  We study the dynamo instability for a Kazantsev-Kraichnan flow with three
velocity components that depends only on two-dimensions u = (u(x, y, t), v(x,
y, t), w(x, y, t)) often referred to as 2.5 dimensional (2.5D) flow. Within the
Kazantsev-Kraichnan frame- work we derive the governing equations for the
second order magnetic field correlation function and examine the growth rate of
the dynamo instability as a function of the control parameters of the system.
In particular we investigate the dynamo behaviour for large magnetic Reynolds
numbers Rm and flows close to being two-dimensional and show that these two
limiting procedures do not commute. The energy spectra of the unstable modes
are derived analytically and lead to power-law behaviour that differs from the
three dimensional and two dimensional case. The results of our analytical
calculation are compared with the results of numerical simulations of dynamos
driven by prescribed fluctuating flows as well as freely evolving turbulent
flows, showing good agreement.
