MHD and gyro-kinetic stability of JET pedestals

EFDA-Jet Contributors

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The pedestal profile measurements in high triangularity JET plasmas show that with low fuelling the pedestal width
decreases during the ELM cycle and with high fuelling it stays constant. In the low fuelling case the pedestal pressure
gradient keeps increasing until the ELM crash and in the high fuelling case it initially increases then saturates during
the ELM cycle.
Stability analysis reveals that both JET plasmas become unstable to finite-n ideal MHD peeling–ballooning
modes at the end of the ELM cycle. During the ELM cycle, n = ∞ ideal MHD ballooning modes and kinetic
ballooning modes are found to be locally stable in most of the steep pressure gradient region of the pedestal owing
to the large bootstrap current, but to be locally unstable in a narrow region of plasma at the extreme edge.
Unstable micro-tearing modes are found at the JET pedestal top, but they are sub-dominant to ion temperature
gradient modes. They are insensitive to collisionality and stabilized by increasing density gradient.
Original languageEnglish
JournalNuclear Fusion
Publication statusPublished - 12 Nov 2013

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