Experimental Investigation of Ion Response to Propagating Alfvén Waves

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The proposed project concerns a laboratory investigation of ion heating in the acceleration region of the fast solar wind. A number of mechanisms for ion heating in the fast solar wind have been proposed and this project will examine the possibility that the ions are directly heated by ion-cyclotron damping of Alfvn waves or that counter-propagating, low-frequency, Alfvn waves generate a turbulent cascade that heats ions by exciting higher frequency waves that then damp on the ions. The experiments will be performed in a space-relevant, laboratory plasma with sufficient diagnostic capability to investigate the evolution of the ion velocity space distribution function of majority and minority ions as they interact with propagating Alfvn waves, to observe Alfvn waves as they approach and possibly reflect from a strong gradient in the Alfven speed, and detect the generation of a nonlinear cascade if created by the counter-propagating waves. The effects of transverse flow on Alfven wave propagation will also be investigated and hybrid code modeling of the plasma will be performed in parallel with the experiments.The essential intellectual merit of the proposed activity is the performance of controlled laboratory experiments on phenomena that may play a key role in the acceleration and heating of the fast solar wind. Although Alfven wave propagation has been investigated by a number of different laboratory plasma research teams, the effects of plasma inhomogeneities, such as an Alfven speed gradient, and plasma flow have only recently been the subject of experimental attention. By choosing plasma conditions for which theory predicts a clearly defined outcome, the proposed experiments will provide a strong test of the theories now being applied to the acceleration region of the fast solar wind.