Author: Jacob R King
Requested Type: Pre-Selected Invited
Submitted: 2016-02-15 14:59:24
Co-authors: K. Barada, K.H. Burrell, X. Chen, A.M. Garofalo, R.J. Groebner, S.E. Kruger, G.R. McKee, M. Ono, A.Y. Pankin, T.L. Rhodes, P.B. Snyder
5621 Arapahoe Ave
Boulder, CO 80303
It is desirable to have an ITER H-mode regime that is quiescent to edge-localized modes (ELMs). ELMs deposit large, localized and impulsive heat loads that can damage the divertor. A quiescent regime with edge harmonic oscillations (EHO) or broadband MHD activity is observed in some DIII-D, JET, JT-60U, and ASDEX-U discharge scenarios [Garofalo et al, PoP (2015) and refs. within]. These ELM-free discharges have the pedestal-plasma confinement necessary for burning-plasma operation on ITER. The mode activity associated with the EHO or broadband MHD is characterized by small toroidal-mode numbers (n≈1-5) and is thus suitable for simulation with global MHD codes. Relative to QH-mode operation with EHO, operation with broadband MHD tends to occur at higher densities and lower rotation and thus may be more relevant to ITER.
Nonlinear NIMROD simulations initialized from a reconstruction of a DIII-D QH-mode discharge with broadband MHD saturate into a turbulent state. The measured toroidal and poloidal rotation profiles are included in the simulation. The simulation develops into a saturated turbulent state and the n=1 and 2 modes become dominant through an inverse cascade. Each toroidal mode in the range of n=1-5 is dominant at a different time. The perturbations are advected and sheared apart in the counter-clockwise direction consistent with the direction of the poloidal flow inside the LCFS. Work towards validation through comparison to ECE, BES and Doppler reflectometry measurements is presented. Consistent with experimental observations during QH-mode, the simulated state leads to large particle transport relative to the thermal transport.
§ This work supported by the U.S. Department of Energy Office of Science and the SciDAC Center for Extended MHD Modeling under contract numbers DE-FC02-06ER54875, DE-FC02-08ER54972 and DE-FC02-04ER54698.