Development of a 32-channel Beam Emission Spectroscopy diagnostic based on Neutral Beam Injection on HL-2A tokamak

Abstract A 32-channel Beam Emission Spectroscopy (BES) diagnostic has been installed and operated on HL-2A tokamak. It covers a wide spatial range of 32 cm in the radial direction (from r = 12 c m / ρ = 0.27 to r = 44 c m / ρ = 0.98 ) and 27 cm in the poloidal direction (from -13.5 cm to +13.5 cm) inside the plasma, providing a capability of measuring density fluctuations in different spatial locations. It has high temporal resolution, 2 MHz, and good spatial resolution, about 1 cm in radial direction and 1.2 cm in poloidal direction. A 2D fiber mount with 135 slots is designed and installed on the curved image plane. Each slot corresponds to a different spatial location inside the plasma. BES channels can be placed in any slots as needed for desired spatial location measurement. More channels can be added up to 128 channels without re-designing collecting optical path & replacing optical components. First experimental results have demonstrated great performance of the system with high signal to noise ratio. Turbulence eddy dynamics can be measured and studied from 2D fast imaging. It will be a keen diagnostic in future plasma turbulence research on HL-2A.