Boron trace amount measurement in LaB6 hollow cathode discharge using an improved actinometry method based on OES

The erosion of hollow cathode critical structures is inevitable for the high-temperature and high-energy ion environment. As the amount of erosion product is very small in a short time, it is difficult to achieve online monitoring by traditional methods. This paper established an improved actinometry method based on optical emission spectroscopy (OES) to achieve online monitoring of the density of boron (B) erosion products from the lanthanum hexaboride (LaB6) cathode emitter without damaging the cathode structure. In this method, the intensity of spectral lines generated by the transitions of xenon (Xe) from its ground state and metastable state was collected. Then, the electron temperature can be calculated using the collisional-radiative model of Xenon spectral lines. Further, the number density of B is obtained through the ratio of spectral lines excited from the ground state of B and Xe, and thereby the rate of production of B erosion products from the emitter per unit time is determined. The erosion rate of the cathode under different operating conditions was measured. It was found that the erosion of the cathode emitter was closely related to the flowrate and low-frequency current oscillations of the cathode. Therefore, it is necessary to avoid low-frequency current oscillations and appropriately increase the gas flowrate of the cathode to improve the lifespan of the cathode emitter.