L–H transition threshold studies in helium plasmas at JET

Abstract

We present a study of the power threshold for L–H transitions (PLH) in almost pure helium plasmas, obtained in recent experiments at JET with an ITER-like wall (Be wall and W divertor). The most notable new result is that the density at which PLH is minimum, ne,min, is considerably higher for helium than for deuterium and hydrogen plasmas. We discuss the possible implications for ITER in its pre-fusion operating power phase.