High-quality Proton Beam Generation Via Multi-laser Pulses Target Interactions

THE acceleration of ion by intense laser pulse interacting with foil target has received a great deal of interest in the past few decades due to its wide potential applications in diverse fields,including the energy generation by fast ignition in inertial confinement fusion,in medical physics to treat the cancer cell using radiation therapy,to produce ion beam radiographs,to produce warm dense matter,etc.The laser-driven ion beams exhibit some unique features as compared with the conventional accelerator-driven ion sources.Moreover,the laser-driven ion beam qualities have been increasing as the state-of-the-art laser technology keeps improving.Although tremendous progress has been made in realizing laser-based accelerators that are cheap and very compact,however,there are still some challenges that have to overcome regarding this field.For example,one has not only to increase the ion beam energy,intensity,and the laser to ion conversion efficiency but also curtail the ion beam energy spread/divergence to establish it in practical use.In this regard,within the framework of this thesis,a novel multi-laser pulses scheme has been investigated to optimize the proton beam qualities.First of all,we have investigated the double-laser pulse(DLP)single-layer target(SLT)interaction to boost the laser to proton energy conversion efficiency hence opti-mizing the proton beam energy.It is seen that the reflection,as well as,the absorption.of the laser pulse could be controlled by employing a pre-pulse prior to the main pulse.The 2D-PIC simulation results have shown that the DLP scheme could enhance the proton beam energy up to two times compared to the single-laser pulse(SLP)scheme using the same laser energy.The pre-pulse reduces the reflection of the main pulse by creating the pre-plasma before the arrival of the main pulse.The main pulse is then self-focused which enhances the absorption of the laser energy by the target electrons.As a result,the proton could be accelerated to high energy with low energy spread for a longer time due to laser breakout afterburner(BOA).The parameters dependence of the proton acceleration indicate that the DLP scheme could produce efficient proton acceleration over a wide range of the laser and target parameters.Then we applied the proposed DLP scheme to accelerate the protons from the double-layer target(DLT).It is found that the DLP scheme also produces effective proton acceleration from the DLT.However,the identified acceleration mechanisms were quite different than the previous case.The acceleration of the proton strongly depends on the pre-target ion charge to mass ratio but independent of the individual charge/mass of the pre-target ion and was optimum for the higher charge to mass ratio case.We further applied the DLP scheme to accelerate the heavy-ion.It is seen that the DLP scheme could produce an efficient ion beam by overcoming some of the difficulties that appear in the case of heavy-ion acceleration.Next,we have investigated the triple-laser pulse(TLP)plasma interactions scheme to enhance the proton beam energy up to GeV.Initially,two identical lower intense linearly polarized Gaussian laser pulses obliquely irradiate the DLT.The oblique lasers create periodic surface structures on the target that reduces the reflection,enhances the focusing,and boosts the energy coupling of the succeeding laser pulse that follows.Two hot-electron bunches are also generated,and they induce a strong electrostatic field in the axial direction.As a result,a proton beam of 1.15 GeV peak energy,very low energy spread?4%,and small divergence angle?5° can be obtained with laser intensities of 1021 Wcm-2,which is one order lower intense than that reported in some recent studies.Moreover,the TLP scheme also produces efficient proton acceleration as compared with the DLP and SLP cases using the same laser and target parameters.Finally,we have studied the proton acceleration by tailoring the target to enhance the proton beam density.We considered the interactions of intense laser pulse with Vacuum Sandwiched Target(VST).The vacuum gap protects the hydrogen layer from the unusual destruction caused by the laser pedestal.It is seen that the proton beam density could be enhanced up to-12.8(2)times compared with the SLT(DLT)case using the same simulation conditions,which is also more than one order higher than that reported in the previous chapters.It is worth noting here that for the proton beam density,the simple VST case is much efficient than the DLP and TLP cases while the proton beam peak energies are significantly higher for the latter cases.The results of this work,in particular the advances in proton beam qualities,have marked an important basis for future research of laser-driven proton acceleration and might enable laser-based implementation of these applications in the future.