Follow up from last meeting

After several iterations and reviews of all transverse and longitudinal parameters, the updated versions of the LIU proton and ion parameter tables have been made available on EDMS

LIU-PM-NOT-0011 v.2

LIU-PM-ES-0004 v.2

The values now match the HL-LHC requests, with the risk levels already discussed several times at these meetings, Cost and Schedule review in October 2016 and Chamonix 2017.

Motivated by a recurrent question on beam parameters of non-LHC beams, which should be also considered every time that a new Beam Intercepting Device (BID) is designed in the framework of LIU, the subject of today is a review of what we know so far on these beams and what could be reasonable to take into account when new devices are designed. Specifying parameters for non-LHC beams is of course beyond the LIU scope and mainly driven by the discussions within the Physics Beyond Colliders (PBC) accelerator working group, however it is desirable that LIU should take the inputs on non-LHC beam requirements into account, if cost neutral, when specifying new equipment. The LIU policy all along has been to put in place upgrades that would improve the quality of the LHC beams without deteriorating the performance of existing physics beams.

Post-LIU beam parameters for LHC and non-LHC beams

• First of all, a general consideration is that, as was discussed in Chamonix, both standard and BCMS variants of the the LHC beams should be considered as of interest for HL-LHC operation, therefore the associated parameters should always be taken into account when providing specifications, e.g. for new BIDs. This is reflected in the LIU parameter tables provided at the links above. Concerning the BCMS beam, although the desired intensity value is the same as for standard beam (2.3e11 p/b), in terms of potential reach, it could be for the moment still limited to 2e11 p/b with 1.4 um at the SPS exit due to TCDI. This is because this was the highest intensity point validated with simulations by EN/STI. As Verena explained a few times, applying a scaling law, one could say that 2.3e11 p/b with 1.7 um at the SPS exit (i.e. the beam that was called BCMS+ in Chamonix – and reported in our parameter table) would still be acceptable, but a full validation from EN/STI is pending to give full green light to these beam parameters. It should be noted that, upstream from the SPS, although the BCMS has a lower emittance and spot size on a possible BID, its intensity per bunch (and total intensity, even if it requires 8 instead of 6 bunches from PSB) is lower.
• ISOLDE beams will benefit from the Linac4 injection at 160 MeV as well as from the new RF system in the PSB. It has been estimated that 1.6e13 p/ring should be reachable out of the PSB in the post-LIU era if Linac4 provides 40 mA (unchopped) and a suitable scheme of transverse and longitudinal painting is put in place. There are still some uncertainties concerning the impact of space charge and potential transverse instabilities along the cycle. 
• nTOF might take more than 1e13 p/shot after the target upgrade. The nTOF beam will certainly benefit from Linac4 (potentially smaller emittance beam, hence lower losses on extraction septum) and injection at 2 GeV into PS (reduced space charge at injection). It is not clear that the fast instabilities at transition crossing could be also mitigated (machine impedance reduced? transverse feedback?).
• AD/ELENA will not require more intensity per shot (maybe more frequent beam delivery for stacking). The AD beam could be also potentially created with lower transverse emittance thanks to Linac4 and 2 GeV upgrade.
• For the SPS
  • HiRadMat beams will probably follow the LHC beams in terms of beam characteristics
  • AWAKE aims at single bunches with 5e11 and as high brightness as possible. The brightness of INDIV-type beams can be possibly improved thanks to Linac4/2 GeV, however a bottleneck at transition crossing in the PS might still be present (similarly to nTOF). In the SPS, RF power upgrade and longitudinal impedance reduction have the potential to make bunch rotation more effective 
  • 4.2e13 p/spill can be assumed as target for BDF with a slow extraction on third integer over 1 s. The production of these beams must be studied from the PSB (constraint on vertical emittance below 4 um to limit losses in SPS) and PS (high intensity MTE).
• Finally, taking into account all this, a set of beam parameters beyond the presently achieved values (both for the LHC and non-LHC beams) are proposed to be used in the specification of PS BIDs, which should cover known requests and include enough margin to extend to even more stretched scenarios.