Ion Currents in Turbulent Counterflow of He II

We report measurements of the attenuation of negative-ion currents in turbulent counterflow, as a function of the heat current, $\dot{q}$, and temperature. The dependence of the attenuation on $\dot{q}$ is well explained by present models of the turbulent state. The magnitude of the effect is in reasonable agreement with Vinen's original model, but disagrees with a modified version recently introduced by Sitton and Moss.