Demonstration of Real-Time Control of Impurity Seeding Plus Outboard Strike-Point Sweeping in JET ELMy H-mode Plasmas
Strike-point sweeping and Real-Time-Controlled (RTC) impurity seeding are both expected to be needed on JET following its upgrade to an all metal wall with enhanced neutral-beam heating. First trials have combined these techniques in high-triangularity Type I H-mode plasmas, using a VUV spectroscopic signal for feedback control of nitrogen injection. Compared with earlier unswept feedforward counterparts, similar strong mitigation of divertor heat load between ELMs was achieved in swept RTC cases for less than half the integrated nitrogen input and correspondingly less adverse effect upon other properties. Both sweeping and RT control contributed to this improvement. Time-average normalised energy confinement ·H95yÒt ~ 1, Greenwald density fraction ·fGwdÒt ~ 0.9, and particularly purity denoted by effective ionic charge ·ZeffÒt 1.7, all remained closer to good reference levels. Transient effluxes in ELMs were also less affected, however, and would require separate active control.