磁重联电磁脉冲定向辐射方法研究

发布时间：2018-01-15 09:33

本文关键词：磁重联电磁脉冲定向辐射方法研究　出处：《中国工程物理研究院》2014年博士论文　论文类型：学位论文

【摘要】：天体物理观测结果表明磁化高能量密度等离子体能以较高的能量转换效率辐射低频非热电磁脉冲。本文研究磁化高能量密度条件下磁重联电磁脉冲定向辐射方法,并分析其物理极限。传统天线辐射机制以电场为初始储能,其峰值功率和转换效率受多种因素限制而达到物理极限。例如,当电场达到原子内部场强量级时,电场能量极有可能以共振形式快速释放,并产生等离子体,对辐射极为不利,此时的能量密度为1011J/m3量级。电中性条件排除了等离子体内部可存在强电场的普适性,特别是对于尺寸较大的等离子体系统。空间电荷效应进一步限制了传统天线辐射峰值功率和效率。与电场储能不同,磁重联电磁辐射机制初始能量储存在磁场中。等离子体内部存在强磁场并不违背电中性条件,对磁感应强度大小的可能物理极限还不明确,从天文观测来看,即使存在物理极限,这一物理极限至少应大于1015G,对应的能量密度1027J/m3量级,比电场储能极限高16个量级。等离子体在自生磁场作用下获得相对论速度,这种复杂的运动必然引起磁力线拓扑结构的重建,辐射磁重联电磁脉冲。相对论效应可极大地提高磁重联电磁辐射效率,同时还能引起定向的相干辐射。相对论、强磁化的高能量密度条件虽然与某些天体环境更为接近,然而目前实验室高能量密度加载能力的不断提升使得本论文的研究也具有现实意义。因此,本文针对磁化高能量密度条件下电流丝结构的产生及其磁重联电磁脉冲定向辐射机制进行了初步探索和尝试,提出一种磁化高能量密度等离子体非热电磁辐射机制。论文主要研究内容和结论如下： 1、讨论了磁化高能量密度条件下电流丝／电流环的形成机制。处于高能量密度状态的等离子体电阻率随温度升高而降低(负斜率),若温度沿磁场方向分布不均匀(即使小扰动),初始温度较高区域的电阻率会以正反馈形式降低,使得该区域的电流密度提高,最后形成波矢平行于磁场方向的电流丝或电流环结构。电流丝／电流环在洛仑兹力作用下以相对论速度碰撞,该过程可辐射强电磁脉冲。通过推导电流丝阵列的色散关系发现,电流丝阵列具有波长与阵列空间周期同量级的本征模式,退激发过程可辐射电磁脉冲,这提供了第二种可能的低频非热辐射机制。只有平行磁场(k||B)的温度扰动模式能产生电流丝结构,该模式的激发对实验加载能力要求很高。基于我们目前的加载能力,开展了k⊥B不稳定性模式的实验研究,实验结果表明不稳定性随时间向长波模式演化,若将这一结论推广至k||B的不稳定性模式,可以预测电流丝阵列的空间周期变大。涨落可提供温度的扰动机制,等离子体内的电磁波也可引起空间周期为波长量级的扰动。扰动机制和正反馈机制保证了磁化高能量密度条件下产生电流丝结构的可能性。 2、讨论了运动电流环和电流丝辐射电磁脉冲机制,提出了实现定向辐射的理论方案。本文理论分析表明,垂直于电流方向的运动更有利于电磁脉冲辐射,外磁场或自生磁场的洛仑兹力(J×B)恰好提供了垂直电流方向的驱动力。相对论效应对电磁脉冲功率和角分布有显著的影响,具体表现为：电磁脉冲功率与电流环/电流丝的峰值运动速度近似满足定标率只ras∝β2γ2-3,速度从0.1c增至0.9c后峰值功率提高三个量级。相对论效应有助于提高辐射定向性。以绕轴匀速转动的电流环为例,非相对论条件下,电磁脉冲在电流环所在平面内(即垂直磁场)取极大值：相对论条件下,电磁脉冲沿磁轴(磁偶极矩)方向取极大值。对于运动电流丝,非相对论条件下,电磁辐射在运动方向(包括沿速度方向和速度反方向)取极大值,垂直于运动方向无辐射；相对论条件下,电磁脉冲集中于沿速度方向的小锥角内,这点与单粒子辐射类似。讨论了表观超光速扰动引起的定向电磁脉冲辐射机制,小角度倾斜或质量沿长度方向调制的双电流丝均可引起表观超光速扰动,其辐射角分布与Cerenkov辐射相同；在相对论条件下,电流丝以较高的对称性运动并不会抑制电磁辐射；反之,非相对论条件下对称性运动会抑制电磁辐射。传统辐射机制的峰值功率受限于多种因素而达到物理极限,磁重联电磁脉冲辐射功率和能量满足∝γ2-3,正比于电流丝/电流环动能的平方/立方,原则上没有物理极限。 3、讨论了弱加载条件下的磁重联实验结果。测量脉冲电流加载下双丝在微波、可见光和X射线三个波段的电磁辐射。热辐射机制能较好解释X射线辐射；可见光波段的电磁辐射则由热辐射和元素特征线辐射共同决定；弱加载条件的低频电磁辐射极有可能是欧姆加热引起金属丝经历固态-液态-气态-等离子体相变所致。
[Abstract]:The results show that magnetized astrophysical observations of high energy density plasma with high energy conversion efficiency of non thermal radiation of low frequency magnetic pulse. This paper studies the magnetization under the condition of high energy density magnetic reconnection electromagnetic pulse radiation method, and analyzes its physical limits. The traditional antenna radiation mechanism for the electric field as the initial energy, peak power and conversion efficiency restricted by many factors and reach the physical limit. For example, when the electric field reaches the atom field magnitude, the electric energy is likely to be released rapidly in resonance form, and generate plasma of radiation is extremely unfavorable, the energy density of the order of 1011J/m3. The condition of electrical neutrality eliminates the strong electric field inside the plasma are universal, especially for the plasma system of larger size. The space charge effect further restrict the traditional antenna radiation power and efficiency and electric field peak. Energy storage, magnetic reconnection electromagnetic radiation mechanism of initial energy stored in the magnetic field. The plasma has a strong magnetic field does not violate the condition of electrical neutrality, physical limit of the magnetic induction intensity is not clear, from astronomical observations, even in the presence of physical limits, the physical limits should be at least more than 1015G, the corresponding energy density the order of 1027J/m3, electric field energy storage limit of 16 orders of magnitude higher. Plasma obtained relative velocity in self generated magnetic field, the complex motion will cause the reconstruction of the topologies of magnetic field, magnetic reconnection electromagnetic pulse radiation. The relativistic effects can greatly improve the efficiency of magnetic reconnection electromagnetic radiation, can also cause orientation coherence radiation. The theory of relativity, the condition of high energy density strongly magnetized although with some celestial environment closer, however, the laboratory of high energy density loading ability and constantly improve. The study of this paper is also of practical significance.
Therefore, in this paper and the current magnetic wire structure under the condition of high energy density magnetic reconnection electromagnetic pulse radiation mechanism for a preliminary exploration and try to put forward a magnetized high energy density plasma non thermal electromagnetic radiation mechanism. The followings are the main research contents and conclusions:
1, discuss the formation mechanism of current filament / current loop magnetization under the condition of high energy density. In the state of high energy density plasma resistivity decreases with the increase of temperature (negative slope), if the temperature along the direction of magnetic field distribution is not uniform (even small perturbations), higher initial temperature resistivity areas will be reduced with the positive feedback form. The current density in the region increased, finally current wire or current loop structure of wave vector parallel to the magnetic field direction is formed. The current filament / current loop in the Lorentz force in relativistic velocity collision, the process of electromagnetic pulse radiation. The dispersion relation of current filament array is found, the eigen modes of current filament array with wavelength and array space cycle of the same level, de excitation process of electromagnetic pulse radiation, which provides second possible low frequency non thermal radiation mechanism. Only the parallel magnetic field (k||B) temperature disturbance The dynamic model can produce current filament structure, the excitation mode of experimental loading capacity is very high. Our current loading capacity based on experiment were carried out to study the anomalous K B instability mode, the experimental results show that the stability with time to long wave mode evolution, if the conclusion is generalized to the instability of k||B mode. Can predict the spatial period of current filament array becomes larger. Disturbance mechanism can provide the temperature fluctuation, disturbance of electromagnetic wave in plasma can also cause the space periodic order of wavelength. The disturbance mechanism and positive feedback mechanism to ensure the possibility of current filament structure magnetization under the condition of high energy density.
2, discussed the motion of current loop and current filament electromagnetic pulse mechanism, puts forward the theoretical scheme to achieve directional radiation. Theoretical analysis shows that the movement is more perpendicular to the current direction to electromagnetic pulse radiation, Lorentz force field or self generated magnetic field (J * B) provides the driving force of the vertical direction of the current. The relativistic effect of electromagnetic pulse has significant influence power and angular distribution, specific performance: electromagnetic pulse power and current loop / peak velocity of filament current approximate scaling to meet the rate of Ras / 2-3 gamma beta 2, speed increased from 0.1C to 0.9c after the peak power is increased by three orders of magnitude. The relativistic effects contribute to the to improve the radiation directivity. Current to rotate around the shaft of the uniform ring as an example, the non relativistic conditions, electromagnetic pulse in the current loop within the plane (i.e. vertical magnetic field) maximum relativistic conditions along the magnetic axis of electromagnetic pulse (magnetic The direction of maximum dipole moment). The movement of current wire, non relativistic conditions, electromagnetic radiation in the direction of motion (including velocity direction and speed reverse direction) maximum, perpendicular to the direction of motion without radiation; relativistic conditions, electromagnetic pulse along the direction of the focus on the speed of the small cone angle, this with the single particle radiation is discussed. Similar to the apparent superluminal disturbance caused by directional electromagnetic pulse radiation mechanism, double filament current can be small angle or quality along the length direction of modulation caused by the apparent superluminal disturbance, the angular distribution of radiation and Cerenkov radiation are the same; in relativistic conditions, current wire with high symmetry the movement and suppression of electromagnetic radiation will not; on the contrary, the non relativistic symmetry will inhibit movement under the condition of electromagnetic radiation. The peak power limitation traditional radiation mechanism in a variety of factors and achieve physical limits, the magnetic reconnection electromagnetic pulse Radiation power and energy to meet / R 2-3, is proportional to the current filament current loop energy / square / cubic, no physical limit principle.
3, the weak under the loading conditions of the magnetic reconnection experiment results are discussed. The measurement of pulse current loading double wire in the microwave electromagnetic radiation, visible light and X ray band three. Thermal radiation mechanism can be used to explain X ray radiation; electromagnetic radiation in visible light by thermal radiation and radiation characteristics of elements determined low frequency electromagnetic radiation; weak loading condition is most likely caused by ohmic heating wire through the solid liquid vapor phase transition induced by plasma.

【学位授予单位】：中国工程物理研究院
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P141

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