Anomalous ion beam scattering by shear Kelvin—Helmholtz wave interactions

We inject a fast ion beam across a magnetic field, through a cylindrical 5 cm diameter plasma. Shear Kelvin-Helmholtz waves, already present in the plasma, are considerably amplified. The ion beam is rapidly slowed and scattered. The observed stopping power exceeds the classical power by over two orders of magnitude. A simple theoretical estimate, ascribing beam energy loss to driving of the waves, agrees qualitatively with observations.