Speaker
Description
See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.101.pdf
We observe the formation of a high-pressure staircase pedestal (~16-20 kPa) in high beta p plasmas (beta p>1.5) in the DIII-D tokamak when large amplitude ELMs are suppressed using resonant magnetic perturbations (RMP). The pedestal cyclically transitions from a one-step structure to a wider two-step staircase structure, with a period of ~40-60 ms. In the wide pedestal phase a strong flattening of the electron density and temperature develops in mid-pedestal, producing the staircase pedestal structure[1]. Also, localized bursting fluctuations are seen in the this flat region (rho~0.95). Fluctuations at the pedestal top (rho~0.8) are periodically enhanced by RMP[1], and drive the narrowing of the pedestal width. Gyrokinetic analysis using the newly developed CGYRO[3] code and experimental fluctuation measurements (BES diagnostic) reveal that the feedback effect of reduced ExB shear in mid-pedestal on the enhancement of transport by trapped electron modes results in transport bifurcation which eventually leads to local flattening of profiles and staircase pedestal formation[3]. By enhancing the confinement and drastically reducing the peak of heat flux to diverter, formation of the staircase pedestal opens a path for optimizing the steady-state operation in ITER and future reactors.
Work supported by US DOE under DE-FC02-04ER54698 and DE-AC02-09CH11466.
[1] R. Nazikian, et al., Nuclear Fusion 58 (2018)
[2] J. Candy, et. al., J. Comp. Phys. 324 (2016)
[3] A. Ashourvan, et al., submitted to PRL
