Abstract
This paper describes a novel scheme for correcting the second order (chromatic sextupole) magnet lattice and its deployment on a fourth generation multibend achromat electron storage ring. The method is analogous to the well-established linear optics from closed orbits scheme, but uses an off-energy orbit response matrix to characterize the second order optics of a lattice. The matrix is constructed from the difference between two orbit response matrices measured at off-nominal energy, and is approximately linear with chromatic sextupole field strengths. This is utilized in a least squares minimization to find a model which minimizes the difference between the measured and model off-energy orbit response matrix. From this model corrections to the chromatic sextupoles of the machine can be calculated. In effect, for the MAX IV 3 GeV ring, the proposed scheme, NOECO (nonlinear optics from off-energy closed orbits), brings initial sextupole strength variations between achromats in the order of $\ifmmode\pm\else\textpm\fi{}8%$ down to the order of $\ifmmode\pm\else\textpm\fi{}1%$. The chromatic machine functions were symmetrized, the measured chromaticities approached the nominal values, and the lifetime of the beam at delivery conditions, with the same level of emittance coupling, increased to 19 h from 11 h at previously used sextupole settings.
Highlights
With the introduction of the fourth generation storage rings the performance of new lattices is being pushed further than ever before
The second section of this paper describes the MAX IV 3 GeV storage ring achromat’s dipole correctors, beam position monitors (BPMs), sextupoles, and octupoles
Beam energy. (iv) The BPM noise was measured at the new beam energy.2 (v) For a bipolar off-energy orbit response matrix (OEORM) measurement the above steps were repeated at an equal positive energy shift δfrom nominal. (vi) The 2nd order dispersion was constructed by taking the difference between the two measured dispersions and normalizing by 2δ.3 (vii) The
Summary
With the introduction of the fourth generation storage rings the performance of new lattices is being pushed further than ever before. A large number of different studies of nonlinear optics are performed at synchrotron facilities around the world Many of these studies are based on extracting information from turnby-turn beam positional data after the excitation of betatron oscillations. The results from an iterative application of this new scheme to the first multibend achromat (MBA) lattice, realized in the MAX IV 3 GeV storage ring [5], will be shown as well as its effect on the dynamic acceptance. The storage ring has 101 independent chromatic sextupole circuits, and no harmonic sextupoles
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