共查询到20条相似文献,搜索用时 15 毫秒
1.
《Physics letters. A》1988,127(2):96-98
It is shown that scattering of electrons off magnetic field fluctuations can result in acceleration of these electrons along the lines-of-force of a large scale background dc-magnetic field. The mechanism proposed is applied to the underdense corona of a large scale produced plasma. 相似文献
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S. Wolschke 《等离子体物理论文集》1976,16(1):65-77
It is shown at first that the ponderomotive laser force appreciably may enhance the values of the dielectric function ?(x) near the critical plasma density. If in some spatial region near ? = 0 a large anomalous collision frequency is assumed, sharply rising at some point, pump field depletion may also lead to strong changes in the density scale length. As a first approach we have calculated the laser reflectivity in the case when the anomalous collision frequency and the density scale length jump at some point near the critical one. We obtain temporal oscillations of the reflectivity if due to thermal plasma expansion the density scale length increases with time. The calculated frequency and amplitude of the reflectivity oscillations are shown to be in good agreement with measured values in the case of Nd-laser heating of solid targets. 相似文献
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The generation of large amplitude (MG) quasi-stationary magnetic fields in a laser produced plasma with density profile steepening in the domain of the critical point is considered. The spatial structure of the generated magnetic fields in this domain is obtained. It is shown that the density profile steepening causes a significant enhancement of the generated magnetic fields with respect to a linear profile. The saturation level of the generated magnetic fields is evaluated. 相似文献
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N. E. Andreev M. V. Chegotov A. A. Pogosova 《Journal of Experimental and Theoretical Physics》2003,96(5):885-896
The propagation of a short intense laser pulse is studied in a gas taking into account the ionization of gas atoms by the high-frequency electromagnetic field of the pulse. The conditions are found under which the ionization structures produced by the laser pulse cause the pulse focusing accompanied by a substantial increase in its intensity. It is shown that the leading edge of the pulse is subjected to ionization refraction at the ionization front, the temporal profile of the pulse becoming steeper. This results in the efficient generation of a wake wave at the ionization front, which is amplified during the development of self-modulation instability. The amplitude of the wake plasma wave achieves a substantial value already at small paths of the pulse in matter (smaller than the diffraction length of the pulse). 相似文献
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P. Zobdeh R. Sadighi‐Bonabi H. Afarideh E. Yazdani R. Rezaei Nasirabad 《等离子体物理论文集》2008,48(8):555-560
In this work we evaluate the interaction of high intense laser beam with a steepened density profile. During laser interaction with underdense plasma by freely expanding plasma regime, modification of density profile is possible. In this paper we have investigated the ultra short laser pulse interaction with nonisothermal and collisionless plasma. We consider self–focusing as an effective nonlinear phenomenon that tends to increase when the laser power is more than critical rate. By leading the expanded plasma to a preferred location near to critical density, laser reflection is obtained, so the density profile will be locally steepened. The electromagnetic fields are evaluated in this new profile. We show the amplitude and period of electrical field oscillation are increased by reducing the steepened scale length. Also our numerical results identify that by reducing the steepened scale length, the electrical field is increased to wave breaking threshold limit. This high gradient electrical field causes the effective beam loading during the wave breaking phenomenon. The wave breaking can be the initial point for other acceleration regime as cavity or channel guiding regime. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
9.
S.J. Pestehe M. Mohammadnejad 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(11):1960-1967
Ultra-short pulse lasers have opened a regime of laser-plasma interaction where plasmas have scale lengths shorter than the laser wavelength and allow the possibility of generating near-solid density plasmas. The interaction of high-intensity laser beams with sharply bounded high-density and small scale length plasmas is considered. Absorption of the laser energy associated with the mechanism of dragging electrons out of the plasma into the vacuum and sending them back into the plasma with the electric field component along the density gradient, so called vacuum heating, is studied. An exponentially decreasing electron density profile is assumed. The vector potential of the electromagnetic field propagating through the plasma is calculated and the behaviour of the electric and magnetic components of the electromagnetic field is studied. The fraction of laser power absorbed in this process is calculated and plotted versus the laser beam incidence angle, illumination energy, and the plasma scale length. 相似文献
10.
An experimental study of the onset of drift wave and flute interchange instabilities in the Helimak configuration is presented. It is shown that the Helimak offers the opportunity to separate the regions where these instabilities are active and to assess their relative role in cross-field anomalous transport and in the self-organization of exponential plasma density profiles with resilient scale length. Some results indicating a period doubling route to turbulence are also presented. 相似文献
11.
Establishment of Configuration with Optimized Current Profile in Pellet Fuelled Discharge on HL-2A
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A sawtooth-free period is produced following the pellet injection in the pellet fuelled discharge of qa = 3.4 (where qa is the safety factor at the plasma boundary) in the HL-2A tokamak. Establishment of the current profile such as in the hybrid scenario is studied under the condition of pellet injection in HL-2A. It is shown that a q-profile of weak negative shear is produced immediately after the pellet injection, and it then evolves to a broad flat profile with q0 〉 1 (where qo is the safety factor at the centre). The measured MHD mode structures evidence consistencies of the evaluated q-profile with locations of the q = 1 surface in the sawtoothing period and of the q = 2 surface in the sawtooth-free period. TRANSP analysis indicates that the energy confinement is enhanced substantially during and after pellet injection, which is resulted from the q-profile optimization and the plasma density peaking. 相似文献
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Corde S Thaury C Phuoc KT Lifschitz A Lambert G Faure J Lundh O Benveniste E Ben-Ismail A Arantchuk L Marciniak A Stordeur A Brijesh P Rousse A Specka A Malka V 《Physical review letters》2011,107(21):215004
The x-ray emission in laser-plasma accelerators can be a powerful tool to understand the physics of relativistic laser-plasma interaction. It is shown here that the mapping of betatron x-ray radiation can be obtained from the x-ray beam profile when an aperture mask is positioned just beyond the end of the emission region. The influence of the plasma density on the position and the longitudinal profile of the x-ray emission is investigated and compared to particle-in-cell simulations. The measurement of the x-ray emission position and length provides insight on the dynamics of the interaction, including the electron self-injection region, possible multiple injection, and the role of the electron beam driven wakefield. 相似文献
13.
采用三维模型,使用混合网格质点法对等离子体入射偶极子磁场产生的磁场膨胀进行数值模拟.在模拟中考虑了高能等离子体注入两种不同类型磁场的情况:等离子体注入没有背景磁场的偶极子磁场和等离子体注入有背景磁场的偶极子磁场.研究表明背景磁场的存在不仅改变了粒子的分布,还改变了磁场膨胀的程度.还研究了注入的高能等离子体的速度对磁场膨胀的影响,结果表明入射的高能等离子体速度越大,磁场膨胀的程度就越大.对于低的入射速度,入射粒子在偶极子磁场中的回旋半径与偶极子磁场的特征长度相比较小,粒子被磁场束缚,对偶极子磁场的影响可以忽
关键词:
网格质点法
磁场膨胀
偶极子磁场 相似文献
14.
X-ray defraction due to the steep density gradient of a laser-produced plasma has been observed. Distribution of the density gradient was determined from the measured refraction angle. Estimation of the radial density profile and the density scale length in the high-density region near the ablation surface are presented. 相似文献
15.
B. M. Law M.D. Brown L. Marchand L. B. Lurio W. A. Hamilton I. Kuzmenko T. Gog S. Satija E. Watkins J. Majewski 《The European physical journal. Special topics》2009,167(1):127-132
It has proven to be a challenging task to quantitatively resolve the
interfacial profile at diffuse interfaces, such as, the adsorption profile
near a bulk binary liquid mixture critical point. In this contribution we
examine the advantages and disadvantages of a variety of experimental
techniques for studying adsorption, including neutron reflectometry, X-ray
reflectometry and ellipsometry. Short length scale interfacial features are
best resolved using neutron/X-ray reflectometry, whereas, large length scale
interfacial features are best resolved using ellipsometry, or in special
circumstances, neutron reflectometry. The use of multiple techniques
severely limits the shape of the adsorption profile that can describe all
experimental data sets. Complex interfaces possessing surface features on
many different length scales are therefore best studied using a combination
of neutron/X-ray reflectometry and ellipsometry. 相似文献
16.
通过数据求解亥姆霍兹波动方程,研究了激光辐射薄膜靶产生的不同厚度、不同标尺长度的薄层等离子体对激光的反射,透射及吸收(逆轫致吸收,共振吸收)率随入射角的变化情况,小角度入射时,短脉冲(~ps量级)激光打靶产生的标尺长度较小的等离子体对激光的吸收率比长脉冲打靶时低,但在大角度入射时,短脉冲打靶时等离子体的吸收率反而比长脉冲打靶时高。 相似文献
17.
F. A. Starikov 《Journal of Experimental and Theoretical Physics》2000,90(2):258-275
A physical model, based on the solution of the quasi-optics equation for the transverse correlation function (TCF) of the field amplitude, is developed for investigating the brightness, angular divergence, and spatial coherence of the amplified spontaneous emission in a laboratory X-ray laser. The model takes account of the spontaneous source of radiation, diffraction, regular refraction, regular amplification taking account of saturation, nonresonance absorption, scattering by small-scale fluctuations of the electron density and the gain, and scattering by random hose-like deviations of the extended plasma medium of the X-ray laser. It is established that the TCF method makes it possible to obtain the final result much more quickly than the basic Monte Carlo method for the parabolic equation for the field amplitude. As a result of the statistical linearization of the equation for the transverse correlation function in the presence of gain saturation, this method overestimates the absolute values of the average intensity of the amplified spontaneous radiation, but the maximum overestimation does not exceed 10%. It is found that fluctuations of the optical parameters of the medium of the X-ray laser degrade the quality of the amplified spontaneous radiation beam, and they are the analog of the nonresonance absorption from the standpoint of the effect on the brightness of the laser and therefore decrease the observed gain. For the characteristic conditions of an X-ray laser with a quasistationary generation scheme, the contribution of small-scale gain fluctuations and random hose-like deviations of the plasma filament of the laser to the scattering of the amplified spontaneous radiation is much smaller than the contribution of small-scale density fluctuations. Calculations of the amplified spontaneous radiation in an X-ray laser, which is produced by unilateral irradiation of a curved target and possesses an asymmetric plasma electron density profile in the gain zone, are performed. It is shown that in the gain saturation regime the coherence length and the coherent power of the amplified spontaneous radiation can be substantially increased, realizing in the gain zone a convex electron density profile instead of a typical concave profile. It is found that this improvement of the coherence occurs only under conditions such that the characteristic depth of the small-scale density fluctuations does not exceed several percent of the typical regular values of the density in the gain zone. 相似文献
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实验上采用比对方法测试了激光不经过固体与经过固体介质产生等离子体削波的脉冲波形信号,获得等离子体削波效应产生的脉冲削波倍数。实验结果表明,在波长1.064 m,脉宽1 ns,聚焦透镜焦距100 mm,薄石英片厚度100 m,约束等离子体的小孔直径80 m情况下,等离子体效应产生的脉冲削波倍数为12~14;分别改变石英片厚度和约束等离子体小孔直径,等离子体脉冲削波倍数不变;增加入射激光能量,脉冲削波倍数增加,且经过等离子体后的激光脉冲波形的后沿逐渐出现很陡的下降沿。在产生脉冲削波的截断点位置进行图形拼接重构得到激光脉冲波形信息。 相似文献
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实验上采用比对方法测试了激光不经过固体与经过固体介质产生等离子体削波的脉冲波形信号,获得等离子体削波效应产生的脉冲削波倍数。实验结果表明,在波长1.064 m,脉宽1 ns,聚焦透镜焦距100 mm,薄石英片厚度100 m,约束等离子体的小孔直径80 m情况下,等离子体效应产生的脉冲削波倍数为12~14;分别改变石英片厚度和约束等离子体小孔直径,等离子体脉冲削波倍数不变;增加入射激光能量,脉冲削波倍数增加,且经过等离子体后的激光脉冲波形的后沿逐渐出现很陡的下降沿。在产生脉冲削波的截断点位置进行图形拼接重构得到激光脉冲波形信息。 相似文献
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《Physics letters. A》1998,237(3):146-151
The Jeans stability of dusty plasmas is re-considered. In contrast to a gas, a dusty plasma can support a plethora of wave modes each potentially able to impart to the dust particles the randomising energy necessary to avoid Jeans collapse on some length scale. Consequently, the analysis of the stability to Jeans collapse is many-fold more complex in a dusty plasma than it is for a charge-neutral gas. After recalling some of the fundamental ideas related to the ordinary Jeans instability in neutral gases, we extend the discussion to plasmas containing charged dust grains. Besides the usual Jeans criterion based upon thermal agitation, we consider two other ways of countering the gravitational collapse: (i) via the excitation of dust-acoustic modes and (ii) via a novel Alfvén-Jeans instability, where perturbations of the dust mass-loaded magnetic field counter the effects of self-gravitation. These two mechanisms yield different minimum threshold length scales for the onset of instability/condensation. It is pointed out that for the study of the Jeans instability produced by density enhancements induced in the plasma by the presence of normal wave modes, even more prohibitive plasma size constraints must necessarily be satisfied. 相似文献