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In the European fusion roadmap, reliable power handling has been defined as one of the most criticalchallenges for realizing a commercially viable fusion power. In this context, the divertor is the key in-vessel component, as it is responsible for power exhaust and impurity removal for which divertor targetis subjected to very high heat flux loads. To this end, an integrated R&D project was launched in theEUROfusion Consortium in order to deliver a holistic conceptual design solution together with the coretechnologies for the entire divertor system of a DEMO reactor. The work package ‘Divertor’ consistsof two project areas: ‘Cassette design and integration’ and ‘Target development’. The essential missionof the project is to develop and verify advanced design concepts and the required technologies for adivertor system being capable of meeting the physical and system requirements defined for the next-generation European DEMO reactor. In this contribution, a brief overview is presented of the works fromthe first project year (2014). Focus is put on the loads specification, design boundary conditions, materialsrequirements, design approaches, and R&D strategy. Initial ideas and first estimates are presented

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The European DEMO power reactor is currently under conceptual design within the EUROfusion Consortium. One of the most critical activities is the engineering of the plasma-facing components (PFCs) covering the plasma chamber wall, which must operate reliably in an extreme environment of neutron irradiation and surface heat and particle flux, while also allowing sufficient neutron transmission to the tritium breeding blankets. A systems approach using advanced numerical analysis is vital to realising viable solutions for these first wall and divertor PFCs. Here, we present the system requirements and describe bespoke thermo-mechanical and thermo-hydraulic assessment procedures which have been used as tools for design. The current first wall and divertor designs are overviewed along with supporting analyses. The PFC solutions employed will necessarily vary around the wall, depending on local conditions, and must be designed in an integrated manner by analysis and physical testing.

The design and development of a novel plasma facing component (for fusion power plants) is described. The component uses the existing "monoblock" construction which consists of a tungsten "block" joined via a copper interlayer to a through CuCrZr cooling pipe. In the new concept the interlayer stiffness and conductivity properties are tuned so that stress in the principal structural element of the component (the cooling pipe) is reduced. Following initial trials with off-the-shelf materials, the concept was realized by machined features in an otherwise solid copper interlayer. The shape and distribution of the features were tuned by Finite Element (FE) analyses subject to ITER Structural Design Criterion In-Vessel Components (SDC-IC) design rules. Proof of concept mock-ups were manufactured using a two stage brazing process verified by tomography and micrographic inspection. Full assemblies were inspected using ultrasound and thermographic (SATIR) test methods at ENEA and CEA respectively. High heat flux tests using IPP's GLADIS facility showed that 200 cycles at 20 MW/m 2 and five cycles at 25 MW/m 2 could be sustained without apparent component damage. Further testing and component development is planned.

This paper presents a simplified rule-based elastic analysis procedure (and its rationale) for the structural integrity assessment of the structural pipe component within monoblock divertor plasma facing components (components constructed from a tungsten block with through cooling pipe and copper interlayer). It is first demonstrated that the conventional fully elastic finite element analysis method used in an elastic code rule assessment must be modified when applied to monoblocks to overcome the problems caused by the assembly of multiple materials (with different yield strengths and different coefficients of thermal expansion causing residual stress). This is done by comparing the result of a fully elastic model with a more representative elasto-plastic model incorporating residual stress simulation. The results show that due to the expected high levels of residual stress, the desired elastic modelling of the structural pipe component can only be used to determine cyclic stress range (but not absolute stress), and even then, only if accompanied by elasto-plastic simulation of the non-structural interlayer (to apply the correct levels of differential expansion loads from the tungsten). This mixed elastic-elasto-plastic method is used in the proposed procedure, and applies the elastic code rules employing cyclic stress range, i.e. rules for ratchetting and fatigue. Additional rules for critical heat flux and allowable material temperatures are added. Example results of an assessment using the procedure are also presented for an ITER-like monoblock divertor target component.

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Design optimization using high-fidelity computational fluid dynamics simulations is becoming increasingly popular, sustaining the desire to make these methods more computationally efficient. A reduction in problem dimensions as a result of improved parameterization techniques is a common contributor to this efficiency. The focus of this paper is on the high-fidelity aerodynamic design of airfoil shapes. A multifidelity design search method is presented which uses a parameterization of the airfoil pressure distribution followed by inverse design, giving a reduction in the number of design variables used in optimization. Although an expensive analysis code is used in evaluating airfoil performance, computational cost is reduced by using a low-fidelity code in the inverse design process. This method is run side by side with a method which is considered to be a current benchmark in design optimization. The two methods are described in detail, and their relative performance is compared and discussed. The newly presented method is found to converge towards the optimum design significantly more quickly than the benchmark method, providing designs with greater performance for a given computational expense. Nomenclature a, b = constant coefficients of polynomial expressions= relaxation factor r LE = airfoil leading edge radius t = airfoil maximum thickness x = airfoil ordinate in the horizontal (chordwise) direction z = airfoil ordinate in the vertical direction z c = airfoil maximum mean thickness (camber) z 00 = airfoil surface second derivative with respect to x = airfoil angle of attack