Nb3Sn triplet (MQXF)
After the successful tests of MQXFA03 and MQXFA04, that allowed last year to obtain the approval of the US contribution by the DOE, MQXFA05 has been tested in May 2021. The magnet (in a vertical dewar and without outer stainless-steel shell, as MQXFA03 and MQXFA04) reached the required performance, confirming the absence of retraining after 2 warm-up/cooldown cycles and a temperature margin enabling to achieve nominal current also at 4.5 K. MQXFA06 started testing in June at BNL, where the test station is back to full operational mode after a critical period in the first half of 2021. MQXFA06 also reached the nominal performance level by the end of June.
At CERN the second prototype was tested in March 2021 (on a horizontal bench and with a welded outer stainless-steel shell), reaching the level of nominal current (which corresponds to 7 TeV) but showing performance limitations around this level at 1.9 K, and a 10% lower current level at 4.5 K. This is the first Nb3Sn 7-m-long magnet able to achieve 11.4 T peak field in the coils. Investigations on the observed performance limitations are ongoing, reviewing the assembly parameters (including coil stress) and the integration of the outer stainless-steel shell, tested at CERN on long Nb3Sn quadrupole magnets for the first time. An optimization of the procedures relative to the outer shell integration has been agreed with the AUP collaboration, shifting the assembly of the first US cold mass with MQXFA03 and MQXFA04 to fall of this year.
Nb-Ti magnets
The test of the second prototype magnet of the nested corrector (CIEMAT collaboration agreement) has confirmed the reproducibility of the performance of the first one, i.e., its ability of reaching the nominal torque, but requiring a retraining when the torque sign is changed. An iteration on the design to improve this aspect will be tested on the third magnet and discussions are undergoing with WP2 regarding the technical requirements. The tender for the series has been attributed to Elytt (Spain), representing the last tender adjudicated for the WP3 magnets.
Two thirds of the series high order correctors (INFN-LASA collaboration agreement) have been completed in SAES-RIAL (Italy), and one third have already been successfully tested at LASA. All the correctors needed for the IT String are already at CERN, ready for the assembly of the prototype corrector package cold mass.
The D1 prototype (KEK in kind contribution) has been completed in Hitachi (Japan) and has been moved to KEK for vertical test and has been powered to nominal current in early July. Besides performance, the main critical point will be the measurement of the field quality of this challenging magnet, where the iron gives a large contribution to the field.
The D2 prototype magnet (INFN –Genova collaboration agreement) is being completed at ASG (Genova, Italy). The two apertures have been successfully collared after some iterations to solve electrical issues. As for the D1 magnet, the main critical issue besides quench performance is the validation of the fine tuning of the cross-section to reach the field quality targets.
After the successful test of the first D2 corrector prototype built by WST (Xi’an, China), as part of the collaboration agreement with IHEP, Beijing, series production of this canted cosine theta magnet (CCT) has started in BAMA, Suzhou. The assembly of the first magnet has been completed and the test in IMP, Lanzhou is foreseen in July. The production is facing some issues with the performance of the coils that are individually tested to qualify the supplier’s procedures in this initial phase of production. In the meantime, CERN has completed the manufacture and test of a second magnet that achieved performance requirements, thereby confirming the robustness of the CERN design and manufacturing processes.