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Experimental studies of H_(2)/Ar plasma in a cylindrical inductive discharge with an expansion region

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Chinese physics B 2024年第10期33卷 321-330页

作者： Shi-Bo Li Si-Yu Xing Fei Gao You-Nian Wang key laboratory of Materials Modification by laser Ionand Electron Beams(Ministry of Education)School of PhysicsDalian University of TechnologyDalian 116024China

The electrical parameters of H_(2)/Ar plasma in a cylindrical inductive discharge with an expansion region are investigated by a Langmuir probe,where Ar fractions range from 0%to 100%.The influence of gas composition and pressure on electron density,the effective electron temperature and the electron energy probability functions(EEPFs)at different spatial positions are *** driver region,with the introduction of a small amount of Ar at 0.3 Pa,there is a rapid increase in electron density accompanied by a decrease in the effective electron ***,the shape of the EEPF transitions from a three-temperature distribution to a bi-Maxwellian distribution due to an increase in electron-electron ***,this phenomenon resulting from the changes in gas composition vanishes at 5 Pa due to the prior depletion of energetic electrons caused by the increase in pressure during hydrogen *** EEPFs for the total energy in expansion region is coincident to these in the driver region at 0.3 Pa,as do the patterns of electron density variation between these two regions for differing Ar *** 5 Pa,as the discharge transitions from H_(2)to Ar,the EEPFs evolved from a bi-Maxwellian distribution with pronounced low energy electrons to a Maxwellian distribution in expansion *** evolve may be attributed to a reduction in molecular vibrational excitation reactions of electrons during transport and the transition from localized electron dynamics in hydrogen discharge to non-localized electron dynamics in argon *** order to validate the experimental results,we use the COMSOL simulation software to calculate electrical parameters under the same *** evolution and spatial distribution of the electrical parameters of the simulation results agree well with the trend of the experimental results.

关键词： inductively coupled plasma transmission and distribution energy distribution functions

Discharge mode and particle transport in radio frequency capacitively coupled Ar/O_(2)plasma discharges

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Chinese physics B 2024年第9期33卷 451-460页

作者： Zhuo-Yao Gao Wan Dong Chong-Biao Tian Xing-Zhao Jiang Zhong-Ling Dai Yuan-Hong Song key laboratory of Materials Modification by laser Ionand Electron Beams(Ministry of Education)School of PhysicsDalian University of TechnologyDalian 116024China

Simulations are conducted on capacitively coupled Ar/O_(2)mixed gas discharges employing a one-dimensional fluid coupled with an electron Monte Carlo(MC)*** research explores the impact of different O_(2)ratio and pressures on the discharge characteristics of Ar/O_(2)*** a fixed Ar/O_(2)gas ratio,with the increasing pressure,higher ion densities,as well as a slight increase in electron density in the bulk region can be *** discharge remains dominated by the drift-ambipolar(DA)mode,and the flux of O(3P)at the electrode increases with the increasing pressure due to higher background gas density,while the fluxes of O(1D)and Ardecrease due to the pronounced loss *** the increasing proportion of O_(2),a change in the dominant discharge mode from a mode to DA mode can be detected,and the O_(2)-associated charged particle densities are significantly ***,Ar+density shows a trend of increasing and then decreasing,while for neutral fluxes at the electrode,Arflux decreases,and O(3P)flux increases with the reduced Ar gas proportion,while trends in O(1D)flux show slight *** evolution of the densities of the charged particle and the neutral fluxes under different discharge parameters are discussed in detail using the ionization characteristics as well as the transport ***,more comprehensive understanding of Ar/O_(2)discharge characteristics in this work will provide a valuable reference for the industry.

关键词： Ar/O_(2) mixed gas discharges electron dynamics transport of charged and neutral particles

Divergence angle consideration in energy spread measurement for high-quality relativistic electron beam in laser wakefield acceleration

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Chinese physics B 2024年第6期33卷 363-368页

作者：卢光伟李曜均胡曦辰陈思宇徐豪祝铭阳闫文超陈黎明 key laboratory for laser plasmas of ministry of education Shanghai Jiao Tong UniversityShanghai 200240China IFSA Collaborative Innovation Center Shanghai Jiao Tong UniversityShanghai 200240China

The thorough exploration of the transverse quality represented by divergence angle has been lacking yet in the energy spread measurement of the relativistic electron beam for laser wakefield acceleration(LWFA). In this work, we fill this gap by numerical simulations based on the experimental data, which indicate that in a C-shape magnet, magnetic field possesses the beam focusing effect, considering that the divergence angle will result in an increase in the full width at half maxima(FWHM) of the electron density distribution in a uniformly isotropic manner, while the length-to-width ratio decreases. This indicates that the energy spread obtained from the electron deflection distance is smaller than the actual value, regardless of the divergence angle. A promising and efficient way to accurately correct the value is presented by considering the divergence angle(for instance, for an electron beam with a length-to-width ratio of 1.12, the energy spread correct from 1.2% to 1.5%), providing a reference for developing the high-quality electron beam source.

关键词： relativistic electron beams acceleration by laser–plasma interactions finite element analysis

Direct observation of shock-induced phase transformation in polycrystalline iron via in situ x-ray diffraction

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Chinese physics B 2024年第10期33卷 337-342页

作者： Fan Zhang Jia-Qin Dong Zhi-Yong Xie Zhi-Yu He Hua Shu Rui-Rong Wang Jun Xiong Guo Jia Zhi-Heng Fang Wei Wang Da-Wu Xiao An-Le Lei Jie Chen Xiu-Guang Huang Collaborative Innovation Center of IFSA(CICIFSA) School of Physics and AstronomyCenter for Ultrafast Science and TechnologyKey Laboratory for Laser Plasmas(Ministry of Education)Shanghai Jiao Tong UniversityShanghai 200240China Shanghai Institute of laser Plasma China Academy of Engineering PhysicsShanghai 201800China Institute of Materials China Academy of Engineering PhysicsMianyang 621700China

Phase transition of polycrystalline iron compressed along the Hugoniot is studied by combining laser-driven shock with in situ x-ray diffraction *** is suggested that polycrystalline iron changes from an initial body-centered cubic structure to a hexagonal close-packed structure with increasing pressure(i.e.,a phase transition fromαtoε).The relationship between density and pressure for polycrystalline iron obtained from the present experiments is found to be in good agreement with the gas-gun Hugoniot *** results show that experiments with samples at lower temperatures under static loading,such as in a diamond anvil cell,lead to higher densities measured than those found under dynamic *** means that extrapolating results of static experiments may not predict the dynamic responses of materials *** addition,neither the face-centered cubic structure seen in previous molecular-dynamics simulations or twophase coexistence are found within our experimental pressure range.

关键词： in situ x-ray diffraction phase transition polycrystalline iron

Abnormal transition of the electron energy distribution with excitation of the second harmonic in low-pressure radio-frequency capacitively coupled plasmas

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Plasma Science and Technology 2024年第8期26卷 58-63页

作者：余乐怡陆文琪张丽娜 key laboratory of Materials Modification by laser Ionand Electron Beams(Ministry of Education)School of PhysicsDalian University of TechnologyDalian 116024People’s Republic of China

The self-excited second harmonic in radio-frequency capacitively coupled plasma was significantly enhanced by adjusting the external variable *** a lower pressure of 3 Pa,the excitation of the second harmonic caused an abnormal transition of the electron energy probability function,resulting in abrupt changes in the electron density and *** changes in the electron energy probability function as well as the electron density and temperature were not observed at the higher pressure of 16 Pa under similar harmonic *** phenomena are related to the influence of the second harmonic on stochastic heating,which is determined by both amplitude and the relative phase of the *** results suggest that the self-excited high-order harmonics must be considered in practical applications of lowpressure radio-frequency capacitively coupled plasmas.

关键词： radio-frequency capacitively coupled plasma harmonics the electron energy probability function

Optoelectronic tuning of plasmon resonances via optically modulated hot electrons

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National Science Review 2024年第5期11卷 134-141页

作者： Jiacheng Yao Cheng Wang Chi Zhang Song Ma Li Zhou Ti Wang Ququan Wang Hongxing Xu Tao Ding key laboratory of Artificial Micro Nano Structure of Ministry of Education School of Physics and Technology Wuhan University department of physics Southern University of Science and Technology

Fast optical modulation of nanoplasmonics is fundamental for on-chip integration of all-optical *** various strategies have been proposed for dynamic modulation of surface plasmons, critical issues of device compatibility and extremely low efficiency in the visible spectrum hamper the application of optoplasmonic nanochips. Here we establish an optoplasmonic system based on Au@Cu2–xS hybrid core–shell nanoparticles. The optical excitation of hot electrons and their charge transfer to the semiconductor coating(Cu2–xS) lead to lowered electron density of Au, which results in the red shift of the localized surface plasmon resonance. The hot electrons can also transport through the Cu2–xS layer to the metal substrate, which increases the conductance of the nanogap. As such, the coupled gap plasmon blue-shifts with a magnitude of up to ～15 nm, depending on the excitation power and the thickness of the coatings, which agrees with numerical simulations. All of this optoelectronic tuning process is highly reversible, controllable and fast with a modulated laser beam, which is highly compatible and sufficiently useful for on-chip integration of nanophotonic devices.

关键词： hot carriers plasmon switching optoplasmonics circuit modelNPoM

Tunable energy spectrum betatron x-ray sources in a plasma wakefield

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Chinese physics B 2024年第8期33卷 344-350页

作者：奚传易寿寅任韩立琦阿卜杜伍普尔·阿布力米提刘晓丹赵研英余金清 Hunan Provincial key laboratory of High-Energy Scale physics and Applications School of Physics and ElectronicsHunan UniversityChangsha 410082China Center for Relativistic laser Science Institute for Basic ScienceGwangjuKorea State key laboratory of Nuclear physics and Technology and Key Laboratory of HEDP of the Ministry of EducationCAPTPeking UniversityBeijing 100871China

X-ray sources with tunable energy spectra have a wide range of applications in different scenarios due to their different penetration ***,existing x-ray sources face difficulties in terms of energy *** this paper,we present a scheme for tuning the energy spectrum of a betatron x-ray generated from a relativistic electron bunch oscillating in a plasma *** center energy of the x-ray source can be tuned from several keV to several hundred keV by changing the plasma density,thereby extending the control range by an order of *** different central energies,the brightness of the betatron radiation is in the range of 3.7×10^(22)to 5.5×10^(22)photons/(0.1%BW·s·mm^(2)·mrad^(2))and the photon divergence angle is about 2 *** high-brightness,energy-controlled betatron source could pave the way to a wide range of applications requiring photons of specific energy,such as phase-contrast imaging in medicine,non-destructive testing and material analysis in industry,and imaging in nuclear physics.

关键词： betatron plasma physics x-ray plasma wakefield acceleration(PWFA)

Human radiological safety assessment for petawatt laser-driven ion acceleration experiments in CLAPA-T

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Matter and Radiation at Extremes 2024年第4期9卷 8-15页

作者： Xiaopeng Zhang Jiarui Zhao Shengxuan Xu Xun Chen Ying Gao Shiyou Chen Kun Zhu Xueqing Yan Wenjun Ma State key laboratory of Nuclear physics and Technology and Key Laboratory of HEDP of the Ministry of EducationCAPTPeking UniversityBeijing 100871China key laboratory of Particle Astrophysics Institute of High Energy PhysicsCASBeijing 100049China Beijing laser Acceleration Innovation Center HuairouBeijing 101400China Institute of Guangdong laser Plasma Technology BaiyunGuangzhou 510540China

The newly built Compact laser Plasma Accelerator-Therapy facility at Peking University will deliver 60 J/1 Hz laser pulses with 30 fs *** by this petawatt laser facility,proton beams with energy up to 200 MeV are expected to be generated for tumor *** high-repetition operation,both prompt radiation and residual radiation may cause safety ***,human radiological safety assessment before commissioning is *** this paper,we simulate both prompt and residual radiation using the Geant4 and FLUKA Monte Carlo codes with reasonable proton and as-produced electron beam *** find that the prompt radiation can be shielded well by the concrete wall of the experimental hall,but the risk from residual radiation is nonnegligible and necessitates adequate radiation *** the basis of the simulation results,we discuss the constraints imposed by radiation safety considerations on the annual working time,and we propose radiation cooling strategies for different shooting modes.

关键词： laser prompt acceleration

Real-Time Observation of Instantaneous ac Stark Shift of a Vacuum Using a Zeptosecond laser Pulse

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Chinese physics Letters 2024年第1期41卷 11-15页

作者：苏丹丹江淼 key laboratory for laser plasmas(ministry of education)and School of physics and Astronomy Collaborative Innovation Center for IFSA(CICIFSA)Shanghai Jiao Tong UniversityShanghai 200240China School of Science China University of Mining and TechnologyBeijing 100083China State key laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyBeijing 100083China

Based on the numerical solution of the time-dependent Dirac equation,we propose a method to observe in real time the ac Stark shift of a vacuum driven by an ultra-intense laser *** overlapping the ultra-intense pump pulse with another zeptosecond probe pulse whose photon energy is smaller than 2mc^(2),electron–positron pair creation can be controlled by tuning the time delay between the pump and probe *** the pair creation rate depends sensitively on the instantaneous vacuum potential,one can reconstruct the ac Stark shift of the vacuum potential according to the time-delay-dependent pair creation rate.

关键词： pump tuning vacuum