[PEPPo] Conical Targets for Enhanced High-Current Positron Sources

[Pavel Degtiarenko]

Thank you Jay,
It's a good idea. I believe there might be a solution for us that implements it, using liquid metal target. Mercury or GaInSn would work. The sketch attached, scale is in cm. The target is made out of the two silver cones with spherical tips (silver is the best thermal conductor and relatively inert chemically). Mercury flows between them from bottom to top. Supply mercury channels should provide enough velocity to reach the tip of the target by inertia. Mercury volume would be fully isolated, welded shut to exclude leaks. The electromagnetic induction pump is controlled from outside without mechanical moving parts and without vibrations. The pressure inside the mercury volume can be made close to the pressure in the beam vacuum enclosure by connecting an interface plane immersed in the beam vacuum and movable on bellows. This way the mechanical stress on the target will be limited. The conical construction also makes the thermal stress at the tips smaller than in flat windows, no big resistance to the radial expanding. I guess the spherical tips can be made thinner. The parameters need to be optimized of course. I guess this solution may be patentable for JLab if anybody is interested. The FLUKA model is simple and it is available.
Best regards,
Pavel
________________________________
From: PEPPo <peppo-bounces at jlab.org> on behalf of Jay Benesch via PEPPo <peppo at jlab.org>
Sent: Tuesday, February 18, 2025 9:35 AM
To: peppo at jlab.org <peppo at jlab.org>
Subject: [PEPPo] Conical Targets for Enhanced High-Current Positron Sources

I wonder if this could be adapted to our use: a tapered ridge of tungsten of appropriate thickness embedded in a thinner copper disk rather than a tungsten annulus of uniform thickness bonded to the OD of a copper disk.

https://arxiv.org/abs/2502.10565

Conical Targets for Enhanced High-Current Positron Sources
Nicolas Vallis, Ramiro Mena-Andrade, Barbara Humann, Yongke Zhao, Paolo Craievich, Jean-Louis Grenard, Andrea Latina, Antonio Perillo-Marcone, Riccardo Zennaro, Fahad Alharthi, Iryna Chaikovska, Robert Chehab, Mike Seidel

    Previous pair-production-driven positron source designs have assumed that the transverse dimension of the target is significantly greater than the secondary beam it generates. This paper explores the use of targets with different transverse profiles with the aim of enhancing positron production. The starting point of this research is the concept of wire targets, proposed by M. James et al. in 1991 for the former SLC positron source. Building on this foundation, this study takes this concept a step further by introducing conical-shaped targets, which can substantially improve the yield by reducing the reabsorption of positrons by the target--an issue that is worsened by the high-field solenoid lenses commonly used for positron capture. Using Geant4 simulations, we propose new conical targets adapted for the parameters of the future collider FCC-ee and its positron source test facility P-cubed (PSI Positron Production experiment) at the Paul Scherrer Institute. We find tha!
 t conical targets can nearly double the positron production at the target and enhance the baseline positron yield of FCC-ee by around 60%. Additionally, we present the thermo-mechanical studies for the conical targets based on the FCC-ee primary beam power requirements and outline the mechanical implementation for a future proof-of-principle demonstration at the P-cubed facility.

Subjects:        Accelerator Physics (physics.acc-ph); High Energy Physics - Experiment (hep-ex)
Cite as:         arXiv:2502.10565 [physics.acc-ph]
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