A compact, purely toroidal magnetic field with major radius and field strength…

PHYSICS · Multi-part · Fermi University Physics · Plasma Physics · The plasma state and single-particle motion · The plasma state and single-particle motion

Plasma Physics, Ch One particle in given fields: gyration and the guiding-centre drifts

Problem

A compact, purely toroidal magnetic field with major radius

R = 0.85\,\mathrm{m}

and field strength

B = 0.50\,\mathrm{T}

confines a hydrogen plasma at temperature

T = 1.0\,\mathrm{keV}

, its field lines running only the long way round with no twist. The minor radius is

a = 0.40\,\mathrm{m}

. ((a)) Find the mean vertical drift speed

2T/eRB

of the ions due to the combined grad-B and curvature drifts. ((b)) Estimate the time for this drift to carry the plasma across the minor radius

a

. ((c)) Explain briefly why this shows that a purely toroidal field cannot confine a plasma.

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