Negative ion sources driven by radio frequency (RF) waves have become the preferred solution for future neutral beam injection systems.

This study aims to monitor the plasma discharge state of each exciter of a high power RF negative ion source by developing a plasma luminescence monitoring system based on a photodiode is designed and constructed.

The intensity of plasma emission was closely related to the number of specific collisions, collision particle density, and collision particle energy. Therefore, the intensity of plasma emission was applied to monitoring plasma parameters qualitatively, and a photodiode-based multichannel plasma luminescence monitoring system was designed and implemented to monitor the plasma discharge state of each exciter of a high power RF negative ion source. Based on a reasonable collision radiation model, plasma parameters were quantitatively obtained by analyzing the intensity of plasma characteristic spectral lines, and the influence of the filtering magnetic field generated by plasma current on plasma emission signals as experimental tested.

Experimental results this monitoring system demonstrate that the real-time intensity information of plasma emission from different positions is successfully collected, and subsequently presented and saved in the form of voltage signals for real-time monitoring and post-data processing by the host computer. The intensity of plasma emission has a good linearity with RF discharge power.

The plasma light monitoring system of this study can accurately and real-time measure the excitation, maintenance, and extinction processes of plasma in the RF exciter.