Experimental scaling of the scrape-off layer particle flux width by outboard divertor Langmuir probes with favorable Bt configuration on EAST

TL;DR

This study extends the scaling of the scrape-off layer particle flux width to the outboard side in EAST, providing experimental evidence and a systematic correction method for more accurate measurements, which aids in understanding heat load predictions.

Contribution

It introduces a new outboard bb_js scaling based on a systematic correction method, extending previous inboard studies and enhancing understanding of SOL width behavior.

Findings

Outboard bb_js scales with W_{MHD}/n_e and P_{tot} similarly to inboard bb_js.

The scaling amplitude differences are likely due to plasma triangularity.

The bb_q/bb_js ratio scaling on Bp is insufficient to explain all SOL heat transport physics.

Abstract

The scrape-off layer (SOL) power width (\lambda_q) is important for predicting the heat load on divertor targets for future magnetically confined devices. Currently, the underlying physics for \lambda_q scaling is not fully understood. This paper extends the previous inboard SOL particle flux width (\lambda_{js}) scaling [Liu et al 2019 Plasma Phys. Control. Fusion 61 045001] to the outboard side in EAST, which can provide more experimental evidence for \lambda_q study. A systematic method has been developed to correct the less reliable upper outer (UO) divertor Langmuir probe (Div-LP) measurements with their more reliable neighboring measurements to reduce the measurement uncertainty of \lambda_js. For the discharges with the favorable Bt and upper single null configurations in the 2019 experiment campaign, about 260 discharges have been selected by certain criteria to ensure good \lambda_js measurements. Three H-mode, L-mode, and Ohmic databases have been constructed and are used for \lambda_js scalings. It is found that the outboard \lambda_js for the H-mode and L-mode plasmas scales as, \lambda_(js,UO)=1.52(W_{MHD}/n_e)^(-0.61) P_{tot}^0.19, where W_{MHD} is the stored energy, n_e is the line-averaged density, and P_{tot} is the total input power. This scaling is similar to the inboard \lambda_js scaling except for the scaling amplitude that is probably due the triangularity. The repeatable scaling dependence on W_{MHD}/n_e confirms the reliability of this dependence even though the regression quality is relatively poor. It is also discussed that the solely scaling of \lambda_q/\lambda_{js} on Bp is not enough to include all the physics of SOL heat transports.