Proton Acceleration In The Radiation Pressure Regime Under Non-ideal Conditions By Super-intensity Laser

In recent years,ion acceleration of the interaction between laser and plasma has attracted widespread attention due to its high acceleration gradient and miniaturization.High quality ion beam produced by the interaction of laser and plasma has very important applications in many fields,such as cancer therapy,inertial confinement fusion,laboratory astrophysics,etc.At present,the main mechanisms of ion acceleration are target normal sheath acceleration,electrostatic shock acceleration,and radiation pressure acceleration,etc.Among them,the radiation pressure acceleration is considered as one of the most promising ion acceleration mechanisms because of its high energy conversion rate and the ability to produce high quality ion beams.At present,in the theoretical and numerical simulation of the radiation pressure acceleration,the ideal ultra-strong laser and ultra-thin target are often used to obtain high quality ion beams,but this brings great challenges to the experimental operation.Based on the current laboratory actual laser thin foil target parameters and under non-ideal conditions,two new schemes of the radiation pressure acceleration that are easier to achieve in the experiment are proposed in this dissertation.One is to accelerate protons by the interaction of two super Gaussian lasers with solid foil target in the radiation pressure regime,and the other is to use a single Gaussian laser to interact with near-critical density composite target to accelerate protons in the radiation pressure regime.The two new schemes are verified by PIC simulation,and high quality proton beams are obtained.The details are as follows:1.For the radiation pressure acceleration,an ultra-wide and ultra-strong laser helps to produce high-quality ion beams.Due to the limited laser energy,it is difficult to produce such a laser in the experiment.So two new schemes of using two lasers to form an ultra-wide and ultra-strong laser are proposed in this dissertation.In the scheme 1,to overcome the limited intensity of an ultra-wide laser,an auxiliary laser overlaps in the intensity with the main laser is used.In the scheme2,to overcome the limited pulse width of an ultra-strong laser,an auxiliary laser overlaps in the pulse width with the main laser to form an ultra-wide and ultrastrong laser.Two-dimensional particle-in-cell simulations show that protons can be stably accelerated by light pressure for a long time in two schemes.Compared to the single laser pulse,the energy and the number of protons increased significantly.In addition,the effects of the auxiliary laser parameters,such as intensity,waist radius and pulse width,on the accelerated protons are investigated.The results show that when the auxiliary laser parameters are changed within a certain range,our schemes are robust.By using the current laboratory laser plasma parameters,a 1.2Ge V monoenergetic proton beam is obtained in our schemes.2.In the radiation pressure acceleration,an ultra-Gaussian laser under ideal conditions is often used to interact with an ultra-thin foil target.However,the thickness of the ultra-thin foil target is only tens to hundreds of nanometers.Such an ultra-thin foil target not only has poor self-supporting property,but also brings greater difficulty to the experimental operation.The laser is usually Gaussian laser in the laboratory,but the Gaussian laser will cause the target bending and proton divergence.In order to obtain high-quality ion beams,the super-Gaussian laser is often used in theory and numerical simulation.In order to increase the thickness of the target and improve the self-supporting property of the target,it is proposed to use the near critical density target.However,under the irradiation of ultrastrong laser,the near-critical density target will not be able to realize the radiation pressure acceleration due to the relativistic self-induced transparency.Therefore,it is proposed to add a high-density layer before the near-critical density target to form a composite target.In order to solve the problem of proton divergence caused by Gaussian laser,it is proposed to use an external longitudinal magnetic field to confine the protons.Therefore,the proton acceleration by radiation pressure of Gaussian laser and the near critical density composite target under external magnetic field is studied in this dissertation.Through 2D PIC simulation,it is found that the proton divergence is reduced and the collimation is improved.