We report systematic studies of laser-driven proton beams produced with micrometer-thick solid targets made of aluminum and plastic,respectively.Distinct effects of the target materials are found on the total charge,c...We report systematic studies of laser-driven proton beams produced with micrometer-thick solid targets made of aluminum and plastic,respectively.Distinct effects of the target materials are found on the total charge,cutoff energy,and beam spot of protons in the experiments,and these are described well by two-dimensional particle-in-cell simulations incorporating intrinsic material properties.It is found that with a laser intensity of 8×10^(19) W/cm^(2),target normal sheath acceleration is the dominant mechanism for both types of target.For a plastic target,the higher charge and cutoff energy of the protons are due to the greater energy coupling efficiencies from the intense laser beams,and the larger divergence angle of the protons is due to the deflection of hot electrons during transport in the targets.We also find that the energy loss of hot electrons in targets of different thickness has a significant effect on the proton cutoff energy.The consistent results obtained here further narrow the gap between simulations and experiments.展开更多
The generation of plasma in a microwave ion source involves confining electrons using a static magnetic field and energizing them with an electromagnetic field that transmitted into the plasma chamber.However,accordin...The generation of plasma in a microwave ion source involves confining electrons using a static magnetic field and energizing them with an electromagnetic field that transmitted into the plasma chamber.However,according to electromagnetics theory,there is always a cut-off size in circular wave guides for a given frequency.For a 2.45 GHz microwave,this dimension is 72 mm,which should theoretically prevent transmission of the microwave into the discharge chamber and no plasma can be generated.Since 2006 Peking University(PKU)has successfully developed a series of permanent magnet 2.45 GHz microwave ion sources(PKU PMECRs)with a discharge chamber less than 50 mm,capable of delivering tens of mA beams for accelerators.To explain this anomalous phenomenon,a hybrid discharge heating(HDH)mode that combines surface wave plasma and electron cyclotron heating has been proposed.This HDH mode not only successfully explains PKU PMECRs,but also predicts that the optimized inner diameter of the plasma chamber is 24 mm,which is confirmed by experiments involving different liners in the miniaturized microwave ion source.展开更多
基金The simulations were performed on the Qilin-2 supercomputer at Zhejiang University.This work was supported by the Science Challenge Project(No.TZ2016005)the National Natural Science Foundation of China(Grant Nos.119210067,11605269,11721091,11775144)the National Grand Instrument Project(Nos.2019YFF01014400,2019YFF01014404).
文摘We report systematic studies of laser-driven proton beams produced with micrometer-thick solid targets made of aluminum and plastic,respectively.Distinct effects of the target materials are found on the total charge,cutoff energy,and beam spot of protons in the experiments,and these are described well by two-dimensional particle-in-cell simulations incorporating intrinsic material properties.It is found that with a laser intensity of 8×10^(19) W/cm^(2),target normal sheath acceleration is the dominant mechanism for both types of target.For a plastic target,the higher charge and cutoff energy of the protons are due to the greater energy coupling efficiencies from the intense laser beams,and the larger divergence angle of the protons is due to the deflection of hot electrons during transport in the targets.We also find that the energy loss of hot electrons in targets of different thickness has a significant effect on the proton cutoff energy.The consistent results obtained here further narrow the gap between simulations and experiments.
基金supported by National Natural Science Foundation of China(Grant Nos.12205019,12147144 and 11975036).The support from State Key Laboratory of Nuclear Physics and Technology,Peking University is appreciated.
文摘The generation of plasma in a microwave ion source involves confining electrons using a static magnetic field and energizing them with an electromagnetic field that transmitted into the plasma chamber.However,according to electromagnetics theory,there is always a cut-off size in circular wave guides for a given frequency.For a 2.45 GHz microwave,this dimension is 72 mm,which should theoretically prevent transmission of the microwave into the discharge chamber and no plasma can be generated.Since 2006 Peking University(PKU)has successfully developed a series of permanent magnet 2.45 GHz microwave ion sources(PKU PMECRs)with a discharge chamber less than 50 mm,capable of delivering tens of mA beams for accelerators.To explain this anomalous phenomenon,a hybrid discharge heating(HDH)mode that combines surface wave plasma and electron cyclotron heating has been proposed.This HDH mode not only successfully explains PKU PMECRs,but also predicts that the optimized inner diameter of the plasma chamber is 24 mm,which is confirmed by experiments involving different liners in the miniaturized microwave ion source.
