The time behaviour of the thermal conductivity during L to H and H to L transitions in JET

Abstract

The change in thermal transport across the L to H transition is studied in detail for those JET high performance H-modes which have a very fast transition. It is found that in these pulses the transport changes very rapidly (<4 msecs) over a very large radial region 0.5< rho <1, and a very large transport barrier is formed. The reasons for the formation of this barrier are discussed.