The Superconducting RF group has been involved in the realization of superconducting particle accelerators since more than 30 years, starting in the 80s with the CERN LEP collider energy upgrade, for subnuclear physics, up to the current In-Kind contribution of important accelerator components for the two large European infrastructures XFEL and ESS, dedicated to the study of the properties of matter with photons and neutrons.
The core expertise of the group is the design, engineering, realization and characterization to their foreseen operational performance of radiofrequency superconducting accelerating systems.
The superconducting technology, thanks to its drastic reduction of ohmic losses in the accelerating structures, allows the realization of particle accelerators producing particle pulses with unprecedented intensity, quality and temporal structure. Thanks to superconductivity, new horizons will open both in fundamental physics facilities and in analytical facilities devoted to the understanding of our world. X-Rays produced by superconducting electron accelerators (like XFEL) or neutron pulses produced by superconducting proton accelerators (like ESS) will allow to produce three-dimensional images of the nanoworld, make movies of chemical reactions, investigate the structure of matter at the atomic/molecular level and study matter in extreme conditions, like those occurring inside planets and stars.
During the years the group has designed and realized, in collaboration with high technology industries, several types of niobium superconducting cavities for different project, as well as cryomodules for their operation. The accelerating structures have then been measured in the vertical cryostats of the LASA experimental area, which allows operation in a wide range of frequencies (350-800 MHz, 1.3 GHz and 3.9 GHz), at temperatures as low as 1.6 K. For the larger project sizes (as XFEL and ESS) the group also performed the necessary technology transfer for their industrial operation and followed the lifecycle of the procured components up to the facility operation.
The group know-how covers every aspect of the superconducting RF systems, from their design to their operation in an accelerator.
The European XFEL tunnel
A walkthrough in the European XFEL tunnel after the completion of the accelerator and X-Ray beamlines installation. The accelerator length is 1,7 km. Nearly half of the 100 superconducting modules have been fabricated in Italy, as an In-Kind contribution to the Project, managed by INFN-LASA.
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The European XFEL will generate, from 2017, ultrashort X-ray flashes at a rate of approximately 30 000 times per second and with a brilliance that is a billion times higher than that of the best conventional X-ray radiation sources.
The short and intense flashes of the European XFEL will open up areas of research that are nowadays inaccessible. Using the X-ray flashes of the European XFEL, scientists will be able to map the atomic details of viruses, decipher the molecular composition of cells, take three-dimensional images of the nanoworld, film chemical reactions, and study processes such as those occurring deep inside planets.
Italy contributed to the realization of the accelerator that drives the free electron laser producing the X-Ray flashes.
LASA designed and procured with the Italian industry approximately half of the main components for the 100 superconducting accelerator modules and various special machine components.
The XFEL Injector
To the right the first accelerating module (yellow), placed after the electron gun, and to the left the special third harmonic module (red), provided by LASA. The injector complex has been operated to its full specifications during the first commissioning phase of XFEL, from December 2015 to July 2016. The whole accelerator complex will start operation within the end of 2016.
The European Spallation Source is an infrastructure for the investigation for the properties of matter at the molecular level by means of short and intense neutron pulses, with a brilliance approximately 100 times greater than the existing sources. ESS pulses will allow enormous progresses in the science of neutron analysis, leading to the development of a new generation of products (e.g. computer chips, fuels, pharmaceutical components, medical implants and batteries) and the solution to complex scientific and medical questions (like the position and function of proteins that determine the DNA structure, or the working mechanisms of the neurons networks in the brain). ESS is in its construction phase and will start user operation in 2023.
Italy contributes to the realization of the superconducting proton accelerator, which allows the production of neutron pulses by means of the nuclear spallation process.
LASA is designing and producing with Italian companies the elliptical cavities for the medium energy section of the accelerator.
Superconducting RF Cavity
PFirst prototype built by LASA of the elliptical proton cavity for the medium energy section of the European Spallation Source accelerator.
The International Linear Collider (ILC) proposes to build a 500 GeV center of mass electron-positron collider that will, among other things, allow precise measurement of the Higgs boson properties. The linear accelerator proposed for the ILC is based on the superconducting RF technology developed in the last decades by the TESLA Technology collaboration, which was successfully brought at the industrial level by the European XFEL. ILC will allow physicist to explore in detail energy regimes never reached by lepton accelerators and will enable extremely precise measurements to investigate in detail the properties of several particles, including the Higgs boson, found at the CERN Large Hadron Collider in 2012. ILC will be a global infrastructure, unique in the world, devoted to the subnuclear physics studies and the realization of its accelerator complex, with a length greater than 30 km, requires a worldwide effort. ILC will host 16,000 superconducting RF cavities, in comparison XFEL has only 800. Japan has proposed to host the ILC realization and a worldwide consortium, in which INFN is a member, has produced all the technical documentation in preparation for a possible start of the project in the next years. In 2014 the Linear Collider Collaboration (LCC) was formed to proceed to the realization phases.
Italy participates to the ILC collaboration activities and holds the intellectual property of its main modular components, the so-called accelerating modules, developed at LASA.
LASA participated to the preparation of the project documents, since the Conceptual Design Report up to the Technical Design Report presented in 2013. LASA members participated to the editorial boards.
A 30 km linear collider
Conceptual scheme of the ILC accelerating complex. The two superconducting linear accelerators (more than 10 km each) send the electron and positron pulses to the detectors lying in the central region.
Particle accelerators, and the neutrons that they can produce, allow today to transform nuclear waste in less radioactive material, in other words to transform a chemical element in another, though the old alchemist dream (of transforming metal into gold) is still not at hand! Nuclear spallation (the frantumation of heavy nuclei hit by protons or neutrons) is the physical process enabling the transmutation of elements. As it often happens, this is one of the possible applications of researches that are motivated from the thirst of knowledge by scientists addressing the properties of materials and chemical compounds.
The spallation process allows to understand the structure of matter in neutron sources like ESS, but can be also used for nuclear energy applications, which is a primary sector for the world economy.
In the modern version of the alchemist dream of transmuting elements this time the goal is not to transform them into the noble metal, but to try to solve the issue of the geological stocking of nuclear waste, which remains radioactive for millions of years, without chances of contaminating the biosphere. Bombarding an element with a neutron beam it is possible to induce a change to its atomic nucleus and to “transform” it in another element (transmutation). A high enough neutron flux is able to transmute the long-lived nuclear waste produced by conventional reactors into material which is still radioactive, but with much smaller half-lives. The waste can be recycled and used as nuclear fuel in special nuclear fission reactors, called Accelerator Driven Systems (ADS).
ADS have an important difference with respect to conventional nuclear reactors: the energy producing chain reaction is not self-sustained, but needs an external neutron source, provided by a powerful superconducting proton accelerator by spallation. The intrinsic safety derives from the fact that when the external source is interrupted, the nuclear reaction cannot proceed autonomously, and the reactor switches off immediately.
The European nuclear industry and several Countries are jointly carrying out feasibility studies for ADS projects (like MYRRHA in Belgium), working together in research programs financed by Euratom (e.g. MAX), in which INFN is involved. These projects allow the construction of prototypes of the main components, to develop a new mode of generating nuclear power, in a new safe and environmentally friendly way. This would avoid to delegate to future generations the issue of living with nuclear waste, potentially harmful for millions of years.
LASA has been involved in the realization of superconducting proton cavities prototypes for ADS since the mid 90s and participated to the commissioning of significative technological demonstration tests during several Euratom Projects.
The fuel cycle closure with ADS
Nuclear waste from conventional reactors is chemically separated: Uranium is retrieved from the spent fuel bars (used for new fuel) and separated from the fission products and transuranic elements. The former, possibly after a “cooling” period, are directed to the geological repository and the latter are reprocessed to form the fuel of an ADS system, where they are transmuted by fission. Reprocessing of the spent ADS fuel allows an efficient transmutation process. The very small part that is left from the process is sent to underground repositories. The superconducting linear proton accelerator that produces through spallation the neutrons needed for the fission process is fed by a portion of the electricity produced by the ADS system, while the rest is sent to the electrical grid.
LASA is active since the 90s in the study and growth of photoemissive materials (antimony and tellurium compounds with alkali metals) to be used as high-brilliance electron sources in radiofrequency (RF) guns and in the development and realization of the ultra-high vacuum systems required for their deposition, handling and transport.These materials, when lighted with lasers synchronized to the accelerator RF, emit electrons due to the photoelectric effect. LASA carried an intense research program for the study of the behavior of these materials and of the properties of the electrons emitted by them. The results of these activities lead to the optimization of the growth processes of the photocathodes, which allowed their use in the modern facilities requiring brilliant electron beams.
Photocathodes grown at LASA are routinely used at: FLASH and PITZ at DESY, APEX at Berkeley, FAST at Fermilab.
The Cs2Te photocathodes produced at LASA are the state-of-the-art in this technology. A total of 140 photocathodes have been produced at LASA until now. Their current operational lifetime in accelerator facilities driven by electron guns operating 24/7 has increased up to 180 days.
View of the photocathode inside the deposition system at LASA.