The DIONISOS (Dynamics of ION Implantation and Sputtering of Surfaces) experiment is described. DIONISOS features steady-state plasma exposure of material surfaces, with simultaneous, in situ, non-destructive depth profiling on the same surfaces with ion beam analysis (IBA). A steady-state RF helicon plasma source produces a fusion ‘edge-like’ low temperature (T∼1–10eV), high-density (⩽10 17–18 m −3 ), steady-state, cylindrical, plasma (ϕ∼50mm). The exposure stage allows for the control of sample surface temperature (300–800K), incident ion energy (10–500eV), and ion beam and magnetic field incident angle (360° rotation), during bombardment with high plasma flux (∼10 20 –10 22 s −1 m −2 ). First results from DIONISOS show a large and evolving concentration of deuterium (∼1000appm) trapped deep (∼5μm) in molybdenum. IBA during plasma exposures shows the surface dynamic deuterium inventory increased by a factor of 2 over the ‘long-term’ trapped inventory at an incident ion flux density of ∼1.5×10 21 D/m 2 s.