First result of CRDS system with cesium operation for radiofrequency negative ion source test facility at ASIPP

Abstract

From September 2017, an advance study project of Negative ion-based Neutral Beam Injection (NNBI) prototype for the China Fusion Engineering Test Reactor (CFETR) was supported by the ministry of science and technology of China. The entire test facility will be integrated at Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). In order to meet requirement of the development of negative ion based neutral beam injection system for CFETR, a negative ion source test facility with radio frequency source is being built. At the same time, cavity ring-down spectroscopy (CRDS) is employed for measurement of negative ion density. CRDS is an ultrasensitive absorption diagnostic technique for density measurement. Based on photo-detachment process of hydrogen negative ions, CRDS can measure integrated line-of-sight density of hydrogen negative ions in high power ion source. In this paper, the principle of CRDS diagnostic system has been introduced. Based on previous tests, the system setup and improvement are mentioned. In this paper, typical ring-down signals and time evolution of density of hydrogen negative ions are reported. With the first time cesium seeding, density of hydrogen negative ions increased obviously. It increased from 6.3E15 m−3 to 1.8E16 m−3, about 2.8 times under the 40 kW RF power discharge. Several days condition up, the density of hydrogen negative ions is up to 3.4 E16 m−3 under the 50 kW RF power discharge.