Generation Of High Quality Ion Beam Based On Radiation Pressure Acceleration

Compared with the traditional accelerator,the acceleration gradient of the particle acceleration mechanisms that based on laser-plasma interaction is higher,about three magnitudes,which can vastly reduce the size of the accelerator.The charged particle can be accelerated to high energy in a short distance.Therefore,particle accelerator that based on laser plasma interaction has many significant applications in different fields.For example,tabletop accelerator,hadron therapy of oncological diseases,the fast ignition in the inertial confinement fusion,and so on.Due to the high energy transfer efficiency and high quality accelerated ions beam,the radiation pressure acceleration(RPA)is regarded as one of the highest promising ion acceleration mechanisms.Theoretically,high quality ion beam can be obtained through the RPA.But,in reality,there still are problems in realizing theoretical expectations.In this dissertation,two main problems in the RPA are investigated.First one is the terrible self-supporting property of the ultra-thin foil target,which is widely used in the RPA experiments.Second one is the nonuniform radiation on the foil target while using a single transversely Gaussian laser,which leads to the curve of the foil and the development of transverse instability.According to these problems,we put forward the corresponding solutions.The theoretical analysis and the particle-in-cell(PIC)simulations are performed to verify our schemes.The summary is as follows:1.In traditional RPA experiments,the thickness of the ultra-thin foil target is only from tens to hundreds of nanometres,which leads to a terrible selfsupporting property and increases the difficulty of experiment operation.If we want to increase the thickness of the target and enhance the self-supporting property of the target,the best substitution is the near critical density(NCD)target.But,in ultra-high laser intensity region,it is hardly to realize the hole-boring precess in the near critical density target because of the relativistic self-induced transparency.In order to generate high quality ion beams through the stable RPA of the NCD target,we propose a new type of target that an ultra-thin high density(HD)layer is attached to the front surface of a NCD target,which has a preferable self-supporting property in the RPA experiments than the ultra-thin foil target.The dense electron layer of the ultra-thin HD layer can effectively reduce the penetrating velocity of the intense laser in the NCD layer,and generated a strong acceleration field.It is found that in one-dimensional PIC simulation,by the block of the HD layer in the new target,there emerges the hole-boring process rather than propagation in the NCD layer when the intense laser pulse impinges on this target.As a result,a typical RPA structure that the compressed electron layer overlaps the ion layer as a whole is formed and a high quality ion beam is obtained finally.And the similar results are also found in the two-dimensional PIC simulation.2.When a normal transversely Gaussian laser impinges on a common flat foil,it doomed to produce a transversely nonuniform acceleration of the target,which contribute to the curve of the foil and the development of transverse instability.In order to overcome the curve of the target and the transverse instability in the RPA of a common flat foil while using a single normal transversely Gaussian laser,we propose a new scheme by using two matched counter-propagating transversely Gaussian lasers,the main pulse and the auxiliary pulse,impinges on the foil target at the meantime.After the theoretical analysis and derivation,we get the the matching condition of the auxiliary laser.By given the parameters of the main laser,a set of parameters of the matched auxiliary laser can be obtained.It is found that in the two-dimensional PIC simulation,by the restraint of the auxiliary laser,the curve and transverse instability of the foil can be effectively suppressed.As a result,a high quality monoenergetic ion beam is generated through an efficient and relatively uniform RPA of the foil target.And the effects on the ions acceleration with different parameters of the auxiliary laser are also investigated.