The dependence of ion heat transport on the ion to electron temperature ratio in JET non-rotating plasmas

Detailed experimental studies of ion heat transport are carried out in JET to explore the T e / T i dependence of ion heat transport in ITER relevant range of parameters ( T e / T i ⩾ 1) using low rotation plasmas with dominant ion cyclotron resonance heating to avoid the coupling of the effects of T e / T i and rotation which affected previous experiments. This experimental setup has led to an accurate determination of the ion temperature gradient (ITG) threshold at varying T e / T i , offering unique opportunities for validation of the well-established theory of ITG driven modes. A rather mild decrease in threshold with increasing T e / T i in the interval of ITER interest was found. The new experimental result has found good agreement with theoretical predictions based on quasi-linear fluid and linear gyrokinetic models.