Introduction to the LNL Accelerators
Since its foundation, Legnaro labs have mainly been involved in fundamental nuclear physics research, the branch of physics focused on the atomic nucleus description in its constituents, protons and neutrons, as well as on the improved comprehensions of physics laws ruling their interactions. However interdisciplinary activities, i.e. the application of main nuclear physics discoveries and tools to other science fields (e.g. biology and medicine) as well as in industry, have always been supported by LNL. Among them, special techniques for materials surface treatments in order to improve mechanical and/or electrical basic parameters may be mentioned.
The main tool used by LNL for probing the nuclear matter is the ion accelerator (an ion is an atom lacking one or more electrons, therefore having positive electrical charge). Such particles, generated from an ion source, are injected into accelerators having different performances where an increase of energy occurs along a pipeline, kept in high vacuum. At the accelerator end, ions are then transported up to the collision point, where they hit a target at rest, causing a microscopic nuclear reaction. The hitting area (or "measurement point ") is surrounded by appropriate tools (i.e. detectors) able to highlight the particles produced in the nuclear reaction and to determine their basic properties (e.g. mass, energy, atomic number, magnetic moment, and other specific nuclei parameters). In such a way a database of main physical data may be collected, which allow researchers to trace, using proper physical-mathematical and computational tools, both the nuclei structure and the nuclear reactions mechanisms involved in the collision between the projectile and the specific target.
Legnaro National Laboratories, born in 1960, have grown around different electrostatic accelerators, for about 20 years. From the 60’s up to the 80’s they have indeed purchased, markedly improved and operated, three electrostatic accelerators having different and complementary performances (CN, AN2000 and Tandem). In the mid-80’s LNL accelerator physicists, having acquired enough know-how and competencies, started with the design and construction of ion accelerators of even higher performance, either to extend the set of accelerators available in the LNL lab, or by taking part in the R&D and construction of accelerators (of both larger size and greater investment level), in collaboration with European and Worldwide partners.
The superconducting linear accelerator (linac) called ALPI became operational at LNL in the early 90’s and is used to give an energy boost to the ions already accelerated by the Tandem. In 2004 the PIAVE accelerator, based on a superconducting RFQ ("Radio Frequency Quadrupole)" configuration, was joined to Tandem as ALPI injector.
Fig.1 shows the ion beam acceleration path from the Tandem (or PIAVE) injector to ALPI superconducting linac and into the experimental halls where targets, as well as the detection apparatuses for the different nuclear reactions to be monitored, are located. When the acceleration path comes to the final stage, after having undergone an acceleration boost in the peculiar U-shape ALPI linac, ions are directed towards one of the three experimental halls. Different measuring stations, comprising both targets and detection apparatuses for the reaction products caused by projectile-target collision, are located there.
In the last 20 years, INFN LNL labs have been generally recognized as a reference in the development of both superconducting linacs and high performance RFQs, either at superconducting or at room temperature working conditions. Thanks to the qualified know-how gained, technologists and researchers working at LNL have been involved in the past, or are collaborating at present, on various projects, among which:
- Pb ion injector for CERN (LHC) in Geneva;
- the IFMIF-EVEDA (International Fusion Materials Irradiation Facility) demonstrator injector: a technologically very ambitious accelerator that will be used for radiation damage testing (under critical conditions) of proper materials for future, fusion-reactions-controlled, thermonuclear reactors. The new frontier to finally get clean nuclear energy in the not so far in future;
- The ISAC-2 linac at TRIUMF laboratory (Vancouver, Canada).
In the last decade INFN has approved (and partly financed) the construction of a new facility to provide the acceleration of the so-called exotic beams (SPES project). The use of an industrial cyclotron, with up to 750 µA beam current at exit port, is foreseen in this facility, to accelerate protons on a Uranium Carbide (UCX) target to start proton-induced fission reactions. The fission fragments nuclei, thus generated, are generally much more neutron-rich than those available in nature (reason why the word "exotic" is used). Once ionized and mass-selected they are, in turn, re-accelerated by using the linacs, presently available at LNL. The impact of such exotic beams on selected targets will let to probe the nuclear matter under conditions similar to those available in the earliest stages of universe, when the heaviest elements agglomeration occurred in the process called "nucleosynthesis": a branch of nuclear research still largely unexplored.