Toward the stationary operation at high $\beta_{N}$ at JET: experiments and modelling

Recently, a route to stationary MHD stable operation at high $\beta _{N}$ has been explored at JET by optimising the current ramp up, preheat start time and the waveform of NBI power in high triangularity plasmas. Transient $\beta _{N}\approx $3.5 and stationary $\beta _{N}\approx $3 have been achieved. The results of the analysis of current drive and transport in these discharges can be summarised as: (a) 50-70{\%} of current is driven non-inductively (NI); (b) a half of this current is due to the bootstrap (BS) current; (c) broad BS current profile is produced since the ITB was deliberately avoided; (d) a large contribution to the BS current is due to the $\nabla $Te term; (e) the GLF23 model predicts the temperature profiles within 20{\%} of discrepancy with the data, this model has been benchmarked in ASTRA, ONE-TWO and TRANSP. Based on this analysis the optimisation of high $\beta _{N}$ scenario towards fully NI stationary operation by optimising the BS current is investigated in predictive modelling coupling the transport, current diffusion and NBI and including the feedback control of $\beta _{N}$. A projection of this regime to ITER will be discussed.