共查询到20条相似文献,搜索用时 15 毫秒
1.
Apruzese J.P. Kepple P.C. Davis J. Pender J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1988,16(5):529-533
A major goal of current X-ray laser research is the achievement of gain in the 23.3-43.7 Å wavelength region, known as the `water window'. Silicon is the lowest atomic number element for which all the heliumlike 3-2 transitions lie in this region. The authors examine the fundamental kinetics of recombination lasing in this species, and conclude that the Si XIII 1s 3d 1D 2-1s 2p 1P 1 line at 39.1 Å is an attractive candidate for recombination-pumped lasing. Attainment of gain in this line is somewhat more energetically favorable than for the hydrogenic Al XIII 3-2 transitions, but radiative trapping may be somewhat more troublesome than for H-like Al 相似文献
2.
Maier W.B. II Kadish A. Buchenauer C.J. Robiscoe R.T. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(6):676-683
Formative times in electrical discharges in overvoltaged gaps are analyzed with a model having no spatial dependence and with simple assumptions about discharge channel temperature T and discharge voltage. The model treats the early temporal evolution of the discharge. Specifically, the dissipative voltage drop, V *, across the discharge is taken to be a step function of T . Thermal quasi-equilibrium is assumed in the discharge medium, and it is shown that d (In t d)/d(In &thetas;)=-1, i.e., &thetas;t d=constant, where &thetas; is the fractional overvoltage and t d is the formative time lag, in agreement with measured values of t d for much of the experimentally explored range of &thetas;. Highly-time-resolved (~92 ps) experimental data are presented for the first 10 ns of electrical discharge initiation; these data suggest that the authors' model should provide a reasonable representation of t d when t d>10-100 ns 相似文献
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4.
Lieberman M.A. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1988,16(6):638-644
A self-consistent solution for the dynamics of a high voltage, capacitive radio frequency (RF) sheath driven by a sinusoidal current source is obtained under the assumptions of time-independent, collisionless ion motion and inertialess electrons. Expressions are obtained for the time-average ion and electron densities, electric field and potential within the sheath. The nonlinear oscillation motion of the electron sheath boundary and the nonlinear oscillating sheath voltage are also obtained. The effective sheath capacitance and conductance are also determined. It was found that: (1) the ion-sheath thickness S m is √50/27 larger than a Child's law sheath for the DC voltage and ion current density; (2) the sheath capacitance per unit area for the fundamental voltage harmonic is 2.452 ϵ0 /Sm, where ϵ0 is the free space permittivity; (3) the ratio of the DC to peak value of the oscillating voltage is 54/125; (4) the second and third voltage harmonics are, respectively, 12.3 and 4.2% of the fundamental; and (5) the conductance per unit area for stochastic heating by the oscillating sheath is 2.98 (λD/S m)2/3 (e 2n 0/mu e), where n 0 is the ion density, λD is the Debye length at the plasma-sheath edge, and u e is the mean electron speed 相似文献
5.
Nardi V. Bilbao L. Brzosko J.S. Powell C. Zeng D. Bortolotti A. Mezzetti F. Robouch B.V. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1988,16(3):374-378
For pt.I see ibid., vol.16, no.3, p.368-73, June 1988. Methods of increasing, by a factor greater than five, the neutron yield/short Y n from D-D fusion reactions in a plasma focus (PF) enhance both the D+-ion acceleration to energy values E d>1-8 MeV and the ion confinement in the pinch region. Nuclear activation of C and N in the (doped) filling gas of the discharge chamber and of solid targets of C and BN bombarded by the ion beam in the direction of the electrode axis (0°) confirms earlier determination of the energy spectrum of the trapped ions (d φt/dE ∝φ0tE -m) and of the ejected beam (d φb/dE ∝φ0bE d-m, m =2.5±0.5 for 0.1 MeV≲E ≲3 MeV). A Thomson (parabola) spectrometer with nanosecond time resolution determines the time of emission t ( E ) of the beam at 0°. Ion acceleration and trapping occur within the small (filamentary) elements of the magnetic fine structure of the pinch, which can be dispersed on a relatively large confinement volume after the pinch disintegration. It has been found that φt/φb≳10-103 for E d≳1 MeV, depending on Y n 相似文献
6.
Mishra G. Maheshwari K.P. Praburam G. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(1):181-186
Linearized Vlasov-Maxwell equations are solved to obtain the growth rate of free electron laser instability from a tenuous relativistic electron beam propagating in a partially dielectric loaded waveguide immersed in combined axial and longitudinal wiggler magnetic fields. The instability appears via cyclotron resonance interactions for wave perturbations very close to w -kV z-w c=nk 0V Z where n is the general harmonic number. For n =0, the gain is similar to a slow wave cyclotron amplifier. For n ⩾1, the growth rate is substantially larger than the standard slow wave free electron laser scheme utilizing a transverse wiggler field 相似文献
7.
It is shown that the slowly varying amplitudes of both high and low frequency extraordinary waves propagating perpendicular to the dc magnetic field in ferromagnetic systems are described by the nonlinear SchrEdinger equation. The extraordinary waves are modulationally stable (unstable) and may evolve as dark (bright) solitons as the frequency ω satisfies ω0 < ω < ωb or ω > ω1(0 < ω < ω0 or ωa ≤ ω < ω1), where ωa, ωb, ω0 and w1 are given in the text. 相似文献
8.
Schott L.W. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1991,19(4):612-618
Experiments are described which show that the reflection coefficient for ion acoustic waves (IAW) from the sheath at a grid is affected by an HF electric field with a frequency f HF≲5f pi(f pi =ion plasma frequency). For peak-to-peak amplitudes of the HF voltage drop across the sheath Φ0≲k B T e/e and f HF>f pi, the energy distribution of the ions passing through the grid develops a hot tail and the reflected wave suffers enhanced Landau damping. If Φ0≳k BT e/e and f HF<f pi, a large-amplitude IAW is excited at the grid; a well-defined ion beam is formed; and local growth of the reflected wave is observed. Test waves launched from the grid show the same propagation characteristics as the reflected waves 相似文献
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Gray P.C. Hudson M.K. Lotko W. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1992,20(6):745-755
Particle simulation in a one-dimensional bounded system is used to examine the formation of acoustic double layers in the presence of two ion species. Double-layer formation depends critically on the details of the distribution functions of the supporting ion populations, and their relative drifts with respect to the electrons. The effect of having two ion components, an H+ and an O+ beam, on double-layer evolution from ion acoustic turbulence driven by an electron drift relative to the H+ beam of ≈0.5u e, where u ue is the electron thermal speed, is examined. The ratio of ion drifts is taken to be consistent with acceleration by a quasi-static auroral potential drop (i.e. V H/V O=√M O/ M H=4.0). Acoustic double layers form in either ion species on the time scale τ≈100ωps-1, where ωps is the ion plasma frequency for species `s' and s =H or O, and for drifts relative to the electrons lower than that required for double layer formation in simulations of single ion component plasma 相似文献
11.
Basu J. Biswas S. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1991,19(4):645-650
A study is presented of the propagation of electron plasma waves in a warm collisional plasma filling a conducting cylinder and magnetized strongly in the axial direction, the plasma parameters being taken to be such that the electron-ion collision is the dominant damping process. The attenuation and phase constants are derived in suitably normalized form by using the electrodynamic method. The dispersion and attenuation characteristics for propagation in the lowest order mode in a hydrogen plasma are obtained for various values of the normalized plasma radius αωpe/c , the electron temperature and electron density being held constant, and the characteristics are compared with those given by the usual quasi-static approximation, which is found to be valid only if αωpe /c ≲1, where α is the plasma radius, ω pe is the plasma frequency, and c is the velocity of light in free space. The effect of the plasma frequency on the characteristics is investigated 相似文献
12.
Meunier J.-L. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1990,18(6):904-910
Observations of the cathodic copper plasma expansion at low pressures of He, Ar, and SF6 showed that, for background gas mass densities of ρg=1 to 4×10-4 kg/m 3 and higher, the plasma and gas are separated into two volumes. A shock wave acts as a boundary between the two volumes. The boundary attains a stationary position once its expansion velocity decreases to the velocity of sound in the background gas. This position corresponds to a distance R c to the cathode that agrees with a snowplow expansion model, giving R c βf =E r, where f is a function of the arc current and background gas characteristics, E r is the erosion rate of the cathode, and β varies between 2.1 and 2.5. The interaction model is based on kinetic energy exchanges between two gas-like volumes without other energy losses. A maximum pressure limit for vacuum arc deposition is set for ρg /I =2 to 9×10-6 kg/m3 A 相似文献
13.
Mori W.B. Decker C.D. Leemans W.P. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(1):110-119
The relativistic harmonic content of large-amplitude electromagnetic waves propagating in underdense plasmas is investigated. The steady-state harmonic content of nonlinear linearly polarized waves is calculated for both the very underdense (w p/w 0)≪1 and critical density (w p/w 0)≃1 limits. For weak nonlinearities, eE 0/mc ω0<1, the nonlinear source term for the third harmonic is derived for arbitrary w p/w 0. Arguments are given for extending these results for arbitrary wave amplitudes. It is also shown that the use of the variable x -ct and the quasi-static approximation leads to errors in both magnitude and sign when calculating the third harmonic. In the absence of damping or density gradients the third harmonic's amplitude is found to oscillate between zero and twice the steady-state value. Preliminary PIC simulation results are presented. The simulation results are in basic agreement with the uniform plasma predictions for the third-harmonic amplitude. However, the higher harmonics are orders of magnitude larger than expected and the presence of density ramps significantly modifies the results 相似文献
14.
Ryiyopoulos S. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1990,18(3):369-386
A set of coupled nonlinear differential equations, involving the slow amplitude and phase variation for each mode, is used to simulate the multimode dynamics in the quasi-optical gyrotron. The interaction among various modes is mediated by coupling coefficients of known analytic dependence on the normalized current I , the interaction length μ, and the frequency detunings Δi corresponding to the competing frequencies ωi. The equations include all the possible resonant combinations of up to four different frequencies, ωi-ωj+ω k-ωl≃0, among a set of N participating modes, keeping terms up to fifth order in the wave amplitudes. The formalism is quite general and can be used to study mode competition, the existence of a final steady state and its stability, and its accessibility from given initial conditions. It is shown that when μ/β⊥≫1, μ can be eliminated as an independent parameter. The control space is then reduced to a new normalized current I and the desynchronism parameters νi=Δiμ for the interacting frequencies. Numerical simulations for cold beams of various cross sections demonstrate that νi is the most important parameter for the system behavior. Overmoding is not determined by the frequency separation δω among the cavity modes per se, but by the separation among the corresponding desynchronism parameters 相似文献
15.
Veerasamy V.S. Amaratunga G.A.J. Milne W.I. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(3):322-328
A model is proposed for the flow of a plasma originating from a cathodic vacuum arc into a curvilinear magnetic field. The model gives good agreement with measurements obtained from a filtered cathodic-arc thin film deposition system. The important parameters involved in the motion of a vacuum arc plasma beam through a magnetic filter are examined. The analysis is based on the use of the guiding center approximation to describe the motion of the charged particles produced in the plasma where the thermal energy is negligible compared to the mass flow energy. Electron-ion collision effects are included within the framework of the drift model. It is shown that under the limiting condition of a collision frequency which is much higher than the cyclotron frequency of the electron, the motion of the plasma ions around the bend becomes independent of the magnetic field, with the number of ions traversing the filter significantly reduced. However, in the collisionless plasma case (cyclotron frequency higher than the collision frequency), the model predicts a square-law relationship between ion-saturation current and magnetic field , I p ∞B 2 相似文献
16.
Dincer M.S. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(4):393-394
Electron-molecule collision frequencies in SF6 are obtained from an equivalent gas number density method in a coaxial gap. At a given equivalent reduced electric field, the collision frequencies increase with increasing B /N 相似文献
17.
Hayess E. Juttner B. Lieder G. Neumann W. Pursch H. Weixelbaum L. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1989,17(5):666-671
The method of laser-induced fluorescence was used to study the behavior of the absolute neutral vapor density of a diffuse vacuum arc on FeCu contacts. The local and temporal resolutions were 1 mm3 and 10 μs, respectively. The arc current had a sinusoidal shape of 5.8-ms duration with peak values of 90 and 510 A. It was found that the maximum densities of the iron and copper atoms are 1.2×10 17 m-3 and 7.5×1017 m-3, respectively. During the arc the density was correlated with the current. At current zero the measured densities decreased to 10 16 m-3. After current zero, an exponential density decay with a time constant of about 100 μs was observed, indicating the recovery of dielectric strength after current zero. Measurements of the neutron iron vapor density at different spatial positions in the electrode gap reveal a nonisotropic distribution. From the measurements of the population distribution of the iron ground-state multiplet a 5D , the excitation temperature was derived. This temperature was low compared with the cathode spot temperature 2500-4000 K and decreased from 1600 K at the current maximum to 1000 K at current zero. The results indicate that the generation of neutrals is caused by flying evaporating metal droplets rather than by molten surface areas 相似文献
18.
Talaat M.E. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1991,19(2):176-188
Equations are derived for predicting the current-voltage characteristic curves of axial RF discharges in noble gases, with turbulent flow. The electrons are considered to be made up of two Maxwellian groups: bulk and tail electrons. The bulk electrons are described by a temperature T b, and have kinetic energies (1/2 mv 2=eV ) from 0 to eV l (eV l=the threshold energy of the first dominant inelastic collision process). The electrons of the depressed tail of the distribution function are described by another temperature, T t<T b, and have (eV >eV l). The terms in these equations correspond to the prevailing processes occurring inside the noble gas discharge. The rate coefficients given are derived, based on the two-electron group model. The effect of the high velocity flow is accounted for by the terms giving the divergence of the flux of particles in the redirection of flow in each of the continuity equations for the primary species and by adding a diffusion coefficient due to turbulence to the static discharge diffusion coefficients of the ions and metastables 相似文献
19.
Vozdvijensky V.A. Sidorov V.A. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1991,19(5):778-781
The dynamics of light emission accompanying the initial stage of electric discharge in a substantially undervoltaged vacuum gap was studied with a knock-down model using high-speed photorecording. Voltage across the gap was maintained within the range of 0.5-5 kV, which corresponded to the minimum operating voltage of vacuum-triggered gaps. It was found that front layers of a plasma cloud near a cathode, formed by a firing pulse, scattered at a speed of (5-8)×106 cm/s. During firing, a channel directed to the opposite electrode was formed from the plasma cloud near the cathode. It was found that the average switch-on delay time of the triggered vacuum gap is ~d (1+h /d ) If-α, where d is the interelectrode gap length, h is the trigger assembly penetration height, and I f is the firing current 相似文献