Onset condition for ELMs in JT-60U

Abstract

For the standard shape of JT-60U at low triangularity , the onset condition for giant ELMs is clearly correlated with the high-n ballooning limit in the first stability regime over wide ranges of plasma parameters (, ...). The limit of the normalized edge pressure gradient (-parameter) increases with elongation (1.5 - 1.8) and internal inductance . Recently, a new connection of the poloidal field coils enabled us to scan triangularity from the original value of up to (currently limited at MA). The -scan showed that the limit of edge density, edge pressure and the -parameter increase with . When both and are high (, ), minute-grassy ELMs appear. The edge -parameter during the minute-grassy ELMs can be higher than that for the onset of giant ELMs.