Study On Two-dimensional Energy Spectrum Of Laser-driven Protons

In recent years,with the further research of inertial confinement fusion and fast ignition,strong-field physics has attracted numerous investigations.In this research background,this thesis focuses on the study of two-dimensional energy spectra on laser-driven protons.The main contents of this thesis are presented as the following four parts:The first part includes Chapter I and Chapter II.Chapter I introduces the development history of ultraintense laser and the research focus related to this thesis.This chapter contents inertial confinement fusion and fast ignition scheme,laser driven hot electrons,laser-driven proton acceleration mechanisms and the application of high quality proton beams.Chapter II mainly discusses the construction of our labortary,which is composed of four parts: the introduction of 200 TW femtosecond laser facility,the vacuum leak hunting of the chambers,the design and establishment of the platform for making metal tiny targets,as well as the laboratory radiation protection work.In the last part,we have detected the radiation dose in both High-harmonic generation experiment and near critical density gas targets experiment by using rmoluminescence dosimeter.For High-harmonic generation experiment,the radiation dose corresponds with the radiation safety standard ‘Basic standards for protection against ionizing radiation and for the safety of radiation sources'.While for gas targets experiment,the radiation dose doesn't satisfy the standard.Therefore,experimenters should avoid standing along the laser propagation direction during the experiment.The second part is composed of Chapter III and Chapter IV.In this part,we mainly concern with the diagnostic techniques in two aspects: electron detection and proton detection.Chapter III describes a real-time electron spectrometer.The electron spectrometer can transform the measured electron signals into optical ones by PI200 plastic scintillator,and transmit the real-time signals to CMOS camera by flexible plastic fibers.The experiment result shows that this design is applicable for high repetition laser system by the advantages of its real-time property and its flexibility.Chapter IV introduces the design and detection results of a two-dimensional proton wide-angle spectrometer(2D WASP),which is the key point of this thesis.The spectrometer is based on Thomson ion spectrometer.By applying a pinhole array in front of the magnets,the spectrometer is capable of measuring the energy spectra and spatial distributions of protons in two dimensions simultaneously,which is verified both theoretically and experimentally.This design provides a new way to study the physical process in laser-driven proton acceleration.The third part is Chapter V.This part mainly focuses on the laser-driven proton acceleration experiments based on the 200 TW femtosecond laser facility.The 2D WASP is applied as the detector for measuring proton energy spectra.During the experiment,we have found two important phenomena.The first is the bending proton spectra detected by 2D WASP when high contrast laser pulse interacting with large foil target(30mm × 15mm).By tracing back the proton traces from the detector,we found there existed a virtual proton source at the rear of the target.This is contrary to the results from published papers.According to the experimental results,we believe that the bending proton spectra are caused by the ‘space charge effect' in the protons,which deserves further investigation.Besides,for those straight resolvable proton spectra,we investigated the effect of laser incidence angle on the directional deviation of proton beams.There is a positive correlation between the proton deviation angle and the laser incidence angle.The experimental results performed on the 200 TW laser system obtains the same trend with the simulation reslut,but the proton deviation angle is much larger experimentally.Based on this work,for the 200 TW laser system,the direction of proton beams were influenced by the electric field parallel to the target surface.The forth part contents Chapter VI.This chapter gives a brief summary of the researching work in this thesis as well as delivers an expectation on future researching works.