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1.
Nonlinear behaviour of electron plasma waves propagating in a planar plasma-loaded waveguide immersed in an infinite magnetic field is analysed including finite temperature and mobile ion effects. It is shown that the wave becomes modulationally unstable if the wavenumber exceeds certain critical value Kc, which decreases with rise of temperature. The growth rate of instability is calculated and is found to increase with the rise of temperature. 相似文献
2.
W-Band Second-Harmonic Gyrotron Traveling Wave Amplifier with Distributed-Loss and Severed Structures 总被引:2,自引:0,他引:2
Yi Sheng Yeh Chien Lun Hung Chi-Wen Su Ting-Shu Wu You-Yan Shin Yu-Tsung Lo 《International Journal of Infrared and Millimeter Waves》2004,25(1):29-42
The second harmonic TE02 gyrotron traveling wave amplifier (gyro-TWT) is a high-power, broadband, millimeter-wave amplifier with a low applied magnetic field. Mode-selective interaction circuits were applied to suppressing spurious oscillations. However, the mode-selective interaction circuit may perturb the operating mode in the gyro-TWT. A multi-stage gyro-TWT design with distributed-loss and severed structures is proposed to stabilize the amplification. This study presents a nonlinear analysis of typical oscillations, including absolute instability, gyrotron backward oscillation (gyro-BWO) and reflective oscillation. The lossy and severed sections of the multi-stage gyro-TWT seem to increase effectively the start-oscillation currents of the absolute instability, gyro-BWO, and reflection oscillation. The multi-stage gyro-TWT is predicted to yield a peak output power of 215 kW at 89.9 GHz with an efficiency of 14.3 %, a saturated gain of 60 dB and a bandwidth of 1.7 GHz for a 100 kV, 15 A electron beam with an axial velocity spread
z/
z = 5%. 相似文献
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5.
H. Himura H. Wakabayashi Y. Yamamoto A. Sanpei S. Masamune M. Isobe S. Okamura K. Matsuoka 《Hyperfine Interactions》2007,174(1-3):83-88
Experimental studies on nonneutral (pure electron) plasmas of finite temperature, trapped in helical closed magnetic surfaces
have been conducted. The helical electron plasmas are produced with thermal electrons launched from the outside of the last
closed flux surface (LCFS). About 150 μs after the electron injection, the plasmas reach equilibrium state. Around the LCFS, a steep gradient of plasma space potential
φ
s
is formed. The corresponding radial electric field is about 2.5 kV/m. On the other hand, around the magnetic axis of helical
magnetic surfaces, φ
s
is almost constant, indicating that there are little electrons there. The volume-averaged electron density is on the order
of 1013 m–3, smaller than the Brillouin density limit. The confinement time seems to be limited by a disruptive instability, and is so
far about 1.5 ms.
相似文献
6.
Yuh HY Kaye SM Levinton FM Mazzucato E Mikkelsen DR Smith DR Bell RE Hosea JC LeBlanc BP Peterson JL Park HK Lee W 《Physical review letters》2011,106(5):055003
Negative magnetic shear is found to suppress electron turbulence and improve electron thermal transport for plasmas in the National Spherical Torus Experiment (NSTX). Sufficiently negative magnetic shear results in a transition out of a stiff profile regime. Density fluctuation measurements from high-k microwave scattering are verified to be the electron temperature gradient (ETG) mode by matching measured rest frequency and linear growth rate to gyrokinetic calculations. Fluctuation suppression under negligible E×B shear conditions confirm that negative magnetic shear alone is sufficient for ETG suppression. Measured electron temperature gradients can significantly exceed ETG critical gradients with ETG mode activity reduced to intermittent bursts, while electron thermal diffusivity improves to below 0.1?electron gyro-Bohms. 相似文献
7.
The kinetic current-convective instability excited in a hot electron plasma, i.e. for Te ? Ti, is investigated in the linear stage. Density and temperature of plasma components have gradients along the x-direction. In the absence of longitudinal current (u = 0) and homogeneous temperature the instability is also excited with maximum growth rate much exceeding that obtained in the case of u ≠ 0. Gradual increasing of the ion temperature over that of the electrons and a large density gradient leads to reduce the instability in the linear stage. 相似文献
8.
《Chinese Journal of Physics (Taipei)》2018,56(5):1834-1844
In this paper, the propagation of Cosh Gaussian laser beam and its interaction with isothermal plasma without temperature gradient as well as the effect of the exponential electron temperature gradient are investigated. Here the ponderomotive nonlinearity force is effective mechanism. This force can modify the electron density distribution. All the investigations are carried out for different initial plasma temperatures. Using Maxwell’s equations we obtained the nonlinear second-order differential equation of the dimensionless beam-width parameter (f) on the distance of propagation for several initial electron temperatures and exponential temperature variations. These equations are solved numerically by taking WKB and paraxial approximation. Under the effect of initial electron temperature, self-focusing and defocusing of hyperbolic cosine (cosh) Gaussian laser beam is distinguished. Furthermore, the exponential temperature gradient cause to stationary propagation mode breaks, and self-focusing or defocusing properties is observable. 相似文献
9.
The resonant parametric decay of a Langmuir wave into a backward propagating Langmuir wave and an ion acoustic (IA) wave is studied in a cylindrical dusty plasma. The analysis shows that the frequency of the IA mode decreases with the parameter δc (where δc is the ratio of the ion density to the electron density) for negatively charged dust grains. The growth rate of the resonance decay instability (RDI) and the threshold required for its onset also decrease with δc and are strongly dependent on the electron to ion temperature ratio for both positively and negatively charged dust grains. The results obtained also illustrate the dependence of the threshold of the resonance decay instability (μth) on the plasma cylinder radius. 相似文献
10.
The thermal instability of a finitely conducting hydromagnetic composite and compressible medium is studied to include the
frictional effects with neutrals. The effect of compressibility is found to be stabilizing. In contrast to the nonoscillatory
modes for (C
p/g)β > 1 in the absence of a magnetic field;C
v, β andg being specific heat at constant pressure, uniform adverse temperature gradient and acceleration due to gravity respectively,
the presence of magnetic field introduces oscillatory modes in the system. The overstable case is also discussed. The magnetic
field is found to have a stabilizing effect on the system for (C
p/g)β > 1. 相似文献
11.
Nielsen and Olesen showed that perturbative vacuum with uniform chromomagnetic field in one space and one color direction
is unstable. This instability is called Nielsen-Olesen instability (NOI), and leads to formation of a ‘spaghetti of flux tubes’
as a model for non-perturbative vacuum and confinement. We re-examine this instability in presence of color sources, quarks
and gluons, at a finite temperature and find that at sufficiently high temperature NOI is stabilized due to an ‘effective
mass’ of gluons arising through plasma effects. This explains how a QGP with no confinement effects may exist at high temperature.
As the temperature is lowered, NOI reappears at a valueT=T
c, which is very close to confinement-deconfinement transition from hadrons to QGP.. 相似文献
12.
It is found that nonlinear ion drift waves in a plasma with ion temperature much larger than the electron temperature (Ti?Te) satisfy certain well-known model evolution equations. The nonlinear development of the ion waves as well as their turbulent behaviour is therefore known in the light of these equations. 相似文献
13.
V. R. Romanovskii 《Technical Physics》2010,55(3):373-380
The effect of a nonuniform temperature distribution in the cross section of a high-temperature superconductor on the formation
of its I–V characteristic and the conditions for conservation of a stable distribution of the input current are analyzed. The equations
permitting us to determine the boundary values of the electric field and current above which current instability can be developed
with allowance for the dimensional effect are derived. It is shown that the input current quench determining the maximal permissible
value of the input current decreases if thermal inhomogeneity of electrodynamic states is taken into account in theoretical
analysis of its stability conditions. It is found that the limiting admissible values of the electric field and current are
nonlinear functions of the thermal resistance of the superconductor, its critical parameters, and external heat-exchange conditions.
Therefore, intense cooling of the superconductor does not result in an increase in the current corresponding to the emergence
of instability in proportion to the increase in its cross-sectional area or critical current density. 相似文献
14.
Experimental evidence of parametric excitation, by an intense external H.F. field, of an electron surface mode and an ion wave is presented. The pumping electromagnetic energy density is equal to or slightly larger than the thermal energy density of the electrons. The value of fpc/f0 (electron plasma frequency/external field frequency) is that for an electron surface wave. Depending on the pressure and field intensity, this decay instability can lead to three types of low frequency oscillations, with frequencies close to the ion plasma frequency. Two of these are described by Aliev and Silin's intense field theory: one is the volume ion plasma oscillation and the other a surface ion plasma oscillation. The third corresponds to no known ion eigenmode. Several other features of the theory by Aliev and co-workers are also confirmed experimentally, such as the harmonic excitation of the instability (nf0 ≈ fpe/√2, where n is an integer), the instability amplitude as a function of fpe/f0 (above threshold conditions), the value of the mismatch parameter as a function of field strength and ion mass, and the existence of a fine structure corresponding to the symmetric and antisymmetric electron surface oscillations. Even at high pump field strengths, the decay products are nearly monochromatic i.e. the plasma does not become turbulent. 相似文献
15.
Elnaz Khalilzadeh Amir Chakhmachi Behrouz Maraghechi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2015,69(11):256
The influence of self-fields on the cyclotron maser instability in a hollow electron beam propagating parallel to a uniform axial magnetic field B 0 ê z in a dielectric loaded waveguide is investigated. The theoretical analysis is carried out within the framework of linearized Vlasov-Maxwell equations. It is assumed that the beam is thin with the radial thickness much smaller than the beam radius. A new dispersion relation for azimuthally symmetric electromagnetic perturbation is derived and analyzed numerically. The influence of self-fields on the cyclotron maser instability in a dielectric loaded waveguide for different dielectric medium is studied. It is found that unlike the hollow waveguide the growth rate is increased by increasing self-fields. The instability band width decreases due to the increasing self-fields. The maximum growth rate increases gradually as self-fields increase as regards a different dielectric medium. 相似文献
16.
The study deals with the effect of an applied transverse magnetic field on the dynamics and parameters of the focused and expanded plasma in a coaxial discharge. The experimental results were found with a 3 kJ Plasma focus device of a Mather geometry. The discharge takes place in hydrogen gas with base pressure of 0.5 Torr. The experiments are conducted with a 10 kV bank voltage, which corresponds to 100 kA peak discharge current with rise time 8 μs. Helmholtz magnetic coils are placed outside the expansions chamber to produce a transverse magnetic field with intensity 280 G perpendicular to the plasma expanded from the coaxial electrodes. The investigations have shown that the plasma flow along the expansion chamber axis is restricted when applying the externally transverse magnetic field and the maximum axial velocity of the expanded plasma is decreased by 33%. X-ray probe has been used to measure the focused plasma electron temperature (Te). The experimental results and the calculations showed that Te is decreased from 2.2 keV to 800 eV with the application of a transverse magnetic field. The expanded plasma electron temperature and density have been measured by an electric double probe, the results cleared that the expanded plasma electron temperature is decreased by 2.6 times while its density is increased by 9 times, when a transverse magnetic field is applied. 相似文献
17.
L. S. Ewe I. Hamadneh H. Salama N. A. Hamid S. A. Halim R. Abd-Shukor 《Applied Physics A: Materials Science & Processing》2009,95(2):457-463
The magnetotransport and magnetoresistive (MR) properties of manganese-based La0.67Ca0.33MnO3 perovskite with different grain sizes are reported. The electrical resistivity was measured as a function of temperature
in magnetic fields of 0.5 and 1 T. The insulator–metal transition temperature, T
IM, shifted to a higher temperature with the application of the magnetic field. In zero field, T
IM is almost constant (∼271 K) for all samples except for the sample with the largest grain size, where T
IM=265 K. The temperature dependence of resistivity was fitted with several equations in the metallic (ferromagnetic) region
and the insulating (paramagnetic) region. The density of states at the Fermi level, N(E
F), and the activation energy of electron hopping were estimated by fitting the resistivity versus temperature curves. The
ρ–T
2 curves are nearly linear in the metallic regime, but the ρ–T
2.5 curves exhibit a deviation from linearity. The variable range hopping model and small polaron hopping model fit the data
well in the high-temperature region, indicating the existence of the Jahn–Teller distortion that localizes the charge carriers.
MR was found to increase with an increase in the magnetic field, an effect which is attributed to the intergrain spin tunneling
effect. 相似文献
18.
《等离子体物理论文集》2017,57(8):351-356
The Weibel instability plays an important role in stopping hot electrons and energy deposition mechanism in fast ignition of inertial fusion process. In this paper, the ion Weibel instability in counter propagating electron‐ion plasmas is investigate. The obtained results show that the growth rate of Weibel instability will be decreased about 40% with the anisotropy velocity as vxe = 2vze = 20; the ion density ratio, b = n 0i 1/n 0i 2, and density gradient, are increasing 50 and 90% respectively. The ion streaming in density gradient of dense plasma leads to increasing the Weibel instability growth rate and its amplification through ion streaming in the large wavenumber. The maximum unstable wavenumber has been decreased with decreasing the ion beam density ratio. For fixed ion density ratio, increasing 90% of the density gradient in the near of fuel plasma corona leads to reducing growth rate and unstable wavenumber about 43 and 42% respectively. 相似文献
19.
Zakharov–Kuznetsov–Burgers (ZKB) equation is derived for electron acoustic shock waves in magnetized e–p–i plasma. In the present model, magnetized plasma containing two electron population with kappa distributed positrons has been considered. The propagation characteristics of three dimensional electron acoustic (EA) shock waves have been studied under the influence of magnetic field. Our present plasma model supports the negative potential shocks. Combined action of dissipation (η), superthermality (κ), concentration of positrons (β), temperature ratio of cold electrons to positrons (σ), and magnetic field (ωc) significantly modify the properties of EA shock waves. The width and amplitude of the shock structures are modified by various physical parameters. It is found that shock wave width decreases with increase in β, η0, and ωc whereas it becomes wider for κ and σ. Further, potential of the shock wave decreases as one departs away from superthermal distribution. 相似文献
20.
Y Hariharan M P Janawadkar T S Radhakrishnan A L E Terrance G A Dixit V S Raghunathan 《Pramana》1986,26(6):513-524
Titanium-rich transition metal alloys are metastable in their quenched boc β phase. The instability is relieved by low temperature
structural transformations. We have investigated this in a series of Ti-Nb alloys, through the measurements of electrical
resistivity (ρ), superconducting transition temperature and upper critical field. Supporting structural evidence has been
obtained from transmission electron microscopy (tem) and x-ray studies. It is shown that both ρ and dρ/dT can be used as useful indices of this instability. The enhanced value of resistivity on account of the instability results
in the enhancement of upper critical field as shown from dH
c2/dT measurements. 相似文献