In order for the images produced by the future MRI to be free of distortions or artifacts, the magnetic field generated by the Iseult magnet must be homogeneous to 0.5 PPM (parts per million) around the patient's brain. To meet this challenging specification, it was necessary to provision means of "shimming" the field, i.e. of correcting all the small defects that would inevitably arise from the manufacturing process. 5904 pieces of shim (small iron platelets) were screwed onto rails and installed inside the magnet tunnel. This first configuration was tested on Thursday, July 9, 2020 by mapping its effect on the magnetic field of Iseult at 3 T. The results are very encouraging as this first shimming iteration allowed to increase the homogeneity of the field in the useful zone from 138.8 to 3.2 PPM (value extrapolated to 11.72 T from magnetic measurements at 3 T).
A year and a half after the delivery of the prototype cryomodule (CM00) to ESS, the first production medium beta cryomodule (CM01) has now arrived at the ESS site. It left CEA on September 22, 2020 for a two-day trip to Lund, Sweden. The Irfu teams had previously validated the RF and cryogenic performances of this cryomodule. It will be tested again on the ESS test bench before being integrated in its final position in the accelerator tunnel. This is a first step. Starting next year, ESS will receive an average of one cryomodule per month for 3 years.