Study On Production And Manipulation Of Intense Pulsed Ion Beams From High Charge State ECR Ion Source

The production of intense pulsed beams of high charged ions is a key technology to improve the performance of synchrotron.In order to fulfill the demands for the high-intensity heavy ion accelerator developing,the beam intensities and charge states of the extracted ion beams from ECR（electron cyclotron resonance）ion sources have to be further improved.Meanwhile,considering the characteristics of synchronization operation,the Afterglow mode which can produce intense pulsed beams of highly charged ions will be more suitable for ECR ion source operation than the traditional CW（Continuous Wave）mode.Based on the theoretical simulation,the effects of plasma parameters on Afterglow beam are studied in this thesis which are consistent with the current basic understanding of ECR ion source physics.At the same time,the model also points out that improving electron density,decreasing ion temperature and enhancing the magnetic field confinement are the key technologies to enhance Afterglow beam intensity and pulse width significantly.Therefore,a series of intense pulsed beams of high charged ions were obtained on SECRAL II,a third-generation ECR ion source with high microwave frequency and power under double frequency heating,which set a new world record for high-charge beam intensity.In addition,the method of Afterglow beam waveform modulation is proposed and implemented for the first time in this thesis,which proves that bias voltage pulse and secondary frequency microwave are effective experimental techniques to manipulate Afterglow waveform.Finally,the application of Afterglow beam operation on HIRFL project accelerator proves that compared with CW mode,Afterglow mode can further improve the beam intensity accumulated of synchrotron and the beam emittance does not increase significantly.By simulation study,the Afterglow process can be described as follows:after the microwave turns off,the electron loss rate in the ECR plasma is much higher than that of the ions,which will cause the rapid destruction of the potential well which could confine ions.Such,this abrupt increase of（cold）electron loss would lead to an intense burst of highly charged ions in a short time.In the simulation study of this process,the physical model can accurately reflect the effects of ECR plasma parameters on Afterglow beam.Increasing electron density,decreasing ion temperature and enhancing the magnetic field confinement could significantly improve the peak current and pulse width of Afterglow beam,which is consistent with the basic understanding of physical process of ECR ion source.Combined with the double-frequency heating technology,a series of Afterglow beams were generated by the superconducting ECR source SECRAL-II of the Institute of Modern Physics and the normal temperature ion source LECR4 with the unprecedented intensities and high charge states,such as 169 eμA of Xe³⁸⁺,63 eμA of Xe⁴²⁺.Compared with the beam intensity records in CW mode,the gain factor is up to1～4.Meanwhile,the Afterglow peak duration obtained in the SECRAL II ion source reaches 2-3 ms,which meets the demands of HIAF project.The study of the influence of microwave parameters shows that not only the current intensity but also the pulse width of the Afterglow beam will increase with the microwave frequency and power.The experimental results demonstrate that bias voltage pulse and auxiliary frequency microwave can effectively manipulate the waveform of Afterglow beam.Bias pulse can not only change the appearance time of Afterglow beam but also broaden Afterglow waveform.The peak current and pulse width of Afterglow waveforms can also be modulated by secondary microwaves In general,in order to optimize Afterglow beam waveform,the bias disk should be operated in DC mode,and the secondary microwave pulse should turn off with the primary microwave simultaneously.Finally,by adjusting the operating clock signal of the HIRFL accelerator,the SECRAL II ion source can operate stably in Afterglow mode and provide beams to the accelerators.Compared with the CW mode,the beam intensity accumulated in the CSRm storage ring is significantly enhanced:the beam intensity of Bi³⁶⁺increases from 60 eμA to 110 eμA,and the beam intensity of Fe¹⁵⁺increases from 120 eμA to205 eμA.Meanwhile,the emittance measurement results of Afterglow peak beam show that Afterglow mode does not cause significant emittance increase.