of small scale plasma turbulence are presented. The turbulence considered is driven by gradients in the electron temperature. It is found that electron temperature gradient (ETG) turbulence can induce experimentally relevant thermal losses in magnetic confinement fusion devices. For typical tokamak parameters, the transport is essentially electrostatic in character. The simulation results are qualitatively consistent with a model that balances linear and secondary mode growth rates. Significant streamer-dominated transport at long wavelengths occurs because the secondary modes that produce saturation become weak in the ETG limit.

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PubMed2000

Generation and stability of zonal flows in ion-temperature-gradient mode turbulence.

We address the mechanisms underlying zonal flow generation and stability in turbulent systems driven by the electrostatic ion-temperature-gradient (ITG) mode. In the case of zonal flow stability, we show the poloidal flows typical of numerical simulations become unstable when they exceed a critical level. Near marginal stability of the linear ITG mode, the system can generate zonal flows that are sufficiently weak to remain stable and sufficiently strong to suppress the linear ITG mode. This stable region corresponds to the parameter regime of the nonlinear Dimits up-shift.

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