Laser Ablation Plasma With Solenoid Confinement

High density high temperature plasma can be produced by focusing a high power laser beam onto a solid surface,which can be used as a source of abundant species of particles,including electrons,ions and photons.In 1969,the idea of using laser-produced plasma as a source of ion for particle accelerator injection were proposed by Peacock and Pease and by Byckovsky.Compared with other kinds of highly charge ion sources,laser ion sources can generate much denser ion pulses with shorter pulse durations.For example,a laser ion source,driven by a nanosecond laser of the energy of joules,can deliver pulsed ion beams with the pulse duration of sub-?s and current density in the order of 10 m A/cm~2at the distance of 1 m away from the target surface.Another advantage of laser ion sources is they can produce ions of refractory elements,while for other kinds of highly charged ion sources,like ECR ion sources and EBIS,to produce such kind of ions,some special techniques must be applied to generate corresponding vapor of low charge state ions firstly,which is usually a technical challenge.In terms of the yields of highly charged ions of laser ion sources,they are the most promising ion sources to meet the require-ment of synchrotrons for the single-turn injection mode.However,the repeatability of laser ion sources is usually poor and the ion pulse duration,in the range of sub-?s to?s,is too short for efficient coupling of a laser ion source and the downstream accelerators,which limited the application of laser ion sources in accelerators.In recent years,the repeatability and stability of laser ion sources have been improved efficiently due to the development of the technology of solid lasers and target manipulation systems.So,the too short pulse duration becomes the major obstacle for the application of laser ion sources.The ion pulse duration of a laser ion source originates from the spread of the ex-panding velocity of the plasma,which depends on the laser power density on the target surface.Therefore,the ion pulse duration is proportional to the expanding length of the plasma with the current density of the ion beams is inversely proportional to the cube of the length.Hence,to get a reasonable ion pulse duration from a laser ion source,people usually extract the ion beams at a distance meters away from the target surface sacrificing quite a part of the ions.To solve the contradiction of the pulse duration and current density,a solenoid was introduced to the plasma expanding region,which can confine the plasma and hence modify the relationship between the pulse duration,cur-rent intensity and the expanding length.The experiments and simulations were carried out to investigate the confinement of the laser produced plasma by a solenoid.The experimental studies of this thesis are composed of two parts:one is about a laser ion source itself with the confinement of a solenoid and the other is about the acceleration of laser-produced carbon ions by a RFQ with the direct plasma injection scheme combined with the confinement of a solenoid.During the first part research,a long solenoid was designed,fabricated and in-stalled at the research platform of the laser ion source at IMP.The effect of the solenoid on the carbon and aluminum plasma was investigated.It was shown that the total charge and peak current of the ion pulses increased with the increasing magnetic field and then saturated.And the more important is that the pulse duration exhibits showed the same trend.This result indicates that the divergence of the laser-produce plasma is com-pressed by the magnetic field.A movable Faraday cup was developed to measure the transverse and longitudinal distributions of the confined plasma.The evolution of the plasma in the magnetic field was derived from the measurement,which shows that the longitudinal distribution of the plasma got more uniform compared with that without magnetic field.These results are of importance for improving the coupling efficiency between the laser ion source and the downstream accelerator.The charge state distribu-tions of the carbon plasma were measured at the different distances from the exit of the solenoid and compared with those without magnetic field.It was shown that all charge states were increased by the magnetic field but to different extent.The repeatability of the laser ion source with the magnetic confinement was investigated.There was no additional instability when the magnetic field of hundreds of Gauss was applied.A solenoid was also applied in the direct plasma injection scheme,in which the laser produced plasma expands until the entrance of the RFQ and then extracted and injected into the RFQ at the same position.The current intensity and pulse duration at the exit of the RFQ increased by a factor of 2?3.This result is meaningful for the development of the compact and low-cost ion injector based the direct plasma injection scheme.In addition,the simulations of the magnetic confinement of laser-produce plasma were carried out.To get the initial conditions of laser-produced plasma,the FLASH code was applied at first.And the output results were used as the input parameter of an-other simulation software,WARP,to simulate the evolution process of the laser-produce plasma in the solenoid.The results were consistent with the experimental results.That means the simulation procedure is reliable.The experiments and simulations about solenoid confined laser ablation plasma ex-pands our understanding of the characteristics of magnetic confinement laser produced plasma.With the modulation of the laser ion beam by magnetic confinement,the laser ion source will be greatly promoted as a pre-injection system for heavy ion accelerators to be applied to future accelerator devices and heavy ion cancer therapy devices.