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    Messages from the 1st SKEKB international task force meeting

    → Europe/Zurich
    Description

    KEK has set-up an international task force to address the limitations encountered by the SKEKB e+e- collider. The Indico page for the first meeting of the task force on July 28th can be found here: 

     https://kds.kek.jp/event/38899/

    Messages from the 1st SKEKB international task force meeting
    Zoom Meeting ID
    69997835379
    Host
    Rogelio Tomas Garcia
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    The meeting started with the presentation by Rogelio giving a brief summary of the the 1st KEKB International Task Force meeting. The slides include links to all relevant material and contact names to join this effort. SKEKB is facing significant limitations that stop beam parameters from reaching the design goals (see slide 4 for a small collection of achieved and design parameters). Following a question by Tobias, Oide-san replied that also betax is a factor 2 or 3 below design.  Main challenges are identified by SKEKB experts as: Severe beam-beam effects,  small DA, lower than expected TMCI threshold and low machine availability with abnormal beam aborts and components aging. Few illustrations of these effects were shown. 

    The plan is to progress to reach another factor 2-3 in luminosity in the coming years with minor hardware upgrades and make a solid proposal by mid 2022 for more significant hardware upgrades in 2026. The current proposals under consideration include:

    -Injector power upgrade

    -Adding 16 quadrupoles for a "perfect match" of optics. This, together with crab waist reduction from 80 to 50%, shows a large increase to DA (~2023)

    -Rotatable sextupoles (2023)

    -Enlarging aperture of final quadrupoles (~2026) 

    -Robust collimation. Improve resistance of collimators to failures but also reduce emittance, optimize locations or even new concepts as the non-linear collimation.

    The task force (TF) should contribute with ideas and actual work to the final proposal by mid 2022. During the first meeting of the TF the following proposals were made:

    ●Try larger chromaticity to mitigate TMCI
    ● Include a sextupole at the IP image point for increased energy acceptance
    ● Tuning knobs for optics parameters between crab sextupoles
    ● Increase betas at collimators (tbc), use the H chroma section for collimators
    ● Measure and benchmark: Amplitude detuning, high order chromaticity and dispersions, W, beam-beam tuneshift, collimator impedance... 

    and in the more administrative or resources side:

    ● Make dedicated study groups 
    ● Make SKEKB lattices available 
    ● Make a MADX lattice 
    ● Motivate colleagues to contribute! (this LNO meeting being an example for this)
    ● Provide CPUs for beam-beam simulations (Belle II will do so) 

    Two study groups have been formed: beam-beam and Optics (see slides for contact details).

    To make the MADX SKEKB lattice a small meeting will take place next week with Demin, Akio, Oide-san, Leon, Felix, Tobias. Ideally a solid converter SAD-> MADX can also be established. 

    Nicolas mentioned that CERN could help in the TMCI problem with little effort. Maybe a new group should be formed to discuss the TMCI matters among experts. Nicolas will explore this possibility. From FCCee Emanuela and Mauro could join it.

    Xavier mentioned that beam-beam and impedances can excite head-tail modes and that there are simple analytical tools to study this. He will explore the possibility of joining the beam-beam group.

    Frank and Oide-san mentioned that it could be interesting to form a group on injector issues. This topic was not very addressed during the 1st TF meeting. People contributing to this topic could be found in FCC and LAF section, Frank will explore this option.

    Tatiana announced an EPFL meeting on the matter: Demin Zhou will give a talk on "Practical experience from beam-beam simulations vs reality in (Super)KEKB". The agenda can be found here:
    https://indico.cern.ch/event/1064274/
    She also mentioned that EPFL is progressing with the tool development for e+e- beam-beam simulations and that it would be possible to apply them to SKEKB in the timeline of the TF.

    The need for a dedicated collimation group was also brought up. We will pass this to the NDC section.

    A second presentation was given by Oide-san on the beam-beam studies performed by Demin for SKEKB. By thoroughly adjusting bunch length and emittance Demin could reproduce the specific luminosity down trend with intensity. At larger intensities the measured luminosity loss is more pronounced than simulations possibly pointing out to actual issues with TMCI (or a combination of beam-beam and impedances). These simulations require very long computing times and therefore help from other teams is highly appreciated.  

     

     

     

     

     

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