Eurofusion Enabling research project DDRM (Investigation of defects and disorder in nonirradiated and irradiated Doped Diamond and Related Materials for fusion diagnostic applications – Theoretical and Experimental analysis)

Coordinators: A.I. Popov and A. Lushchik (Tartu University)

Duration: 2021-2023

Undoped polycrystalline diamond disks with a respectable size from several tens of millimetres up to 180 mm produced by plasma assisted chemical vapour deposition (PACVD) in a microwave reactor are state of the art in functional optical and dielectric windows. Diagnostics, heating and current drive systems need these components as filters for well-defined frequency bands in IR, VIS, UV-VUV, microwaves and sub-millimetre waves (THz-range) as well as window materials for transmission of low and high-power electromagnetic waves. A series of functional materials were already investigated in relation to primary radiation defects (vacancies, F-type centres, trapped holes on cation vacancies, etc.) in previous projects. Especially in diamond, the influence of intrinsic defect structures – introduced during the growing process – (nitrogen, hydrogen and oxygen) on optical and dielectric material properties were considered. On the other hand, for systems in plasma diagnostics, doping in diamond (B, P) has a strong influence on the optical transmission and the electrical properties of such filters and windows. We plan here theoretical and experimental studies, to explain fundamental mechanisms of absorption and emission in diamond in different spectral ranges depending on the dopant and the defect concentrations. The nitrogen content can have e.g. a compensation or amplification effect to the dopant concentrations in diamond. To determine experimentally the defect influences, we propose different spectroscopic and magnetic methods (EPR, RAMAN, IR, VIS, UV-VUV). Additionally, we will measure the electrical conductivity dependence on diamond doping concentrations.

Theoretical calculations of the material properties by means of first principle quantum chemical methods are foreseen to substantiate complement and interpret the experimental results. These calculations will be accompanied with theoretical analysis of the experimental defect annealing kinetics, which allow to extract defect mobility and its dependence on the radiation-induced materials disordering. This is a key for prediction and control of radiation tolerance of candidate materials.

Important for understanding the crystal and defect structures, phonon spectroscopy by means of neutron scattering will be carried out in case of undoped and doped diamond. Optionally, a comparison of these results with single crystalline diamond and silicon could help to understand the basic mechanisms.