Numerical Simulation Of Ion Acceleration Driven By Ultra-intense Ultra-short PW Laser

Research of particle acceleration and radiation has been promoting the progress of science.So far,more than half of the Nobel Prize in physics are related to particle acceleration and its applications.Conventional particle accelerator is huge in size and high in cost,which is close to the limit of economy and technology.This greatly limits the application and promotion of the accelerator.To realize the desktop particle accelerator,researchers continue to explore new and efficient acceleration technology.Compared to conventional particle accelerator,ultra-intense laser driven particle acceleration has obvious advantages,including large acceleration gradient（generally three orders of magnitude higher than that of traditional accelerator）,short pulse width（picosecond,femtosecond）and high beam density.With the emergence of chirped pulse amplification technology（CPA）and optical parametric CPA（OPCPA）technology,the laser technology develops very rapidly.At present,the focused ultrashort ultra-intense laser pulse with intensity higher than 10²² W/cm² can be obtained in the laboratory,providing a great opportunity for the development of small-size particle accelerator.Due to the advantages of concentrated energy release at the end of range,strong local ionization,high stopping power and accurate positioning,ion beam has the important applications in inertial confinement fusion,proton imaging,medical therapy,formation of warm dense matter state,and heavy-ion collision,etc.Therefore,ion acceleration driven by ultra-intense laser pulse is a frontier and hot issue in the field of high energy density physics.The physical process of laser ion acceleration is complex,involving many physical phenomena of laser plasma interaction.At present,laser ion-acceleration experiments mainly focus on protons or lighter ions（e.g.,carbon ions）,and the energy conversion efficiencyηfrom laser to ions is very low,usually a few percent.It is a great challenge to improve both the ion energy and energy conversion efficiency from laser to ions as well as develop efficient high-Z ion acceleration.In this paper,we carry out the theoretical analysis and numerical simulation for the dynamics of laser ion acceleration process driven by petawatt-class laser pulse.The main research contents are as follows:Firstly,we studied the proton acceleration process of several petawatt（PW）laser pulse interacting with near-critical density plasma.It is found that the magnetic vortex acceleration is the dominant mechanism to produce energetic protons.The numerical simulation results show that an electron filamentation with 100 Me V energy appeared in the near-critical density plasma channel due to the pondermotive force of the laser.When it escapes from the back surface of the target,strong self-generated magnetic field and charge separation field are induced.The magnetic pressure and charge separation forces can effectively accelerate the proton to more than 100 Me V.Besides,in a large range of plasma parameters,the proton beam with cutoff energy greater than 100 Me V can be obtained.Our research is useful for the laser ion acceleration experiments carried out on the current PW laser facilities.Secondly,we propose an efficient ion acceleration mechanism in dusty plasma driven by ultra-short laser pulses.It is found that the laser will heat and expel the electrons in the dust particles,thus creating a strong space charge field in the dust particle,resulting in the acceleration of the isotropic expansion of ions in the dust particle.Using laser pulses with intensity of3.1×10^{2 0}W/cm²,duration of 50 fs and energy of 12 J,C⁶⁺ions and protons with maximum energy of 350 Me V and 46 Me V are obtained.The energy conversion efficiency from laser to C⁶⁺ions and protons is up to 60%and 5%,respectively.The high energy conversion efficiency from laser to heavy ion can maintain for a wide parametric range,and the cut-off energy of heavy-ion increases linearly with the normalized laser intensity and the charge number Z of the grain-ion,which indicates that this mechanism is very conducive to accelerating the high Z ion beam.Thirdly,the nonlinear physical process of the interaction between hundreds PW laser and the gold dust plasma is studied.We demonstrate that hundreds-Ge V Au⁷⁹⁺ions can be generated by ultrashort 10^22-24 W/cm² lasers.In such extremely intense laser fields,the laser-plasma interaction enters the radiation dominated near-QED regime.Strongγ-ray radiation has resulted in massive laser energy loss,and almost half of the laser energy is converted toγphotons.The capture of electrons by the radiation reaction force weakens the acceleration of heavy ions.However,ηfrom laser to heavy ions is still 32%high due to hole-boring acceleration from the ponderomotive force of ultrarelativistic laser pulses and multi-body expansion acceleration of high-Z Au⁷⁹⁺grains.The energetic heavy ions are mainly along the laser propagation direction.These heavy ions have entered the energy category of heavy ion collision in experimental research.This indicates that it is possible to carry out nuclear physics and quantum chromodynamic phase transition research by using the hundreds-petawatt laser facility under building.Fourthly,we studied the radiation pressure dominant acceleration of high-Z ions driven by hundreds-PW linearly polarized（LP）ultra-intense ultrashort（UIUS）laser pulse.It is found that a quasi-monoenergetic Au⁷⁹⁺ion beam with a central energy of165 Ge V can be obtained for a laser pulse of intensity3.4×10^{2 3}W/cm² and duration 33fs.In the interaction of a LP laser pulse and high-Z foil,the radiation damping force can effectively suppress the undesirable spatial expansion of high-Z plasma originating from transverse instabilities and electron heating by the oscillating part of the ponderomotive force.The foil is thus relatively opaque and can be accelerated forward as a whole.The spectral and spatial properties of high-Z ion beam are significantly improved,compared to that without the radiation damping.Finally,the gold cone is used to enhance the acceleration of high-Z ions for a hundreds-PW laser pulse.We find that the gold cone can effectively modulate the waveform of laser pulse so that we can obtain higher-intensity laser pulse.When the focused laser pulse interacts with the attached ultra-thin foil,the energy and energy conversion efficiency of high-Z ions can be improved greatly.This provides an optimization scheme and parametric support for the experimental research of high-Z ion acceleration in future.