Pedestal width and ELM size identity studies in JET and DIII-D; implications for ITER

Abstract

The dependence of the H-mode edge transport barrier width on normalized ion gyroradius (ρ * = ρ/a) in discharges with type I ELMs was examined in experiments combining data for the JET and DIII-D tokamaks. The plasma configuration as well as the local normalized pressure (β), collisionality (ν * ), Mach number and the ratio of ion and electron temperature at the pedestal top were kept constant, while ρ * was varied by a factor of four. The width of the steep gradient region of the electron temperature (T e ) and density (n e ) pedestals

H-mode pedestal scaling in DIII-D, ASDEX Upgrade, and JET

“…These deficiencies have been corrected in the present paper, and only data obtained in high triangularity plasma have been used for JET. In the determination of the JET pedestal width in [35] in turned out that both instrumental effects cancel out, and the qualitative conclusions in [35] are still valid and are in agreement with the results presented here.…”

“…The deconvolution from the 22mm wide instrument kernel has a significant effect on both the derived temperature pedestal width and position, demonstrating that this procedure is essential in determining the T e profile structure. In a previous paper, [35], the deconvolution procedure underestimated both the solid angle of view and the effect of the angle of the field lines with respect to the laser path. As a result the width of the instrument kernel was underestimated.…”

“…As a result the width of the instrument kernel was underestimated. In addition, it has since been discovered that the data used in [35] do not have accurate calibration factors for the electron temperature in the pedestal foot leading to an underestimation of T e there.…”

Global and pedestal confinement and pedestal structure in dimensionless collisionality scans of low-triangularity H-mode plasmas in JET-ILW

“…Concerning the scaling with β p ped , the OLS fit is relatively consistent with the scaling implemented in EPED (which assumes γ β = 0.5), while the (3) using the values in [65] and assuming Z eff = 1.3. No dependence of the pedestal width with ρ * has been observed so far [55,59], so the extrapolation to ITER might be reasonable even if the normalized Larmor radius is not considered. At ITER collisionality, no significant difference between the KBM constraint and the extrapolation of the experimental data is observed.…”

“…Note that the effect of the other dimensionless parameters is not considered in the KBM constraint. Concerning the dependence with ρ * , multi-machine studies performed in AUG, DIII-D and JET-C show a very weak or no dependence with the normalized Larmor radius [55,59]. Concerning the dependence with ν * , the DIII-D results [60] show a reduction of the density pedestal width at high density which is ascribed to the reduction of the neutral penetration length [61].…”