bohm diffusionmedical dictionary

<radiobiology> A rapid loss of plasma across magnetic field lines caused by microinstabilities. Theory formulated by the physicist David Bohm.

Semiempirical formula for the diffusion coefficient given by Bohm in 1946 (noted by Bohm, Burhop, and Massey, who were developing a magnetic arc for use in uranium isotope separation). Bohm diffusion was proposed (not derived from first principles) to scale as 1/B rather than the 1/B^2 scaling predicted by classical diffusion. A 1/B scaling results from assuming that particles diffuse across field lines at an optimum rate (effective collision frequency=cyclotron frequency). The 1/B scaling is observed (approximately) in most reactors.

See: diffusion, microinstabilities, field lines.

(09 Oct 1997)

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