Choose timezone
Your profile timezone:
Powered by Indico
v3.3.5-pre
Participants:
Foteini Asvesta, Fanouria Antoniou, Hannes Bartosik, Ilias Efthymioupoulos, Giovanni Iadarola, Leandro Intelisano, Nikos Karastathis, Sofia Kostouglou, Parthena Stefania Papadopoulou, Tirsi Prebibaj, Kyriacos Skoufaris, Guido Sterbini, Georges Trad, Natalia Triantafyllou, Michail Zampetakis.
Guido opened the meeting by recalling the follow-up of the last meeting on the wire simulations. The last results from Axel show an agreement between the MAD-X footprints and the SIXTRACK FMAs, ruling out major issues in the MAD-X/SIXTRACK interface. Further investigation on tune scans are on-going.
Guido presented the effect of the burn-off (BO) in the emittance blow-up (BU) based on the studies and papers by R. Bruce.
After having recalling the probability of burn-off interaction as function of the particle action (for Gaussian beams), Guido presented the analysis in the normalised trace-space. Combining the probability of the burn-off interaction with the action distribution of the beam one can obtain the evolution of the action distribution of the beam, therefore the beam rms emittance evolution (blow-up). For a typical (average) 15% of BO one can compute ~4% of emittance blow-up.
To complete the analysis, Guido recalled how to transform the action distribution of the beam in the a beam profile via the Abel transform. The rms emittance obtained via a Gaussian fit of the beam profile is larger than the one obtained by the average actions.
Finally the semi-analytical results were compared with a numerical integration from Ilias. The agreement is good.
Stéphane commented that the blow-up due to elastic interaction is negligible (due to the fact that the system is Hamiltonian).
Guido asked if and how one should include the presented mechanism in the model. Ilias commented that one could compare systematically in the model the result of the semi-analytical approach with the numerical integration. Gianni commented that, together with this mechanism, one should also include the effective emittance reduction due to the high amplitude scraping, not to have a bias in the results.
Georges commented that this mechanism is symmetric in the x-y planes but, on the other hand, the observed emittance BU in the vertical plane is much more critical.
Stéphane, Ilias, Xavier and Georges commented that it would be interesting evaluate with a similar approach the action depletion due to position luminosity levelling. Stéphane added that one could also explore this effect in MD during Run3.
Stefania presented the luminosity model from a user perspective.
After having recalled the evolution of the luminosity model since 2015, an overview of the mechanism of the luminosity model were presented (IBS, SR and luminosity burn-off, coupling).
The four different flavors of the luminosity model were presented:
pure model
extra losses
extra emittance growth
calculated
A python notebook showing how to use the output data of the model was shown and commented (FILL 7334).
Most of the discussion focused on the discrepancy between the model of the vertical emittances and their actual behavior.
Ilias commented that these features are not constant during the different years of Run2 so it is difficult to draw general conclusion.
Stéphane commented that, at some point and in particular in view of Run3, the effect of the different ATS tele-indexes has to be included.
Nikos added that a benchmark of the luminosity model with two different tele-indexes was performed, showing a marginal effect of the optics on the experimental result.
Stéphane commented that the inconsistency between the model and the experimental results of the vertical emittance could be related to the coupling, the changing of the crossing angle during the leveling or the IP1/5 rephasing during the beta* steps.
Fanouria observed that during the beta* levelling there is a change of the slope of the vertical emittance. Georges commented that this exclude a problem in the BSRT local optics (in this case one should observe an offset and not a slope variation).
Gianni added that the time filtering/averaging of the emittance data is quite heavy and one should look more carefully to the bbb information to exclude transverse instabilities that could bias the conclusions.
Guido asked if also the MD fills are systematically analyzed with the luminosity model. Ilias answered that the automatic analysis would have problem in most of the MDs due to the very specific set of beam conditions. On-demand, the MD closer to the operation condition can be analyzed. Stefania added that the BSRT calibration fills are anyhow included in the luminosity model repository.
AOB
There were not AOB.
Follow-ups
Generalize the effect of the BO to the emittance BU including luminosity levelling by separation.