Simulation And Experimental Studies On Highly Charged Laser Ion Source And Direct Plasma Injection

With the developments of relevant research fields of heavy ion beam, there is an urgent demand for beams with higher energy, intensity and better quality. It is a challenge for heavy ion accelerator facility and ion sources. At present, laser ion source(LIS) is one of the ion sources that may satisfy the demands, which can provide pulsed beam with highest intensity within microseconds time, especially the refractory metal elements. But the beam’s quality, stability and repeatability of LIS are bad, and also the ions’ energy spread is too large. Generally, the beam properties of LIS are mainly determined by the initial conditions of the laser produced plasma, which changes a lot under different laser, target and lens parameters. Then detailed studies of the influence of above parameters were carried out in this dissertation. Also, the direct plasma injection scheme(DPIS) was simulated and simulation results were partially verified by experiments. These works on optimizing the abundance of highly charged ions were fundamental research for the demand of HIAF accelerator and were also very meaningful for the injector’s development of heavy ion cancer therapy facility.LIS has produced several ion species(C, Al, Ti, Ni, Ag, Ta and Pb) with beam intensity magnitude of m A and pulse width of several μs at IMP, and the maximum charge states observed in our experiments were C6+, Al12+, Ti16+, Ni19+, Ag21+, Ta13+ and Pb12+ respectively. A series of experiments were carried out on carbon target to optimize the yield of C6+ by changing the incident laser energy, angle, wave lengthet al. The results showed that larger energy, fundamental frequency and small incident angle were helpful to increase the beam intensity and abundance of highly charged ions.The particle number reached 5x1010 ppp after optimization. It was confirmed that the beam fluctuation, less than 5%, was mainly affected by manipulator system, and lens with longer focus length could improve the stability of ion source. A double pulse laser was constructed with pulse delay ns and energy ratio could be changed continuously online, which has been approved effectively to increase the charge yield and DPIS efficiency. We also simulated the process of laser plasma interaction qualitatively using fluid model, then the simulation results were compared with the experimental ones.The ions produced by LIS after preliminary acceleration with DPIS method may satisfy the demand of single turn injection of synchrotron, so we investigated and studied this injection method. A C6+ beam with peak current 13 m A, energy 593 ke V/u has been accelerated successfully by DPIS. Because the extracted beam of LIS was a pulsed one, we calculated each prifile as dc beam in DPIS simulation. Both the simulation and experiment results show that the transmisson efficiency of C6+ after RFQ is less than 40% and the beam pulse width is shorter after acceleration. Also, the extracion electrode and plasma drift distance were optimized by simulation, at the other hand, ion beam injection by double pulse laser, electrostatic or magnetic lenses were discussed. The simulation results showed that the particle number of C6+ captured by RFQ would be four to five times larger after optimization, as much as 1010 ppp, which need to be verified by experiments in the future. Overall, DPIS method may satisfy the single turn injection of cancer therapy facility and is very meaningful for miniaturization of it.