Second set of coils in RMM reaches again 17 T in a 50 mm cavity

During the past few weeks, the RMM2 demonstrator has been tested at CERN. The assembly is based on three decks of racetrack coils, with the central deck providing a closed 50 mm cavity. RMM stands for Racetrack model magnet: this program was launched at CERN in 2015 by D. Tommasini with the goal of demonstrating a 16 T field with a Nb3Sn conductor . The magnet reached fields well above 16 T several times in the first assembly, RMM1a, in the period 2019-2022 and in subsequent configurations, exploring different preload conditions, including a complete disassembly and the introduction of a fishbone structure.

For RMM2, the entire set of three coils was replaced with new, previously untested coils—what we call in our jargon “virgin coils.” The coils were manufactured for the first time using the HFM conductor, namely a 1.0 mm 162/169 subelements with 0.9 of Cu fraction.

The demonstrator had its first quench above 14 T and then trained rapidly through 15 and 16 T at 1.9 K. A maximum field of 17.0 T in the bore was reached after 15 quenches. A 12-hour holding-current test was also successfully performed. After thermal cycle, first quench was above 16 T. New flat quench antenna were used for this test.

The results will be presented by the SM18 team at an HFM Forum in the coming week. An overview of the test campaign was also presented by Juan Carlos at ASC last week in Pittsburgh. This concludes the very successful program launched in the framework of EuroCirCol. At present, no further activities are planned on the RMM front, but if you have ideas or suggestions for additional tests, please let us know !

RMM training plot (over several years)

RMM cross section