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LIU Beam Parameter WG meeting #3
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Europe/Zurich
865/1-D17 (CERN)
Notes:
After Chamonix, there was a recommendation from the C-MAC that the gap between LIU and HL-LHC beam parameters should be bridged (with an effort from both projects). In the future, we should avoid showing tables with different sets of parameters, but rather emphasise the efforts to make these values match.
LIU ion beam specifications (Hannes)
Hannes presented the LIU ion beam specifications, providing the expected beam parameters for a baseline scenario (50 ns in the LHC through bunch splitting in the PS and slip stacking in the SPS) and for an alternative scenario (25 ns in the LHC through bunch splitting + batch compression in the PS and slip stacking in the SPS).
The LIU baseline ion beam parameters have been used as a solid base to compile the EDMS document that represents the response of LIU to the HL-LHC document published by J. Jowett on the beam parameters required at LHC injection to satisfy the integrated luminosity requested by ALICE post-LS2. This document will be soon released for approval.
In view of exploring more deeply the proposed alternative scenario, which has the potential to fill the gap with the HL-LHC parameters and also allow for some margin for e.g. losses during the slip stacking (Elena said that one should consider few percent even in the most ideal case), it is important to prove the feasibility of the production mechanism by testing the batch compression at flat top with two bunches, which should be already possible with the existing PS cavities. The cost of the additional required broad-band cavity to allow this beam manipulation with 4 bunches is roughly estimated to be around 1-2 MCHF.
By the time of the Cost & Schedule Review next October, it is important to have this alternative scenario solidly established in terms of possible planning and extra-cost + all the input from machine studies necessary to prove its feasibility. Action: Heiko.
Intensity limitations from SPS protection devices and transfer line collimators? (Verena)
Verena summarised the constraints on beam parameter limitations in the design of intercepting devices and the SPS situation. The general guideline has always been to make sure that all devices should withstand beams with 288 bunches of: 1) "standard" 2.3e11 p/b within 2.1 um, or 2) BCMS 2.0e11 p/b within 1.3 um. Limitations in the design are posed by the total intensity (showers on nearby elements) or by the brightness (attenuation, robustness against stress). However, while te attenuation scales like the brightness, the stress is not directly proportional to the brightness, but roughly to the ratio of intensity over emittance to the 0.75 power. This implies that designing for a certain intensity does not directly mean that a higher intensity (compatible with the limit from the showers) with the same brightness is still within limits. For instance, in the case of the future BCMS beam (2.3e11 p/b within 1.7 um), the robustness limit is found to be still o.k. since the design was made for 2.0e11 with 1.3 um. On the other hand, this simple scaling law could be inaccurate, so in principle to validate the protection devices design for a high intensity BCMS, one should re-do all the detailed simulations. It has to be taken into account that the margin with which the devices are also designed with respect to the beams mentioned above is quite thin because we are already at the limit .
Looking at the situation of all dump, protection, collimation devices in both the SPS and transfer lines (current status and foreseen upgrade), it seems that in general there is no showstopper for the targeted beam parameters (in some cases, intensity interlocks will have to be implemented). However, the present design would prevent the transfer of 4 batches with 80 bunches (320 bunches) unless the intensity per bunch is lowered by a factor 320/288=1.11 (general limitation on intensity and also limitation on intensity per shot on TBSJ?)
Verena will re-discuss this with our EN/STI colleagues on a meeting scheduled to take place on Tuesday 23 February at 11:00 in Room 774-2-058.
In general, from the point of view of the protection devices, we can extend the intensity reach of the SPS to the desired HL-LHC parameters (standard beam). At the next meeting, scheduled on 11 March, Elena will review the SPS limitations in terms of longitudinal instabilities, the perspectives after impedance reduction as in the LIU-SPS baseline and the potential gains with a 200 MHz RF system in LHC.
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