An Overview Of The Motional Stark Effect Diagnostic On DIII-D And Design Work For An ITER MSE

Improvements in the H-mode pedestal pressure and global energy confinement were observed on DIII-D with both 3 and 6 MW of neutral beam (NBI) heating with neon injection. The pedestal pressure increased, primarily associated with a significant increase in the pedestal density with a relatively smaller decrease in the pedestal temperature. At the same neon injection rate, a rapid decrease in edge localized mode (ELM) frequency and ~35% increase in plasma stored energy were observed in the 3 MW discharge, while in the 6 MW discharge, the ELM frequency was gradually decreased and the plasma stored energy gradually increased by up to 20%. The measured pedestal widths from both 3 and 6 MW discharges matched the EPED1.0 width scaling, ∆ ψN = 0.089β 1/2 p,ped , within 20% deviations before and after neon injection. The peeling-ballooning mode (PBM) stability analysis showed that after neon injection, the ballooning stability boundary was increased, while the peeling stability boundary only dropped once the neon level was relatively high. The ballooning stability boundary increase with neon injection is consistent with increase of the ion diamagnetic stabilization (i.e. including the contribution from carbon, neon as well as deuterium ions) which is used in the criterion to determine when the calculated linear growth rates of PBM are unstable. Consequently, the new ELITE computed PBM boundaries were more consistent with the operating points than when only deuterium was included. This in turn indicates that the impurity may help to improve pedestal pressure through affecting ion diamagnetic frequency in the pedestal region, which could positively lead to the ballooning stability boundary extension.

Section: Experimental Setup Profile Fitting and Mhd Equilibrium Gener...mentioning

confidence: 99%

H-mode pedestal improvements with neon injection in DIII-D

Lan¹,

Osborne²,

Groebner³

et al. 2020

“…For instance, the optical system is complex and sensitive, requiring precise calibration. Additionally, its reliance on neutral beam injection (NBI) and restrictions on the observation space are factors that cannot be overlooked [34][35][36][37]. Due to the potential sensitivities and uncertainties associated with diagnostic methods, our approach of refining equilibrium calculations, as will be demonstrated in section 4, is applicable regardless of the availability of the diagnostics from MSE or POINT.…”

Section: Current Constraint Of East Equilibrium Reconstructionmentioning

confidence: 99%

Equilibrium reconstruction constrained by the consistency of current simulation on EAST

Qian,

Xiang,

Huang

et al. 2024

The attainment of a reliable equilibrium is a critical aspect of tokamak experiments and physics analysis. A common method for establishing a reliable equilibrium current involves reconstructing it from indirect measurements, such as those obtained from polarimeter-interferometers (POINT) and motional Stark effect (MSE) systems. However, uncertainties still exist in the reconstruction results. For the equilibrium reconstruction on the EAST tokamak, which is based on the POINT system, the primary sources of uncertainty are the limited scope of measurements and the sensitivity of the reconstruction process. This paper proposes an enhanced approach that utilizes current simulation as a constraint to maintain consistency between the initial equilibrium and the simulated results. The Radio Frequency waves driven current is identified as a particularly influential component due to its interaction with the q profiles of the equilibrium and the deposition region of the waves. Two specific discharges are presented to illustrate how a new equilibrium can be achieved, which enhances consistency between the equilibrium and the simulated current, taking into account the dependencies of various components.

“…Note that the fast ion pressure, is negligible in the pedestal while it could contribute significantly to the core pressure. The core current density is constrained by the MSE diagnostic [44] while the edge current density profile is calculated based the ONETWOtime module, as the sum of the parallel bootstrap current estimated from the Sauter model [45,46], the Ohmic current density and the neutral beam driven current. Then an iteration was carried out and the total pedestal pressure is readjusted to match the recomputed kinetic equilibrium and the pedestal current density is recalculated to resolve the effects of the flux geometry.…”

Section: Experiments Setupmentioning

confidence: 99%

Compatibility of divertor detachment and ELM suppression in DIII-D high- β

Wu,

Wang,

Wang

et al. 2024

Integration of transient and steady-state divertor heat fluxes control with a high-performance core is necessary for future fusion reactors. In recent DIII-D high- β p experiments, divertor detachment and simultaneous edge localized mode (ELM) suppression are demonstrated while the plasma confinement quality is maintained high in ITER-similar shape. By optimizing the neon injection in high- β p scenario with ITER-similar shape, deep detachment and ELM suppression are achieved with a high-performance core ( β N ∼ 2.8, β p ∼ 2.3) at q 95 ∼ 7.5. Partial divertor detachment and suppression of large ELMs are achieved at q 95 ∼ 6. The stability analyses suggest that with low neon injection, the density pedestal becomes higher and steeper and the T i profile also increases, therefore the increased edge pressure and higher current density destabilize the Peeling-Ballooning mode (PBM), which would lead to a large ELM collapse. With strong neon gas puffing, the significantly reduced pedestal pressure and current density, due to the degraded T e pedestal, lead to the stabilization of PBM and ELMs are suppressed. For both cases, the coupling between the large radius internal transport barrier (ITB) and edge pedestal is the key reason for maintaining high global performance. The formation of large radius ITB compensates for pedestal degradation. Such results could provide an attractive scenario to well control the transient and steady-state heat flux onto the divertor plates while maintaining good plasma performance, which is an important step toward the steady-state operation of future fusion reactors.