  Reflection and implantation of low energy helium (He) ions by tungsten (W)
substrate are studied using molecular dynamics (MD) simulations. Motivated by
the ITER divertor design, our study considers a range of W substrate
temperatures (300 K, 1000 K, 1500 K), a range of He atom incidence energies
($\le$100 eV) and a range of angles of incidence ($0^{\circ}$-$75^{\circ}$)
with respect to substrate normal. The MD simulations quantify the reflection
and implantation function, the integrated moments such as the particle/energy
reflection coefficients and average implantation depths. Distributions of
implantation depths, reflected energy, polar and azimuthal angles of reflection
are obtained, as functions of simulation parameters, such as W substrate
temperature, polar angle of incidence, the energy of incident He, and the type
of W substrate surface. Comparison between the MD simulation results, the
results obtained using SRIM simulation package, and the existing experimental
and theoretical results is provided.
