Interim progress summary: ITER Imaging X-ray crystal spectrometer design Sam Davis - UKAEA Robin Barnsley - ITER

Aims Aims of current design activity: Determine most appropriate location of crystals and detectors – i.e. within or behind equatorial port plug 3 Determine required and achievable bandwidths …. and the corresponding shielding required Determine whether the full plasma cross section can be viewed from equatorial port, simplify etc Factors affecting these decisions include Diagnostic: n-γ flux – noise, activation, component life Others: ease of maintenance The main focus so far has been to create a CAD model suitable for efficiently investigating the effects of various features on nuclear performance using Atilla. Results are expected for the next ITPA.

Design for wavelength & bandwidth Chosen parameters fmfm Crystal-detector lengthWant this high for good resolution, but constrained by available space. 1m max for inside the plug θBθB Central Bragg angle50° - chosen based on line spectra to be observed, available crystals and spherical crystal imaging properties ΔλBandwidth0.5% - minimum for Doppler width and shift of a single spectral line giving temperature and rotation 2% sufficient for a group of lines δθ B Crystal width aberrationRequire <10 -4 for resolution – drives crystal width Derived parameters RRowland circle radius Δθ B Variation in Bragg angle wCrystal width fsfs Distance to focus in plasma

tunnel to plasma neck crystal Conical shape – basic profile is rotated around the normal to the crystal centre to extent required for spatial coverage View tunnel for 5% bandwidth, θ B =60° (illustrative only) View tunnel for 0.5% bandwidth, θ B =50° Note narrower neck Basic tunnel shape generation The geometry of the tunnels through the port plug through which the spectrometers view the plasma directly affects the neutron and gamma flux The tunnel shape required to accommodate all the required X-rays is generated by CAD by constructing the nominal ray paths from the chosen instrument parameters. The appropriate geometric constraints and previous equations are included in the model, allowing rapid and efficient modification. tunnel to detector crystal detector Rowland circle

Design for spatial coverage Plasma coverage by toroidal viewsPlasma coverage by radial views Necessary to reduce the crystal-detector distance for the furthest-forward toroidal view spectrometer Yellow represents view tunnel within the port plug and its virtual extension into the plasma Aim is to view the tangent to all plasma flux surfaces Spatial coverage drives detector height View from top of plug radial toroidal

1) Maximum shielding Δ λ=0.5% 2) Minimum shielding Δ λ=2% 3) Straight shield (not shown right) 4) ‘Squared off’ shield rather than conical shape for easier construction Shielding tunnel liners to be investigated Shielding options for the tunnel through the plug to the plasma form nested layers These can be modelled as vacuum or steel in Atilla to investigate their effect Liners could be fitted later for high neutron flux operations, allowing higher bandwidth during earlier campaigns

Other options under investigation Different thicknesses of different materials around detector Different widths for tunnel to detector depending on the tuning required – again modeled as adjacent layers Option to model vacuum / neutron absorbers behind crystal to avoid direct line-of-sight scattering into the detector crystal detector

Atilla modelling considerations Atilla is able to accept solid models for nuclear analysis, however every volume must be occupied by precisely one component – i.e. no voids or clashes Port plug structure - current solid model has been simplified to remove features which complicate geometry (and hence meshing) but which either –have negligible effect on radiation – e.g. bolts –can be approximated – e.g. by modelling components as water/steel mix cooling systems can be omitted This will be used by other analyses and remains linked in VPM to the detailed model so it will be automatically updated. Other diagnostic systems are modelled as vacuum to ensure their neutron transparency is included All other volumes are modelled as homogeneous water/steel mix with more steel at the front and more water at the back of the plug.