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1.
We report here an experimental study of the ionic keV X-ray line emission from magnesium plasma produced by laser pulses of
three widely different pulse durations (FWHM) of 45 fs, 25 ps and 3 ns, at a constant laser fluence of ∼1.5 × 104 J cm − 2. It is observed that the X-ray yield of the resonance lines from the higher ionization states such as H- and He-like ions
decreases on decreasing the laser pulse duration, even though the peak laser intensities of 3.5 × 1017 W cm − 2 for the 45 fs pulses and 6.2 × 1014 W cm − 2 for the 25 ps pulses are much higher than 5 × 1012 W cm − 2 for the 3 ns laser pulse. The results were explained in terms of the ionization equilibrium time for different ionization
states in the heated plasma. The study can be useful to make optimum choice of the laser pulse duration to produce short pulse
intense X-ray line emission from the plasma and to get the knowledge of the degree of ionization in the plasma. 相似文献
2.
M. R. Talukder S. Bose M. A.R. Patoary A. K.F. Haque M. A. Uddin A. K. Basak M. Kando 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(2):281-287
A simple empirical formula is proposed for the rapid
calculation of electron impact total ionization cross sections both for the
open- and closed-shell neutral atoms considered in the range 1≤
Z≤92 and the incident electron energies from threshold to about
104 eV. The results of the present analysis are compared with the
available experimental and theoretical data. The proposed model provides a
fast method for calculating fairly accurate electron impact total ionization
cross sections of atoms. This model may be a prudent choice, for the
practitioners in the field of applied sciences e.g. in plasma modeling, due
to its simple inherent structure. 相似文献
3.
Multiphonon ionization of the H2 molecule under the action of a weak (probe) field, which provides the initial population of the low-lying (working) level,
and intense monochromatic linearly polarized radiation is studied. The multiphoton ionization process occurs under the conditions
of strong field perturbation of two intermediate Rydberg series, np0(1Σ
u
+
and np2(1Πu), of the optical R(0)branch which have different ionization potentials. The series are occupied simultaneously as a result of single-photon
absorption by an excited H
2
*
molecule in the working state 4s
σH′1Σ
g
+
(v=0). As a result of the irregularity in the arrangement of the intermediate levels from a large group of states that are combined
in the multiphoton ionization process a sharp and irregular change occurs in the dependence of the shifts and widths Γn of the levels on the intensity f of the strong field in a transition from one level to another. It is shown that for field intensities f such that the level widths remain much less than the splitting between the levels (Γn≪/n
3) the stabilizing effect (i.e., the field-induced narrowing of the levels as f→∞) in the form Γn ∝ 1/f
2 (as happens in atoms with a structureless core) is not observed in molecular systems.
Zh. éksp. Teor. Fiz. 115, 1987–2000 (June 1999) 相似文献
4.
A. A. Kruglov 《Radiophysics and Quantum Electronics》2011,54(1):24-37
We study the plasma conductivity within the framework of the magnetohydrodynamic approximation under conditions typical of
the coronas of the Sun and stars of the late spectral classes. The problem of finding the elements of the plasma conductivity
tensor is reduced to derivation of approximate formulas and numerical values. It is shown that two regimes of dissipation
of the current running across the magnetic field can be realized in the corona, namely, one due to the friction of the ion
and neutral plasma components (Cowling conductivity) and the other, due to the friction of two different ion components. The
first regime is realized in the larger part of the lower corona, whereas the condition for realization of the second regime,
i.e., B/n
e < 10−9 G·cm3, where B is the magnetic field and ne is the electron number density, can be satisfied in the base of the solar corona or
in coronal streamers. In the second regime, the rate of the transverse-current dissipation increases tenfold compared with
the hydrogen plasma. The longitudinal and Hall components of the conductivity tensor differ only slightly from their values
for the electron–proton plasma. The paper draws attention to the fact that along with the momentum exchange due to the charge
exchange, the momentum exchange due to ionization and recombination during electron collisions plays a significant part in
the friction of neutral and ionized hydrogen atoms. 相似文献
5.
U. Yusupaliev 《Bulletin of the Lebedev Physics Institute》2009,36(8):245-251
Using an ionization sensor, it was found that weakly ionized plasma with an ionization degree larger than 10−6 is formed under exposure to UV radiation of a high-current pulsed electric discharge in gas (air, nitrogen, xenon, and krypton)
at atmospheric pressure at a distance of ∼1.2–2.5 cm from the discharge boundary. It was shown that the structure of such
discharge includes, in addition to the discharge channel, a dense shell and a shock wave, also a region of weakly ionized
and excited gas before the shock wave front. The mechanism of discharge expansion in dense gas is ionization and heating of
gas involved in the discharge due to absorption of the UV energy flux from the discharge channel and the flux of the thermal
energy transferred from the discharge channel to the discharge shell due to electron thermal conductivity. 相似文献
6.
V. D. Zvorykin A. O. Levchenko A. G. Molchanov I. V. Smetanin N. N. Ustinovskii 《Bulletin of the Lebedev Physics Institute》2010,37(2):60-64
The grazing mode of microwave propagation in a hollow plasma waveguide formed by ionization of atmospheric air with a small
easily ionized additive by strong UV pulses of the Garpun KrF laser (λ = 248 nm, the pulse duration and energy are ∼70 ns and ∼50 J) was experimentally demonstrated for the first time. The annular
laser beam produced a hollow tube ∼10 cm in diameter with an electron density of ∼1012 cm−3 in a plasma wall ∼1 cm thick, over whichmicrowave radiation with λ
mw
∼ 8 mm was transmitted to a distance of 60 m. Themicrowave signal transmitted by the waveguide was amplified by a factor
of 6 in comparison with propagation in free space. 相似文献
7.
N. Kishimoto M. Matsumoto E. Matsumura K. Ohno 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(1):75-84
Stereodynamics in ionization of toluene and o-, p-chlorotoluenes by collision
with He*(23S) metastable atoms were investigated by two-dimensional
collision-energy/electron-energy-resolved Penning ionization electron
spectroscopy. Anisotropic interactions around the molecule were studied by
the collision energy dependence of partial ionization cross-sections
(CEDPICS) as well as model potential calculations, and shielding effect by
the methyl group was observed in CEDPICS for ionization from Cl lone-pair
orbitals of o-
chlorotoluene. Attractive interaction with He*(23S)
around the π orbital region was found to be larger for toluene rather
than o-, p-
chlorotoluenes. Exterior electron density (EED) calculation of
partial ionization cross-sections in Penning ionization and negative CEDPICS
for ionization band observed in ca. 4 eV in electron energy indicated that
π-2π+1 shake-up state was observed in
Penning ionization electron spectroscopy of toluene. 相似文献
8.
A 3.7 GHz system, which is meant for LHCD experiments on ADITYA tokamak, is used for producing ECR discharge. The ECR discharge
is produced by setting the appropriate resonance magnetic field of 0.13 T, with hydrogen at a fill pressure of about 5 × 10−5 Torr. The RF power, up to 10 kW (of which ∼50% is reflected back), with a typical pulse length of 50 ms, is injected into
the vacuum chamber of the ADITYA tokamak by a LHCD grill antenna and is used for plasma formation. The average coupled RF
power density (the RF power/a typical volume of the plasma) is estimated to be ∼5 kW/m3. When the ECR appears inside the tokamak chamber for the given pumping frequency (f = 3.7 GHz) a plasma with a density (n
e) ∼ 4 × 1016 m−3 and electron temperature ∼8 eV is produced. The density and temperature during the RF pulse are measured by sets of Langmuir
probes, located toroidally, on either side of the antenna. Hα signals are also monitored to detect ionization. An estimate of density and temperature based on simple theoretical calculation
agrees well with our experimental measurements. The plasma produced by the above mechanism is further used to characterize
the ECR-assisted low voltage Ohmic start-up discharges. During this part of the experiments, Ohmic plasma is formed using
capacitor banks. The plasma loop voltage is gradually decreased, till the discharge ceases to form. The same is repeated in
the presence of ECR-formed plasma (RF pre-ionization), formed 10 ms prior to the loop voltage. We have observed that (with
LHCD-induced) ECR-assisted Ohmic start-up discharges is reliably and repeatedly obtained with reduced loop voltage requirement
and breakdown time decreases substantially. The current ramp-up rates also decrease with reduced loop voltage operation. These
studies established that ECR plasma formed with LHCD system exhibits similar characteristics as reported earlier by dedicated
ECR systems. This experiment also addresses the issue of whether ECR plasma formed with grill antenna exhibits similar behavior
as that formed by single waveguide ECR antenna. Our experimental observations suggest that the characteristics of (LHCD system-induced)
ECR-assisted Ohmic start-up discharges show similar properties, reported earlier with normal ECR-assisted Ohmic start-up discharges
and hence LHCD system may be used as ECR system at reduced toroidal magnetic field for other applications like wall conditioning.
相似文献
9.
Yu. P. Snitovskii 《Technical Physics》2009,54(6):907-911
A near-electrode nonuniform magnetic field crossed with an electric field is found to strongly affect the rate of etching
of silicon dioxide on glass substrates in a CF4 + O2 plasma when the Larmor frequency (≈109 s−1) is much higher than the frequency of collisions of an electron with surrounding plasma particles (≈106 s−1) and the frequency of the applied rf electric field (≈107 s−1). The confinement of electrons by the magnetic field in the immediate vicinity of the substrate surface to be treated increases
the rate of generation of chemically active particles, which increases the etching rate of silicon dioxide. 相似文献
10.
The return current induced in a plasma by a relativisitc electron beam generates a new electron-ion two-stream instability
(return current instability). Although the effect of these currents on the beam-plasma e-e instability is negligible, there
exists a range of wave numbers which is unstable only to return current (RC) instability and not to e-e instability. The electromagnetic
waves propagating along the direction of the external magnetic field, in which the plasma is immersed, are stabilized by these
currents but the e.m. waves with frequencies,ω
2≪Ω
e
2
≪ω
pe
2
(Ω
e andω
pe being cyclotron and plasma frequency for the electrons of the plasma respectively) propagating transverse to the magnetic
field get destabilized. Heuristic estimates of plasma heating, due to RC instability and due to decay of ion-acoustic turbulence
generated by the return current, are made. The fastest time scale on which the return current delivers energy to the plasma
due to the scattering of ion-sound waves by the electrons can be ∼ω
pi
−1
(ω
pi being the plasma frequency for the ions). 相似文献
11.
S. R. Kreitzman T. Pfiz S. Sun-Mack T. M. Riseman J. H. Brewer D. Ll. Williams T. L. Estle 《Hyperfine Interactions》1991,64(1-4):561-566
The ionization of muonium centers in Si and GaAs have been studied using radio frequency (RF) resonant techniques. In Si all
three muonic centers are detectable by RF. No evidence was found for delayed Mu and Mu* states at any temperature. However, our results on the diamagnetic final state (μ
f
+
) show that it is composed of prompt fractions (as seen by conventional μSR) and delayed fractions arising from the ionization
of Mu* and Mu. We observe a full μ
f
+
fraction at 317 K when the Mu relaxation rate is above 10 μs−1. GaAs differs from the situation in Si in that we observed only a partial conversion of Mu* and Mu to a μ+ final state up to 310 K in spite of the fact that the transverse field relaxation rates become very high at 150 and 250 K
respectively. 相似文献
12.
Summary The Li-like to He-like ion population ratio for calcium at the onset of solar flares is observed to be about 60% higher than
in steady-state ionization balance. The measurement of the duration of this initial period of transient ionization and of
the population ratios of adjacent ionization states allows an estimate of the electron density of the coronal plasma at flare
onset. The density found in this study, within 1·109 and 7·109 cm−3 is comparable with the density typical of pre-flare active regions. 相似文献
13.
L. V. Kulik A. I. Tartakovskii A. V. Larionov E. S. Borovitskaya V. D. Kulakovskii 《Journal of Experimental and Theoretical Physics》1997,85(1):195-199
The paper reports on an investigation of changes in the photoluminescence linewidth and lifetime of excitons and electron-hole
plasma over a wide range of densities between 3×107 and 3×1012 cm−2 at a temperature of 77 K in GaAs/AlGaAs quantum wells. The roles played by thermal ionization of excitons at low densities
of nonequilibrium carriers, exciton-exciton and exciton-electron collisions, and ionization of excitons at high pumping power
densities have been studied.
Zh. éksp. Teor. Fiz. 112, 353–361 (July 1997) 相似文献
14.
An analysis is made of the ionization of deep impurity centers by high-intensity far-infrared and submillimeter-wavelength
radiation, with photon energies tens of times lower than the impurity ionization energy. Within a broad range of intensities
and wavelengths, terahertz electric fields of the exciting radiation act as a dc field. Under these conditions, deep-center
ionization can be described as multiphonon-assisted tunneling, in which carrier emission is accompanied by defect tunneling
in configuration space and electron tunneling in the electric field. The field dependence of the ionization probability permits
one to determine the defect tunneling times and the character of the defect adiabatic potentials. The ionization probability
deviates from the field dependence e(E) ∝ exp(E
2/E
c
2
) (where E is the wave field, and E
c is a characteristic field) corresponding to multiphonon-assisted tunneling ionization in relatively low fields, where the
defects are ionized through the Poole-Frenkel effect, and in very strong fields, where the ionization is produced by direct
tunneling without thermal activation. The effects resulting from the high radiation frequency are considered and it is shown
that, at low temperatures, they become dominant.
Fiz. Tverd. Tela (St. Petersburg) 39, 1905–1932 (November 1997) 相似文献
15.
An optogalvanic effect in a pulsed copper-vapor laser is discovered and investigated. It is found that the generalized deexcitation
rate constant of the resonance level to the ionization state of the active medium is <σv>∼ (3±1)·10−7 cm3·s−1. An optothermal effect caused by the hysteresis of the optogalvanic phenomenon is found experimentally. The feasibility of
measuring the stepped ionization constants of resonance and metastable states for a number of metal atoms in a pulse-discharge
plasma is discussed.
Institute of Physics of Semiconductors of the Siberian Branch of the Russian Academy of Sciences; Institute of Atmospheric
Optics of the Siberian Branch of the Russian Academy of Sciences; Institute of High-Current Electronics of the Siberian Branch
of the Russian Academy of Sciences; Tomsk State University. Translated from Izvestiya Vysshikh Uchebhykh Zavedenii, Fizika,
No. 8, pp. 57–62, August, 1999. 相似文献
16.
Experimental results on interaction of a rotating relativistic electron beam with plasma and neutral gas are presented. The
rotating relativistic electron beam has been propagated up to a distance of 150 cm in a plasma. The response of the plasma
to the rotating electron beam is found to be of magnetic diffusion type over a plasma density range 1011–1013 cm−3. Excitation of the axial and azimuthal return currents by the rotating beam and subsequent trapping of the azimuthal return
current layer by the magnetic mirror field are observed. A field-reversed configuration has been formed by the rotating relativistic
electron beam when injected into neutral hydrogen gas. We have observed field reversal up to three times the initial field
in an axial length of 100 cm. 相似文献
17.
S. I. Nanobashvili Z. R. Beria L. R. Gakheladze G. V. Gelashvili G. E. Gogiashvili M. O. Mdivnishvili I. S. Nanobashvili G. I. Rostomashvili 《Czechoslovak Journal of Physics》1999,49(6):999-1004
The properties of plasma injected into an open magnetic trap of uniform field from an independent UHF source have been investigated.
Plasma is created in the UHF source at the frequency of 2400 MHz (power input 150 W) in the electron cyclotron resonance (ECR)
regime at the pressure of neutral argon (10−5−10−2) torr. It is established that a rather quiescent target plasma with controlled density within the range of (2 × 108−2 × 1012) cm−3 and temperature 2–3eV is accumulated in the trap. It turned out that plasma lifetime in the trap is determined by a classical
mechanism of particle escape at the expense of collisions, at fixed value of magnetic field in the trap it practically is
not changed with the variation of neutral gas pressure and reaches the value ≈ 4×10−3 s at the magnetic field strength in the trap equal 1600 Oe. 相似文献
18.
A. V. Kudrin L. E. Kurina G. A. Markov 《Journal of Experimental and Theoretical Physics》1997,85(4):697-704
An investigation is made of the self-interaction of whistler waves (whistlers) involving the formation of waveguide channels
in a collisional magnetoactive plasma as a result of its additional ionization by the field of the propagating wave. Simplified
equations are derived to describe the behavior of the whistler field in a channel of enhanced plasma density in the presence
of electron collisions. Self-consistent distributions of the field and the plasma corresponding to steady-state ionization
self-channeling of whistlers are obtained by numerically solving the equations for the field together with balance equations
for the electron density and energy. Our estimates indicate that this effect can be observed under laboratory conditions.
Zh. éksp. Teor. Fiz. 112, 1285–1298 (October 1997) 相似文献
19.
K. Blaum D. Beck G. Bollen P. Delahaye C. Guénaut F. Herfurth A. Kellerbauer H.-J. Kluge U. Köster D. Lunney S. Schwarz L. Schweikhard C. Yazidjian 《Hyperfine Interactions》2005,162(1-4):173-179
We have demonstrated for the first time that element-selective laser ionization in combination with ultra-high resolution
mass spectrometry can be used to prepare isomerically pure ion ensembles. Together with β–γ coincidence studies this method allowed a determination of the low-energy structure and the unambiguous identification of
triple β-decaying isomerism in 70Cu. By selective resonant ionization and measurement of the masses of these three states using ISOLTRAP at ISOLDE/CERN with
a relative uncertainty of δm/m ≈ 5 ⋅ 10−8 a clear state-to-mass assignment was possible which resolved the assignment puzzle in 70Cu. 相似文献
20.
V. E. Fortov V. Ya. Ternovoi S. V. Kvitov V. B. Mintsev D. N. Nikolaev A. A. Pyalling A. S. Filimonov 《JETP Letters》1999,69(12):926-931
The electrical conductivity of a nonideal hydrogen plasma is measured under shock-wave compression to pressures ∼1.5 Mbar.
It is found that the conductivity increases sharply (by five orders of magnitude) at a density ρ∼0.3−0.4 g/cm3, reaching close to liquid-metal values ∼103 S/cm. The data obtained can be described by a nonideal-plasma model taking into account the increase in the number of conduction
electrons as a result of “ionization by pressure.”
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 12, 874–878 (25 June 1999) 相似文献