Level crossings, excess times and transient plasma-wall interactions in   fusion plasmas
  Based on a stochastic model for intermittent fluctuations in the boundary region of magnetically confined plasmas, an expression for the level crossing rate is derived from the joint distribution of the process and its derivative. From this the average time spent by the process above a certain threshold level is obtained. This provides novel predictions of plasma-wall interactions due to transient transport events associated with radial motion of blob-like structures in the scrape-off layer. 
Audun Theodorsen and Odd Erik Garcia
physics.plasm-ph