Shafranov shift bifurcation of turbulent transport in the high β_p scenario on DIII-D

Abstract

Shafranov shift stabilization of turbulence creates a bifurcation in transport, leading to multiple confinement states in the high βp scenario on DIII-D: An H-mode confinement state with a high edge pedestal, and a higher confinement state with a low pedestal and an internal transport barrier (ITB). The bifurcation is observed experimentally in the ion energy transport with respect to mid-radius (ρ = 0.6) pressure gradient. Here, we propose a mechanism for the often observed spontaneous transition between states and formation of an ITB at fixed βN . The high pedestal results in the plasma at large radius

The dominant micro-turbulence instabilities in the lower q 95 high β p plasmas on DIII-D and predict-first extrapolation

“…First, the high β p scenario has been developed by extending to lower q 95 ∼ 6.0 and lower rotation with excellent confinement, which is a more reactor relevant regime [5,6]. Second, an improved physics understanding has been gained by identifying that high β p plasmas undergo a bifurcation in transport leading to the formation of a large-radius ITB, which is the signature and the source of high confinement of high β p scenario on DIII-D and usually locates at ρ ∼ 0.7 [7][8][9]. Even with this kind of large-radius ITB, energy transport in the high confinement plasma is still not completely neoclassical.…”

Progress in the development and understanding of a high poloidal-beta tokamak operating scenario for an attractive fusion pilot plant

“…But this state is limited by ELMs in DIII-D discharges. A connection between these two states-a fast transition by ELMs, was reported (McClenaghan et al 2019). Figure 10b shows the waveform of n = 1 magnetic field perturbation during an ELM.…”

“…N reached the same level before collapse and H 98y2 became even higher. This discharge is also discussed in McClenaghan et al (2019). This example shows robustness of high P scenario in plasma operation.…”

“…Two confinement states in DIII-D high-P experiments were identified and analyzed (Ding et al 2017c;McClenaghan et al 2019). One is an H-mode confinement state with a high edge pedestal.…”

“…Since 2013, intensive joint research activities by the DIII-D and EAST teams have successfully applied this scenario to both tokamaks. More importantly, various aspects of this scenario has been individually extended to reactor relevant conditions, but not yet simultaneously, e.g., stationary operation, low toroidal rotation, intermediate q 95 ∼ 6 , line-averaged density above Greenwald limit, high core confinement quality ( H 98y2 ) with fully detached divertor, etc., with deepened physics understandings (Garofalo et al 2015(Garofalo et al , 2018Ren et al 2016;Ding et al 2017aDing et al , b, 2020aDing et al , 2021aJian et al 2019Jian et al , 2021aMcClenaghan et al 2019;Huang et al 2020;Wang et al 2021a, b;Qian et al 2021). There is also recent active high-P related research on EAST (Garofalo et al 2017;Gong et al 2022), KSTAR (Na et al 2015;Park et al 2019;Kwak et al 2020;Kim et al 2022) and HL-2A (Chen et al 2022).…”