Departure from quasilinear heating in a cross-field ion beam experiment

The heating of an ion beam by the ion acoustic turbulence generated as the beam streams across a weak magnetic field through magnetized electrons was investigated. A quasilinear (QL) relationship between the spatial heating rate delta T/sub i// delta x and the spatially growing noise energy density Psi was sought, as was any departure therefrom as Psi is varied. For the broadband turbulence encountered, QL theory gives delta T/sub i// delta x varies as Psi tau , where tau is the autocorrelation time of the turbulence. If tau remains independent of Psi , then delta T/sub i// delta x varies as Psi /sup beta /, with beta =1 for QL heating. The experiment was carried out in a double-plasma device.<>