ABSTRACT
The stability of plasmas in magnetic fields is one of the primary research subjects in the area of controlled thermonuclear fusion and both theoretical and experimental investigations have been actively pursued. If a plasma is free from all possible instabilities and if the confinement is dominated by neoclassical diffusion in the banana region, then the energy confinement time τE is given by
τE ≈ (3/2)a 2
5.8χG.S. ≈ (3/2)
5.8 q23/2
( a
ρΩi
)2 1 νii
,
where a is the plasma radius, ρΩi is the ion Larmor radius, and νii is the ion-ion collision frequency. For such an ideal case, a device of a reasonable size satisfies ignition condition. (For example, with B = 5T, a = 1m, Ti = 20 keV, q = 3, and inverse aspect ratio = 0.2, the value of nτE ∼ 3.5× 1020 cm−3 · sec.)
A plasma consists of many moving charged particles and has many magnetohydrodynamic degrees of freedom. When a certain mode of perturbation grows and induces fluctuations in the electric and magnetic fields, it enhances anomalous diffusion. These instabilities are called the magnetohydrodynamic (MHD) instabilities or macroscopic instabilities.
