【作者】 张静；

【导师】 唐跃进； 庄革；

【作者基本信息】 华中科技大学 ， 脉冲功率与等离子体， 2012， 博士

【摘要】 托卡马克放电会产生等离子体(包含电子和离子),同时存在的还有等离子体周围的、未被离化的中性粒子。这些粒子之间以及其与电磁场之间的相互作用,会伴随有电磁波的辐射。当托卡马克等离子体处于热力学平衡或局部热力学平衡状态,即系统内质点(分子、原子、离子、电子等)的能量分布可以用一定温度下的玻耳兹曼分布表示时,此时系统产生的电磁辐射行为广义上称为热辐射。热辐射是高温等离子体能量输运和耗散的一个重要途径,测量热辐射可以很好的了解能量平衡,同时通过对热辐射的测量可以给出等离子体的许多信息,如组分、电离状态等。因而在托卡马克等离子体物理研究中,热辐射测量是基本的诊断。论文主要的研究工作为J-TEXT托卡马克的热辐射测量系统的设计及其应用,以及对欧姆放电情况的实验观测和物理分析。主要内容有以下几个方面：(1)由于在目前的托卡马克温度下,对托卡马克等离子体的热辐射有显著贡献的电磁波谱多落在真空紫外波段及软X射线波段,因此根据J-TEXT托卡马克等离子体密度、温度等参数,可以估算出热辐射的主要贡献波段及辐射总功率,并由此选用合适的探测器(光电二极管)和设计合适的接收光路,搭建热辐射测量系统。整个系统根据其功能可分为两大部分：极向阵列和环向阵列。极向阵列主要用于探测辐射总功率,反演辐射功率剖面,观测极向热辐射的时间和空间演化过程。环向阵列分立于大环圆周的9个小窗口之上,可以研究环向热辐射的对称性(特别是在破裂放电情况下以及破裂缓解过程中)及验证磁面的完备性。其设计具有一定的创新意义。(2)实验发现在J-TEXT托卡马克欧姆放电中,平顶阶段的热辐射总功率大约占欧姆加热功率的20-80%,由此可见热辐射在能量平衡中扮演了非常重要的角色。基于极向热辐射阵列测量结果反演出来的辐射功率剖面原则上可以反映出温度大致的空间分布情况和等离子体中的杂质情况(如,组分、比例等)。在J-TEXT欧姆放电中,实验发现辐射功率剖面的基本形状主要有两种：峰化状和中空状。峰化状剖面芯部(r=0-0.2a,a为等离子体小半径)的辐射强度占总辐射强度的30%左右,边界部分(r=0.7a-a)为15%,分析表明芯部辐射主要由重杂质线辐射(FelI等)提供的；中空状剖面的芯部(r=0-0.2a)的辐射强度占总辐射强度的15%左右,边界部分(r=0.7a-a)为20%,这一部分的辐射主要由轻杂质(如C等)的线辐射提供。(3) J-TEXT热辐射测量系统采用光电二极管阵列作为其探测器,这种探测器的响应速度为0.5μs (AXUV16ELG),基本上可以满足一些MHD行为的观测要求。实验发现在J-TEXT欧姆放电情况下,热辐射信号在极向上和环向上都明显受到锯齿和其它MHD不稳定性的调制。在有剧烈Mirnov振荡的放电中,极向热辐射探测阵列甚至可以推演出磁岛(主要是m/n=2/1)所在的位置。(4)目前,J-TEXT托卡马克放电破裂事例中的71%是出撕裂模不稳定性导致的,其中m/n=2/1的模式占主要地位,同时还可能伴随有m/n=3/1等其它模式。在这类破裂放电中,热辐射强度在破裂之前并没有明显变化,但在破裂发生后却急剧增加。这说明热辐射并非是这类破裂的主要触发机制但却是破裂时能量损失的主要通道。估算表明,在破裂的热猝灭(TQ)阶段,由辐射损失的能量可以达到等离子体总内能的10%左右。(5)在J-TEXT托卡马克静态扰动场实验中,发现投入扰动场之后,芯部热辐射强度减小而边界热辐射强度增加,这可能主要是粒子的约束变差以及温度的变化造成的。在杂质气体(He气,Ne气,Ar气)补充充气实验中,发现脉冲送气并不能使辐射功率显著增加,而超声分子束补充送气却可以,增加量随气体的有效电荷数、送气压强和脉宽而不同。更多还原

【Abstract】 There are electrons, ions and neutral atoms in the Tokamak plasma. The interactions between these particles as well as these particles and the electromagnetic fields often produce electromagnetic wave radiation. When the plasma is in thermodynamics equilibrium or local thermodynamics equilibrium state, that is, the particles’(molecule, atom, ion, electron etc.) distribution of the system can be described by the Boerziman distribution under a certain temperature, the electromagnetic radiation is called heat radiation. It is an important way of the transport and diffusion for the energy in the high-temperature plasma. Through the measurement of radiation, the energy balance can be understood well. Furthermore, the composition, ionization state, temperature and density can be obtained, so the radiation measurement is a basic diagnosis.The thesis introduces the design and application of the radiated power measurement system in the J-TEXT tokamak, as well as the experimental results and the physical analyses. The major contents are as follows:(1) At the current temperature, the dominated wavelength of the radiation is between extreme Vacuum ultraviolet (XUV) and soft X-ray. According to the density, temperature and other parameters of the J-TEXT Tokamak, the main wavelength of the radiation and the total radiated power can be estimated. Then based on these parameters, the appropriate detectors (photodiodes) and the appropriate receiving optical path can be chosen and the radiated system can be designed. The system includes poloidal arrays and toroidal arrays. The former ones are intended to measure the radiated power, radiated power profiles and the radiation evolution process in the poloidal direction. The latter ones, which are in nine small ports can study the radiation symmetry (especially the process of the disruption and the disruption mitigation) of the toroidal direction and proof the completeness of the magnetic surface.(2) In the J-TEXT tokamak ohmic discharges, the total radiated power is about20%-80%of the ohmic power in the current flattened stage, so the total radiated power play an important role in the power balance. The radiated power profiles got by the poloidal arrays can reflect the temperature profiles of the plasma and the composition, proportion of impurities. In the J-TEXT discharges, there are two kinds of profiles:peak shaped profile and hollow shaped profile. For the peak shaped profile, the radiated power is about30%of the ohmic power at the center of the plasma(r=0-0.2a), which mainly comes from the impurity line radiation (Fell, etc.); at the boundary (r=0.7a-a), the radiated power is about15%.For the hollow radiation profile, the radiated power is about15%at the center (r=0-0.2a) and at the boundary, the radiated power is about20%, which are mainly provided by the light impurities.(3) The photodiode is applied in the J-TEXT tokamak. Its response time is0.5μs (AXUV16ELG), therefore the fast MHD instability information can be obtained by analyzing the radiation signals. It is found that the radiation signals are modulated by the sawtooth and other MHD instabilities in the poloidal direction and toroidal direction. When the Mirnov oscillation is strong, the magnetic island (main the m/n=2/1) location can be deduced by the radiation signals.(4) In the current discharges, the disruption is mainly caused by tearing mode instability. Among them, the m/n=2/1mode dominates, accompanied by m/n=3/1mode. In this kind of disruption, the radiated power doesn’t change obviously before the disruption. But after the disruption, it significantly increases. This indicates that the radiation is not a trigger mechanism but a channel of energy loss. According to the estimation, the radiated energy is about10%of the thermal energy during the thermal quench (TQ).(5) In the static magnetic perturbation field experiments (SFX) of the J-TEXT tokamak, it is found that after the perturbation field applied, the core radiation intensity decreases but the edge radiation intensity increases. This may be because the confinement gets worse and the temperature changes. In the noble gas (He, Ne, Ar) injection experiments, the radiated power doesn’t increase obviously by gas puffing. However, when the gases are injected by supersonic molecular beam (SMBI), the radiated power increases obviously and the increased rate changes as the Zeff, pressure and the gases pulses.更多还原