Divertor tungsten source monitoring by A visible spectroscopy diagnostic on EAST

• A combination of mirror and lens is installed in an isolated vacuum tube with double-sealing structure to tangentially observe tungsten sources in both the inner and outer divertor target plates. • Flexible optical fibers transmit the divertor visible light to three types of detector assemblies outside the device, achieving high spectral resolution, high temporal resolution, and high spatial resolution. • The 2-D image of W I line emission in the lower outer divertor reveals the non-uniform toroidal distribution of W source on the target, which could be related to the geometry of W-PFC modules. EAST has been upgraded with top and bottom tungsten divertors to facilitate the high power long pulse operation. A visible spectroscopy diagnostic has been developed progressively to monitor W source as well as line emissions from other particles (e.g., D, He, Li, B, C, N, O, Ne, Ar, Mo, D 2 , WD) in the divertors. Two sets of lens installed in mid-plane port view tangentially the top and bottom divertors, respectively. Two types of optical fibers transfer the plasma light collected by the lens to three different detecting modules. High spectral resolution (λ/Δλ ∼ 14000) can be achieved by the detecting module consisting of spectrometer and Electron-Multiplying Charge Coupled Device (EMCCD), high temporal resolution (50 μs) is obtained by filtered photoelectric multiplier (PMT), and high spatial resolution (1 mm) is acquired by Complementary Metal-Oxide-Semiconductor Transistor (CMOS) camera with collimation optics. The multichannel optical fiber array with 500 μm core diameter is used to connect the lens and the first two detecting modules. The imaging fiber bundle with 30 μm core diameter transmits the two-dimensional divertor plasma light to the third detecting module, i.e. collimation optics and CMOS camera. The diagnostic is operated automatically in normal EAST discharges to support experimental operation and divertor physics study. The paper presents a technical description of the diagnostic and typical measurements during EAST discharges.