Technological Alfvén waves

Though common in astrophysics, Alfvén waves have, so far, made little technological impact. The paper investigates their applicability in large homopolar energy-storage devices for use in areas such as fusion technology where up to gigawatt powers may be required for periods of the order of 1 s. Sodium is proposed for the liquid rotor. A wave device offers the attractive characteristic of delivering constant power into a resistive load, which can be matched to the characteristic impedance of the device. This impedance may be raised by the use of inductive coupling provided current reversal can be tolerated. After a discussion of ideal systems, in which dissipation is neglected, the various sources of energy loss and undesirable 3-dimensional effects (secondary flow) are investigated in order-of-magnitude terms, with reference to the relatively scanty experimental information already available. Hitherto unpublished results by Jameson concerning laboratory Alfvén waves in sodium are presented. The conclusion is that, even in the largest systems, ohmic effects on the waves cause nontrivial losses, and the advantages of an Alfvén-wave system over alternative schemes would have to be very compelling before the formidable technological task of developing large Alfvén devices could be undertaken. When the stored kinetic-energy density reaches the higher levels, secondary flow during wave transits may become a major difficulty.