The Frascati National Laboratories

1 A national laboratory on the Tusculum hills

The Frascati National Laboratories are part of the extraordinary journey made by Italian nuclear and particle physics between 1926, the year Enrico Fermi became professor of Theoretical Physics in Rome, and 1953, when a project for the construction of an electron synchrotron was approved by the brand new National Institute for Nuclear Physics (INFN). This period saw the rise of modern physics in Italy whose small but brilliant scientific community was nearly destroyed by the racial laws and severely damaged by the war and by consequent lack of resources. As soon as war ended, plans for the renewal and reconstruction of Italian physics started.

In parallel, a few visionary scientists, conceived the idea of creating an international laboratory for fundamental research, a center for nuclear physics, which should relaunch European science, hosting one or more large particle accelerators. In September 1954, the Conseil Européen pour la Recherche Nucléaire (CERN), officially came into being, with Edoardo Amaldi its first Secretary General. Such a project would unite European scientists and allow sharing the costs of ambitious nuclear physics facilities, but at the same time required to have its feeding grounds in national laboratories, where the new accelerator science could also be fostered.

In Italy this led to the ambitious plan to build a particle accelerator and to the consequent decision to build the Frascati National Laboratories to host such large-scale facility. The official decision to build an accelerator with an energy not inferior to 500 million electron Volts (MeV) was taken by the INFN board of directors on 19th January. The approval of an accelerator to be built from scratch represented the quantum jump Italy needed to overcome the destructions of the war, the pre-war exodus of Italian scientists and the growing gap with respect to the international community.

Acting on the proposal by INFN president Gilberto Bernardini, the organization and direction of the project was given to the 33-year-old Giorgio Salvini (fig. 1), who took up the challenge of building an accelerator of energy 500-1000 MeV of a type not yet well defined, in a national laboratory still to be built, in a site to be decided.

By February 10th 1953, a first core of senior scientists was in place in Pisa, where Salvini was professor of Experimental Physics. Mario Ageno and Ruggero Querzoli joined to assist him from the Istituto Superiore di Sanità (ISS), where they had gained invaluable experience with the Cockcroft-Walton accelerator. From the University of Rome, Enrico Persico accepted to lead the theoretical work and Italo Federico Quercia, an expert in cosmic rays, came back from India to lead electronics and radiofrequency groups. Among the young members of the team there were Fernando Amman, later to direct the construction of ADONE, and Carlo Bernardini, a major protagonist of AdA’s construction and operation. Envisaging the growth of the laboratory and the administrative responsibilities, Salvini secured the collaboration of Icilio Agostini and Stanislao Stipcich. The group was organized as an INFN branch, based in Pisa, called Sezione Acceleratore, whose members in 1953 are shown in Table I.

After a trip to the United States taken by Gilberto Bernardini and Salvini in Summer 1953, the final decision was made to construct a weak focusing electron synchrotron. This decision was taken also considering that CERN – where Gilberto Bernardini was Director of Research – had planned two proton machines. An electron machine would allow Italy to reach the desired maximum energy of about 1 GeV as a realistic aim.

The choice of the laboratory site was initially left undecided. At the end, the choice fell on a location near the town of Frascati, on the slopes of the ancient Tusculum hill, in a location called “Macchia dello Sterparo”, some 10 km downhill from the town (fig. 2).

The availability of the site opened the way to the construction of the new laboratory, which started during the second half of 1954. The scientific management was handed over to INFN and university personnel, while the financial costs for buildings and infrastructures as well as the costs for hiring new staff were covered by the National Committee for Nuclear Research, Comitato Nazionale per le Ricerche Nucleari CNRN, soon to be renamed CNEN, presently ENEA.

While the construction of the laboratory was going ahead, the synchrotron parts were prepared in Pisa, until, in May 1955, people and machinery were moved to Rome, transferred to the designated site in 1957. The synchrotron team had now expanded to include a large number of scientific and technical staff (fig. 3). By the end of the year, all the basic elements for a synchrotron had been built and were ready to be assembled together, the magnet had been mounted and its power source tested, the Cockcroft-Walton accelerator (C-W), to inject electrons in the ring, had arrived from the Istituto Superiore di Sanità, the vacuum chamber was almost ready, the synchrotron building, the power station, the machine shops and the cryogenic liquefier plant, were in place.

The year 1958 saw the joining of all the synchrotron parts. On February 9^th, 1959, electrons circulated in the vacuum chamber, accelerated to an energy of 1100 MeV. On that day, Italy had joined the club of particle accelerator builders. The day was celebrated with a dinner in Frascati. It was a great moment for the staff, and this success was proudly reported in the national and international press. A table top model for the synchrotron was exhibited at the 1956 Fiera di Milano.

After an impressive inauguration ceremony, which brought to Frascati the President of the Italian Republic Giovanni Gronchi, the scientists in Frascati started to use the new accelerator. A number of experiments, shown in Table II, were already running by June 1960 with INFN, ISS (see, pp. 119-138) or university personnel.

In the meantime, the CERN Proton Synchrotron had started operation, accelerating protons up to an energy of 10 GeV and being for a brief period the world’s highest energy particle accelerator. This new phase opened a wider perspective in the participation of Italian physicists in research activities at CERN and in their contribution to the building of future more powerful machines as well as their association in top managerial and leading positions of great responsibility for the exploitation of the scientific potential of CERN accelerators.

2 AdA and the birth of electron-positron colliders

In June 1960, the innovation capacity of the laboratory and its team of scientists, technicians and engineers reached a high point. In parallel to the experiments running at the synchrotron, a totally new type of particle accelerator was already under construction.

This project had started after a meeting held in Frascati on February 17^th, 1960. During a discussion about future programs for the laboratory, Bruno Touschek proposed to transform the synchrotron into an electron-positron collider, in order to investigate the physics resulting from electron-positron annihilations. Such experiment – from which deeper insight into fundamental particle physics could be gained – should be, in Touschek’s own words, “the future goal” of Frascati Laboratories. The danger to the synchrotron experiments was averted by Giorgio Ghigo, who suggested preparing a scaled-down project, which would be a proof-of-concept, using the synchrotron photon beam for injecting electrons and positrons in the smaller machine. The proposal was accepted on March 7th. A working group constituted by Carlo Bernardini, Gianfranco Corazza, Giorgio Ghigo, and Bruno Touschek was charged with preparing a prototype for an accelerator where stored bunches of electrons and positrons would be made to collide at center of mass (c.m.) energy of 500 MeV. It would be a machine quite smaller than the synchrotron, only 130 cm diameter vs. 720 of the synchrotron. It would be called AdA, for Anello di Accumulazione, storage ring in English. On that day, starting from the Frascati Laboratories, high energy physics took a new turn.

AdA represented the perfect synthesis between the new ideas surging in mid 1950’s. On the one side, there was the discovery of non-conservation of parity in weak interactions and the demonstration of the existence of anti-protons and anti-neutrons, further stimulating theoretical investigations about symmetries and invariances in quantum field theories.

According to Nicola Cabibbo, AdA’s concept began to materialize in Frascati and Rome after a seminar by Wolfgang Panofsky, who presented a project, then under construction at Stanford, for two tangent rings in which electrons would circulate in opposite directions. The main aim of such a colliding-beam experiment was to test QED. In the USSR, unknown to most, a similar project was under study by G. Budker and his group. Touschek immediately raised the question about making electrons and positrons collide, as opposed to the American project. He focused on the much more innovative idea of matter-antimatter annihilation which would enable access to new particle states and probe the structure of the quantum vacuum. The seminar in Frascati took place on October 26th, 1959. Soon after, Cabibbo, Raoul Gatto and other theorists in Rome started discussions about electron-positron physics.

Following the March 7^th approval, financing was rapidly obtained and AdA started working in February 1961, placed next to the synchrotron (fig. 4). The original team had counted on Gianfranco Sacerdoti and Mario Puglisi, respectively for constructing the magnet and the radiofrequency, assisted by the valiant team of technicians who had built the synchrotron. AdA’s operation was presented in June at the CERN Conference on Theoretical Aspects of Very High-energy Phenomena, during the session on Electromagnetic Interactions. Touschek startled the audience by saying that “Frascati is developing two storage rings [...] designed for storing electrons and positrons”. One was AdA, already undergoing tests, the other was ADONE, still at a planning stage. This announcement at CERN led to solving one of AdA’s initial problems, namely an insufficient number of electrons (and positrons) produced by the photon beam extracted from the synchrotron. Two French physicists, Georges Charpak and Pierre Marin, from Orsay, intrigued by the idea, came to visit Frascati in July 1961, and the suggestion arose of using the intense electron beam from the Orsay linear accelerator as injector.

One year later, AdA was moved to Orsay, the Italian team now including Giuseppe Di Giugno and Ruggero Querzoli. On the French side, the group consisted of Jacques Haïssinski, Francois Lacoste and Pierre Marin. Important effects in the colliding beam operation were discovered, such as the Touschek effect, the charge and volume effects. While annihilation in new particles could not be observed because of still insufficient luminosity, in 1964 collisions were proved to have taken place by observing the process $e^{+}e^{-} \rightarrow e^{+}e^{-} \gamma$. In the meanwhile, following AdA, the construction of a more powerful collider, ADONE, had started in Frascati, while the French, inspired by AdA’s success, had initiated their own electron-positron collider ACO, Accélérateur de Collisions d’Orsay, and projects for similar machines had been set in motion in Europe, the USSR and the USA.

3 ADONE

ADONE’s project first appeared in a memo Touschek drafted in November 1960 where an electron-positron ring with beam energy of 1.5 GeV was proposed. This machine was to go beyond a proof-of-concept, such as AdA, and the goal of reaching 3.0 GeV in the center of mass was ambitious, but within the laboratory capability and realistic financial costs. Following Touschek’s memo, an official proposal, signed by Fernando Amman, Carlo Bernardini, Raoul Gatto, Giorgio Ghigo and Touschek was prepared on January 27^th, 1961, less than a year after Touschek had suggested to build AdA5. The construction of ADONE was approved in 1963 and Fernando Amman (fig. 5) was appointed to direct it.

Although in his 1961 talk at CERN Touschek had placed ADONE’s completion in 1964, the complexity of the project took much more time. The beam started circulating only in 1968, but students unrest in the universities and a series of labor strikes led to interruptions and delays, so that ADONE’s operation resumed only in 1969. By this time, two other electron-positron colliders in the GeV energy range had been in operation, ACO in Orsay, and VEPP-II in Novosibirsk, while the construction of a ring, with 4 GeV in the c.m., was underway in Stanford. The delay resulted in Orsay and Novosibirsk arriving first in systematically studying the nature and importance of vector mesons. Another near miss was being only second (to VEPP-II) in the observation of photon-photon collisions. Still, as soon as ADONE started, its higher energy paid back the efforts which had been made and the next few years allowed Frascati to make important discoveries.

3.1 Early successes: multihadron production, photon-photon scattering

Experimentation with ADONE started on November 17th, 1969, with five different experiments, as shown in Table III. Photon-photon collisions, resulting in four final-states particles, were observed and confirmed by QED calculation. But a surprise came with an abundant production of pions and kaons, registered by the different experiments at ADONE (Table III). The production was found to be higher than expected as the beam energy increased. A set of second-generation experiments, with up-to-date detector capabilities, confirmed the observed excess. This phenomenon, which became known as multihadron production (fig. 6), was a proof of the validity of the quark model for the structure of hadrons.

The list of participants to the first- and second-generation experiments, included scientists from the synchrotron, as well as a whole new generation who, starting from 1959, had enrolled in physics, following a world-wide trend, ignited by the Sputnik exploit. In Italy, a contribution to the jump in physics enrollment had also come from the large publicity given to the successful construction of the synchrotron and from Giorgio Salvini’s lectures, broadcasted on national television since 1959.

The experimental results were not fully understood at the beginning. This was partly due to large errors, mostly because the discrepancy between data and expectations needed the concept of color, which was not yet widely accepted. The interpretation became clear not long after, with the development of the quark-parton model and Quantum Chromodynamics. However, Touschek was not daunted by the contradictions or large errors: he was convinced that new states of matter were created during the annihilation, and that something new, and (for many) unexpected, was appearing as the energy increased.

3.2 $J/\Psi$: a missed discovery

While ADONE in Italy, ACO in France, and VEPP-II in USSR had been taking their first steps, confirming that the existing particle zoo could be explained in terms of three types of quarks, labeled as up, down and strange, the existence of a fourth quark, called charm, had been theoretically suggested. Its detection was however experimentally challenging in traditional fixed-target accelerators. In 1973 an experiment at the Brookhaven’s Alternating Gradient Synchrotron began measuring the process $p+A \rightarrow e^{+}e^{-}$ + anything, in search for possible new states of matter to appear as an electron-positron pair in the region between 2 and 5 GeV. In the meanwhile, in 1972, the Stanford Positron Electron Asymmetric Ring (SPEAR) started functioning at a center-of-mass energy between 2.8 and 4 GeV. Inspired by the Frascati multihadron excess findings, also observed at the Cambridge Electron Accelerator (CEA), the Mark I detector at SPEAR started a search for multihadron final states. By Summer 1974 the unexpected production had been confirmed (fig. 6, right panel) and the SPEAR experimental group started a detailed study, changing the beam energy one MeV at a time.

Indeed, on November 11^th, 1974, the discovery of a bound state of charm-anticharm pairs, which would be called $J/\Psi$, was announced in a joint press conference by Brookhaven and SLAC. In the same night of November 11th, a phone call from US broke the news of the discovery to Giorgio Bellettini, the Frascati Laboratory director, telling him that a new particle had been found with mass around 3 GeV. The search at ADONE (fig. 7) started immediately.

Since ADONE had been designed and was operating at a maximum c.m. energy of just 3 GeV, this value posed a serious dilemma to the laboratory: could the machine be pushed to reach (and go a bit higher than) 3.105 GeV? Giorgio Salvini was confident that it could be done without damage to the machine. The current in the magnets was increased and on November 13th, the search started anew. As the machine came close to 3.1 GeV, the $\gamma\gamma 2$ control stack suddenly lit up like a Christmas tree and a startling, and, so far unheard of, “crazy” ticking of the electronic counters signaled that a new state of matter was being created.

The article from Frascati, confirming the discovery, was received on November 18^th, and published in the same issue as those from Brookhaven and SLAC, respectively received on 12^th and 13^th November. The discovery was ground breaking and the leaders of the two American teams were awarded the 1976 Nobel Prize “for their pioneering work in the discovery of a heavy elementary particle of a new kind”.

Bruno Touschek (fig. 8) had been a member of the Accademia dei Lincei since 1972 and his contribution to colliding beam physics was recognized by the Matteucci Medal awarded to him by the Accademia dei XL. Over the years he had provided theoretical understanding of many effects influencing the operation of high-energy colliders, from the Touschek effect in AdA to infrared QED corrections for ADONE, for which he developed a resummation technique, later applied to determine the $J/\Psi$ width soon after its discovery. Touschek’s legacy to Frascati goes beyond his contribution to the birth of electron-positron colliders. Starting from the early 1960's, with Nicola Cabibbo and Raoul Gatto, he had nurtured a tradition of theoretical physics which lasted and flourished long after his early death in 1978.

4 After the $J/\Psi$: new particle detectors, nuclear physics, synchrotron radiation, FENICE

When a SuperADONE project for Italy was not approved, Frascati joined international collaborations preparing experiments at planned new large installations, which dwarfed national efforts for new accelerators. After the 1974 discovery of the $J/\Psi$, experimentation at ADONE continued until 1977, when the decision was made to operate ADONE with a single beam and exploit its potential for nuclear- and solid-state physics research.

But ADONE had left a major legacy to experimental particle physics. Experiments at ADONE had required the construction and operation of state-of-the-art particle detectors and of the related readout electronics. The LNF became therefore an important hub for the development of such instruments. In particular, there was a focus on gaseous detectors which resulted in the invention of the plastic streamer tubes by E. Iarocci and collaborators in the early 80’s. At the time it became clear that major progress in high-energy physics could only come mainly from experiments at very-high-energy facilities, such as the Tevatron at Fermilab, or the SPS and LEP at CERN, or from large-volume underground detectors, such as those designed for the Gran Sasso Underground Laboratory. Consideration of cost-effectiveness and robustness became therefore crucial in the design of the new apparata. The Iarocci tubes had the advantage of being relatively cheap and easy to build and operate, features which allowed their use in the ALEPH and OPAL detectors at LEP or MACRO at the Gran Sasso laboratory. A major contribution from LNF was also made in the construction of the CDF detector at Fermilab, which would eventually discover the top quark.

After the synchrotron was closed in 1976, ADONE was operated with a single beam and restructured around new facilities in the INFN-LNF site, along well-established lines of research.

Nuclear physics experimentation had taken place at the synchrotron since early days. In parallel with the photon beam extracted from the synchrotron to create electron and positron pairs in AdA, the electron beam impinging on a target inside the synchrotron ring had allowed the measurement of energy and momentum of nucleons inside the nucleus. In 1965 the extraction of the electron beam had been successfully performed by a group with Angelo Turrin, one of Persico’s assistants, Ubaldo Bizzarri, who had participated in early Frascati efforts with AdA, and Italo Federico Quercia, director of the Laboratory in 1961-1963. This innovative technique enlarged the range of nuclear physics experiments, with the ISS group playing a leading role. When the synchrotron was closed, nuclear activities first moved to exploit the LINAC, at the new Laboratorio Esperienze Acceleratore Lineare Elettroni, LEALE, and then continued at ADONE, operating as a single beam. Two highly innovative techniques where developed. One of them was called LADON, for LAser against ADONE (fig. 9), consisting of backward Compton scattering against high-energy electrons from ADONE, which later inspired the ideas about a photon collider. With LADON, a beam of 100% polarized photons against a nuclear target could extract information on the detailed structure of both heavy and light nuclei. The other technique was the Jet Target experiment, in which scattering of electrons on a gaseous target could be observed and the interaction dynamics be studied. The technique showed that it was possible to insert a gas target in ADONE without damaging the high vacuum of the storage ring (fig. 10).

This activity established the laboratory as a new player in the international nuclear physics community, and played an important role for the formation of a new generation of young Italian physicists who would become both protagonists and actors in the large European and American nuclear physics facilities of the 1980’s, such as CEBAF at Jefferson Lab, MAMI in Mainz, etc.

Alongside particle and nuclear physics experiments, studies connected to synchrotron radiation, at both the synchrotron and ADONE, had a major impact on the development of the field. The light emitted by the acceleration of charged particles, first observed in a laboratory with synchrotrons, could be exploited to study the properties of biological or condensed matter, in a wide range of applications. At the Frascati synchrotron, a French-Italian collaboration was started in 1963 by Yvette Cauchois and the ISS, with Mario Ageno. The collaboration, which inspired the synchrotron radiation program later developed at ACO, was the first in Europe to use light emitted by an accelerator to study X-ray spectra of heavy elements. In 1970, the Frascati X-ray spectroscopy group was formed, and in 1974 a dedicated program for synchrotron radiation experiments at ADONE, called PULS, was proposed (fig. 11). The range of ADONE’s light emission was extended into the high-frequency X-rays through the insertion of a special magnet, called wiggler (fig. 12), consisting of a series of magnets with alternating polarization. The radiation emitted by the electrons as they moved through the wiggler was used by the Project Wiggler ADONE (PWA) for medical applications, archeological and artwork studies.

In 1990, ADONE returned to electron-positron operation to explore the region around the nucleon anti-nucleon threshold, one of the topics Touschek had included in his original November 1960 planning for ADONE. A large group of Italian universities and INFN sections, from Cagliari, Ferrara, Padua, Rome, Turin, Trieste, gathered in Frascati around the experiment FENICE, based on new state-of-the-art detector techniques. FENICE took measurements until April 6th 1993, when ADONE was closed down, and dismantled, leaving the grounds for the construction of a totally new electron-positron accelerator, the Double Accelerator For Nice Experiments (DAFNE), promoted by Nicola Cabibbo, then President of INFN (fig. 13).

5 DAFNE

The discovery of the charm quark and of mesons made of charm, called D-mesons, was followed in 1977 by the discovery at FermiLab of the b-quark, a fifth type of quark. The study of flavor, the property identifying different types of quarks, became a new frontier in particle physics. Soon after, it became clear that in order to being able to perform precision tests of CP violation and of the CKM mechanism, responsible for transitions between quarks of different flavors, high-luminosity $e^{+}e^{-}$ machines were needed, capable to produce billions of well-tagged flavored mesons. Since the scientific focus of these machines was primarily the study of flavor physics, they were immediately dubbed as “flavor factories”.

While in the US and Japan attention was put on the construction of a B-meson factory, INFN decided to concentrate efforts in the realization of a smaller and less expensive $\phi$-factory. The $\phi ( 1020 ) $ resonance decays primarily into charged and neutral kaons allowing precision tests of the CKM mechanism in the d-s sector to be performed. However it was clear that in order to achieve the required statistical accuracy, a collider with luminosity of order 5×10³² cm^–2s^–1 was needed, more than two orders of magnitude larger than what was obtained by similar machines built thus far.

A $\phi$-factory showed also another very interesting peculiarity: the quantum-mechanics description of $\phi \rightarrow K^{0}\bar{K}^{0}$ decays implies an anti-correlated initial state that evolves in time preserving this characteristic. This feature can be exploited to perform several quantum-mechanics tests, as well as precision test for discrete symmetries conservation, in particular of the CP and CPT symmetry. Studies for the construction of a $\phi$-factory with the above characteristics were made also at KEK in Japan, Novosibirsk in Russia and UCLA in the USA; in the end only the INFN project received formal approval in 1990 and the design of the machine started under the leadership of Gaetano Vignola.

A large collaboration was also formed with the purpose of building a detector capable of performing a large variety of measurements in the field of CP violation, CKM parameter measurements and quantum interferometry with neutral kaons. The KLOE (K LOng Experiment) was thus designed under the leadership of Paolo Franzini and Juliet Lee-Franzini and the technical coordination of Sergio Bertolucci.

Important contributions came from the groups of Bari, Karlsruhe, Lecce, Napoli, Pisa, Roma La Sapienza, Roma Tor Vergata, Roma Tre, Trieste. The construction of the apparatus was a challenge (fig. 14).

In general, the dimensions of the detector at a collider scale with the centre-of-mass energy of the collisions. However, in the case of KLOE, the need of maximising the capability for observing decays of long-lived particles, such as the $K_L$ and the charged kaons, translated into the design of a big apparatus, 4 m in radius and 7 m long. Therefore the world largest drift chamber ever built to date was realized in the LNF workshops. For the first time carbon fiber was used to realize its mechanical structure, a solution which was soon after adopted by other high-energy physics experiments. An extremely hermetic electromagnetic calorimeter was also built, using a peculiar and innovative sandwich of subtle lead foils and scintillating fibers. KLOE was ready for operation in late 1999 (fig.15).

It was also realised that the peculiar nature of the beam of charged kaons produced at DAFNE, i.e. the fact that it is a monochromatic and perfectly tagged beam, could allow one to perform also unique studies in the field of kaon-nucleon interactions and low-energy QCD. Therefore the FINUDA and DEAR collaborations were formed with the study of Λ-hypernuclei levels and lifetimes and the measurement of the kaonic hydrogen X-ray spectrum, respectively, as topics of interest.

Although DAFNE allows in principle for collisions in two separate interaction points, it was decided to operate one experiment at a time, since the small dimensions of the main rings allowed optimization of the luminosity in only one interaction point.

DAFNE started operations in the spring of year 2000 for KLOE. It was immediately clear that achieving the maximum design luminosity would have been a very hard task, since the circulation of very intense beams into a relatively short machine translated, among other things, into short beam lifetimes and high backgrounds in the detector. The performance of the machine was therefore improved slowly but continuously along the years, reaching a record peak luminosity of 1.6×10³² cm^-2s^-1 in 2007.

Between years 2000 and 2007, KLOE acquired 2.5 fb^–1 of data, FINUDA 1.2 fb^–1 and DEAR 60 pb^–1.

The analysis of this impressive amount of data has led to important results published by all of the three collaborations. The precise determination of the Vus parameter (namely the Cabibbo angle) of the CKM by KLOE and, by the same experiment, the determination of the hadronic contribution to the muon anomaly, a particularly hot topic due to the yet unresolved tension between the measured value of this quantity and its Standard Model prediction are worth mentioning. FINUDA was able to detect neutron-rich hypernuclei, Λ-6-H, Λ-7-H and Λ-12-Be, and in the last phase of its activity identified a signal of a possible deeply bound K-pp system of exotic nature, which did not find confirmation by other experiments though. DEAR performed the most precise measurement to date of kaonic hydrogen transitions to the fundamental level.

In 2010 under the lead of Pantaleo Raimondi, the DAFNE team has implemented a new collision scheme based on large crossing angle, small beam size at the crossing point, and compensation of beam-beam interaction based on the use of sextupoles creating a “crab-waist” configuration in the interaction point. The new configuration has allowed reaching a record luminosity of 4×10³² cm^–2s^–1 for the SIDDHARTA experiment, a successor of DEAR. This is considered a breakthrough achievement for collider physics; the crab waist is nowadays used as an important element for the design of all future electron-positron machines. With these data, SIDDHARTA could perform the first measurement of kaonic helium-3 and kaonic helium-4 transitions to the 2p level, as well as other light kaonic atoms measurements.

Using this new collision strategy DAFNE has also provided, between 2012 and 2018 an additional 5 fb^–1 to the KLOE-2 experiment, the upgraded successor of KLOE.

6 The future of LNF accelerators

A new ambitious program has been launched in 2018 with the publication of the conceptual design report of the EuPRAXIA@SPARC_LAB facility. In this machine, a high brightness GeV-range electron beam, generated by a X-band RF Linac, will drive a plasma accelerator module able to boost the beam energy up to a factor of 5, which in turn will drive a Free Electron Laser user facility to produce a high photon flux in the range of 3 nm. This FEL radiation opens the road to novel, time-resolved studies which are of particular relevance in the fields of material science, biology and life science in general.

The project has received the endorsement of the INFN management in 2019 and has been granted a funding of about 100 million Euros distributed along 10 years from the Italian Ministry of Science. It is expected to become operational in 2028.

The interest in the machine, and its main challenge, resides in the fact that it aims at being the first user facility that exploits plasma acceleration. This innovative accelerator method is seen as one of the possible options which can allow us to build very-high-energy machines overcoming the technical and budget problems connected to the use of conventional RF-based techniques.

Experiments on plasma acceleration have been and are being carried out in several laboratories in the world. Recently, in Frascati the SPARC_LAB facility has obtained a very important result: a 85 MeV, 20 pC “witness” electron beam has been accelerated to a gradient of 250 MeV/m by a plasma generated by a 350 pC “driver” one. Although the above gradient is not particularly high, the very important result in this experiment is that for the first time the energy spread of the witness was kept at the 0.2% level, orders of magnitude better than what obtained so far, and a key requirement for using plasma acceleration as a tool for operating a user facility.

EuPRAXIA@SPARC_LAB is conceived as the first phase of an ambitious European project aiming at building two plasma acceleration facilities, the LNF one based on a beam-driven acceleration technique, and a second one, in a site yet to be decided, exploiting a laser-driven acceleration strategy.

It will serve a wide community of users, with topics of interest ranging from studies on innovative materials science to the research on biomolecules, viruses and microscopic processes.

Several new ideas and concepts have been developed in the conceptual design of EuPRAXIA; it will be the very first infrastructure of this kind, and will be the pioneering step in developing several kinds of compact sources.

It is expected that many Italian and European companies participate in the creation of critical and innovative components of the machine, which strengthens the laboratory’s role as a hub for innovation and for societal development.

Necessarily EuPRAXIA will absorb most of the laboratory’s resources in the years to come. However LNF aims at maintaining its prominence role in the fields of accelerator and detector development with participation to many international scientific enterprises, such as the highluminosity LHC or the yet to be approved future ultra-highenergy lepton collider.

7 Conclusions

The Frascati laboratories, whose creation was decided by INFN in 1953, started with a small team of scientists, engineers and senior technicians (see Table I). By 1958, when the synchrotron was about to start functioning, the number had become 40.

Today the number of employees has grown to more than 300. The laboratories were built to make a modern-type particle accelerator, and fulfilled these expectations, beyond what could have been envisaged. The activities have vastly diversified among fundamental research, outreach and applied physics. We are aware that the overview presented here cannot be fair to all the lines of research developed through the almost seventy years of history of Frascati laboratories, and for this we apologize to all our friends and colleagues. It is our hope that the essential list of references will help to close the gap.

Acknowlegments

We acknowledge the invaluable support of the LNF Scientific Information and Dissemination Service, in particular from Gianni Di Giovanni from the Photographic Laboratory, and of Antonino Cupellini and Davide Cirillo from the LNF Library. We are indebted for useful consultations with Rinaldo Baldini, Giorgio Bellettini, Antonio Bianconi, Orlando Ciaffoni, Enzo De Sanctis, Paolo Gaucci, Enzo Iarocci, Corrado Mencuccini, Simone Pacetti. Further thanks go to an anonymous referee for useful comments. We are also grateful to the Physics Department Library at Sapienza University in Rome for consultation of the Archives and bibliographic assistance, and to Archives, History & Records Office and Research Library of SLAC National Accelerator Laboratory for permission to use the plot shown in fig. 6. We thank Francis Touschek for permission to reproduce figs. 7 and 8.