{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"8bb526ce5d545ed0099405edeba346d5ac50ac2f347555b918c2ead5ba55181b","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"8e4731b60bbd3a1c8a303ea5d9a90295665ea168ce13bbee4d84fbe6bcf3a90d","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"beams.csr-microbunching.ring-csr-instability-threshold","kind":"well-posed","literature_status":"partially-resolved","n":"1","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_csr,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":null,"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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