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ELM Precursors in NSTX: Results and Theory Review

Explore the findings and analysis of ELM precursors in NSTX, shedding light on their behavior without lithium, spectrogram annotations, and ELM identification with nRMP. Discover the correlation with ELMs in DIII-D, slow vs. fast growing ELM modes, and the role of SOL currents. Delve into the mechanisms behind transient events, thermoelectric currents, and the self-amplification process leading to ELM crashes. Gain insights into the interplay of pedestal pressure gradients, homoclinic separatrix tangles, and heat flux dynamics in plasma behavior.

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ELM Precursors in NSTX: Results and Theory Review

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  1. ELM Precursors in NSTX F. Kelly* E. Fredricksona, S.Gerhardta, R. Maingib, J. Menarda, S. Sabbaghc, H. Takahashia *Unaffiliated aPrinceton Plasma Physics Laboratory, Princeton, NJ USA bOak Ridge National Laboratory, Oak Ridge, TN USA cColumbia U., New York, NY USA 2009 NSTX Results and Theory Review PPPL Room B318 September 15, 2009

  2. NSTX 129015 - without lithium Time domain 1(a) 661.415 ms 661.502 ms 661.589 ms

  3. NSTX 129015 - without lithium Spectrogram

  4. NSTX 129015 - ELMs at 0.3400 and 0.3410 s

  5. NSTX 129030 w / lithium - ELM precursors for 0.4292 s n =1 ~ 50 kHz n = 2 ~ 75 kHz

  6. NSTX 129030 w / lithium - ELM at 0.4292 s

  7. NSTX 130670 w / nRMP – ELM at 0.6036 s

  8. J. Menard ELM-FIT code

  9. SOLC correlated with ELMs in DIII-D by Takahashi et al Takahashi et al, NF 44 (2004) 1075.

  10. Discussion of Results n = 2,3,4,5,6 modes -> slowly growing ELM that are smaller n= 1 modes appear to be necessary for fast growing, large amplitude ELMS SOL currents are likely candidates for n= 1/ n= 2 modes ELM sequence outlined by T. Evans et al. JNM 390-391 (2009) 789. • Transient event initiated by peeling-ballooning mode as pedestal pressure gradient limit > marginal stability limit. Initial pulse of heat and particles propagates into preexisting homoclinic separatrix tangle. • Onset of thermoelectric current driven between outer and inner target plates due to Te difference between plates from initial heat pulse. • Original helical filament grows explosively as thermoelectric currents amplify the lobes of the homoclinic tangle and induce strong pedestal stochasticity. Results in self-amplification ob lobes due to positive feedback loop between lobe size, stochastic layer width and increase heat flux to target plates driving the current. • ELM crash- temperature in pedestal drops enough for plasma to become more collisional and resistive. A) Shuts down energy source for thermoelectric currents collapsing lobes to pre-ELM configuration. B) Decrease electron collisional mfp compared to connection length of filamentary lobes which reduces parallel thermal conductivity and shuts down heat flux to target plates.

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