Abstract
Significant magnetic cross talks were observed between neighboring magnets on the Extremely Brilliant Source (EBS) low emittance storage ring. The main sources for these cross talks are the short longitudinal distances between magnets, which reach 47 mm in some cases. It affects mainly the dipole bending angles and the quadrupole gradients. A 1% bending angle correction was applied to the (permanent) bending magnets before their installation in the storage ring to compensate for the cross talks, while gradient errors as high as 1.8% were observed on quadrupoles. Intensive 3D magnetic simulations gave the longitudinal distribution of the cross talk errors for various magnet pairs and current settings. The error distribution depends on the magnet pairs: cross talks may create errors at magnet edges or all along the magnets, with same or opposite polarity. The simulations were validated by magnetic measurements, the discrepancies between measured and simulated values being in the ${10}^{\ensuremath{-}4}$ range with respect to the nominal gradients. Cross talk induced gradient errors were added to all quadrupoles and neighboring magnets in the lattice model. Even if it complicated the commissioning, the cross talks have no impact on the final performances of the lattice as the design machine parameters were reached for the most part.
Highlights
The Extremely Brilliant Source (EBS) is an upgrade of the European Synchrotron Radiation Facility (ESRF) light source. It relies on a new low emittance storage ring based on the Hybrid Multibend Achromat lattice (HMBA) [1], derived from the Multibend Achromat lattice implemented at MAX IV in Sweden [2]
The cross talk between permanent magnet (PM) dipoles and quadrupoles was simulated at the early stage of the project [22] and was measured on preseries magnets in
We identified two reasons for these moderate cross talks: the increased distance between magnets at the location of high gradient quadrupoles, and the reduced magnet apertures that allow higher gradients to be reached
Summary
The Extremely Brilliant Source (EBS) is an upgrade of the European Synchrotron Radiation Facility (ESRF) light source. As a new type of storage ring, it inspired several light source upgrade projects around the world [3,4,5,6], some of them being in the construction phase All of these storage rings are characterized by an increased number of bending magnets (the ESRF-EBS counts seven dipoles per arc) and by strong quadrupoles with gradients ranging from 50 to 100 T=m. The magnetic saturation is another contributor to cross talks Due to their high gradients and dc operation, the ESRF-EBS storage ring quadrupoles were designed to work in the saturation region. When these dipoles were finely tuned in the laboratory with stretched-wire measurement benches (Sec. II B), it was necessary to evaluate the influence of the neighboring quadrupoles on the bending angle. The results, and the impact of cross talks on the ESRF-EBS performance, are summarized in the last section
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