The formulae for parameters of a negative electron affinity semiconductor(NEAS)with large mean escape depth of secondary electrons A(NEASLD)are deduced.The methods for obtaining parameters such asλ,B,E_(pom)and the m...The formulae for parameters of a negative electron affinity semiconductor(NEAS)with large mean escape depth of secondary electrons A(NEASLD)are deduced.The methods for obtaining parameters such asλ,B,E_(pom)and the maximumδandδat 100.0 keV≥E_(po)≥1.0 keV of a NEASLD with the deduced formulae are presented(B is the probability that an internal secondary electron escapes into the vacuum upon reaching the emission surface of the emitter,δis the secondary electron yield,E_(po)is the incident energy of primary electrons and E_(pom)is the E_(po)corresponding to the maximumδ).The parameters obtained here are analyzed,and it can be concluded that several parameters of NEASLDs obtained by the methods presented here agree with those obtained by other authors.The relation between the secondary electron emission and photoemission from a NEAS with large mean escape depth of excited electrons is investigated,and it is concluded that the presented method of obtaining A is more accurate than that of obtaining the corresponding parameter for a NEAS with largeλ_(ph)(λ_(ph)being the mean escape depth of photoelectrons),and that the presented method of calculating B at E_(po)>10.0 keV is more widely applicable for obtaining the corresponding parameters for a NEAS with largeλ_(ph).展开更多
Based on a simple classical model specifying that the primary electrons interact with the electrons of a lattice through the Coulomb force and a conclusion that the lattice scattering can be ignored, the formula for t...Based on a simple classical model specifying that the primary electrons interact with the electrons of a lattice through the Coulomb force and a conclusion that the lattice scattering can be ignored, the formula for the average energy required to produce a secondary electron （ε） is obtained. On the basis of the energy band of an insulator and the formula for e, the formula for the average energy required to produce a secondary electron in an insulator （εi） is deduced as a function of the width of the forbidden band （Eg） and electron affinity X. Experimental values and the εi values calculated with the formula are compared, and the results validate the theory that explains the relationships among Eg, X, and ei and suggest that the formula for εi is universal on the condition that the primary electrons at any energy hit the insulator.展开更多
A compact, low cost, multipoint Thomson scattering diagnostic system for HT-7 superconducting tokamak has been in operation since 1999. Its capability of measuring electron temperatures is in the range of 200 eV to 2 ...A compact, low cost, multipoint Thomson scattering diagnostic system for HT-7 superconducting tokamak has been in operation since 1999. Its capability of measuring electron temperatures is in the range of 200 eV to 2 keV at a density of a few times IO12 cm-3, with a spatial resolution of 2.4 cm for 5 spatial points and a temporal resolution of 1 ms-1 s for 8 time points. The main components of the diagnostic system include a 20-25 J Nd: glass laser with 35 ns pulse width (8 pulses per burst), a KDP frequency-doubling unit, spherical mirrors of multipass input optical system, a wide-angle collection objective, a bandpass glass filter for reducing the stray light to zero a f/2.5 polychromator, a fiberglass collimator, a photomultiplier's box with electronic preamplifier, high gain and high signal/noise ratio, CAMAC data acquisition and so on. The multipass optical system has been successful at increasing the quantity of scattered photons by passing the probing laser beam 10 times through the plasma under investigation. The HT7 Thomson scattering diagnostic has provided successfully the information on two-dimensional electron temperature in the plasma of HT-7 tokamak with LHCD and IBW.展开更多
Based on a simple classical model that primary electrons at high electron energy interact with the electrons of lattice by the Coulomb force,we deduce the energy of secondary electrons.In addition,the number of second...Based on a simple classical model that primary electrons at high electron energy interact with the electrons of lattice by the Coulomb force,we deduce the energy of secondary electrons.In addition,the number of secondary electrons in the direction of velocity of primary electrons per unit path length,n,is obtained.According to the energy band of the insulator,n,the definition of the probability B of secondary electrons passing over the surface barrier of insulator into the vacuum and the assumption that lattice scattering is ignored,we deduce the expression of B related to the width of the forbidden band(E_(g))and the electron affinityχ.As a whole,the B values calculated with the formula agree well with the experimental data.The calculated B values lie between zero and unity and are discussed theoretically.Finally,we conclude that the deduced formula and the theory that explains the relationships among B,χand E_(g) are correct.展开更多
Based on the main physical processes,we deduce the relationships among the incident energy Wp0 of the primary electron,the number of released secondary electrons(i.e.δ_(PEθ))per primary electron entering the metal a...Based on the main physical processes,we deduce the relationships among the incident energy Wp0 of the primary electron,the number of released secondary electrons(i.e.δ_(PEθ))per primary electron entering the metal at incident angleθand the angleθitself.In addition,the relationship ofδPEθatθ=0°,i.e.δ_(PE0),with Wp0 is determined.From the experimental results,the relationship of the ratio atθ=0°,i.e.β_(0) which is the ratio of the average number of released secondary electrons generated by a single primary electron backscattered at the metal surface to that generated by a single primary electron entering the metal,with Wp0 is determined.Moreover,the relationships among the ratioβθ,Wp0 andθare obtained.Based on the relationships among the secondary electron yield atθ(i.e.δθ),the yield atθ=0°(i.e.δ_(0)),the backscattering coefficient atθ(i.e.η_(θ)),the coefficient atθ=0°(i.e.η0),δ_(PEθ)andδ_(PE0),we deduce the universal formula forδ_(θ),δ_(0),η_(θ),η_(0),and W_(p0) for the primary electrons at an incident energy of 2–10 keV.The secondary electron yields calculated from the universal formula and the experimental yields of some metals are compared,and the results suggest that the proposed formula is universal for estimation of secondary electron yields atθ=0°−80°.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11873013)。
文摘The formulae for parameters of a negative electron affinity semiconductor(NEAS)with large mean escape depth of secondary electrons A(NEASLD)are deduced.The methods for obtaining parameters such asλ,B,E_(pom)and the maximumδandδat 100.0 keV≥E_(po)≥1.0 keV of a NEASLD with the deduced formulae are presented(B is the probability that an internal secondary electron escapes into the vacuum upon reaching the emission surface of the emitter,δis the secondary electron yield,E_(po)is the incident energy of primary electrons and E_(pom)is the E_(po)corresponding to the maximumδ).The parameters obtained here are analyzed,and it can be concluded that several parameters of NEASLDs obtained by the methods presented here agree with those obtained by other authors.The relation between the secondary electron emission and photoemission from a NEAS with large mean escape depth of excited electrons is investigated,and it is concluded that the presented method of obtaining A is more accurate than that of obtaining the corresponding parameter for a NEAS with largeλ_(ph)(λ_(ph)being the mean escape depth of photoelectrons),and that the presented method of calculating B at E_(po)>10.0 keV is more widely applicable for obtaining the corresponding parameters for a NEAS with largeλ_(ph).
基金Project supported by the Special Funds of the National Natural Science Foundation of China (Grant No. 51245010)the Natural Science Foundation of Jiangsu Province, China (Grant No. 10KJB180004)
文摘Based on a simple classical model specifying that the primary electrons interact with the electrons of a lattice through the Coulomb force and a conclusion that the lattice scattering can be ignored, the formula for the average energy required to produce a secondary electron （ε） is obtained. On the basis of the energy band of an insulator and the formula for e, the formula for the average energy required to produce a secondary electron in an insulator （εi） is deduced as a function of the width of the forbidden band （Eg） and electron affinity X. Experimental values and the εi values calculated with the formula are compared, and the results validate the theory that explains the relationships among Eg, X, and ei and suggest that the formula for εi is universal on the condition that the primary electrons at any energy hit the insulator.
文摘A compact, low cost, multipoint Thomson scattering diagnostic system for HT-7 superconducting tokamak has been in operation since 1999. Its capability of measuring electron temperatures is in the range of 200 eV to 2 keV at a density of a few times IO12 cm-3, with a spatial resolution of 2.4 cm for 5 spatial points and a temporal resolution of 1 ms-1 s for 8 time points. The main components of the diagnostic system include a 20-25 J Nd: glass laser with 35 ns pulse width (8 pulses per burst), a KDP frequency-doubling unit, spherical mirrors of multipass input optical system, a wide-angle collection objective, a bandpass glass filter for reducing the stray light to zero a f/2.5 polychromator, a fiberglass collimator, a photomultiplier's box with electronic preamplifier, high gain and high signal/noise ratio, CAMAC data acquisition and so on. The multipass optical system has been successful at increasing the quantity of scattered photons by passing the probing laser beam 10 times through the plasma under investigation. The HT7 Thomson scattering diagnostic has provided successfully the information on two-dimensional electron temperature in the plasma of HT-7 tokamak with LHCD and IBW.
基金Supported by the Natural Science Foundation of Jiangsu Provincial Universities under Grant No 10KJB180004.
文摘Based on a simple classical model that primary electrons at high electron energy interact with the electrons of lattice by the Coulomb force,we deduce the energy of secondary electrons.In addition,the number of secondary electrons in the direction of velocity of primary electrons per unit path length,n,is obtained.According to the energy band of the insulator,n,the definition of the probability B of secondary electrons passing over the surface barrier of insulator into the vacuum and the assumption that lattice scattering is ignored,we deduce the expression of B related to the width of the forbidden band(E_(g))and the electron affinityχ.As a whole,the B values calculated with the formula agree well with the experimental data.The calculated B values lie between zero and unity and are discussed theoretically.Finally,we conclude that the deduced formula and the theory that explains the relationships among B,χand E_(g) are correct.
基金by Scientific Research Fund of Nanjing University of Information Science and Technology(No S8108197001)the Natural Science Foundation of Jiangsu Provincial Universities(No 10KJB180004).
文摘Based on the main physical processes,we deduce the relationships among the incident energy Wp0 of the primary electron,the number of released secondary electrons(i.e.δ_(PEθ))per primary electron entering the metal at incident angleθand the angleθitself.In addition,the relationship ofδPEθatθ=0°,i.e.δ_(PE0),with Wp0 is determined.From the experimental results,the relationship of the ratio atθ=0°,i.e.β_(0) which is the ratio of the average number of released secondary electrons generated by a single primary electron backscattered at the metal surface to that generated by a single primary electron entering the metal,with Wp0 is determined.Moreover,the relationships among the ratioβθ,Wp0 andθare obtained.Based on the relationships among the secondary electron yield atθ(i.e.δθ),the yield atθ=0°(i.e.δ_(0)),the backscattering coefficient atθ(i.e.η_(θ)),the coefficient atθ=0°(i.e.η0),δ_(PEθ)andδ_(PE0),we deduce the universal formula forδ_(θ),δ_(0),η_(θ),η_(0),and W_(p0) for the primary electrons at an incident energy of 2–10 keV.The secondary electron yields calculated from the universal formula and the experimental yields of some metals are compared,and the results suggest that the proposed formula is universal for estimation of secondary electron yields atθ=0°−80°.
