Elettra | Machine Elettra 2.0, a technology driver for basic and applied science The Elettra 2.0 project has been approved by the Italian Government and, according to the current schedule, it will start serving users in 2027. The design phase has met several and sometimes conflicting requirements: • make Elettra 2.0 a fully transversely coherent source up to 0.5 keV-photon energy; • double the Elettra total average current at the maximum energy of 2.4 GeV; • diversify the type of experiments by providing a very broad range of photon energies, from few tens of eV to several tens of keV; • maximize the number of light source points, in excess of two-times the machine periodicity; • minimize the transition time, ensure smooth commissioning phase, and a robust operation of the light source. To achieve those goals, several systems of the accelerator complex will be either upgraded or replaced, such as the injection scheme, the high-performance magnetic lattice, ultra-vacuum mechanical components, and insertion devices. All these steps imply major technological advancements, based on R&D both in-house and synergy with industry. A symmetric six-bend achromat was produced by using longitudinal and transverse gradient-dipoles, and quadrupole magnets off-set with respect to the reference orbit to act as “reverse bends”. Consequently, the electron optics is not purely of the multi-bend type, but also uses dispersion minimizers to further reduce the horizontal emittance by a total factor of 47 compared to the present machine, at the energy of 2.4 GeV. Reduction of emittance, flat-beam configuration and refurbishment of the entire vacuum system, will produce up to three orders of magnitude brilliance increase and 60fold higher coherence at 1 keV. The Elettra 2.0 electron optics requires a significant number of magnets and additional coils to be energized individually. More than 1200 DC power converters (PCs) are foreseen. Multipoles PCs will be an in-house development. A synergic design of the magnets and the associated PCs led to standardization. Super-bends are dipole magnets supplied with superconducting coils to reach dipolar field intensities much larger than possible with ordinary room-temperature coils. An innovative compact design, including superconducting, side quadrupole magnets, is being developed for Elettra 2.0. The novel cryogenic solution will combine the benefits of a liquid-He cooled inner magnet with a liquid-Hefree upper cooling stage. For the new high-performance beamlines that are planned to take advantage of the lower electron beam emittance, new undulators are being designed and constructed. They are all based on NdFeB permanent magnets, in pure or hybrid configuration. The vacuum chamber of Elettra 2.0 will be made of different materials: stainless steel (~30%), aluminium (~20%) and copper (~50%), with more than 90% of the chamber coated with NEG film. A rhomboidal cross section of internal dimensions 28 mm x 18 mm is installed inside multipole magnets. Ti-V-Zr sputtering on metal surfaces allows the significant reduction of the inner pressure during machine operation, hence, a longer beam lifetime related to residual gas scattering. NEG coating is also expected to reduce significantly the conditioning time of the vacuum system. The extensive use of NEG coating, however, increases the machine impedance. To minimize that impact, the average coating thickness in Elettra 2.0 is set to 0.5 mm along the beam path, and to 1.5 mm elsewhere. With the maximum single particle energy loss of 670 keV per turn via synchrotron radiation, and 400 mA stored average current, the average beam power amounts to 268 kW. The momentum acceptance of Elettra 2.0, in excess of 3%, specifies a total peak voltage of 2 MV at 2.4 GeV. Four independent and identical RF plants fulfil the Elettra 2.0 specifications. The design of the RF system relies on solid state amplifiers (SSA) as RF power sources. Present sources easily provide more than 100 kW of output power at 500 MHz. The SSA were commissioned and set into operation with the accelerating cavities already in Elettra. One of the concerns about beam stability in Elettra 2.0 is the effect of a high harmonic cavity on the stored beam due to the presence of a “dark gap” in the beam filling pattern. This gap will be adopted to avoid ion trapping instability. A simulator based on an analytical frequency-domain model was developed to evaluate the variation of the synchronous phase and synchrotron frequency along the bunch train, as well as the distortion of the bunch profile. Experiments have been carried out in Elettra to characterize the harmonic cavity and to measure the effect of transient beam loading by using the longitudinal multi-bunch feedback system. A possible future development allowed by the lattice is the use of RF transverse deflecting cavities in the long-term operation of Elettra 2.0 aims to provide extreme ultra-violet and x-ray pulses of 1–5 ps FWHM pulse duration from IDs, with maximum repetition rate of 1.15 MHz and relative flux at the sample in the range 1–10% of the standard single bunch emission. Two superconducting RF cavities resonant at a 3 and 3.25 GHz will determine a steady-state configuration of vertically tilted bunches, with varying inclination along the ring circumference. A vertical slit at some distance from the ID samples the central portion of the stretched photon pulse, thus selecting a short portion in time, although at a reduced flux. The Elettra Booster ring magnetic lattice, whose circumference is of 118.8 m, is composed of one family of 28 dipoles, one of 18 focusing quadrupoles, and one of 18 defocusing quadrupoles. The Booster has been in operation for the last 15 years, bringing the electron beam energy from 100 MeV to 2.4 GeV. Elettra Highlights 2024–2025 142
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