[PEPPo] Ce+BAF meeting on Wednesday, September 24 @ 11am EDT

Tue Sep 30 09:53:53 EDT 2025

Dear Colleagues,

The minutes for the last week Ce+BAF meeting have been added to the meeting page<https://jeffersonlab.sharepoint.com/:u:/r/sites/PositronSource/SitePages/2025-09-24-Ce+BAF.aspx?csf=1&web=1&e=Th3gXh>.

Best regards,
Andriy

---

Minutes
Victor presented simulations of the LERF e- injector.
The goal: to create design of injector part from gun to the end of booster and to find the available beam parameters at the front end of the e- injector.
Two layouts have been considered:

  1.
CEBAF style booster with up to 200 kV gun and 2- and 7- cells cavities
  2.
~350 kV gun and QCM Booster with two 5-cells cavities.

The simulations and optimization (minimization of bunch length, energy spread and normalized emittance) have been performed in GPT using farm nodes via Max's python interface in JupyterHub. The space charge was included in the simulations for the beam current up to 1 mA (~4 pC at 249 MHz). The emittance grows is compensated by the solenoids. It is important to have a small beam size at the entrance of the 1st cryomodule to reduce the effect of edge fields degrading the beam phase space.
Joe: Design work on the electron injector (Max, Victor) fitting to the multi-pass accelerator is closely related to the design of electron beamline for the irradiation of Xelera liquid metal target.
Alex: Is the photogun MTE (mean transverse energy) of 50 meV related with the temperature?
Jay: MTE is defined by the room temperature.
Jay: Does 1D field maps used for the QCM Booster include the effect of fundamental power couplers (kick of beam)?
Victor: Effects connected with the couplers are not included for the case of 1D cavity field maps, but included for the 3D field maps.
Volker: 1st solenoid does not change the beam much. Can this solenoid be removed?
Victor: Some diagnostics will be used in this area and the first solenoid will be needed for that.
Joe: Solenoid 1 is needed for the buncher. We need a lens upstream the buncher to control the beam waist.
Salim has suggested to increase the number of macroparticles later after the initial optimization is completed with a relatively low number of macroparticles.
Yves: The normalized emittance of 1 mm mrad is used for modeling of beam at 12 GeV CEBAF. The estimated emittance for the LERF injector is below 1 mm mrad, that means the new design is compatible with the CEBAF.
Victor: The emittance can be increased from ~0.7 mm mrad to 1 mm mrad and the bunch length or energy spread can be decreased if it is needed.
Bob: Victor, are you using the frequency 250 MHz?
Victor: Yes, 250 MHz was used to consider the worst case with the highest bunch charge (~4 pC).
Joe: We have 1497 MHz buncher cavity. 1 mA (250 MHz, 4 pC) is a beam for the Ce+BAF. It it the highest bunch charge. The bunch charge can be lower for the multi passes.
Yves: Alex is designing 650 MeV injector. Is the beam optics optimized for so high bunch charge?
Alex: The optics is not yet optimized for the high bunch charges and that optimization will be performed.
Joe: 1 mA at 8 MeV is the electron source current for the target testing and Ce+BAF. What the current is would we like to have for 22 GeV injector upgrade?
Alex: 100 µA is the current for the energy upgrade.
Joe: How the connection of 8 MeV beam line with the other part of injector can be done?
Jay: The merge region is nontrivial: 8 MeV beam merges with the multiple high energy beams.
Alex: We (CASA) can take care about the merger region.
Joe: FEL injector was not designed for polarized beams (photogun goes directly to the booster). For the TDR report, the layout of the injector needs to be changed to have some space for the laser light.
Final remarks: Victor and Max will continue working on the designs with two options for the electron booster at LERF (2 + 7 cells cavities and 5 + 5 cells cavity) and provide all required information (data, design, etc.) to Alex. Alex with other CASA colleagues design the multi-pass injector including the merger region and define the location of beam lines merger.

________________________________
From: Andriy Ushakov
Sent: Monday, September 22, 2025 21:10
To: peppo <peppo at jlab.org>
Subject: Ce+BAF meeting on Wednesday, September 24 @ 11am EDT

Dear e+ Colleagues,

A quick reminder: we will have the Ce+BAF meeting on Wednesday, Sep 24 at 11am EDT in TL-1227 and via Zoom.

Agenda

  *   Victor - Update on the design layout of the LERF electron injector

Meeting page: Ce+BAF Meeting - September 24, 2025<https://jeffersonlab.sharepoint.com/:u:/r/sites/PositronSource/SitePages/2025-09-24-Ce+BAF.aspx?csf=1&web=1&e=Th3gXh>

Zoom link: https://jlab-org.zoomgov.com/j/1607642988?pwd=K2VMVlkwLzFwR0l0VjNWMFUvSGtrUT09

The minutes of last week's meeting have been added:  2025-09-17-Ce+BAF<https://jeffersonlab.sharepoint.com/:u:/r/sites/PositronSource/SitePages/2025-09-17-Ce+BAF.aspx?csf=1&web=1&e=g8O0KJ>
Best regards,
Andriy

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