Someone argues: "The diamagnetic current density must be carried by particles whose…

PHYSICS · Subjective · Fermi University Physics · Plasma Physics · The plasma state and single-particle motion · Fluid and magnetohydrodynamic description

Plasma Physics, Ch From particles to fluids: the distribution function, its moments and the two-fluid model

Problem

Someone argues: "The diamagnetic current density j∗=B×∇p/B2\mathbf{j}_* = \mathbf{B}\times\nabla p/B^2 must be carried by particles whose guiding centres physically drift with velocity u∗=−∇p×B/(qnB2)\mathbf{u}_{*} = -\nabla p\times\mathbf{B}/(qnB^2). Since this velocity is nonzero wherever the pressure has a gradient, each guiding centre itself moves with this drift, in exactly the same way that a nonzero E×B\mathbf{E}\times\mathbf{B} drift means every guiding centre moves at vE\mathbf{v}_E." Find the error in this argument, and explain in a few sentences what does carry the diamagnetic current if not guiding-centre motion.

Browse the problem library