Fine structure in the energy deposition in a heated rotating toroidal plasma

Abstract

In the laboratory frame, the helical path followed by an ion contained in a rotating toroidal plasma is determined to leading order by three factors: its velocity nu /sub /// parallel to the magnetic field, the q-factor of the flux surface on which the ion travels, and the velocity of bulk toroidal rotation VR(q) of the flux surface itself. A parameter q*(q, VR(q), nu /sub ///) is calculated, which determines whether the helical path in the laboratory frame is closed (rational-q*) or open (irrational-q*). In general the spatially localised region where ion heating, or the creation of energetic ions following neutral injection, takes place is fixed in the laboratory frame. Those ions which have rational-q* paths that pass through this region return to it with a greatly enhanced repetition rate. This gives rise to fine structure in the deposition of energy among the ions.