The roughness evolution during plasma deposition of amorphous hydrogenated carbon (a-C:H) films is investigated. Films were deposited from an inductively coupled methane plasma using a wide range of process parameters. Plasma deposition is uniquely described by the dissipated energy per source gas molecule Emean. Depending on Emean, a specific set of radicals contributes to film growth causing a characteristic roughness development. The film roughness is measured using atomic force microscopy and spectroscopic ellipsometry and is expressed using the static and dynamic scaling coefficients α and β, respectively. For low Emean<20eV, α∼0.65 and β∼0.19 indicating film deposition via a growth precursor with a large surface diffusion length. For Emean>20eV, α∼0.9 and β∼0.25 indicating film deposition via a growth precursor with a small surface diffusion length.

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To solve climate change and to achieve the “2050 carbon neutrality,” fusion energy has to contribute to the power grid as soon as possible. Nonetheless, DEMO reactor concepts proposed so far were focused on producing 1 GW electricity with the best plasma performances and a very effective power conversion rate deduced by simple 0D/1D system codes. There are open questions and issues about how fusion energy would contribute to the electricity market timely. This paper asks questions and issues on the construction and operation of a DEMO reactor such as (1) identity, (2) net electricity output, (3) construction cost, and (4) public acceptance of fusion energy. Those questions are not simple to answer, but they must be clarified very soon. To achieve the 2050 carbon neutrality in time, a two-pathway approach towards the realization of fusion energy is suggested, and a conclusion is given.