Demonstration of ITER operational scenarios on DIII-D

Abstract

The DIII-D programme has recently initiated an effort to provide suitably scaled experimental evaluations of four primary ITER operational scenarios. New and unique features of this work are that the plasmas incorporate essential features of the ITER scenarios and anticipated operating characteristics; e.g. the plasma cross-section, aspect ratio and value of I/aB of the DIII-D discharges match the ITER design, with size reduced by a factor of 3.7. Key aspects of all four scenarios, such as target values for βN and H98, have been replicated successfully on DIII-D, providing an improved and unified physics basis for transport and stability modelling, as well as for performance extrapolation to ITER. In all four scenarios, normalized performance equals or closely approaches that required to realize the physics and technology goals of ITER, and projections of the DIII-D discharges are consistent with ITER achieving its goals of ⩾400 MW of fusion power production and Q ⩾ 10. These studies also address many of the key physics issues related to the ITER design, including the L–H transition power threshold, the size of edge localized modes, pedestal parameter scaling, the impact of tearing modes on confinement and disruptivity, beta limits and the required capabilities of the plasma control system. An example of direct influence on the ITER design from this work is a modification of the physics requirements for the poloidal field coil set at 15 MA, based on observations that the inductance in the baseline scenario case evolves to a value that lies outside the original ITER specification.

Reduction of Edge-Localized Mode Intensity Using High-Repetition-Rate Pellet Injection in TokamakH-Mode Plasmas

“…This power is about 10% above the L mode to H-mode transition power as has also been shown in earlier experiments with this configuration [15] and typically results in a low type-I natural ELM frequency of $5 Hz.…”

“…A set of experiments were carried out on DIII-D by injecting the slow (100-150 m=s) pellets on the LFS in an ITER-like shape plasma [15] and a feedback controlled normalized ¼ 1:8 with 2.8 MW of neutral beam injection heating. This power is about 10% above the L mode to H-mode transition power as has also been shown in earlier experiments with this configuration [15] and typically results in a low type-I natural ELM frequency of $5 Hz.…”

“…The type I ELMs in the ITER-like shape discharges without pellets are believed to be caused by intermediate wavelength (n $ 3-30) MHD instabilities that are driven by the sharp pressure gradient and bootstrap current across the edge barrier (pedestal) [15]. The ELMs are then triggered, and the pedestal pressure constrained, by the onset of these ''peeling-ballooning'' modes [20].…”

Limits to the H-mode pedestal pressure gradient in DIII-D

“…Discharges developed to study the ITER baseline scenario [21] have long periods between ELMs and exhibit a large variation of pedestal parameters during the inter-ELM cycle. Due to these factors, these discharges provide clear trends on the evolution of pedestal profiles between ELMs.…”

Analysis of Alfven eigenmode destabilization in ITER using a Landau closure model

“…Several advanced operation scenarios have been proposed for ITER [45,46,47,48,49,50,51]. Among them, the reverse shear [52,53,54], hybrid [55,56,57] and steady state operation [58,59,60] scenarios are the configurations with the best potential performance.…”