Design of a two-photon laser-induced fluorescence system on Experimental Advanced Superconducting Tokamak (EAST)

•The neutral density has not yet been measured in the EAST tokamak. So, a design of two photon-laser induced fluorescence (TALIF) system was made to measure the edge neutral density of the plasma in the Experimental Advanced Superconducting Tokamak (EAST).•The TALIF system and the horizontal Thomson scattering (TS) diagnostic system can share the same port, beam path, collection optical and optical fibers. The horizontal TS diagnostic system can be further developed to a TV Thomson scattering (TVTS) diagnostic system by using a CCD detector. The TALIF system and the TVTS diagnostic system can even share the detector system.•The expected signal of the TALIF was calculated and compared with the background of the a Balmer emission line of deuterium (Dα), which was measured by the filterscope system, showing that the expected signal is much bigger than the signal of background. The neutral gas surrounding the fusion plasma in a tokamak has a significant effect upon its quality; however, it is difficult to measure the properties of neutral particles in a tokamak, such as particle density, isotopy, or temperature. Herein, we transform a recently designed horizontal Thomson scattering (TS) diagnostic system into a two-photon laser-induced fluorescence (TALIF) system that measures the edge neutral density of the plasma in Experimental Advanced Superconducting Tokamak (EAST). The TALIF system can measure the neutral density from 0.95 to 1.1 in normalized poloidal flux coordinates and includes 10 measurement points in the radial direction with spatial resolution of 5 mm and a temporal resolution of 1 ms at a cadence of 10/30 Hz. These two systems, TALIF and TS diagnostic, can share the same port, beam path, collection optics, and optical fibers. The horizontal TS diagnostic system can be further developed into a TV Thomson scattering (TVTS) diagnostic system via a CCD detector. The TALIF system and the TVTS diagnostic system can even share a detector. This TALIF system can play a significant role in allowing neutral particle measurement in current and future fusion tokamaks.