Biomedical subjects

F L Waelbroeck

Publications and source records attributed to F L Waelbroeck.

3 recordsLinked to original sources

PubMed2005

Natural velocity of magnetic islands.

The phase velocity of magnetic islands is calculated in the semicollisional regime with cold ions. Two solution branches arise, corresponding to islands propagating with the ions and with the electrons. For the ion branch the phase velocity and the polarization current are small. For the electron branch, the phase velocity depends on the ratio of W, the half-width of the island, and rho(s), the Larmor radius calculated with the electron temperature. For W >>rho(s) the phase velocity is larger than the electron drift velocity and the polarization current is destabilizing. For W << rho(s), the situation is reversed provided that the density and temperature gradients point in the same direction.

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PubMed2002

Analytic solution for low-frequency rf sheaths in pulsed discharges.

The equations governing the evolution of rf-driven sheaths are solved analytically in the regime where the rf frequency is small compared to both the ionic plasma frequency and the ion transit time in the sheaths. Poincaré's map of first return is used to gain geometric insight into the dynamics of the circuit-sheath system. The requirements of minimizing wall bombardment while maximizing the efficiency of the coupling to the substrate sheath are shown to lead to an optimum value for the blocking capacitance in asymmetric discharges. This optimum value is also favorable for rapid relaxation to the steady state in pulsed discharges. The analytic solution is applied to the problem of negative-ion extraction in afterglow plasmas.

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PubMed2001

Finite Larmor-radius theory of magnetic island evolution.

Gyrokinetic theory is used to investigate the effect of the polarization drift on magnetic island evolution. Three regimes are found. For island phase velocities between the ion- and electric-drift velocities, the polarization current is shown to be stabilizing. For phase velocities between the electric- and electron-drift velocities, the island emits drift waves. This results in a radiative drag force. For all other phase velocities the polarization current is destabilizing, in agreement with the fluid limit.

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