VAriable Dipole for the Elettra Ring: Prototype acceptance test

I.FAST Innovation Fostering in Accelerator Science and Technolog y Horizon 2020 Research Infrastructures GA n° 101004730 MILESTONE REPORT VAriable Dipole for the Elettra Ring: Prototype acceptance test MILESTONE: MS27 Document identifier: IFAST-MS27 Due date of deliverable: End of Month 54 (October 2025) Report release date: 19/12/2025 Work package: WP7: High Brightness accelerators for light sources Lead beneficiary: ELETTRA Document status: Final ABSTRACT The VAriable Dipole for the Elettra Ring (VADER) task, driven by the I.FAST European project (Deliverable 7.3), aimed at developing a prototype of a new full length variable field dipole design magnet which includes a transverse gradient allowing a further reduction of the horizontal emittance in the upgraded ELETTRA storage ring. A prototype of this magnet was designed by the CIEMAT laboratory and fabricated by KYMA company. This note presents and discusses the magnetic measurement serving as acceptance tests of the magnet prototype conducted at ELETTRA. PROTOTYPE ACCEPTANCE TESTS Milestone: MS27 Date: 19/12/2025 Grant Agreement 101004730 PUBLIC 2 / 11 I.FAST Consortium, 2021 For more information on IFAST, its partners and contributors please see https://ifast-project.eu/ This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730. IFAST began in May 2021 and will run for 4 years. Delivery Slip Name Partner Date Authored by D. Castronuovo, D. Caiazza, E. Karantzoulis, M. Dominguez Martinez, F. Toral Y. Papaphilippou R. Righi ELETTRA CIEMAT CERN KYMA 18/12/2025 Reviewed by M. Vretenar, L. Celona [on behalf of Steering Committee] CERN 19/12/2025 Approved by Steering Committee 19/12/2025 PROTOTYPE ACCEPTANCE TESTS Milestone: MS27 Date: 19/12/2025 Grant Agreement 101004730 PUBLIC 3 / 11 TABLE OF CONTENTS 1 INTRODUCTION ......................................................................................................................................... 4 2 MAGNETIC MEASUREMENTS ............................................................................................................... 4 3 CONCLUSION ............................................................................................................................................. 9 PROTOTYPE ACCEPTANCE TESTS Milestone: MS27 Date: 19/12/2025 Grant Agreement 101004730 PUBLIC 4 / 11 Executive summary The Variable Dipole Elettra Ring (VADER) was specified by CERN for reducing the emittance for the ELETTRA ring up to a factor of two, by using a novel PM concept with a hyperbolic field profile and peak field at the centre reaching 2.3 T. After the magnetic design at CIEMAT, the magnet was fabricated at KYMA and measured at ELETTRA. The measurements show an excellent agreement with the predicted magnetic field in both dipole and quadrupole component and good field quality. This report presents the magnetic measurement set-up and results which served as acceptance tests. 1 Introduction In the framework of I.FAST WP7 a magnet prototype based on an innovative dipole magnet design with longitudinal varying dipole field, including a transverse gradient has been built (Task 7.3). The magnet concept was already established for the case of the CLIC damping rings, and the study demonstrated the significant reduction of the horizontal emittance. The design has been modified and adapted to the lattice of the upgraded ELETTRA light source storage ring, in order to reduce up to a factor two the horizontal emittance beyond the 140 pm proposed for ELETTRA 2.0 study. The use of such new magnet involves the optics calculations for the storage ring Multi-Bend Achromat cell, by replacing all the dipoles with longitudinally varying ones with an optimised hyperbolic field profile. CIEMAT carried out the magnetic and mechanical design, and the magnet prototype has been manufactured by KYMA, a leading industrial partner in the magnet technologies for X-ray sources and, in particular, insertion devices. Finally the magnet has been measured at ELETTRA and this report presents the magnetic measurement and results which served as acceptance tests. 2 Magnetic measurements An overview of the final VADER magnetic system is shown in fig. 1 (more details are reported in Deliverable 7.3), the magnet has been realized at Kyma (fig.2) and then moved to ELETTRA Sincrotrone Trieste for magnetic measurements and acceptance testing where has been positioned close to the bench specifically designed (fig.3). PROTOTYPE ACCEPTANCE TESTS Milestone: MS27 Date: 19/12/2025 Grant Agreement 101004730 PUBLIC 5 / 11 Fig. 1 VADER final design and main characteristics. Fig. 2 Photo of the assembled VADER magnet in KYMA. PROTOTYPE ACCEPTANCE TESTS Milestone: MS27 Date: 19/12/2025 Grant Agreement 101004730 PUBLIC 6 / 11 Fig. 3 Picture of the magnetic measurement set-up bench at ELETTRA including the bench and 3D field mapper. After the phase of mechanical pre-alignment and magnetic alignment, the field produced by the magnet was mapped on the median plane on a rectangular strip measuring L x W = 1100 x 52 mm. A SENIS 3D Digital Teslameter 3MH4 calibrated from 0 to 7 Tesla was used for the measurement (characteristics reported in Annexe 1). In order to evaluate the quality of the field in a potentially real case, the trajectory of a single electron at 2.4 GeV was calculated on the mapping as above. The values of the vertical magnetic field By, its quadrupole component B2 and the first three multipole errors (B3, B4 and B5) were then evaluated on this trajectory in the gradient field region of +/- 5mm. In order to compare as best as possible the design results with the measurements, the same was done on the field mapping obtained in the Opera simulation. In Fig.4, the plots of the simulation and measurement results are shown, in particular the field mapping together with the field values on the calculated trajectory and the limits of the relative good field region for the dipole component of the magnet. PROTOTYPE ACCEPTANCE TESTS Milestone: MS27 Date: 19/12/2025 Grant Agreement 101004730 PUBLIC 7 / 11 Fig. 4 Simulated and measured dipole field including the considered good field region (top) and corresponding electron trajectory estimated with two methods (bottom). PROTOTYPE ACCEPTANCE TESTS Milestone: MS27 Date: 19/12/2025 Grant Agreement 101004730 PUBLIC 8 / 11 Finally fig. 5 shows the main dipole and quadrupole components as measured along the VADER magnet. As can be seen, there is an excellent correlation between the simulated and measured values, indicating excellent modelling and, at the same time, the construction of the actual magnet. Small asymmetries were observed in the longitudinal distribution of By and B2 which may be linked to very small alignment errors in the assembled parts and/or inhomogeneity of the ferrous parts. A future action would be to carry out accurate tuning of the assembly in order to minimise these differences and, at the same time, obtain a measure of the mechanical sensitivities for this. Fig. 5 Main dipole and quadrupole components as measured along the VADER magnet. PROTOTYPE ACCEPTANCE TESTS Milestone: MS27 Date: 19/12/2025 Grant Agreement 101004730 PUBLIC 9 / 11 3 Conclusion The final magnetic measurements carried out on VADER magnet at ELETTRA show an excellent agreement of the main components with respect to the predicted values by simulations, including a good field quality. Small deviations with respect to the simulated values will be addressed in a later phase by adjustments of the measurement mole positioning including positioning of the magnet but also mechanical adjustments with which the magnet is equipped for fine field tuning. The positive acceptance tests will shape the industrialisation procedure towards a series fabrication of such an innovative magnet device and its full inclusion in the upgrades of ELETTRA and of other synchrotron light sources.