Abstract
In this paper the influence of betatron coupling on the transverse beam emittances is described using the resonance driving terms formalism. Betatron coupling and vertical dispersion generated by magnetic and installation errors are major sources of vertical emittance. A new scheme for minimizing the latter is presented here, together with results from measurements carried out in 2010 at the ESRF electron storage ring, which provided vertical emittance of about 4.4 pm, a record low for this machine. Two schemes for the automatic compensation of coupling introduced by insertion devices are also presented with results from the first implementation tests. This paper is also an attempt to clarify the various definitions and meanings of vertical emittance in the presence of coupling.
Highlights
Third-generation light sources and modern lepton colliders are characterized by low transverse beam emittances
An orbit response matrix (ORM) measurement with the latest corrector setting of 2009 was launched in order to verify the error model, by comparing the vertical apparent emittances from the Accelerator Toolbox (AT) model and the ones measured at the in-air x-ray monitors
All measurements and correction discussed were carried out with open insertion devices (IDs) gaps, referring to the bare machine
Summary
Third-generation light sources and modern lepton colliders are characterized by low transverse beam emittances (below 10 nm and 20 pm for the horizontal and the vertical plane, respectively). In 2006 even more general formulas for the equilibrium beam distribution were derived and applied to coupling (both betatron and synchrobetatron) and intrabeam scattering [8,9,10]: This formalism is used in the present paper to connect the RDTs to the equilibrium eigenemittances. [16,17,18,19] provides a quantitative description of coupling effects in terms of the ideal lattice parameters (Twiss parameters and dispersion functions) and the magnet errors (modeled as localized skew quadrupole integrated strengths). This is done through the two coupling RDTs f1001 and f1010 of Refs.
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