Lower hybrid current drive

Lower hybrid current drive is used in a large number of present day tokamaks in order to extend the length of operating pulses beyond what is possible with inductive current drive. Since absorption of lower hybrid waves takes place away from the centre of the plasma, it also produces a modification of the current profile, which it may be possible to exploit in order to improve the stability of the machine. A major objective of research on current drive in the longer term is to find a way of driving a tokamak reactor in a steady state, while keeping the level of power which has to be recirculated back into the reactor within reasonable bounds. Here we review some of the basic properties of lower hybrid current drive and discuss some recent work on theoretical modelling.