共查询到20条相似文献,搜索用时 62 毫秒
1.
Chandu Venugopal 《Pramana》1987,28(2):181-193
A dispersion relation for the near perpendicular propagation of the electromagnetic ion cyclotron wave has been derived in
a fusion plasma that has deuterium as a majority species, hydrogen as a minority species and fully ionized oxygen as an impurity
constituent; all being modelled by loss cone distribution functions. The wave has a frequencyω around the deuterium ion gyrofrequency-ΩD and a wavelength much longer than its Larmor radiusγ
LD(k
⊥
γ
LD<1); the plasma itself being characterized by large ion plasma frequencies (ω
PD
2
>Ω
D
2
). Two modes, a low frequency (LF) and a high frequency (HF) mode of opposite electrical energy can propagate in the plasma;
the instabilities that arise are thus due to an interaction of modes of opposite energies. We find that while hydrogen tends
to destabilize the plasma, the impurity oxygen ions have the reverse effect. Also the plasma is most stable when the ratios
of the perpendicular components of oxygen-to-deuterium and hydrogen-to-deuterium temperatures are kept low. Detailed studies
of the wave propagation characteristics and energy reveal the close resemblance of a loss cone plasma containing oxygen to
a stable Maxwellian plasma in regard to wave stability, propagation and energy. 相似文献
2.
A magnetized, low-β plasma in pure toroidal configuration is formed and extensively studied with ion mass as control parameter. Xenon, krypton
and argon plasmas are formed at a fixed toroidal magnetic field of 0.024 T, with a peak density of ∼1011 cm−3, ∼4 × 1010 cm −3 and ∼2 × 1010 cm −3 respectively. The experimental investigation of time-averaged plasma parameter reveals that their profiles remain insensitive
to ion mass and suggests that saturated slab equilibrium is obtained. Low-frequency (LF) coherent fluctuations (ω < ω
ci) are observed and identified as flute modes. Here ω
ci represents ion cyclotron frequency. Our results indicate that these modes get reduced with ion mass. The frequency of the
fluctuating mode decreases with increase in the ion mass. Further, an attempt has been made to discuss the theory of flute
modes to understand the relevance of some of our experimental observations. 相似文献
3.
Md. Salimullah R. R. Sharma V. K. Tripathi 《Applied Physics A: Materials Science & Processing》1981,25(3):361-365
Using the fluid model for the nonlinear response of ions, we have studied the nonlinear scattering of an electromagnetic ion
cyclotron wave off the ion acoustic wave in a plasma. The low frequency nonlinearity arises through the parallel ponderomotive
force on ions and the high frequency nonlinearity arises through the nonlinear current density of ions. For a typical nonisothermal
plasma (T
e/T
i∼10) the threshold for this instability in a uniform plasma is ∼1mW/cm2. At power densities ≳102 W/cm2, the growth rate for backscatter turns out to be ∼104s−1. 相似文献
4.
Large-amplitude solitary waves are investigated in a relativistic plasma with finite ion-temperature. The mass of electron
is also considered. The Sagdeev’s pseudopotential is determined in terms ofu, the ion speed. It is found that there exists a critical value ofu
0, the value ofu at which (u′)2=0, beyond which the solitary waves cease to exist. The critical value also depends on the parameters likeν, the soliton velocity;μ, the electronion mass ratio orσ, the temperature ratio of ion to electron. This result reproduces our previous result [Czech. J. Phys., Vol. 54 (2004), No.
4, 489–496] when the ion temperature is neglected. 相似文献
5.
M. Nagata 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(3):429-440
Two weakly ionized plasmas (the ionization-degree a′′ = 10-6
and 10-5) and an intermediately ionized plasma
(a′′ = 10-4) are investigated. In previous work, the
negative magnetoresistance effect (the increase-phenomenon of the discharge current) in a
gas plasma in the case where electrons are scattered only by heavy neutral atoms was only
touched upon. In this work, under the condition that electrons are scattered by heavy
neutral atoms and by the Coulomb force of heavy helium ions, the dependences of “the drift
velocity of electrons” and “the increase-phenomenon of the discharge current in the
magnetoresistance effect” on the ionization-degrees and the active radii of the Coulomb
force of a helium ion are examined. And it is pointed out that the increase-phenomenon of
the discharge current in the magnetoresistance effect appears from neither the wellknown
Langevin equation nor the Fokker-Planck equation. 相似文献
6.
Shear mechanical anisotropy of side chain liquid-crystal elastomers: Influence of sample preparation
Rogez D Francius G Finkelmann H Martinoty P 《The European physical journal. E, Soft matter》2006,20(4):369-378
We study the mechanical anisotropy of a series of uniaxial side chain nematic elastomers prepared with the same chemical composition
but with different preparation protocols. For all the compounds, the experiments performed as a function of temperature show
no discontinuity in both G'
// and G'
⊥ (the labels // and ⊥ stand for the director parallel, respectively perpendicular to the shear displacement) around the nematic-isotropic
(N-I) phase transition temperature determined by DSC. They also all show a small decrease in G'
// starting at temperatures well above this temperature (from ∼ 4°
C to ∼ 20°
C depending on the compound studied) and leading to a small hydrodynamic value of the G'
⊥/G'
// ratio. The measurements taken as a function of frequency show that the second plateau in G'
// and the associated dip in G
//” expected from dynamic semi-soft elasticity are not observed. These results can be described by the de Gennes model, which
predicts small elastic anisotropy in the hydrodynamic and linear regimes. They correspond to the behavior expected for compounds
beyond the mechanical critical point, which is consistent with the NMR and specific heat measurements taken on similar compounds.
We also show that a reduction in the cross-linking density does not change the non-soft character of the mechanical response.
From the measurements taken as a function of frequency at several temperatures we deduce that the time-temperature superposition
method does not apply. From these measurements, we also determine the temperature dependence of the longest relaxation time
τE of the network for the situations where the director is either parallel or perpendicular to the shear velocity. Finally,
we discuss the influence on the measurements of the mechanical constraint associated with the fact that the samples cannot
change their shape around the pseudo phase transition, because of their strong adherence on the sample-bearing glass slides. 相似文献
7.
The results of a study of the generation of a gigawatt-level pulsed ion beam formed by a diode with an explosive-emission
potential electrode in self-magnetic insulation mode are presented. The experiments have been performed on the TEMP-4M ion
accelerator operating in double-pulse formation mode: the first pulse is negative polarity (300–500 ns, 100–150 kV) and the
second is positive (150 ns, 250–300 kV). The ion current density is 20–40 A/cm2; the beam consists of protons and carbon ions. To increase the efficiency of the ion current generation, a circular geometry
diode is proposed. It is shown that with the new design, the plasma is effectively formed over the entire working surface
of the graphite potential electrode. During ion beam generation, magnetic insulation of the electrons is achieved over the
entire length of the diode (B/B
cr ≥ 3). Because of the high drift velocity, the transit time of electrons in the anode-cathode gap is 3–5 ns, whilst the transit
time of C+ carbon ions exceeds 8 ns. This indicates low efficiency self-magnetic insulation for this geometry of diode. At the same
time, it has been observed experimentally that during ion current generation (the second pulse), the electron component of
the total current is suppressed by a factor of 4–5. A new mechanism of limiting the electron emission, which explains the
decrease in the electron component of the total current in the circular diode with self-magnetic insulation, is proposed. 相似文献
8.
U. D. Jentschura B. J. Wundt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(3):357-366
The current discrepancy of theory and experiment observed recently in muonic hydrogen
necessitates a reinvestigation of all corrections to contribute to the Lamb shift in
muonic hydrogen (μH), muonic deuterium (μD), the muonic
\hbox{3He{}^3{\rm He}}
3
He
ion (denoted here as μ
3He+), as well as in the muonic
\hbox{4He{}^4{\rm He}}
4
He
ion (μ
4He+). Here, we choose a semi-analytic approach and evaluate a
number of higher-order corrections to vacuum polarization (VP) semi-analytically, while
remaining integrals over the spectral density of VP are performed numerically. We obtain
semi-analytic results for the second-order correction, and for the relativistic correction
to VP. The self-energy correction to VP is calculated, including the perturbations of the
Bethe logarithms by vacuum polarization. Subleading logarithmic terms in the
radiative-recoil correction to the 2S–2P Lamb shift of order
α(Zα)5
μ
3ln(Zα) / (m
μ
m
N
)
are also obtained. All calculations are nonperturbative in the mass ratio of orbiting
particle and nucleus. 相似文献
9.
We use an Eulerian Vlasov code to study the problem of the formation of a plasma sheath with plasma detachment (i.e. no plasma
transport to the wall) at a plasma-wall transition, in front of an absorbing wall. The ions are described by a kinetic equation
in the full velocity space which integrates exactly the ion orbits. We consider a one-dimensional slab geometry, where the
inhomogeneous direction is perpendicular to the wall. The electrons, assumed to only move along the magnetic field lines,
are described by a parallel-B kinetic equation. The magnetized electrons are restricted to move along the magnetic field because the surface-parallel diamagnetic
and electric drifts are equal and opposite. The present study shows how an ambipolar flow in the direction normal to the wall
is established. For very small values of the angleα between the magnetic field and the plane of the wall, steep density and potential gradients are established in front of the
plate surface with almost no plasma transport towards the wall.
Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreux, Switzerland, June 23–24,
2002. 相似文献
10.
T. Mills L. G. Kaake X.-Y. Zhu 《Applied Physics A: Materials Science & Processing》2009,95(1):291-296
Electrolytes are finding applications as dielectric materials in low-voltage organic thin-film transistors (OTFT). The presence
of mobile ions in these materials (polymer electrolytes or ion gels) gives rise to very high capacitance (>10 μF/cm2) and thus low transistor turn-on voltage. In order to establish fundamental limits in switching speeds of electrolyte gated
OFETs, we carry out in situ optical spectroscopy measurement of a poly(3-hexylthiophene) (P3HT) OTFT gated with a LiClO4:poly(ethyleneoxide) (PEO) dielectric. Based on spectroscopic signatures of molecular vibrations and polaron transitions,
we quantitatively determine charge carrier concentration and diffusion constants. We find two distinctively different regions:
at V
G≥−1.5 V, drift-diffusion (parallel to the semiconductor/dielectric interface) of hole-polarons in P3HT controls charging of
the device; at V
G<−1.5 V, electrochemical doping of the entire P3HT film occurs and charging is controlled by drift/diffusion (perpendicular
to the interface) of ClO4
− counter ions into the polymer semiconductor. 相似文献
11.
Pogorelsky I. V. Polyanskiy M. N. Babzien M. Yakimenko V. Dover N. P. Palmer C. A. J. Najmudin Z. Schreiber J. Shkolnikov P. Dudnikova G. 《Laser Physics》2011,21(7):1288-1294
A picosecond CO2 laser was used successfully in a number of experiments exploring advanced methods of particle acceleration [1]. Proton acceleration
from gas-jet plasma exemplifies another advantage of employing the increase in laser wavelength from the optical to the mid-IR
region. Recent theoretical- and experimental-studies of ion acceleration from laser-generated plasma point to better ways
to control the ion beam’s energy when plasma approaches the critical density. Studying this regime with solid-state lasers
is problematic due to the dearth of plasma sources at the critical electron density ∼1021 cm−3, corresponding to laser wavelength λ = 1 μm. CO2 laser offers a solution. The CO2 laser’s 10 μm wavelength shifts the critical plasma density to 1019 cm−3, a value attainable with gas jets. Capitalizing on this approach, we focused a circular polarized 1-TW CO2 laser beam onto a hydrogen gas jet and observed a monoenergetic proton beam in the 1–2 MeV range. Simultaneously, we optically
probed the laser/plasma interaction region with visible light, revealing holes bored by radiation pressure, as well as quasi-stationary
soliton-like plasma formations. Our findings from 2D PIC simulations agree with experimental results and aid in their interpretation. 相似文献
12.
V. P. Dyakonov R. Szymczak A. D. Prokhorov E. Zubov A. A. Prokhorov G. Petrakovskii L. Bezmaternikh M. Berkowski V. Varyukhin H. Szymczak 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(3):291-298
Magnetic and electron paramagnetic resonance (EPR) properties of
EuFe3(BO3)4 single crystals have been studied over the
temperature range of 300–4.2 K and in a magnetic field up to 5 T. The
temperature, field and orientation dependences of susceptibility,
magnetization and EPR spectra are presented. An antiferromagnetic ordering
of the Fe subsystem occurs at about 37 K. The easy direction of
magnetization perpendicular to the c axis is determined by magnetic
measurements. Below 10 K, we observe an increase of susceptibility connected
with the polarization of the Eu sublattice by an effective exchange field of
the ordered Fe magnetic subsystem. In a magnetic field perpendicular to the
c axis, we have observed an increase of magnetization at T < 10 K in the
applied magnetic field, which can be attributed to the appearance of the
magnetic moment induced by the magnetic field applied in the basal plane.
According to EPR measurements, the distance between the maximum and minimum
of derivative of absorption line of the Lorentz type is equal to 319 Gs. The
anisotropy of g-factor and linewidth is due to the influence of crystalline
field of trigonal symmetry. The peculiarities of temperature dependence of
both intensity and linewidth are caused by the influence of excited states
of europium ion (Eu3+). It is supposed that the difference between the
g-factors from EPR and the magnetic measurements is caused by exchange
interaction between rare earth and Fe subsystems via anomalous Zeeman
effect. 相似文献
13.
Performance of the backward wave oscillator (BWO) is greatly enhanced with the introduction of plasma. Linear theory of the
dispersion relation and the growth rate have been derived and analysed numerically for plasma-filled rippled wall rectangular
waveguide driven by sheet electron beam. To see the effect of plasma on the TM01 cold wave structure mode and on the generated frequency, the parameters used are: relativistic factor γ = 1.5 (i.e. v/c = 0.741), average waveguide height y
0 = 1.445 cm, axial corrugation period z
0 = 1.67 cm, and corrugation amplitude ε = 0.225 cm. The plasma density is varied from zero to 2 ×1012 cm − 3. The presence of plasma tends to raise the TM01 mode cut-off frequency (14 GHz at 2 ×1012 cm − 3 plasma density) relative to the vacuum cut-off frequency (5 GHz) which also causes a decrease in the group velocity everywhere,
resulting in a flattening of the dispersion relation. With the introduction of plasma, an enhancement in absolute instability
was observed. 相似文献
14.
Treating the coulomb interaction between ion species as a perturbation on the Waisman-Lebowitz solution for direct correlation
function within the hard core region, the total direct correlation function in K-space has been formulated, which gives a
direct method of evaluating the partial structure factors between different ion species of the fused salts through the use
of Pearson-Rushbrooke equations. The partial structure factors so obtained have been applied to evaluate the partial radial
distribution functions of ion pairs. In addition, many other important associated functions such as the static correlations
of total number, mass and charge densities have been computed by particular linear combination of partial structure factors.
The charge neutrality relate the partial structure factors to the isothermal compressibility for the wavevectorK → 0 and hence the evaluation of the compressibilities of ions in fused KBr is possible, which agrees well with the observed
value. As such the present method is very useful in investigating the structure of molten salts since only the parametersσ
ij
, the distances of closest approach between ions andɛ, the effective dielectric constant (which can be estimated from the literature) are enough for this work. 相似文献
15.
M.H. Thoma S. Leupold U. Mosel 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):219-223
Assuming that ρ-mesons exist in a quark-gluon plasma at temperatures close to the QCD phase transition, we calculate the
dilepton production rate from q-ˉq annihilation via a ρ-meson state using Vector Meson Dominance. The result is compared to the rates from direct q-ˉq annihilation and from π+-π− annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the
quark-gluon plasma.
Received: 8 September 1999 / Revised version: 22 October 1999 相似文献
16.
A. É. Myasnikova É. N. Myasnikov 《Journal of Experimental and Theoretical Physics》1999,88(1):101-104
Owing to a funadmentally erroneous approach to calculations of the effective polaron mass (calculations that use a model without
spatial dispersion of the lattice polarizability), the polaron inertial mass has never before been distinguished from the
mass as a measure of kinetic energy. In this paper we derive an expression for the tensor of the inertial mass of a large
polaron. The tensor is found to be fully determined by two components: the longitudinal component, corresponding to the case
where the force acting on the polaron is parallel to the polaron velocity, and the transverse component, corresponding to
the case where the acceleration is perpendicular to the polaron velocity. The components of the polaron inertial mass tensor
depend quasirelativistically on the polaron velocity due to the quasirelativistic compression of the polarization field in
the direction of motion, which constitutes the effect of spatial dispersion of the lattice polarizability. We derive a formula
that approximates the dependence of the components of the polaron mass tensor on all the parameters: the frequency and dispersion
of the phonons, the polaron velocity, and the effective dielectric constant.
Zh. éksp. Teor. Fiz. 115, 180–186 (January 1999) 相似文献
17.
V. Antoni R. Bartiromo L. Carraro D. Desideri E. Martines M. E. Puiatti F. Sattin P. Scarin G. Serianni M. Spolaore L. Tramontin M. Valisa B. Zaniol 《Czechoslovak Journal of Physics》2000,50(12):1387-1396
The experimental determination of the radial electric fieldE
r and the associatedE ×B drift velocity at the edge of RFX is presented and possible mechanisms responsible for its generation are discussed.E
r measurements by means of an array of Langmuir probes and those deduced from Doppler spectroscopy of impurity lines agree
fairly well. In particular the rotation velocity of the plasma edge has been determined from the Doppler shift of a C III
emission line. The observation of other ions characterised by different radial positions, such as B IV and C V, has allowed
an estimate of the velocity shear. Typical values of plasma rotation at the edge are around 10 km/s while the velocity shear
is of the order of (105−106)s−1 in the spontaneous layer, a few cm thick, usually observed in standard discharges. Plasma rotation has been artificially
modified by both positive and negative edge biasing and the associated increase or decrease of the fluid velocity is well
in agreement with the radial electric field change. The modification ofE
r during edge biasing and Pulsed Poloidal Current Drive (PPCD) are also reported and interpreted within a momentum balance
model. Analytical and self-consistent Monte Carlo models at the plasma edge suggest that impurities have a relevant role in
the generation of the radial electric field, due to their relatively large Larmor radius.
Presented at the Workshop on Role of Electric Fields in Plasma Confinement and Exhaust, Budapest, 18–19 June 2000. 相似文献
18.
K L Baluja 《Pramana》1995,45(6):533-536
The first relativistic correction of orderα
2 to the dipole polarizability of a hydrogenic ion has been investigated by using mean excitation energy of the ion within
the second-order perturbation theory. The density-dependent mean excitation energy is estimated via Bethe theory for the stopping
cross section for a moving point charge interacting with the hydrogenic ion. In this approach only the unperturbed Dirac wavefunctions
are required to evaluate the appropriate matrix elements. The first relativistic correction turns out to be − (13/12)(αZ)2. This has the correct sign and is within 5% of the exact result which is −(28/27)(αZ)2. 相似文献
19.
U. Yusupaliev S. A. Shuteev E. E. Vinke V. G. Elenskii 《Bulletin of the Lebedev Physics Institute》2012,39(3):89-94
The effect of diffusion anisotropy of material particles in toroidal vortices (TVs) is experimentally studied in plasma TVs
in air, in vortex rings in air and water. The essence of this effect consists in the fact that diffusion coefficients of material
particles in TVs in the direction perpendicular to the rotation axis D
⊥ are much lower than in the direction parallel to this axis D
‖. The coefficient D
⊥ is determined for propane molecules in air TVs, and the dependence of the coefficient D
⊥ of ink particles in water TVs on the rotation angular velocity ω is studied. It is shown that the coefficient D
⊥ can decrease with increasing ω by a factor of 10–25 in comparison with the coefficient D
‖. 相似文献
20.
In numerical simulations of nonabelian plasma instabilities in the hard-loop approximation, a turbulent spectrum has been
observed that is characterized by a phase-space density of particles n(p)∼p
−ν
with exponent ν≃2, which is larger than expected from relativistic 2↔2 scatterings. Using the approach of Zakharov, L’vov and Falkovich,
we analyze possible Kolmogorov coefficients for relativistic (m≥4)-particle processes, which give at most ν=5/3 perturbatively for an energy cascade. We discuss non-perturbative scenarios which lead to larger values. As an extreme
limit we find the result ν=5 generically in an inherently non-perturbative effective field theory situation, which coincides with results obtained by
Berges et al. in large-N scalar field theory. If we instead assume that scaling behavior is determined by Schwinger–Dyson resummations such that the
different scaling of bare and dressed vertices matters, we find that intermediate values are possible. We present one simple
scenario, which would single out ν=2. 相似文献