C-Mod/DIII-D edge similarity experiment

D. Mossessian, A. Hubbard, M. Greenwald, S. Wolfe, MIT

R. Groebner, R. Moyer, T. Osborne, GA

ABSTRACT

The idea of the experiment was to study similarity of H-mode pedestal on two different tokamaks in plasmas with matched local edge dimensionless parameters (such as beta, normalized gyroradius, collisionality, aspect ratio) and matched shape (same elongation, triangularity and safety factor). This should allow an assesment of the relative importance of so-called “plasma physics” versus “atomic physics” in controlling the pedestal widths, amplitudes, and gradients which have been shown to critically impact the quality of H-mode confinement. In addition, this experiment will provide an opportunity to explore the parameter space for obtaining quasi-coherent edge modes and possibly EDA H–modes in DIII–D.

Key questions that would be answered by these experiments include:

Do pedestal parameters scale with dimensionless parameters
Are P_SOL and I_p scalings universal?
Do the observed scalings depend on shape or H–mode type (ELM-free, EDA, ELMy)?
Is there a size scaling between different devices?

Basic parameters of a DIII-D shot 105535 and C-Mod target shot 1000616004 (time traces)
Comparison of shape and scaled plasma parameters (current, field, beta) of a typical DIII-D shot and the target C-Mod shot
Comparison of scaled DIII-D and C-Mod pedestal profiles from dimensionlessly similar shots:

DIII-D shot 105548 (red) , C-Mod shots :