Negative ion production near a divertor plate

In detached divertor operation, typical plasma parameters in front of target plates are densities from 1019 m−3 up to 1020 m−3 and temperatures below 3 eV. In this regime, production of negative hydrogen ions can occur, mainly through vibrational excited molecule or by negative surface ionization of hydrogen ions. To study this effect, we have developed a 1D-3 V Particle-in-Cell electrostatic model of the electro-negative sheath. The motion of charged particles (e, H+, H2+ and H−) in their self-consistent electric field and of excited neutral-particle states (H (n = 1, 2, 3) and H2(X1Σg+,v=0,…,14)) is simulated. Surface and volumetric processes have been included by using different Monte Carlo Collision methods. The importance of negative ions for the sheath potential and hydrogen fluxes on to the divertor will be calculated for different parameters.