{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"0926a5c97fcadadad16f2cb9df7226d40ae9a36bdbc11ed76b18d02554865b71","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["827078db8b86be8c6ca9c24116c3f8bd9d1982b932aeefa502f0a17866acce15","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"ef9fda297e27f75bca20f320bbc19e574fd48c3b2e7a71f146419a8297ead7c5","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":["ai:gpt-5.5"],"external_id":"beams.csr-microbunching.ring-csr-instability-threshold","kind":"well-posed","literature_status":"partially-resolved","n":"2","parents":[],"plain":"In storage rings run with very short bunches, above a certain current the bunch breaks into ripples and emits bursts of far-infrared light; the threshold and the bursting pattern are only partly predicted.","posed_since":"","precise":"For a Gaussian bunch in an electron ring with the shielded steady-state CSR impedance, Vlasov-Fokker-Planck calculations give a threshold in the dimensionless current $S_{\\mathrm{csr}}$ of approximately $S_{\\mathrm{csr}},\\mathrm{th} = 0.5 + 0.12$ $\\Pi$, with $\\Pi$ the shielding parameter, plus a narrow low-threshold region near $\\Pi \\sim 0.7$ (2010). Determine whether the threshold and the period and amplitude of sawtooth bursting above it are predicted within 20 percent once the full ring impedance, potential-well distortion and finite chamber geometry are included, in low-momentum-compaction operation of several rings.","problem_ref":"827078db8b86be8c6ca9c24116c3f8bd9d1982b932aeefa502f0a17866acce15","references":"","settled_by":"Bunch-by-bunch measurements of threshold current and burst spectra versus Pi in two or more rings, compared with Vlasov-Fokker-Planck solutions that use independently measured impedances.","status_note":"Measured thresholds in low-momentum-compaction modes of several rings in the 2010s were broadly consistent with the scaling law; bursting dynamics above threshold are reproduced only qualitatively (moderate confidence, not rechecked for 2024-2026).","title":"Threshold and bursting dynamics of the CSR instability in electron 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