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865/1-D17 (CERN)
BWS Taskforce Meeting - 30.06.2023
SPS BWS Task Force (June 30, 2023) · Indico (cern.ch)
Present: Carlo Zannini, Raymond Veness, Antony Harrison, Nabil El-Kassem, Benoit Salvant (Zoom), Rama Calaga, Federico Roncarolo, Federico Carra, Giannis Papazoglou, Thibaut Lefevre, Jonathan Emery, Giulia Papotti (Zoom), William Andreazza, Kevin Shing Bruce Li
Ray started the meeting by discussing the events during the technical stop and the upcoming IPP meeting. He emphasized that no high-intensity beams should be used until next Thursday to avoid potential wire breakage.
William provided an update on the changes made to the wire scanners during the technical stop. One of the wire scanners was rotated from a vertical to a horizontal position. In the horizontal scanner, six ferrites were used, while the vertical scanner had five ferrites and a coupler. The temperature probes were not placed directly on the ferrites due to space constraints but are located close to them. The recovered wire needs to be analyzed.
Federico asked if there was any difference observed between the wire scanner that was used and the one that was not used in Aril. William replied that they look almost the same.
Ray emphasized the importance of understanding whether the wires broke at the ends or melted within the tank.
William shared the findings from the April intervention, where a wire was recovered in one tank, while the other tank had a trace on the bottom of the same size as the wire. However, it couldn't be proven if the trace was pre-existing. They are exploring different options, such as positioning the wire in a different place or using a different fixation material.
Thibaut suggested improving the mechanical setup to enhance thermal conduction throughout the wire and forks.
Federico presented macro analysis results, showing temperature peaks every few cycles in April. These peaks are believed to represent the wire's temperature as it continues cooling down even after beam dump. However, we’re not fully sure if this is only the wire temperature or if there’s other beam coupled effects at play. The temperature measurements are not completely synchronized with the beam yet. In June, no peaks in temperature have been observed so far. The coupler seems to affect the temperature, and the nominal temperature is decreasing with the coupler.
Carlo commented that we don’t expect the ferrites to cause any improvement at Flat bottom and that no significant difference between using five and six ferrites is to be expected according to simulations. He also mentioned that the repetition rate is lower.
Jonathan shared pictures of the probes, some active and some passive. He pointed out that the ambient temperature in the tunnels fluctuates, which could be similar to the temperature variations seen in the plots. Rama confirms same seen in LSS6. Conclusion is that nothing really seen yet. There is a significant improvement in wire temperature in June compared to April. The temperature difference between tanks with and without the coupler is around 100 to 150 degrees Celsius. He mentioned a special case with a drop in temperature likely caused by thermionic emission, which changes the resistivity and cannot be measured by the circuit. Last slide - perhaps ignore as there were special conditions (Rama). SFTPRO beam - much less heating.
Rama presented data from just after the technical stop, focusing on peaks at 0.8 GHz. Higher amplitudes were observed at 800 MHz, indicating the need to mitigate this frequency, which correlates with simulations. There is 4W coming out of the coupler. This could explain the difference between H and V, but there are also 5 vs, 6 ferrites.
Giulia cautioned against quickly concluding that the coupler is causing the significant temperature difference between the tanks, as further research is needed.
Kevin (Start-up) addressed the plan to conduct six additional MDs (Machine Development) for high-intensity beams. Two options were discussed, including performing the MDs concurrently with experts involved in the ramp-up process, while some MDs would rely on the Beam Wire Scanners (BWS). The order in which the MDs should be carried out was deliberated upon, with consideration given to initiating an emittance blow-up MD at flat bottom, which might result in a delay in the intensity ramp-up. It was noted that the ramp-up for LHC (Large Hadron Collider) beams had already been completed at 1.6, even with a surplus number of bunches. Rama suggested that a total of 72 bunches may be required. The timing for the next intensity steps, namely 2.1 and 2.3, was raised as a question. The necessity of using the BWS for the ion run in the SPS (Super Proton Synchrotron) was also discussed. The proposed ramp-up strategy involved gradually increasing beam intensity while progressively decreasing bunch length. However, there was a concern that waiting until the end of August could lead to the loss of scrubbing, and it was preferred to have no more than two weeks without 288 bunches, a flat top, and an intensity of 2.1e11.
The meeting concluded with the understanding that further upgrades and data collection are necessary to determine the limit of the BWS. The task force will continue investigating wire breakage and the effects of different parameters. The stress-testing of wires will be conducted strategically to minimize risks and ensure essential MDs can still be performed.
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