In the magnetic field measurement of accelerator magnets, efficient and accurate positioning of the magnetic field measurement system and the magnet is a critical process. By analyzing the mechanical structure and working principle of harmonic coil magnetic field measurement system, an automatic positioning technology is proposed in this research for the high-precision and fast positioning of multipole magnet and harmonic coil magnetic field measurement system. Through the special design and comprehensive application of multi-camera photogrammetry system, control system and six-degree-of-freedom (6DoF) attitude automatic adjustment system, fast non-contact measurement and automatic attitude adjustment of harmonic coil magnetic field measurement system and multipole magnet can be realized. The proposed automatic positioning system and operation scheme can not only save labor costs, but also improve the reliability of harmonic coils and the positioning efficiency of magnetic field measurement system. The proposed research can also monitor the position changes of the harmonic coil and the multipole magnet in the magnetic field measurement process in real time through the multi-camera photogrammetry system, and further control the accuracy of the magnetic field measurement of the harmonic coil.
The design, construction, and commissioning of a conduction-cooled Nb3Sn demonstration superconducting radio frequency (SRF) electron accelerator at the Institute of Modern Physics of the Chinese Academy of Sciences (IMP, CAS) will be presented. In the context of engineering application planning for Nb3Sn thin-film SRF cavities within the CiADS project, a 650MHz 5-cell elliptical cavity was coated using the vapor diffusion method for electron beam acceleration. Through high-precision collaborative control of 10 GM cryocooler, slow cooldown of the cavity crossing 18K is achieved accompanied by obviously characteristic magnetic flux expulsion. The horizontal test results of the liquid helium-free (LHe-free) cryomodule show that the cavity can operate steadily at Epk=6.02MV/m in continuous wave (CW) mode, and at Epk=14.90MV/m in 40% duty cycle pulse mode. The beam acceleration experiment indicates that the maximum average current of the electron beam in the macropulse after acceleration exceeds 200mA, with a maximum energy gain of 4.6MeV. The results provide a principle validation for the engineering application of Nb3Sn thin-film SRF cavities, highlighting the promising industrial application prospects of a small-scale compact Nb3Sn SRF accelerator driven by commercial cryocoolers.
A 325 MHz aluminum prototype of a spatially periodic rf quadrupole focusing linac was developed at the Institute of Modern Physics, Chinese Academy of Sciences, as a promising candidate for the front end of a high-current linac. It consists of an alternating series of crossbar H-type drift tubes and rf quadrupole sections. Owing to its special geometry, cavity fabrication is a major hurdle for its engineering development and application. In this paper, we report the detailed mechanical design of this structure and describe its fabrication process, including machining, assembly, and inspection. The field distribution was measured by the bead-pull technique. The results show that the field errors of both the accelerating and focusing fields are within an acceptable range. A tuning scheme for this new structure is proposed and verified. The cold test process and results are presented in detail. The development of this prototype provides valuable guidance for the application of the spatially periodic rf quadrupole structure.
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