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, thereby anticipating exhaust-control requirements plus the materials planned for ITER. Preliminary trials in the previous carbon device 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 normalized energy confinement (t) similar to 1, Greenwald density fraction (t) similar to 0.9 and particularly purity denoted by effective ionic charge (t) approximate to 1.7, all remained closer to good reference levels. Transient effluxes in ELMs were also less affected, however, and would require separate active control