Speaker
Description
A Lithium Beam Emission Spectroscopy (Li-BES) has been successfully developed on EAST [S. Zoletnik et al 2018 Rev. Sci. Instrum. 89 063503], providing measurement of density fluctuation in the pedestal and SOL regions with high spatial and temporal resolutions. This diagnostic enabled us to conduct a series of important physics studies. A non-axisymmetry distribution of edge coherent mode (ECM) induced by resonant magnetic perturbation was observed when ELMs were suppressed, and the lower-hybrid-wave-induced turbulence transition from the ECM with a lower k_⊥ to a broadband turbulence with a higher k_⊥ was also reported in an ELMy H-mode pedestal. Blob characteristics variation in the SOL determined by different auxiliary heating schemes was studied, as well as edge turbulence and shear flow evolutions approaching the density limit in L-mode plasmas. Moreover, nonlinear interactions during the initial establishment and saturation phases of the ECM can also be investigated by applying a nonlinear correlation algorithm. However, the Li-BES system also suffers from high levels of background stray light noise and incurs high operation and maintenance costs. An upgrade to the Na-BES system is now underway. Comparing with the Li-BES, the maximum beam current of Na injector is doubled while the maximum lifetime of ion source is increased by more than one order of magnitude, thus the O&M costs would be significantly reduced. The spectral region surrounding the target Na-I line is exceptionally clean, with no strong emissions, thereby resulting in substantially reduced stray light interference. Performance prediction of upgrading lithium beam emission spectroscopy diagnostic to sodium beam emission spectroscopy diagnostic has been performed, suggesting a significantly improved measurement performance, including approximately 2‒6 times the effective beam emission signal intensity captured by each detector in the edge region of EAST, a substantially enhanced effective spatial resolution, and a marked reduction in background emission interference. The enhanced performance of the Na-BES enables more comprehensive measurements of large-scale coherent modes and turbulence in the pedestal region, thus facilitating better understanding of their contributions to regulating the pedestal and controlling ELMs.