Significantly Large Negative Ion Formation in Grazing Scattering of Neutral Deuterium and Tritium Atoms from a CsI(100) Surface

We present the theoretical evidence of the formation of significantly large fractions of negative ions during grazing scattering of deuterium (D) and tritium (T) atoms from a CsI(100) surface. The negative ion conversion efficiency increases to an impressive ≥50%, and the maximum value even reaches 86% and 82% within projectile velocity ranges of v ∈ [0.15,0.43] a.u. and v ∈ [0.15,0.35] a.u., respectively, for D and T atom incidence. A detailed electron-capture energy defect calculation reveals that these results are obtained primarily because the large anion and cation polarizations of 6.43 and 3.34 ų lead to a large Mott–Littleton polarization interaction, which reduces the energy defect of the valence band electron capture to below 2.4 eV near the surface anion sites and drastically increases the electron-capture probability. The destruction of negative ions is not due to the electron loss to the unoccupied conduction band or neutral exciton states, but results from the affinity electron detachment via Coulomb barrier tunneling to the vacuum level during the interaction with the surface anion sites along their trajectories. Our results indicate that the collision system presented here can pave the way for the design of intense, directional and stable D^– and T^– ion beam sources for fusion DT fuel injection, the production of high-energy neutral beams to heat large fusion plasmas using D^– ions as precursors and the design of high intensity D–D or D–T neutron generators which are widely used in neutron logging.