## 5 Conclusions  
The analyses performed revealed the mechanical behavior of the magnet holder. The obtained positioning range guarantees the possibility of magnet positioning and calibration within the required range of \(\pm 0.15\) mm. Finally, the following conclusions can be drawn:  
* The multidisciplinary numerical (FEM) and experimental research conducted on the test bench effectively verified the design of the magnet holder. The calibration and adjustment of screws ensured stability and repeatability of the results, which is crucial for the further development and implementation of the mounting system in practical applications.
* The boundary conditions related to the design of the magnet holder were fully met. The study confirmed the possibility of using the proposed solution for positioning large magnets magnetized with relatively high force while providing quite a large calibration range.
* The results of the experimental measurement with the use of dial indicators and DIC are similar both quantitatively and qualitatively. They are also consistent with the results of the FEM analyses.
* The calibration conducted over the load variation range confirmed the linear behavior of the magnet holder throughout the entire predicted load range.
* The adjusting process conducted via adjusting screws has an almost linear and repeatable influence on the displacement of the magnet. The influence of the magnetic force on the structure deformation can be compensated during the holder's assembly process by changing the individual thickness of the brass shims.
* The determined curves of magnet positioning can be used for the magnet-calibration process during the final installation process of the THz undulator.
* The results allowed the estimation of the minimum and safe torque values for the mounting bolts and screws required during assembly. Additionally, the development of the assembly procedure and its testing under real conditions proved to be a significant outcome.
* The application of DIC analysis made it possible to perform full-size measurements of the frame with a high accuracy of several/dozen micrometers.
* Gained experience and learned behavior of the magnet holders made it possible to develop a safe, reliable, and repeatable installation procedure for both men and equipment.  
Despite the positive experimental validation of a single magnet holder, further research should be performed on the issue of calibration of the set of magnet holders mounted on the undulator jaw. It is also necessary to develop procedures for grouping magnets, determining magnet position in the Halbach array, and determining a coarse vertical position of the magnet relative to the electron beam.  
Conceptualization, P.J.R., J.W., D.Z., R.N. and P.K.; methodology, P.J.R., J.W., D.Z. and R.N.; investigation, P.J.R., J.W. and D.Z.; data curation, P.J.R. and J.W.; writing--original draft preparation, P.J.R., J.W. and R.N.; writing--review and editing, P.J.R., J.W. and R.N.; supervision, P.K.; project administration, P.K.; funding acquisition, P.K. All authors have read and agreed to the published version of the manuscript.  
Development of the presented THz undulator has been a part of the PolFEL project. The project received funding from the European Regional Development Fund in the framework of the Smart Growth Operational Programme, Measure 4.2: Development of modern research infrastructure of the science sector. Grant number: POIR.04.02.00-00-B002/18-00.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors on request.  
**Conflicts of Interest:** The authors declare no conflicts of interest.