## 4 Discussion  
In this paper, we demonstrated the first results of synthetic diagnostics Cherab package development for usage with SolEdge3X-HDG code and WEST tokamak. It includes bolometer and visible camera simulated signals as well as a comparison of the 2D transport code results with experimental data. At first, the bolometer submodule was verified with an existing ray-tracing code SYNDI. Even with a simplified tokamak PFCs model in the absence of reflections, the comparison is almost perfect. This means that the geometry set in both codes, as well as line integration, are identical. However, later, a more detailed WEST CAD model will be used, and this will give more relevant synthetic signals compared to the experimental ones. Moreover, when the new vertical bolometer systems are commissioned, Cherab-WEST package might be used to check the geometry and relative position of both cameras and tokamak elements. Figure 7: Simulated images for visible pinhole camera for limiter (**a**) and divertor flat-top (**b**) phases of the discharge, experimental visible camera images (**c**,**d**) and a filtered pinhole camera for the WI 401.22 nm line (**e**,**f**) for the similar discharge stages. Another useful implementation of these WEST digital twin will be a proper selection of surface material model. As was shown in Section 3.2, there might be a difference of order of magnitude in the case of different optical PFC properties. Not only the value of the modeled signal, but also the shape of the bolometer signals profile can change significantly. This may cause a systematic error while interpreting experimental results in terms of the locations of the highest radiation. Together with the BRDF measurements [14], a better refined CAD model, and better Cherab and Raysect libraries, a physically reliable WEST tokamak model should be implemented. In comparison with the experimental data, using deuterium, tungsten, and proxy oxygen showed the sensitivity of our bolometer digital twin to the different sources of radiation. However, it also revealed discrepancies, which were caused by the model's simplicity and uncertainties. Nonetheless, having such a confrontation tool will allow us to more easily improve the model in SolEdge3X-HDG, as well as in ERO2.0. In addition, the very availability of a full-discharge, entire-plasma-domain simulation with SolEdge3X-HDG allows us to perform benchmarking for the diagnostics which use line-integrated signals, i.e., cover the core plasma. Consequently, there is a possible co-use of synthetic diagnostics and this novel code dedicated to improvement of the existing experimental tools. For example, bolometers are not yet able to perform real-time tomography measurements during discharge. For these purposes, machine learning can be used [31; 32]. At the same time, SolEdge3X-HDG could be utilized to obtain the training set as the vertical bolometer system was not in use before. Therefore, there is no opportunity to get the 2D radiation profiles from only horizontal systems without strict assumptions on its distribution. Profiles obtained from simulation have another advantage over experimental ones; they are less noisy, and the code can cover more regimes in less time than in desired experiments. Among these applications, Cherab can be also employed for performing the conventional tomography inversions, which also should be implemented for the upcoming campaign. Moreover, it is a very straightforward tool with which to obtain geometry matrices for further usage with other software, for example, ToFu [27], which is designed for tomography inversions. The filtered visible camera demonstration shows the ability to use such a device in the real experiments. In the easiest case, it can show the approximate location of the particle sources. However, it is possible to make a tomographic inversion into the 2D radiation profile [8], which can further be interpreted in terms of particle fluxes.