Calculation and measurement of D⁺, D₂⁺, and D₃⁺ fraction in KAERI ion beam irradiation facility by D collisional-radiative model and ExB probe

Ion beam irradiation facility was developed using an Applied-Field MPD thruster to study divertor engineering such as the evaluation of plasma facing materials [1, 2]. The AF-MPD thruster was chosen because it can produce high-density plasmas which is necessary for achieving high particle flux as the divertor region. The D ion flux measured by a Langmuir probe was 1×10²³ m^-2s^-1 when the plasma was ignited by 5 kW input power. The electron temperature at the downstream region is in the range of 4-5 eV and the electron density is in the range of (1-4)×10¹⁸ m^-3. The energy of the D ion beam was measured as 15-18 eV by a Retarding Potential Analyzer. In the D plasmas, both atomic and molecular ions (D⁺, D₂⁺, and D₃⁺) are generated. Thus, it is important to know the fraction of D⁺, D₂⁺, and D₃⁺ for obtaining precise D particle flux. In order to calculate the fraction of D⁺, D₂⁺, and D₃⁺, we developed a D collisional-radiative (CR) model including D, D₂, D⁺, D₂⁺, and D₃⁺ species. Our model predicts that D⁺ ions are dominated over D₂⁺ and D₃⁺ in our plasmas. To confirm the calculated results, we plan to build an ExB probe: this probe can distinguish ions having different charge-to-mass ratio. The details and preliminary results of the ExB probe will be shown in the paper.