Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot...Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers(e.g. the Extreme Light Infrastructure).We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3 D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP,providing an opportunity for comparison with existing charge separation models.展开更多
After a population of laser-driven hot electrons traverses a limited thickness solid target,these electrons will encounter the rear surface,creating TV/m fields that heavily influence the subsequent hot-electron propa...After a population of laser-driven hot electrons traverses a limited thickness solid target,these electrons will encounter the rear surface,creating TV/m fields that heavily influence the subsequent hot-electron propagation.Electrons that fail to overcome the electrostatic potential reflux back into the target.Those electrons that do overcome the field will escape the target.Here,using the particle-in-cell(PIC)code EPOCH and particle tracking of a large population of macro-particles,we investigate the refluxing and escaping electron populations,as well as the magnitude,spatial and temporal evolution of the rear surface electrostatic fields.The temperature of both the escaping and refluxing electrons is reduced by 30%–50%when compared to the initial hot-electron temperature as a function of intensity between 1019 and 1021 W/cm^2.Using particle tracking we conclude that the highest energy internal hot electrons are guaranteed to escape up to a threshold energy,below which only a small fraction are able to escape the target.We also examine the temporal characteristic of energy changes of the refluxing and escaping electrons and show that the majority of the energy change is as a result of the temporally evolving electric field that forms on the rear surface.展开更多
基金funding from EPSRC grants EP/L01663X/1 and EP/L000644/1the Newton UK grant+1 种基金the National Natural Science Foundation of China NSFC/11520101003the LLNL Academic Partnership in ICF
文摘Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers(e.g. the Extreme Light Infrastructure).We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3 D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP,providing an opportunity for comparison with existing charge separation models.
基金funding from EPSRC Grant Nos. EP/J003832/1, EP/K022415/1, EP/R006202/1the use of the Scarf simulation cluster
文摘After a population of laser-driven hot electrons traverses a limited thickness solid target,these electrons will encounter the rear surface,creating TV/m fields that heavily influence the subsequent hot-electron propagation.Electrons that fail to overcome the electrostatic potential reflux back into the target.Those electrons that do overcome the field will escape the target.Here,using the particle-in-cell(PIC)code EPOCH and particle tracking of a large population of macro-particles,we investigate the refluxing and escaping electron populations,as well as the magnitude,spatial and temporal evolution of the rear surface electrostatic fields.The temperature of both the escaping and refluxing electrons is reduced by 30%–50%when compared to the initial hot-electron temperature as a function of intensity between 1019 and 1021 W/cm^2.Using particle tracking we conclude that the highest energy internal hot electrons are guaranteed to escape up to a threshold energy,below which only a small fraction are able to escape the target.We also examine the temporal characteristic of energy changes of the refluxing and escaping electrons and show that the majority of the energy change is as a result of the temporally evolving electric field that forms on the rear surface.
