2nd interaction region design meeting

Wednesday 7 May 2025, 09:00 → 10:00 Europe/Zurich

6/2-008 (CERN)

InjectionRegion-3.pdf

Present: Steffen Doebert, Eleonora Belli, Patric Muggli, Michele Bergamaschi, Marlene Turner

Discussion points: 

• Dechirper: Patric reached out to company in the US, device would be several meters long, this space is not available. Additionally, the head of the bunch is more energetic than the tail. As Steffen explains, this configuration is necessary to preserve low emittance: the beam must be rapidly accelerated in the gun, transitioning from 30 degrees off-crest to on-crest. Moreover, the chirp cannot be adjusted during velocity bunching, as passing through a chirp minimum would increase the emittance again due to space charge effects. Decision: no dechirper.
  
  
• Optics studies removing Sextupoles, Octupoles and Fringe fields: Eleonora added results to the action document, but says that additionally, the line should be reoptimized for each of these configurations. Action--> Eleonora.
  • Fringe fields and energy spread drive the need for the Sextupoles and Octupoles. Energy spread drives the need for sextupoles (to correct chromatics effects) and octupoles (to correct non-linear effects given by sextupoles). On top of that, high order magnets are also needed to compensate for fringe fields. The line has been designed already assuming double of the energy spread of the input, i.e. Steffen simulated an input beam with 0.1% momentum spread, in simulations we assume 0.2%. Simulations with 0.4% (double of what we assumed) showed an increase of about 45% in the requirements at injection.
  • Steffen: for the Run 1 beamline the problem was that the dipole fringe fields were not correct in the simulations.
  • Should ensure that this time the fringe fields are correctly included in the simulations, e.g. fringe fields from existing magnets (quadrupoles, dipoles, sextupoles) should be measured. Action --> Eleonora to discuss this and get input from Philip Schwarz.
    • Philip previously explained that magnetic field simulation results are very accurate, however, did that also include the fringe fields?
  • Rebeccas papers should be re-read and discussed: 

    https://doi.org/10.1016/j.nima.2023.168094, 

    https://doi.org/10.1103/PhysRevAccelBeams.25.101602

     

• Updated input beam distribution from the gun: ongoing. Action --> Steffen to finish simulations and share the result with Eleonora.
  
  
• Remove tail particles when evaluating beam size and emittance: suggestion to evaluate beam size and emittance e.g. using only 95- or 90% of the particles. Action --> Eleonora.
  
  
• Conflicts near the interaction region: Eleonora explains that Octupole footprint has been reduced from 600x600mm to 370x370mm and that cable connections can be on the other side, leaving sufficient space to the proton beam. She already asked F. Galleazzi to update the integration drawing. This conflict is removed. For the Sextupole, she is investigating repositioning.
  
  • It should be checked whether the corrector can can either be repositioned or combined with another magnetic element.
    
  • The BTV will likely become a screen that is part of the interaction region
    
  • Q: How will the electron beam be aligned to a point in space at the second plasma entrance? Normally one would need two correctors, but there is only one corrector right now.
    
  • Action --> Eleonora to follow up.
    
    
• Laying out the strategies, disussing interfaces: Commissioning and experimental plans should be prepared by each team (electron gun, laser beamlines, electron beamline, experiment) and discussed with the other teams to ensure that all requirements can be met. Action -->(all) prepare these discussion for a future TB/PEB meeting.