Beam-Beam and Luminosity Studies meeting

Europe/Zurich
6/R-012 - Salle conference BE (CERN)

6/R-012 - Salle conference BE

CERN

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Guido Sterbini (CERN), Yannis Papaphilippou (CERN)
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Beam-Beam_and_Luminosity_Studies_meeting
Name
Beam-Beam_and_Luminosity_Studies_meeting
Description
Beam-beam and luminosity meeting
Extension
10402410
Owner
Nikos Karastathis
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Participants:

Leandro Intelisano, Stéphane Fartoukh, Sofia Kostoglou, Konstantinos Paraschou, Axel Poyet, Ilias Efthimiopoulos, Guido Sterbini, Natalia Triantafyllou.


Guido presented an update of the machine orbit stability during the vdM scan 6868.

This scan was very long (more than 20 h). The SVD analysis of the different modes show that the second and third mode are compatible with a hysteresis effects. This is also (partially) confirmed with the localization of the kick (it is located in the separation bump). From the mode 4 on, the motion of the orbit does not seem physical but related to temperature variation in the BPM crates and to the erratic behavior of one BPM.

Guido showed also how to compute the BB encounter schedule. He stressed that some bunches of B1 get unstable during the scan. In particular, high transverse activity is visible when the beam are separated. He commented that this could have an impact (in addition to the BB effect itself) on the beam distribution. Ilias agrees that it is very important to pay attention to the bunch stability in vdM scans. Sophia asked if the activity on the transverse plane could be due to the 50 Hz lines interaction with the beam spectrum. Guido commented that this cannot be excluded, but given the systematic relation with the beam separation, it appears to be, likely, related to the missing Landau damping from the BB HO.


During first AOB, Axel presented a status of the BB wire compensation focusing on the Run3 simulation.

He compared the DA gain in the proposed configuration (quadrupolar, TCTC with wires) with tertiary collimator at 8.5 $sigma_{coll}$ (2018 setting) and 7.5 $sigma_{coll}$ (proposed during the last Chamonix, https://indico.cern.ch/event/676124/contributions/2767832/attachments/1591277/2518560/2018.01.29--Chamonix_2018_LHC_Configuration_169.pdf). As expected, the configuration at 7.5 $sigma_{coll}$ is better from the compensation perspective.

He also investigated the cross-talk between the octupole and wire settings (in the configurations of MD3, single wire powered in the collimators, and MD4, two wires powered in the collimators). Negative octupoles are beneficial, but the wires increase the DA if compared to an octupoles scan without wire. Beam stability considerations are not taken into account in this study.

Crossing angle scans show that 10-20 urad can be gained during Run3 at constant DA,  confirming the MD4 experimental observation.

Finally, the results, adding the BB contribution of IP2 and IP8, were presented. The wire gain is still visible. 

Guido  pointed out that, the overall DA gain on the wire for Run3 is expected to be in the order of 0.5 sigma, due to the limits of the wire demonstrators. Larger gain is expected in HL-LHC type scenarios.


During the second AOB, Axel presented a python package he wrote to launch generic jobs on HTCondor batch. The package is available on github at https://github.com/apoyet/pyHTC.

SWAN cannot be used to launch HTCondor jobs (EOS file systems is not yet supported). One solution is to use lxplus. One can launch a jupyter notebook from lxplus following the instructions in http://bblumi.web.cern.ch/how-tos/#how-to-run-a-jupyter-notebook-from-lxplus

The package will be compatible with pandas dataframes to configure the simulation scan and to recover their results.

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