Experimental response of the divertor particle flux to internal transport barrier dynamics in EAST high-βN discharges

摘要

Experiments in EAST have concentrated on studying the internal transport barrier (ITB) regime in high normalized beta (βN) discharges, where the study of the compatibility between ITB dynamics and divertor plasmas is an important step for future steady-state and high-performance plasma operations. In this work, the characteristics of the divertor particle flux and their responses to ITB dynamics have been studied in high-βN discharges. In order to describe the characteristics, the ITB duration is divided into two phases: phase I (i.e. ITB formation) and phase II (i.e. ITB degradation), according to the variation of plasma stored energy. In phase I, the particle flux near the inner strike point (SP) is continuously enhanced during the inter-edge-localized mode (ELM) phase in both the lower single-null and upper single-null configurations. The total particle flux in the scrape-off layer (SOL) region reveals a similar trend with an increase of the flux near the SP. However, in the private flux region (PFR) the total particle flux shows a reduction. Meanwhile, a movement of the SP away from the divertor corner is also observed during the ITB formation. In phase II, the particle flux near the inner SP, the total particle flux in the inner SOL and PFR region recover to their initial level before ITB formation, respectively. Additionally, the particle decay length is obviously reduced in phase I and then gradually enhanced in phase II. The continuous variation of the particle flux at the inner divertor target is in accordance with a compression of the magnetic flux surfaces due to ITB formation, which increases the gradient of electron density in the edge region. It is indicative that the ITB has a feasible impact on the behavior of divertor plasmas by means of increasing the Shafranov shift during the inter-ELM phase.