Beam-Beam Meeting at SLAC

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Spencer Gessner, SLAC

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January 19, 2024

Overview

• The Beam-Beam Collaboration is motivated by design and simulation needs for a future 10 TeV pCM wakefield collider.
• There is skepticism that
• My interpretation: HEP funding for a 10 TeV wakefield collider design gives AAC community enough rope to hang ourselves.
• The US will fund a wakefield collider design study, but will not directly fund contributions to HALHF.
• There are many parallels between the two studies and opportunities for collaboration.

P5 Report is Positive on 10 TeV+ Wakefield Colliders

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Credit to Cameron Geddes for defending the work of the advanced accelerator community in P5.

P5 Report Supports FCC and ILC

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This likely means increased US involvement in ILC Technology Network (ITN)

P5 Report Supports Additional Funding for Acc. R&D

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Current HEP GARD funding is about $95M/year.

New GARD + Collider Accelerator R&D is $45M/year.

That’s almost a 50% increase in accelerator R&D funding!

P5 Report Supports Additional Funding for Acc. R&D

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Current HEP GARD funding is about $95M/year.

New GARD + Collider Accelerator R&D is $45M/year.

That’s almost a 50% increase in accelerator R&D funding!

Even if most of the new money goes to Higgs Factories and Muon Collider, this is still a very positive report for PWFA.

Review Panel Around Time of FCC decision

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Opportunity to present collider designs around 2027

Commentary

• At SLAC’s post-P5 meeting, Tor Raubenheimer said (paraphrasing):
• “The targeted panel is not just an opportunity, but a deadline. You need to show credible designs for 10 TeV colliders or we should go another direction.”
• My interpretation: HEP funding for a 10 TeV wakefield collider design gives AAC community enough rope to hang ourselves.
• The US will fund a wakefield collider design study, but will not directly fund contributions to HALHF.
• There are many parallels between the two studies and opportunities for collaboration.

Next Steps (what I hope will happen)

• Discussions between SLAC, LBNL, and ANL to outline a collider study group.
• Likely to have similar structure to HALHF collaboration:
• Sources
• Linac
• Structure wakefield
• Beam-driven plasma
• Laser-driven plasma
• Beam delivery
• Plasma lenses
• Beam-beam studies
• Establish connections with HALHF and ILC. Create “Liaison Working Groups” or directly contribute to each other’s efforts.
• Access to wide-range of expertise.

BDS and Beam-Beam for HALHF

• From Carl:
• Give an assessment of:
• Is the current proposal [i.e., ILC BDS but with smaller beta functions] even feasible?
• How does the length or cost of each part scale with the parameters like emittance, energy, etc? Having some clarity in this would help a lot in optimising the new iteration of HALHF.
• Example questions:
• Oide limit?
• Possible to lengthen bunch in BDS?
• Remove energy collimation (achieve in linac)?

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Accelerator physicists can provide menu of options, but requirements must come from physics program and detector.

Discussion for HALHF

• The ILC design is stringent and conservative
• Zero particles lost in final doublet.
• No synchrotron photons hit inner tracker of the detector.
• Accelerator requirements flow upstream from IP.
• Proposal for HALHF. Create two designs:

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1. Cheap and messy design that meets luminosity requirements
2. Design that matches ILC requirements (no losses, no photons)

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These two designs can be used to bracket future discussions.

Cheap, Compact, and Messy?

L^*

Exit 𝛽 = 𝛽_m , 𝛼 = 0

Final plasma stage

Plasma lens

IP 𝛽^*

Soft dogleg

R₅₆ ≠ 0, D = 0

BDS and Beam-Beam

• As part of Snowmass, we created a “Beam-Beam Collaboration” to start looking at issues relevant to 10 TeV colliders.
• Main effort so far: develop WarpX as a replacement for GUINEA-PIG and CAIN.
• Tim Barklow (SLAC) using CAIN to model 𝛾𝛾-colliders.
• Arianna Formenti (LBNL) using GUINEA-PIG to model e⁺e^--colliders.
• Plan to extend modeling beyond beam-beam to include:
• Plasma lenses
• Multi-foil final focus

First Results

• In order to simulate 10 TeV collisions, we must first validate code at 250 GeV.
• Arianna Formenti (LBNL) performed simulations of ILC collisions in WarpX with longitudinal resolution 128X greater than what can be achieved in GUINEA-PIG.
• Cannot show these results because still running validation and convergence tests.
• The results are really cool. . .
• Please invite Arianna to present at a future HALHF meeting!
• She is aware of HALHF parameters and will simulate them next.

Beam-Beam Working Group

Near Term

Speculative

WarpX validation

Contributions to ILC and C³ BDS

Contributions to HALHF BDS

Contributions to 10 TeV pCM e+e-

Contributions to 10 TeV pCM 𝞬𝞬

Design of XCC 𝞬𝞬

Mid Term

Plasma lenses and multi-foil focusing.

Laser-based collimation.

QED collider studies

Plasma Lens Experiments

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C. A. Lindstrøm et al. “Emittance Preservation in Aberration-Free Plasma Lens.” PRL (2018)

C. Doss, M. Litos, CU Boulder

E308: Passive Plasma Lens Experiment

Beam-Beam Codes

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GUINEA-PIG, Author: D. Schulte

CAIN, Author: K. Yokoya

GUINEA-PIG and CAIN are well-established, well-benchmarked codes, but they have their limitations. For example, they do not compute the fields of electron-positron plasmas produced under conditions of extreme beamstrahlung.

NLQED in PIC

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F. Del Gaudio et al. “Bright γ rays source and nonlinear Breit-Wheeler pairs in the collision of high density particle beams.” PRAB (2019)

A. Formenti, LBNL: Comparison of WarpX and GUINEA-PIG for extreme beams

Growing interest in laser-plasma community to develop PIC codes for NLQED experiments and to support beam-beam simulations.

Plan for QED PIC codes

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GUINEA-PIG, CAIN: beam-beam codes with 2D Poisson solves of beam slices for EM fields effects

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OSIRIS, VLPL, WarpX: Electromagnetic Particle-In-Cell codes with 3D Maxwell solves for EM field effects

Plan for QED PIC codes

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GUINEA-PIG, CAIN: beam-beam codes with 2D Poisson solves of beam slices for EM fields effects

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OSIRIS, VLPL, WarpX: Electromagnetic Particle-In-Cell codes with 3D Maxwell solves for EM field effects

Testing now

Plan to test codes in well-benchmarked regimes (e.g. ILC 250 GeV) and demonstrate significant speedup, convergence, and accuracy.

BDS for HALHF

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“The HALHF beam-delivery system (BDS) is, unsurprisingly, highly asymmetrical. It is modelled here on that for the ILC, which is designed for the same energy (500 GeV). . . it can be seen that the electron BDS is in fact the driver for the total length of the HALHF facility. This strongly motivates further research into more compact beam-delivery systems.”

ILC BDS

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