Super Laser Irradiation Composite Target Can Produce Ultra High Collimation Ion Beam

With the rapid development of laser technology, the laser pusle with intensity of1022W/cm2and ultrahigh contrast of1012is now available. During the laser-solid interaction, the quasistatic accelerating field can reach values of above1012V/m close to the axis. Under such conditions, protons can be accelerated to tens of MeV energy within several microns, which prompts the development of the tabletop accelerator. Laser-driven ion acceleration has been of much recent interest because of its broad scientific and technical applications. Protons with tens to hundreds MeV energies are useful for high resolution imaging, cancer therapy, fast ignition in inertial confinement fusion, et al., and ions with still higher energies (GeV, even TeV) are relevant to high energy physics research, laboratory modeling of astrophysical phenomena, etc.The ion acceleration mechanisms are mainly focused on:target normal sheath acceleration, relativistically induced transparency acceleration or breakout afterburner, collisionless shock wave acceleration, radiation pressure acceleration or phase-stable acceleration, et al. However, because of the involved instability the acceleration length is limited to less than hundreds of microns and it is difficult to increase protons to further higher energy. The thesis is devoted to studying a two-phase proton acceleration scheme using an ultra-intense laser pulse irradiating a foil with a tenuous heavier-ion plasma behind it. radiation pressure acceleration (RPA) and wakefield acceleration. The RPA foil protons can be trapped by the wakefield and further accelerated over a long distance and thus to very high energies (TeV). Some results in the thesis are given as follows:1, The foil electrons are compressed and pushed out as a thin dense layer by the radiation pressure and propagate in the plasma behind at near the light speed. The protons are in turn accelerated by the resulting space-charge field and also enter the backside plasma, but without the formation of a quasistationary double layers. The electron layer is rapidly weakened by the space-charge field. However, the laser pulse originally behind it now snowplows the backside-plasma electrons and creates an intense electrostatic wakefield. The latter can stably trap and accelerate the pre-accelerated proton layer there for a very long distance and thus to very high energies. The two-phase scheme is verified by particle-in-cell simulations and analytical modeling; which also suggests that a0.54TeV proton beam can be obtained with a1023W/cm2laser pulse.2、For a species of heavy-ion in the two-phase acceleration regime, the dynamical behavior of relativistic heavy-ion can be given, which shows the maximum energy gain scales with the charge number Z. Furthermore, the final quasi-monoenergetic heavy-ion beam duration can be modulated by the wakefield structure, which agrees well with the theoretical prediction based on the classic wakefield theory.3、The multicascade wakefield acceleration of proton beams during the interaction of an ultraintense laser pulse with a foil connected with two-density underdense gas is proposed. In the two-density interface, there is a density singularity, which causes a rapid change of the intensity and size of the wakefield. The latter can improve the accelerated proton beam quality in terms of duration and energy spectrum.4、In multidimensional cases, the full problem includes the envelope evolution of laser pulse, as well as controlling the proton beam quality in terms of collimation. Proton acceleration by ultra-intense laser pulse irradiating a target with cross-section smaller than the laser spot size and connected to a parabolic density channel is thus investigated. In two-dimensional (2D) case, the target splits the laser into two par-allel propagating parts (twin-pulses), which snowplow the back-side plasma electrons along their paths, creating two adjacent parallel wakes (twin-wakes) and an intense return current in the gap between them. The radiation-pressure pre-accelerated target protons trapped in the wake fields now undergo acceleration as well as collimation by the quasistatic wake electrostatic and magnetic fields. It is shown by PIC simulation that an ultrashort, collimated, mono-energetic proton beam with high energy gain can be generated by an ultraintense circularly polarized laser pulse. In the3D case, the dynamic behavior of the accelerated protons is very similar with that in2D case, while laser-plasma interaction form a propagating torus instead of twin wakes.