Modelling of microwave heating and current drive at STEP

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To effectively drive plasma current non-inductively and support steady-state operation in future fusion power generation systems, the use of a combination of mechanisms, specifically Electron Cyclotron Current Drive (ECCD) and the excitation of Electron Bernstein Waves (EBW), are highly desirable. The application of these process may be separate i.e. for low density plasmas ECCD can be preferable while EBW-CD can be used for high density plasma. There are also regimes when plasma conditions are such that both mechanisms can be simultaneously employed. One of the aims of the project will be to carry out studies to derive and understand the criteria for switching the heating mechanisms i.e. from ECCD to EBW-CD or employing both simultaneously. The evolution of the plasma in time also evokes the possibility of varying the RF frequencies and the launch direction of the RF beams and modulation of the power used to drive the currents. The criteria which dictate the changing of the RF beams: frequencies, powers, directions will be also considered to provide the roadmap to maintain stable and continuous operation. The stability of the chosen parameters in regards with small variations of plasma parameters for given equilibria should be also analysed. Although the studies will be carried out from general perspectives, the specific STEP design which takes into consideration specific STEP engineering requirements, will be considered during the project and used as a driver for the parameter optimisations.The project will be based on analytical and numerical studies using a set of codes like GENRAY, CQL3D and JETTO. UKAEA are also developing in-house codes which will be used to provide benchmarking of CQL3D and GENRAY.