Independent research and development and innovative applications of high-intensity proton cyclotrons toward serialization

Cyclotrons are indispensable scientific equipment and platforms for cutting-edge research and are widely applied in nuclear science and life science, as well as the innovative development of nuclear technology. The difficulties and corresponding key technologies of compact high-intensity proton cyclotron research are fourfold: the insufficient axial focusing force of a compact cyclotron frustrates improvements in beam energy and beam intensity; the smelting capacity of large-scale magnets and modern manufacturing restricts magnetic field accuracy, which affects the dynamic performance of high-intensity beams; high-beam dynamic loads and coupling resonance considerably influence the stable operation of cyclotrons; and high-intensity negative hydrogen ion sources, the coupling of multiple physical fields in the narrow space of the central region, and the high-precision six-dimensional matching of beam optics in the extraction region are also great challenges for compact high-intensity cyclotrons. To solve these problems, a strong focusing theory of radially modulated magnetic field gradients was innovatively created by a cyclotron team at the China Institute of Atomic Energy (CIAE), and a parallel computing algorithm and software for multi-cluster high-intensity beam dynamics were also invented. These innovations extend the acceleration energy limit of compact cyclotrons and help increase beam intensity substantially under the restriction of space charges. A magnet shimming algorithm for isochronous fields and nonideal harmonic fields, based on the shape function of odd and even triangles, was developed to improve axial focusing effectively and solve problems in magnet engineering. Key RF technologies, such as suppression of "transmission line-resonator" system coupling oscillation and dynamic loading changes, were researched, and then a long-term operation with high stability was achieved for the entire machine. A high-intensity cyclotron prototype with strong focusing was built based on these innovations, effectively promoting the beam intensity of miniaturized cyclotrons from 50-100 mu A to 300-500 mu A. Subsequently, more than ten high-intensity compact cyclotrons have been developed at the CIAE, and these cyclotrons can provide beam intensity at the mA order after necessary upgrades. The main performance indexes of the cyclotrons, such as intensity, injection efficiency, and extraction efficiency, are world-class. Cyclotron applications are also applied in the projects of the CIAE, National Space Science Center, Irradiation Hardening Application Technology Innovation Center, and Peking University and contribute much to scientific research. We provide proton beams for similar to 100 units to perform scientific and technological research related to nuclear technology and its applications. The research and applications prompt the development of high-intensity proton cyclotrons.