Interim progress summary: ITER Imaging X-ray crystal spectrometer design

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

2. 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.

3. Design for wavelength& bandwidth

4. Basic tunnel shape generation crystal Rowland circle • 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. detector tunnel to plasma tunnel to detector crystal neck Conical shape – basic profile is rotated around the normal to the crystal centre to extent required for spatial coverage View tunnel for 5% bandwidth, θB=60° (illustrative only) View tunnel for 0.5% bandwidth, θB=50° Note narrower neck

5. Design for spatial coverage Plasma coverage by radial views Plasma coverage by toroidal views radial • 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 toroidal Necessary to reduce the crystal-detector distance for the furthest-forward toroidal view spectrometer

6. 1) Maximum shielding Δλ=0.5% 2) Minimum shielding Δλ=2% 3) Straight shield 4) ‘Squared off’ shield rather than conical shape for easier construction (not shown right) 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

7. Other options under investigation Different thicknesses of different materials around detector crystal 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

8. 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.