High-Intensity Heavy-Ion Accelerator Facility (HIAF)

Updated 18 November 2025

HIAF is a flagship heavy-ion accelerator complex at IMP, CAS that delivers high-current proton and heavy-ion beams for advanced studies in nuclear physics, rare isotope science, and muon research.
The facility employs fast-cycled superferric dipole magnets and sophisticated beam dynamics with slice optics, ensuring precise control of high-intensity beams and resonance mitigation.
HIAF supports diverse experimental programs including heavy-ion collisions, rare isotope and hypernucleus experiments, muon and neutrino research, and plasma wakefield acceleration R&D.

The High-Intensity Heavy-Ion Accelerator Facility (HIAF) is a flagship accelerator complex developed at the Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS), designed to deliver high-current proton and heavy-ion beams from the injection regime up to multi-GeV per nucleon energies. It provides a platform for forefront research in high-energy nuclear physics, rare isotope science, high-density QCD matter, and advanced accelerator technologies. The facility is engineered for maximal flexibility and intensity, supporting precision experiments with rare isotopes, hypernuclei, exotic atoms, muons, and multi-messenger nuclear observables.

1. Facility Architecture, Subsystems, and Magnet Technology

HIAF consists of a superconducting ECR ion source (SECR), a superconducting linac (iLinac, 17 MeV/u for U³⁵⁺), a rapid-cycling Booster Ring (BRing, 569 m circumference, Bρ≤34 T·m), a High-Energy FRagment Separator (HFRS, 192 m two-stage beamline, Bρ≤25 T·m, angular acceptance x′=±30 mrad, y′=±25 mrad, Δp/p=±2%), a high-precision Spectrometer and Storage Ring (SRing), and terminal experimental halls—e.g., the Huizhou Hadron Spectrometer (HHaS) (An et al., 29 Apr 2025, Xu et al., 28 Feb 2025).

A defining feature is the deployment of fast-cycled superferric dipole magnets with warm iron and superconducting NbTi/Cu cable windings (operated at 4.2 K). The field reaches up to 2.25 T in a 2.6 m effective length with a vertical gap of 120 mm; ramp rates to 1.125 T/s are achieved, reducing ring circumference and supporting high extraction repetition rates. The coil/cryostat system employs 316L/316LN stainless, a 30-layer thermal shield at 80 K, and an assembly of twelve G10 rods at coil corners plus two Ti-alloy mid-span struts to control stress (<60% of material limits), thermal contraction (≈2.6 mm per support on cooldown), and vacuum loading (cryostat deformation <0.5 mm during evacuation) (Zhang et al., 2015). Finite-element mechanical analyses verify safety factors >1.5 for quench prevention.

The injector system includes a normal-conducting IH-DTL (81.25 MHz), accelerating 238U³⁴⁺ from 0.35 to 1.3 MeV/u (5.0 emA) with a 2.678 m tank (average gradient ≈2.48 MV/m, transmission 94.95%, normalized RMS emittance growth ≈8.0%) using KONUS beam dynamics and magnetic quadrupole triplets delivering up to 98 T/m (Dou et al., 2013).

Table 1. Representative Magnet System Parameters

Component	Value/Description	Reference
Dipole field, gap	2.25 T, 120 mm	(Zhang et al., 2015)
Ramp rate	1.125 T/s	(Zhang et al., 2015)
NB coil/magnet support	12 G10 rods, 2 Ti-alloy struts	(Zhang et al., 2015)
IH-DTL (U³⁴⁺) gradient	2.48 MV/m avg, 10.2 MV/m peak	(Dou et al., 2013)

2. Beam Dynamics, Lattice Design, and Optics Control

BRing operates with a three-superperiod FODO lattice: each arc contains 16 dipoles and 16 quadrupoles, straights have 10 quadrupoles. Nominal working points are Qₓ=9.470, Qᵧ=9.430. High-fidelity beam dynamics are achieved by slicing each dipole/quadrupole into hundreds of segments according to measured B(z) profiles; this enables modeling of fringe fields, field overlap, and longitudinal inhomogeneities. Sliced models (as implemented in the LACCS control/TAO/MAD-X) display residual tune shifts of ΔQₓ≈−0.036, ΔQᵧ≈−0.024, and β-function deviations |Δβ/β|≲0.5%, with dispersion variations <0.1 m in the straights (Wang et al., 10 Jun 2025, Wang et al., 16 Oct 2025).

Slice optics reduce the horizontal closed-orbit RMS distortion by an order of magnitude (to ≈5×10⁻⁴ m) compared to ideal models and expand the dynamic aperture by 30–50% before chromaticity correction; after applying sextupole families (ξₓ=ξᵧ=0), the acceptance is comparable to the original lattice. Betatron- and dispersion-function variations under alignment/field errors are kept at the 10⁻³–10⁻² m level, and sensitivity to alignment is minimized, optimizing online tune feedback and resonance avoidance during beam commissioning (Wang et al., 16 Oct 2025).

The SHER ring employs a fourfold symmetric FODO cell for large acceptance (30 mm·mrad, Δp/p ≃ ±0.45%) and can operate in "isochronous" mode (γₜ=1.835, αₚ=0.297, βₓ,max=150 m, Dₓ,max≈30 m) for TOF mass spectrometry (resolving power up to 10⁶ with 30 ps TOF detectors), or in a storage/cooling mode (γₜ=3.41, αₚ=0.086, βₓ,max=50 m) for rare isotope collection (Gao et al., 2013).

3. High-Intensity Operation: Space-Charge Dynamics, Injection, and Stacking

High-intensity operation is enabled by multi-turn stacking using fixed barrier bucket (BB) injection and electron cooling, achieving up to 5.8×10¹¹ U³⁴⁺/cycle with six injections (96.5% stacking efficiency). Electron cooling (15 m cooling length, I_e=1.5 A at θ=0.55 mrad crossing) stabilizes emittance at ≈30 π mm mrad, with the Laslett tune shift maintained at ΔQ_sc≈−0.078, below resonance thresholds. The barrier bucket system forms momentum wells of (Δp/p)_max≈2.5×10⁻⁴ (with V_peak=1000 V, η=−0.008), and the cycle employs a fast switched "flat-top" for injection, cooling, and capture (Shen et al., 2016).

Resonance crossing due to space charge and field imperfections is mitigated via space-charge–Twiss–modified resonance driving terms (RDTs). Implementing compensation based on these "modified RDTs" reduces half-integer and third-order resonance-induced emittance growth by >90% for relevant beam parameters (Δν_{sc, x/y}∼0.05–0.4). This approach raises usable beam current by 20–30% before the onset of space-charge–induced limits (Guo et al., 4 Aug 2024).

4. Experimental Capabilities: Rare Isotope, Hypernuclear, Muon, and Precision Physics

HIAF supports a comprehensive research program:

Heavy-ion collisions and the nuclear EOS: Fixed-target experiments (1–2 AGeV/nucleon) explore the QCD phase diagram at high baryon density; Fermi-energy collisions (30–50 MeV/nucleon) enable symmetry energy extraction via n/p and π⁻/π⁺ observables, with proton and heavy-ion beams up to intensities of 10¹² p/s and 10¹⁰–10¹¹ ions/s, respectively (Nagamiya, 2022, Feng, 2018).
Rare isotope and hypernucleus science: The LQMD transport model guides experiments tagging neck fragmentation, isospin diffusion, kaon/hyperon production, and multi-strangeness hypernuclei at moderate and high energies, using advanced fragment separators, storage rings, and 4π detectors (Feng, 2018).
Muon beams and rare process detection: The HFRS delivers up to 8.2×10⁶ μ⁺/s at 3.5 GeV/c (purity ~2%) and 4.2×10⁶ μ⁻/s at 1.5 GeV/c (purity ~20%). Purification schemes deliver 10⁵ μ/s at 100% purity, supporting muon tomography and BSM searches (e.g., μ→eγγ, μ–N→e–N conversion down to 10⁻¹⁹). Muonic atom spectroscopy and other high-precision muon studies are enabled by X-ray MMCs/TES with ∼1 eV resolution (Xu et al., 28 Feb 2025, An et al., 29 Apr 2025).
Neutrino and neutron science: HIAF supports HIAF-to-JUNO neutrino beams (L=260 km, 3.78×10²² POT/yr, δ_CP reach ~10°) and coherent elastic ν–N scattering in high-mass CsI(Na) detectors, as well as neutron β-decay symmetry tests (An et al., 29 Apr 2025).
Precision tests of symmetries/quantum nuclear effects: Programs include 0νββ nuclear matrix element support, atomic EDM limits (Schiff moments to 10⁻³⁰ e·cm), quantum tomography, and tests of quantum correlations and entanglement (An et al., 29 Apr 2025).

5. Advanced Applications: Plasma Wakefield Acceleration and Accelerator Technology R&D

HIAF heavy-ion beams have been simulated as drivers for plasma wakefield acceleration (PWFA). A ^{209Bi⁸³⁺} bunch at 9.58 GeV/u and σ_r=0.1 mm excites stable wakefields up to 6 GV/m in plasma (density n_0=2.8×10¹⁵ cm⁻³), enabling acceleration of electron bunches from 16 MeV to 675 MeV within a meter of plasma. GV/m-level fields are sustained due to high beam charge and mass, with stable wake evolution and tolerable dephasing lengths. The facility supports proof-of-principle PWA experiments coupling the high-intensity heavy-ion delivery line with plasma cells and electron injectors (Li et al., 17 Jun 2025).

Key technical advances at HIAF include the use of superferric, fast-cycled superconducting dipoles, KONUS-based IH-DTL acceleration for efficient injector operation, online lattice correction with high-fidelity slice models, and integration of advanced space-charge compensation methodologies.

6. Collaborations, Strategic Position, and Future Directions

HIAF constitutes a cornerstone of China’s high-precision physics infrastructure, aligned with the Accelerator-Driven Subcritical System (CiADS) and projected CNUF expansion. The facility enables unique synergies across hadron, muon, neutrino, neutron, and quantum nuclear science. International collaboration frameworks involve leading laboratories at J-PARC, PSI, ORNL, NUMEN@LNS-INFN, JLab, FAIR, NICA, and DESY.

Strategically, HIAF fills the mid-energy accelerator gap (1–10 GeV/u) between FAIR and NICA, and is the sole Asian installation combining high-intensity heavy-ion, muon, neutrino, and cold-neutron programs. It is positioned to support large-scale, medium-, and small-scale projects, including the Super η Factory, muon cLFV searches, 3D nucleon tomography, quantum entanglement in nuclei, and advanced nuclear detectors (An et al., 29 Apr 2025).

7. Timeline, Milestones, and Operational Outlook

Construction of the major subsystems was completed by 2025, with commissioning targeting autumn 2025 and full operation by 2027. Early physics campaigns will initially focus on beam intensity maximization, optics verification, and pilot rare-isotope and muon beam experiments. The roadmap foresees integration and expansion towards multi-GeV/u uranium acceleration (CNUF), and the realization of precision flagship experiments in hadron structure, fundamental symmetries, rare decay searches, and plasma-based advanced acceleration.

References:

(Zhang et al., 2015, Dou et al., 2013, Wang et al., 16 Oct 2025, Wang et al., 10 Jun 2025, Li et al., 17 Jun 2025, Xu et al., 28 Feb 2025, Gao et al., 2013, Shen et al., 2016, Nagamiya, 2022, Feng, 2018, An et al., 29 Apr 2025, Guo et al., 4 Aug 2024)