The RF dipole prototype cryomodule foreseen for tests with beam in the SPS tests was successfully repaired and commissioned in the SM18 facility at CERN in 2024. During the year-end technical stop (YETS) 2024-25, the cryomodule was installed in the SPS-LSS6 bypass dedicated to the crab cavity tests in the SPS. Immediately after the installation, the cryomodule was cooled down to its nominal temperature of 2K in March 2025 and high power RF processing of the cavities started, in preparation for the machine development (MD) program with RFD cavities foreseen through the operational run of 2025.
Figure 1 RF Dipole cryomodule installed in the SPS long straight section 6 on the movable bypass. HL-LHC WP4
During the beam scrubbing run in March 2025, the cavities were moved into the circulating beam for the first time, to scrub the crab cavity bypass line which resulted in significant improvement of vacuum conditions. This improvement was observed by injecting up to 4 batches of 72 bunches and bunch intensities close to or above the HL-LHC target of 2.3 x 1011p/b. Up to 2 batches of 72 bunches could also be accelerated to 450 GeV without any issues. During this period, higher order mode measurements could also be carried out to validate the damping performance and compatibility with the impedance budget for the HL-LHC.
After a period of RF conditioning, the cavities could be moved to operational mode and ramped up to 2 MV in continuous wave (CW) mode, limited by the cryogenic load of the SPS facility. The first machine development slot (MD) is foreseen for May 28, where both cavities will be commissioned with beam to crab the proton beams and carry out the necessary setup for future MDs on instabilities and emittance growth.
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