--- title: Bellotti Ion Beam Facility at LNGS url: https://www.emergentmind.com/topics/bellotti-ion-beam-facility type: topic --- # Bellotti Ion Beam Facility at LNGS The **Bellotti Ion Beam Facility** (BIBF) is an underground ion-beam installation at the Istituto Nazionale di Fisica Nucleare–Laboratori Nazionali del Gran Sasso (LNGS), recently installed in Hall B and named in honour of Prof. Bellotti. It is described as a major advance for studying nuclear processes in an underground environment, and as the first megavolt-class accelerator operating underground at Gran Sasso. In the LNGS nuclear-physics planning literature, it is based on a 3.5 MV “Inline” Singletron accelerator that complements the existing 400 kV LUNA electrostatic machine and has been optimized for the ultra-quiet background conditions provided by 3800 m w.e. of rock overburden [2512.19059]. In a proposed rare-event application, the same facility is presented as a tunable accelerator-based source for light scalar bosons, coupled to large-volume low-background detectors already operating or under construction at LNGS [2509.03486]. ## 1. Institutional setting and underground context LNGS is characterized as one of the largest underground physics laboratory, with a peculiar environment suited for experiments in Astroparticle Physics, Nuclear Physics and Fundamental Symmetries. Within that setting, BIBF occupies a specific role: it extends the underground accelerator program beyond the 400 kV LUNA machine and broadens the accessible parameter space for direct low-background measurements. The Mid Term Plan workshop organized at LNGS framed the facility as part of a coordinated national strategy of the Nuclear Physics Division of the Istituto Nazionale di Fisica Nucleare, with explicit discussion of opportunities enabled by state-of-the-art detection systems and by synergy among LUNA, BIBF, ERNA at CIRCE, and other laboratories such as LNS and LNF [2512.19059]. The underground environment is described through two complementary measures. One source emphasizes the 3800 m w.e. overburden that enables ultra-quiet operation, while another states that the accelerator hall sits beneath approximately 1 400 m of rock, yielding a cosmic-ray muon flux reduction by a factor of approximately $10^6$ relative to surface laboratories [2512.19059; 2509.03486]. A common simplification is to treat BIBF as merely a replacement for LUNA; the facility descriptions instead present it as a complement to LUNA, with dedicated solid-target and windowless gas-target stations and a program extending from direct nuclear astrophysics to detector calibration, applied-physics studies, fundamental-symmetry tests, and proposed beyond-the-Standard-Model searches. ## 2. Accelerator platform, beam production, and transport optics In the nuclear-physics workshop report, BIBF is based on a 3.5 MV “Inline” Singletron accelerator manufactured by HVEE. The accelerator body includes an ion source at ground potential, a 3.5 MV high-voltage column, a first $90^\circ$ bending magnet for mass separation, a short switchyard where gas or solid targets may be installed, and a second $90^\circ$ analyzer feeding one of two target stations. In the light-scalar study, the facility is instead described as built around a 3.5 MV tandem accelerator originally developed in the LUNA program, connected to a straight 6 m transfer line with three $45^\circ$ analyzing magnets and two differential-pumping stages [2512.19059; 2509.03486]. This suggests that the literature is documenting different operational descriptions or beamline emphases rather than a single uniformly presented layout. The ion species explicitly listed for the facility are $\mathrm{H}^+$, $\mathrm{H}_2^+$, $\mathrm{H}_3^+$, $\mathrm{He}^+$, and $\mathrm{C}^+$. Typical beam currents at the target entrance are up to 1 mA for protons, 0.5 mA for helium, and 0.15 mA for carbon. The accelerator delivers up to 3.5 MeV terminal voltage with a ripple of 30 V pp and long-term stability better than 20 V over days, while adjustable ion optics allow final beam energies between a few hundred keV per nucleon and 3.5 MeV per charge. The source and focusing elements are water-cooled or $\mathrm{LN}_2$ cooled to ensure temperature stability and beam emittance $\sim 0.5 \pi \ \mathrm{mm \ mrad}$ [2512.19059]. The scalar-boson proposal gives a more run-specific operating picture for proton mode: beam energies from threshold up to 3.5 MeV, a typical physics run at $E_p \simeq 3$ MeV, terminal-voltage variation in steps of about 1–2 keV over the 0.1–3.5 MeV range, maximum DC proton current $I_p \le 1$ mA with nominal 0.5–1.0 mA in extended runs, energy stability better than 1 keV over multi-hour runs, energy spread $\Delta E/E \simeq 10^{-4}$, and an essentially continuous-wave duty cycle with scheduled interruptions only for beam tuning or maintenance, corresponding to less than 5% downtime [2509.03486]. Beam transport downstream of the bending system employs quadrupole doublets and triplets to tailor the beam spot on target to diameters down to 1–2 mm, with Faraday cups, beam-profile monitors, optical viewers, and collimators supporting reproducible steering and alignment [2512.19059]. ## 3. Target stations, diagnostics, and detector infrastructure The facility is organized around two beam lines and two target environments. Solid-target and windowless gas-target stations are installed on these beam lines, and the gas-target station can be configured either for nuclear-astrophysics experiments or for detector-calibration and applied-physics studies. Upstream beamline vacuum is maintained at $10^{-6}$ mbar, while target chambers operate at $10^{-5}$ mbar or, for the gas target, at mbar-level pressures in the interaction region with differentially pumped stages. In the scalar-search configuration, the beamline is housed in a stainless-steel vacuum tank with outer dimensions $2 \ \mathrm{m} \times 0.6 \ \mathrm{m}$, the target chamber has diameter 50 cm and length 60 cm, and the beamline and chamber reach approximately $10^{-7}$ mbar and $10^{-6}$ mbar under beam, respectively [2512.19059; 2509.03486]. At the solid-target station, the beam stop can be either an $\mathrm{LN}_2$-cooled copper-strip calorimetric beam stop or a water-cooled Faraday cup. A movable flange can host HPGe detectors with 100–140% relative efficiency, plastic and BGO anti-Compton shields, or large-area Si drift-detector arrays consisting of 64 channels of 1 mm-thick SDDs with 190 eV FWHM at 8 keV. The gas-target station includes a windowless, differentially pumped He or $\mathrm{H}_2$ gas cell, an internal beam calorimeter for current measurement, an array of eighteen ${}^3\mathrm{He}$ counters embedded in polyethylene moderators with approximately 40% neutron-detection efficiency, and three HPGe detectors in close geometry for prompt $\gamma$-ray capture studies. A separate BGO array of six 28 cm-long prisms forms a segmented $4\pi$ calorimeter with 11% energy resolution at 1.33 MeV, explicitly intended for radiative-capture measurements [2512.19059]. The facility also incorporates low-background signal-processing and shielding subsystems. Fast digitizers at 3.2 GS/s coupled to AI-based classifiers distinguish single-site from multi-site and noise pulses in HPGe and BEGe detectors, suppressing electronic and environmental backgrounds at the few-counts-per-day level. Multi-tier passive shields of 25 cm OFHC lead plus 1 cm electrolytic copper, enclosed in nitrogen-flushed boxes, reduce $\gamma$ background by approximately $10^{-5}$ below 2 MeV, while polyethylene layers reduce environmental neutrons [2512.19059]. In the scalar-boson proposal, local passive shielding around the beamline is specified as 30 cm of low-activity lead and 5 cm of borated polyethylene, with the vacuum tank also serving as a Faraday cage for electromagnetic isolation [2509.03486]. This suggests a program-dependent shielding configuration superposed on the core underground low-background environment. A specialized thick-target configuration is described for proton-induced rare-event production. In that setup, the proton beam impinges on a solid, self-supporting $\mathrm{TaF}_ Source: https://www.emergentmind.com/topics/bellotti-ion-beam-facility