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874/R-018 - salle de réunion activité CCC (CERN)
BWS Taskforce Meeting - 08.06.2023
SPS BWS Task Force (June 8, 2023) · Indico (cern.ch)
Present: Federico Roncarolo, Francesco Maria Velotti, Jonathan Emery, Raymond Veness, William Andreazza, Elena De La Fuente Garcia, Giannis Papazoglou, Anthony Harrison, Carlo Zannini, Benoit Salvant, Christine Vollinger, Alexandre Mariet, Michael Stephen Sullivan, Giulia Papotti, Nabil El-Kassem
Meeting Discussion:
Federico presented on the total intensities reaching flat top, focusing on LHC target beams. He mentioned that in 2022, the beam intensities were lower. For safety, they should stay below the intensities that caused wire breakage in April. Federico suggested negotiating to stay at lower intensities during the first week after TS1 to gather data. During last year's scrubbing, they didn't exceed 1.5 ppb, but this year they are already at 1.6 ppb. The previous wire breakage occurred with short flat top.
Carlo stated that they probably won't run the beams with the same intensities as during the scrubbing, but it's more about the repetition rate. He explained that significant heating occurs with only one bunch, as the power is more broadband. The heat dissipation will be distributed almost equally across the 6 ferrites.
Benoit mentioned that the next MD is scheduled two weeks after the TS. He proposed one week without high-intensity MDs, which is likely feasible. He suggested making a specific request for MDs in this regard.
Giulia shared that they need to aim for 1.6-1.8 ns bunch length to fit in the LHC bracket. For high-intensity MDs, they aim for the highest intensity possible to gather more information for the longer term. She mentioned that the shortest bunch length they had so far is 1.4 ns with full intensity. They are considering 2.5*1e11 ppb intensity. Regarding cooling down the ferrites, Giannis explained it is challenging since they don't lose much heat through induction. The temperature of the ferrites was around 200°C.
Jonathan provided an update on temperature measurements with bunch length. He mentioned that the higher the intensity, the higher the temperature of the wires. He referred to Slide 7, where the green line represents the mean bunch length. He requested further information from Mike regarding the maximum temperature, which could be a combination of voltage perturbation and resistance changes. He also inquired about the possibility of seeing local power dissipation on the wire. However, changing the parking position requires time and cannot be done during the TS. He suggested considering stick temperature measurements if there are different numbers of tiles in the tanks.
Ray expressed confidence that they won't break the wires this time based on Elena's simulation, which didn't take into account the repetition rate.
Elena provided an update on power loss simulations. She mentioned that the breakage conditions occur at 1.8e11 ppb, with power deposition on the wire shown in Slide 5. The wire sees 60% impedance without ferrites and only 10% with ferrites. To stay safe, they need to stay below 6.55W. The highest power they had was 17.5W at resonance, but statistically, 175W is the absolute maximum that can be dissipated on the wire. Slide 8 showed a broader resonance, with the highest occurrence at 6.2W. With 6 tiles, they have an even broader resonance, but always below the breakage conditions even in the worst-case scenario. When the bunch length decreases, the power increases. Elena clarified that these simulations are computationally demanding.
Anthony shared that currently, they have fired 13 tiles in total.
Michael Sullivan presented his findings using the Eigenmode solver, which is more pessimistic. He studied 1, 2, and 3 tiles, finding that 3 tiles result in lower impedance but more peaks. However, broader peaks with 3 ferrites catch more lines, which may not necessarily be beneficial. He suggested that 6 tiles might be better than 3, but there may still be a better-optimized 2 or 3 tile solution. He discussed the parking position at +/- 20 degrees and the steep curve between 0 and -20 degrees, indicating a potential investigation. Some measurements would be necessary to proceed.
Tony provided updates on ferrite measurements. He mentioned that 8 two-hole tiles and 5 one-hole tiles will be ready for measurement on June 12th. The ferrites are expected to have no significant effect on the pump down process, similar to the previous intervention in April. The exposure time to air during the intervention was around 1 hour, and they anticipate a pressure in the Kickers section to increase to approximately 2e-8 mbar.l.s-1 after reopening the valve.
William confirmed readiness for the intervention and discussed the installation of ferrites on the horizontal WS.
Giannis presented steady-state analysis results, indicating temperatures of 144°C on the ferrite and 35°C on the outside of the tank with 1.8e11 ppb. He observed the build-up process, which takes around 2 hours to reach steady state. Scrubbing at 5 seconds increased the temperature to a maximum of 160°C, compared to 144°C without scrubbing. For 2.3e11 ppb with an average power of 24W, the temperature reached 216°C, with 49°C on the outside of the tank. The steady-state wire heating at 2.3W is 1050°C, which is not a significant concern.
There was a discussion about the number of ferrites, with consideration of using 6 ferrites in one WS and 2 in the other. Ray highlighted the importance of not installing the coupler if the number of tiles in the WS differs, as it would complicate troubleshooting in case of wire breakage.
The meeting concluded with scheduling the next meeting for the following Friday at 9:00 AM. Ray mentioned the points to be discussed at the upcoming IEFC meeting, including high duty cycles during scrubbing, the first high-intensity MD two weeks after, and the HiRadMat experiment.
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