  A stochastic differential equation for the plasma density dynamics is
derived, consistent with the experimentally measured distribution and the
theoretical quadratic nonlinearity. The plasma density is driven by a
multiplicative Wiener process and evolves on the turbulence correlation time
scale, while the linear growth is quadratically damped by the fluctuation
level. The sensitivity of intermittency to the nonlinear dynamics is
investigated by analyzing the Langevin representation of two intermittent
distributions, showing the agreement between the quadratic nonlinearity and the
gamma distribution.
