Review of laboratory experiments on Alfvén waves and their relationship to space observations

Abstract

Hannes Alfvén predicted the existence of a hydrodynamic wave in a perfectly conducting fluid in 1942. It took 6 years before this discovery was accepted and 10 years before Alfvén waves were first observed in the laboratory. Now it is widely recognized that these waves are ubiquitous in space plasmas and are the means by which information about changing currents and magnetic fields are communicated. Alfvén waves have been observed in the solar wind, are thought to be prevalent in the solar corona, may be responsible for parallel electric fields in the aurora, and can cause particle acceleration over large distances in interstellar space. They have also been considered as a candidate for heating thermonuclear plasmas and are potentially dangerous to confinement. Alfvén waves have been difficult to observe in basic laboratory experiments because of their low frequencies and long wavelengths. In this paper we present a review of plasma Alfvén wave experiments performed in recent years. The quality of the laboratory data have paralleled advances in plasma sources and diagnostics. In the past few years the quantum jump in data collection on the Freja and FAST missions have lead to the reevaluation of the importance of these waves in the highly structured plasma that was probed. Recent laboratory experiments have examined, in great detail, shear waves generated by filamentary currents in both spatially uniform and striated plasmas. Tone bursts, short pulses, and interference effects have been studied with emphasis on structures;of the order of the skin depth, c/ωpe. These are features of significant interest to the space community. In fact, it appears that the phenomena observed in laboratory experiments show striking similarities to what has been observed in space. A comparison of these results will be given. Copyright 1999 by the American Geophysical Union.