The Nb_(3)Sn thin film cavity,having the potential to be operated at a higher temperature and higher gradient compared to the cavity made from bulk niobium,is one of the most promising key technologies for the nextgen...The Nb_(3)Sn thin film cavity,having the potential to be operated at a higher temperature and higher gradient compared to the cavity made from bulk niobium,is one of the most promising key technologies for the nextgeneration radio-frequency superconducting accelerators.In our work,several 1.3 GHz single-cell TESLA-shaped Nb_(3)Sn thin film cavities,coated by the vapor diffusion method,were tested at Peking University and Institute of Modern Physics,Chinese Academy of Sciences.It was observed that the performance of the Nb_(3)Sn thin film cavities in the tests without the slow cooling down procedure and the effective magnetic field shielding was significantly improved by using a low temperature baking at 100℃for 48 hours.Although the peak electric field of the cavity remained unchanged,the rapid drop of the unloaded Q value(Q0)with the increasing accelerating field(Q-slope)was effectively eliminated,resulting in an improvement of the Q0 in the intermediate field region by~8 times.Furthermore,under better test conditions with the shielded magnetic field less than 5 mG and the slow cooling down procedure in the temperature range of 25-15 K,the Q0 was still improved by about 20%.Our study shows that the low temperature baking can be an effective supplement to the effective post-treatment for the Nb_(3)Sn thin film cavity.展开更多
Low-temperature synthesis of Nb_(3)Sn thin-film cavity is of great significance in the field of superconducting radio frequency(SRF).The bronze process can grow only stable Nb_(3)Sn phase at 700℃,so it is considered ...Low-temperature synthesis of Nb_(3)Sn thin-film cavity is of great significance in the field of superconducting radio frequency(SRF).The bronze process can grow only stable Nb_(3)Sn phase at 700℃,so it is considered to be the most promising process for low-temperature synthesis of Nb3Sn thin-film cavity.We successfully fabricated the worldwide first Nb_(3)Sn thin-film cavity by bronze process.We technically solved the key problems of precursor preparation,characterized and analyzed the uniformity of the Nb_(3)Sn film,and tested the performance of the cutout samples and the whole cavity of the Nb_(3)Sn film.It is obtained that the Q0value of the cavity at 4.2 K is about 1.2×10^(9),which is greater than the performance of the bulk-niobium cavity under the same conditions.This result means that the preparation of Nb_(3)Sn by bronze process has the great potential to more practical copper-based Nb_(3)Sn thin-film cavity,which is expected to achieve a substantial improvement in the performance of SRF cavity and comprehensive engineering applications.展开更多
For the application of high intensity continuous wave （CW） proton beam acceleration, a new superconducting accelerating structure for extremely low β protons working in TE210 mode has been proposed at Peking Univer...For the application of high intensity continuous wave （CW） proton beam acceleration, a new superconducting accelerating structure for extremely low β protons working in TE210 mode has been proposed at Peking University. The cavity consists of eight electrodes and eight accelerating gaps. The cavity＇s longitudinal length is 368.5 mm, and its transverse dimension is 416 mm. The RF frequency is 162.5 MHz, and the designed proton input energy is 200 keV. A peak field optimization has been performed for the lower surface field, The accelerating gaps are adjusted by phase sweeping based on KONUS beam dynamics. The first four gaps are operated at negative synchronous RF phase to provide longitudinal focusing. The subsequent gaps are 0° sections which can minimize the transverse defocusing effect. Solenoids are placed outside the cavity to provide transverse focusing. Numerical calculation shows that the transverse defocusing of the KONUS phase is about three times smaller than that of the conventional negative synchronous RF phase. The beam dynamics of a 10 mA CW proton beam is simulated by the TraceWin code. The simulation results show that the beam＇s transverse size is under effective control, while the increase in the longitudinal direction is slightly large. Both the TraceWin simulation and the numerical calculation show that the cavity has a relatively high effective accelerating gradient of 2.6 MV/m. On the whole, our results show that this new accelerating structure may be a possible candidate for superconducting operation at such a low energy range.展开更多
An Accelerator Driven System（ADS） has been launched in China for nuclear waste transmutation. For the application of high intensity proton beam acceleration, the quadrupole asymmetry effect needs to be carefully eva...An Accelerator Driven System（ADS） has been launched in China for nuclear waste transmutation. For the application of high intensity proton beam acceleration, the quadrupole asymmetry effect needs to be carefully evaluated for cavities. Single spoke cavities are the main accelerating structures in the low energy front-end. The single spoke cavity has small transverse electromagnetic field asymmetry, which may lead to transverse RF defocusing asymmetry and beam envelope asymmetry. A superconducting single spoke resonator（PKU-2 Spoke） of β=0.12 and f =325 MHz with a racetrack-shaped inner conductor has been designed at Peking university. The study of its RF field quadrupole asymmetry and its effect on transverse momentum change has been performed. The quadrupole asymmetry study has also been performed on a β=0.12 and f =325 MHz ring-shaped single spoke cavity. Our results show that the quadrupole asymmetry is very small for both the racetrack-shaped and the ring-shaped single spoke cavity.展开更多
基金Supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2020410)the Major Research Plan of National Natural Science Foundation of China(Grant No.91426303)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)the National Postdoctoral Program for Innovative Talents(Grant No.BX201700257).
文摘The Nb_(3)Sn thin film cavity,having the potential to be operated at a higher temperature and higher gradient compared to the cavity made from bulk niobium,is one of the most promising key technologies for the nextgeneration radio-frequency superconducting accelerators.In our work,several 1.3 GHz single-cell TESLA-shaped Nb_(3)Sn thin film cavities,coated by the vapor diffusion method,were tested at Peking University and Institute of Modern Physics,Chinese Academy of Sciences.It was observed that the performance of the Nb_(3)Sn thin film cavities in the tests without the slow cooling down procedure and the effective magnetic field shielding was significantly improved by using a low temperature baking at 100℃for 48 hours.Although the peak electric field of the cavity remained unchanged,the rapid drop of the unloaded Q value(Q0)with the increasing accelerating field(Q-slope)was effectively eliminated,resulting in an improvement of the Q0 in the intermediate field region by~8 times.Furthermore,under better test conditions with the shielded magnetic field less than 5 mG and the slow cooling down procedure in the temperature range of 25-15 K,the Q0 was still improved by about 20%.Our study shows that the low temperature baking can be an effective supplement to the effective post-treatment for the Nb_(3)Sn thin film cavity.
基金supported by the National Natural Science Foundation of China(Grant Nos.12075295 and 12105335)。
文摘Low-temperature synthesis of Nb_(3)Sn thin-film cavity is of great significance in the field of superconducting radio frequency(SRF).The bronze process can grow only stable Nb_(3)Sn phase at 700℃,so it is considered to be the most promising process for low-temperature synthesis of Nb3Sn thin-film cavity.We successfully fabricated the worldwide first Nb_(3)Sn thin-film cavity by bronze process.We technically solved the key problems of precursor preparation,characterized and analyzed the uniformity of the Nb_(3)Sn film,and tested the performance of the cutout samples and the whole cavity of the Nb_(3)Sn film.It is obtained that the Q0value of the cavity at 4.2 K is about 1.2×10^(9),which is greater than the performance of the bulk-niobium cavity under the same conditions.This result means that the preparation of Nb_(3)Sn by bronze process has the great potential to more practical copper-based Nb_(3)Sn thin-film cavity,which is expected to achieve a substantial improvement in the performance of SRF cavity and comprehensive engineering applications.
基金Supported by Major Research Plan of National Natural Science Foundation of China(91026001)
文摘For the application of high intensity continuous wave （CW） proton beam acceleration, a new superconducting accelerating structure for extremely low β protons working in TE210 mode has been proposed at Peking University. The cavity consists of eight electrodes and eight accelerating gaps. The cavity＇s longitudinal length is 368.5 mm, and its transverse dimension is 416 mm. The RF frequency is 162.5 MHz, and the designed proton input energy is 200 keV. A peak field optimization has been performed for the lower surface field, The accelerating gaps are adjusted by phase sweeping based on KONUS beam dynamics. The first four gaps are operated at negative synchronous RF phase to provide longitudinal focusing. The subsequent gaps are 0° sections which can minimize the transverse defocusing effect. Solenoids are placed outside the cavity to provide transverse focusing. Numerical calculation shows that the transverse defocusing of the KONUS phase is about three times smaller than that of the conventional negative synchronous RF phase. The beam dynamics of a 10 mA CW proton beam is simulated by the TraceWin code. The simulation results show that the beam＇s transverse size is under effective control, while the increase in the longitudinal direction is slightly large. Both the TraceWin simulation and the numerical calculation show that the cavity has a relatively high effective accelerating gradient of 2.6 MV/m. On the whole, our results show that this new accelerating structure may be a possible candidate for superconducting operation at such a low energy range.
基金Supported by Major Research Plan of National Natural Science Foundation of China(91026001)
文摘An Accelerator Driven System（ADS） has been launched in China for nuclear waste transmutation. For the application of high intensity proton beam acceleration, the quadrupole asymmetry effect needs to be carefully evaluated for cavities. Single spoke cavities are the main accelerating structures in the low energy front-end. The single spoke cavity has small transverse electromagnetic field asymmetry, which may lead to transverse RF defocusing asymmetry and beam envelope asymmetry. A superconducting single spoke resonator（PKU-2 Spoke） of β=0.12 and f =325 MHz with a racetrack-shaped inner conductor has been designed at Peking university. The study of its RF field quadrupole asymmetry and its effect on transverse momentum change has been performed. The quadrupole asymmetry study has also been performed on a β=0.12 and f =325 MHz ring-shaped single spoke cavity. Our results show that the quadrupole asymmetry is very small for both the racetrack-shaped and the ring-shaped single spoke cavity.
