Biomedical subjects

J Egedal

Publications and source records attributed to J Egedal.

4 recordsLinked to original sources

PubMed2005

Laser-induced fluorescence measurement of the ion-energy-distribution function in a collisionless reconnection experiment.

Observations in space and laboratory plasmas suggest magnetic reconnection as a mechanism for ion heating and formation of non-Maxwellian ion velocity distribution functions (IVDF). Laser-induced fluorescence measurements of the IVDF parallel to the X line of a periodically driven reconnection experiment are presented. A time-resolved analysis yields the evolution of the IVDF within a reconnection cycle. It is shown that reconnection causes a strong increase of the ion temperature, where the strongest increase is found at the maximum reconnection rate. Monte Carlo simulations demonstrate that ion heating is a consequence of the in-plane electric field that forms around the X line in response to reconnection.

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PubMed2005

In situ discovery of an electrostatic potential, trapping electrons and mediating fast reconnection in the Earth's magnetotail.

Anisotropic electron phase space distributions, f, measured by the Wind spacecraft in a rare crossing of a diffusion region in Earth's far magnetotail (60 Earth radii), are analyzed. We use the measured f to probe the electrostatic and magnetic geometry of the diffusion region. For the first time, the presence of a strong electrostatic potential (1 kV) within the ion diffusion region is revealed. This potential has far reaching implications for the reconnection process; it accounts for the observed acceleration of the unmagnetized ions out of the reconnection region and it causes all thermal electrons be trapped electrostatically. The trapped electron motion implies that the thermal part of the electron distributions are symmetric around v( parallel)=0: f(v( parallel),v( perpendicular)) approximately f(-v( parallel),v( perpendicular)). It follows that the field aligned currents in the diffusion region are limited and fast magnetic reconnection is mediated.

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PubMed2003

Dynamical plasma response during driven magnetic reconnection.

Direct measurements of a collisionless current channel during driven magnetic reconnection are obtained for the first time on the Versatile Toroidal Facility. The size of the diffusion region is found to scale with the electron drift orbit width, independent of the ion mass and plasma density. Based on experimental observations, analytic expressions governing the dynamical evolution of the current profile and the formation of the electrostatic potential that develops in response to the externally imposed reconnection drive are established. This time response is closely linked to the presence of ion polarization currents.

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PubMed2001

Single-particle dynamics in collisionless magnetic reconnection.

The role of single-particle dynamics in driven magnetic reconnection in collisionless plasmas is investigated experimentally and analytically. The trapping of particle orbits in the magnetic cusp is observed to allow fast reconnection in the absence of a macroscopic current layer, at a rate identical to that of vacuum. The development of an electrostatic potential structure around the magnetic X line during reconnection is predicted theoretically and observed experimentally.

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