Calculation of the Kolmogorov Entropy for Motion Along a Stochastic Magnetic Field

where 15BI«B„B,might result from any shortwavelength plasma microinstabilities. When 5B exceeds a very small value such that neighboring magnetic islands overlap, the field structure becomes stochastic, and can be characterized by two geometrical properties. ' First, a given field line diffuses in x, and, second, two neighboring field lines diverge from each other —the mean distance between them increasing as d exp(z/I. ,). The diffusion of a field line has obvious implications for the confinement of particles orbiting along the field and has been calculated using quasilinear theory. ' However, the divergence of field lines is also important in calculating transport since it prevents the reversible wandering of a particle back and forth along a single field line as velocity is reversed by collisions. ' The value 1/L, is called the Kolmogorov entropy and is defined by the formula'