We perform the theoretical simulation of the concentric-ring patterns between two parallel electrodes covered with thin dielectric layers within the scope of a two-dimensional diffusion-drift model at atmospheric pres...We perform the theoretical simulation of the concentric-ring patterns between two parallel electrodes covered with thin dielectric layers within the scope of a two-dimensional diffusion-drift model at atmospheric pressure. The time evolution of the discharge patterns is studied and the concentric-ring patterns with different radii shift alternately. The spatial-temporal evolution of electron density in a cycle at different time scales is performed.展开更多
The existence of two diffe1：ent discharge modes has been verified in an rf （radio-frequency） atmospheric pressure glow discharge （APGD） by Shi [J. Appl. Phys. 97, 023306 （2005）]. In the first mode, referred to ...The existence of two diffe1：ent discharge modes has been verified in an rf （radio-frequency） atmospheric pressure glow discharge （APGD） by Shi [J. Appl. Phys. 97, 023306 （2005）]. In the first mode, referred to as a mode, the discharge current density is relatively low and the bulk plasma electrons acquire the energy due to the sheath expansion. In the second mode, termed γ mode, the discharge current density is relatively high, the secondary electrons emitted by cathodc under ion bombardment in the cathode sheath region play an important role in sustaining the discharge. In this paper, a one-dimensional self-consistent fluid model for rf APGDs is used to simulate the discharge mechanisms in the mode in helium discharge between two parallel metallic planar electrodes. The results show that as the applied voltage increases, the discharge current becomes greater and the plasma density correspondingly increases, consequentially the discharge transits from the a mode into the γ mode. The high collisionality of the APGD plasma results in significant drop of discharge potential across the sheath region, and the electron Joule heating and the electron collisional energy loss reach their maxima in the region. The validity of the simulation is checked with the available experimental and numerical data.展开更多
This paper performs a numerical simulation of concentric-ring discharge structures within the scope of a twodimensional diffusion-drift model at atmospheric pressure between two parallel circular electrodes covered wi...This paper performs a numerical simulation of concentric-ring discharge structures within the scope of a twodimensional diffusion-drift model at atmospheric pressure between two parallel circular electrodes covered with thin dielectric layers. With a relative high frequency the discharge structures present different appearances of ring structures within different radii in time due to the evolvement of the filaments. The spontaneous electron density distributions help understanding the formation and development of self-organized discharge structures. During a cycle the electron avalanches are triggered by the electric field strengthened by the feeding voltage and the residual charged particles on the barrier surface deposited in the previous discharges. The accumulation of charges is shown to play a dominant role in the generation and annihilation of the discharge structures. Besides, the rings split and unify to bring and annihilate rings which form a new discharge structure.展开更多
A space-resolving transmission grating spectrometer is established on the ＂Shenguang-III＂ prototype laser facility and an iterative procedure for unfolding the X-ray spectrum with spatial resolution is described. Th...A space-resolving transmission grating spectrometer is established on the ＂Shenguang-III＂ prototype laser facility and an iterative procedure for unfolding the X-ray spectrum with spatial resolution is described. The diagnostics is applied to measure the X-ray spectrum from laser-entered gold target and the typical space-resolved spectrum is provided. The relative standard uncertainty of the X-ray spectrum from the laser-generated plasma is also determined.展开更多
A technique of flat crystal x-ray spectrometer for quantitative spectral measurement is described.For the flat crystal spectrograph geometry,the quantitative reduction of relating the CCD counts back to the photon flu...A technique of flat crystal x-ray spectrometer for quantitative spectral measurement is described.For the flat crystal spectrograph geometry,the quantitative reduction of relating the CCD counts back to the photon flux from the x-ray source is established.The absolute calibrations of the integral diffraction coefficients of the crystal and the CCD sensitivity make it possible to measure absolute photons flux within the energy range of 2000–5000 eV.The uncertainty analysis of the calibrations is carried out to obtain the energy resolved uncertainties of crystal and CCD.Thus,the experimental spectra with spectral resolved intensity uncertainties are available.Then,a performing experiment of laser-produced Ti plasma is carried out and the absolute x-ray spectra with intensity uncertainty less than 8.5%are obtained.The technique is promising for absolute spectral measurement of high temperature plasmas in a kilo-electron-volt region.展开更多
A transmission grating coupled with an X-ray charge coupled device （CCD） is used to quantitatively measure the proportion of high-order harmonics of the soft-X-ray source of beam line 4B7B. The results show that the...A transmission grating coupled with an X-ray charge coupled device （CCD） is used to quantitatively measure the proportion of high-order harmonics of the soft-X-ray source of beam line 4B7B. The results show that the monochromatic X-ray has third-order and second-order harmonics. The proportion of second-order harmonic of 4B7B is less than 9.0% and the third- order harmonic is below 0.7% when no suppressing method is applied. When suppression methods are used, the proportion of second-order harmonic is less than 1.7% and the third-order harmonic is ignorable.展开更多
An X-ray radiation source with approximately constant radiation temperature is realized by irradiating golden hohlraum with a shaped laser pulse. A simple theoretical model based on power balance is used to design the...An X-ray radiation source with approximately constant radiation temperature is realized by irradiating golden hohlraum with a shaped laser pulse. A simple theoretical model based on power balance is used to design the shape of the drive laser pulse. Experiments are carried out on the Shenguang III prototype laser facility, and the experimentM results are presented for radiation sources with the flat-top lasting about 2.5 ns at two different peak temperatures of about 150 eV and 170 eV, respectively, including the the drive laser pulses and the time integrated possible improvements are discussed. time histories of the temperatures, the shapes of radiation spectra. The validity of the model and展开更多
Radiation flow through gold-doped hydrocarbon foam is investigated and a model is presented to calculate effective opacity for an inhomogeneous,pressure-equilibrated gold/foam mixture based on the Levermore–Pomraning...Radiation flow through gold-doped hydrocarbon foam is investigated and a model is presented to calculate effective opacity for an inhomogeneous,pressure-equilibrated gold/foam mixture based on the Levermore–Pomraning method for binary stochastic media.The effective opacity dependance on the size of the gold particles and the foam temperature are studied.The results suggest that when the mixture temperature is lower than 250 eV,the opacity difference between the 5μm particle mix case and the atomic mix case is large enough to induce a significant discrepancy in radiation transport,which is confirmed by the hydrodynamic simulation.展开更多
Hot dense titanium plasma was produced by irradiating a CH foam coated titanium layer with nanosecond laser pulses.The time-integrated emission spectra of He-like titanium were measured by using an absolutely calibrat...Hot dense titanium plasma was produced by irradiating a CH foam coated titanium layer with nanosecond laser pulses.The time-integrated emission spectra of He-like titanium were measured by using an absolutely calibrated flat crystal spectrometer.The synthetic spectra obtained by the steady collisional-radiative(CR)equilibrium model associated with the hydrodynamic simulations were compared with the experimental spectra.The results show that the electron density increases up to 5×10^(21) cm^(-3) with CH foam of density 40 mg/cc.This work indicates that an overlay of CH foam on a solid target is beneficial to create an optimum condition for K-shell emissions from a high density plasma region.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 50537020 and 50528707.
文摘We perform the theoretical simulation of the concentric-ring patterns between two parallel electrodes covered with thin dielectric layers within the scope of a two-dimensional diffusion-drift model at atmospheric pressure. The time evolution of the discharge patterns is studied and the concentric-ring patterns with different radii shift alternately. The spatial-temporal evolution of electron density in a cycle at different time scales is performed.
基金Project supported by the National Natural Science Foundation of China（Grant Nos 50528707 and 50537020）.
文摘The existence of two diffe1：ent discharge modes has been verified in an rf （radio-frequency） atmospheric pressure glow discharge （APGD） by Shi [J. Appl. Phys. 97, 023306 （2005）]. In the first mode, referred to as a mode, the discharge current density is relatively low and the bulk plasma electrons acquire the energy due to the sheath expansion. In the second mode, termed γ mode, the discharge current density is relatively high, the secondary electrons emitted by cathodc under ion bombardment in the cathode sheath region play an important role in sustaining the discharge. In this paper, a one-dimensional self-consistent fluid model for rf APGDs is used to simulate the discharge mechanisms in the mode in helium discharge between two parallel metallic planar electrodes. The results show that as the applied voltage increases, the discharge current becomes greater and the plasma density correspondingly increases, consequentially the discharge transits from the a mode into the γ mode. The high collisionality of the APGD plasma results in significant drop of discharge potential across the sheath region, and the electron Joule heating and the electron collisional energy loss reach their maxima in the region. The validity of the simulation is checked with the available experimental and numerical data.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.50537020 and 50528707)
文摘This paper performs a numerical simulation of concentric-ring discharge structures within the scope of a twodimensional diffusion-drift model at atmospheric pressure between two parallel circular electrodes covered with thin dielectric layers. With a relative high frequency the discharge structures present different appearances of ring structures within different radii in time due to the evolvement of the filaments. The spontaneous electron density distributions help understanding the formation and development of self-organized discharge structures. During a cycle the electron avalanches are triggered by the electric field strengthened by the feeding voltage and the residual charged particles on the barrier surface deposited in the previous discharges. The accumulation of charges is shown to play a dominant role in the generation and annihilation of the discharge structures. Besides, the rings split and unify to bring and annihilate rings which form a new discharge structure.
基金supported by the National High Technology Program 863 of China
文摘A space-resolving transmission grating spectrometer is established on the ＂Shenguang-III＂ prototype laser facility and an iterative procedure for unfolding the X-ray spectrum with spatial resolution is described. The diagnostics is applied to measure the X-ray spectrum from laser-entered gold target and the typical space-resolved spectrum is provided. The relative standard uncertainty of the X-ray spectrum from the laser-generated plasma is also determined.
基金by the National High-Tech Program of China and the National Natural Science Foundation of China under Grant Nos 10734140,10874156 and 10875109.
文摘A technique of flat crystal x-ray spectrometer for quantitative spectral measurement is described.For the flat crystal spectrograph geometry,the quantitative reduction of relating the CCD counts back to the photon flux from the x-ray source is established.The absolute calibrations of the integral diffraction coefficients of the crystal and the CCD sensitivity make it possible to measure absolute photons flux within the energy range of 2000–5000 eV.The uncertainty analysis of the calibrations is carried out to obtain the energy resolved uncertainties of crystal and CCD.Thus,the experimental spectra with spectral resolved intensity uncertainties are available.Then,a performing experiment of laser-produced Ti plasma is carried out and the absolute x-ray spectra with intensity uncertainty less than 8.5%are obtained.The technique is promising for absolute spectral measurement of high temperature plasmas in a kilo-electron-volt region.
文摘A transmission grating coupled with an X-ray charge coupled device （CCD） is used to quantitatively measure the proportion of high-order harmonics of the soft-X-ray source of beam line 4B7B. The results show that the monochromatic X-ray has third-order and second-order harmonics. The proportion of second-order harmonic of 4B7B is less than 9.0% and the third- order harmonic is below 0.7% when no suppressing method is applied. When suppression methods are used, the proportion of second-order harmonic is less than 1.7% and the third-order harmonic is ignorable.
文摘An X-ray radiation source with approximately constant radiation temperature is realized by irradiating golden hohlraum with a shaped laser pulse. A simple theoretical model based on power balance is used to design the shape of the drive laser pulse. Experiments are carried out on the Shenguang III prototype laser facility, and the experimentM results are presented for radiation sources with the flat-top lasting about 2.5 ns at two different peak temperatures of about 150 eV and 170 eV, respectively, including the the drive laser pulses and the time integrated possible improvements are discussed. time histories of the temperatures, the shapes of radiation spectra. The validity of the model and
文摘Radiation flow through gold-doped hydrocarbon foam is investigated and a model is presented to calculate effective opacity for an inhomogeneous,pressure-equilibrated gold/foam mixture based on the Levermore–Pomraning method for binary stochastic media.The effective opacity dependance on the size of the gold particles and the foam temperature are studied.The results suggest that when the mixture temperature is lower than 250 eV,the opacity difference between the 5μm particle mix case and the atomic mix case is large enough to induce a significant discrepancy in radiation transport,which is confirmed by the hydrodynamic simulation.
基金Supported by the Foundation of China Academy of Engineering Physics under Grant No 2011A0102005the Foundation of Science and Technology on Plasma Physics Laboratory under Grant No 9140C680203110C6804.
文摘Hot dense titanium plasma was produced by irradiating a CH foam coated titanium layer with nanosecond laser pulses.The time-integrated emission spectra of He-like titanium were measured by using an absolutely calibrated flat crystal spectrometer.The synthetic spectra obtained by the steady collisional-radiative(CR)equilibrium model associated with the hydrodynamic simulations were compared with the experimental spectra.The results show that the electron density increases up to 5×10^(21) cm^(-3) with CH foam of density 40 mg/cc.This work indicates that an overlay of CH foam on a solid target is beneficial to create an optimum condition for K-shell emissions from a high density plasma region.
