Quench Behavior of 18-mm-period, 1.1-m-long Nb₃Sn Undulator Magnets

A novel Nb ₃ Sn-based superconducting undulator (SCU) was developed and integrated into the Advanced Photon Source (APS) at Argonne National Laboratory. The SCU achieved user operation within an accelerator environment. Compared to its Nb-Ti counterpart, the Nb ₃ Sn SCU operates at substantially higher currents. Thus, a detailed experimental evaluation of the SCU magnets’ performance was necessary under both “wet” and indirectly cooled conditions to ensure its reliability during operation. Our study indicated that the cooling method has a noticeable influence on the magnet's behavior. Specifically, energy dissipation in the magnets during quenches was observed to be greater under indirect cooling than with “wet” cooling. This investigation provided insights into the safe operational limits. Guided by these insights the more challenging high-current tests were successfully carried out at the end of the user phase. The SCU achieved the design undulator field of 1.17T at 820A and 4.2K, with a magnetic gap of 9.5 mm and a period of 18 mm. Actual performance exceeded the specifications, reaching 850A.