{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"688fe4f85d0969514157052c7054d44320f3e885d542ca2db799aa76775f5101","created":"2026-10-03T07:18:08Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"d35b414ac9fe0731b9019773b0bccd4c4cd434f427ed5306ac86e99a91d63d5b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"plasma.wakefield-accelerators.efficiency-instability","kind":"well-posed","literature_status":"partially-resolved","n":"1","parents":[],"plain":"To be efficient, the accelerated bunch must extract much of the wake's energy, but that also makes the bunch wobble sideways and break up. How efficient a stable plasma accelerator can be is not known.","posed_since":"2017","precise":"Strong beam loading raises wake-to-witness energy-transfer efficiency but also strengthens the transverse wakefield that drives the hosing (beam-breakup) instability. Determine the maximum efficiency compatible with a given tolerable emittance growth and driver-witness misalignment, including damping by energy spread, ion motion and plasma-density tailoring. An answer is an upper bound on efficiency versus tolerance, validated by simulation.","problem_ref":null,"references":"","settled_by":"A derived bound confirmed by 3D particle-in-cell simulations and by measured instability growth in a high-efficiency stage.","status_note":"Lebedev, Burov and Nagaitsev (2017, https://doi.org/10.1103/PhysRevAccelBeams.20.121301) derived an efficiency-instability relation; 2025 simulations (arXiv:2501.10602) show it is only a lower limit on instability strength, and a bound including all damping mechanisms is lacking.","title":"Fundamental trade-off between efficiency and beam-breakup 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