Elettra 2.0

Abstract

Introduction Elettra was one of the first third-generation synchrotrons in the world, and the first soft X-ray storage ring in Europe, having begun user operation in 1994. Over the years, many improvements have been made to the facility; for instance, the injection system was upgraded from a linac to a booster synchrotron, and top-up mode was implemented. There are 28 beamlines, including 10 using light from dipole magnets, and two using light provided by a superconducting 49-pole, 64mm period, 3.5 T wiggler. About 75% of userdedicated time is at 2 GeV with the remaining 25% at 2.4 GeV. Elettra is the only facility to operate at two energies, and at both energies, top-up mode is provided. Currently, the ring currents are 310 mA at 2 GeV and 160 mA at 2.4 GeV [1]. Since Elettra’s construction in the 1990s, there has been enormous progress in synchrotron technology, and so the management of Elettra decided some time ago that the whole machine should be upgraded by implementing these advances, in order to provide even better experimental facilities to users. Beginning in 2014, a series of workshops was organized to consult users and partners on their needs, specialized meetings of accelerator physicists discussed the best new designs, and new beamlines were planned. A preliminary Conceptual Design Report was produced in 2017 [2] and the project for a diffraction-limited light source, named Elettra 2.0, was presented to the Italian government. It was approved in 2019 with full funding [3]. Since then, a detailed technical design report was prepared [4] and work has proceeded on the planning, detailed design, and the initial steps of the upgrade, in spite of delays due to the pandemic and supply chain issues over the last year. The goal is to build an ultra low emittance light source, which delivers the highest number of photons per second, per unit area and per unit angle, in a small bandwidth; in other words, the maximum brilliance. It is well-established that the emittance of an electron bunch in a storage ring scales as the inverse cube of the number of dipole (bending) magnets, so that the design philosophy is clear: the existing dipole magnets must be replaced by a larger number of weaker magnets, and the design optimizes this requirement against factors such as geometric constraints, cost/benefit ratios, etc.