电子回旋波与快波协同效应的数值研究

在考虑了电子的反弹平均效应及高能电子的相对论效应下,通过数值求解电子的Fokker-Planck方程,研究了托卡马克等离子体中快波与电子回旋波电流驱动问题。采用九点差分法对方程进行离散,应用近似LU因子分解法对方程进行了数值求解。计算结果表明快波与电子回旋波联合电流驱动具有很强的协同效应,在两波联合电流驱动下,驱动电流大于单波电流驱动之和。     

电子回旋波驱动的托卡马克芯部等离子体极向旋转

提出了一个驱动托卡马克芯部等离子体极向旋转的新途径：用电子回旋波产生芯部等离子体极向旋转.物理机制如下：在高功率的电子回旋波加热的托卡马克等离子体中，共振局域化现象将产生极向电场从而形成极向外高内低的离子密度分布；这个极向离子的积累可以克服来自磁泵的阻尼而使等离子体极向旋转退稳定.从流体力学方程和漂移动力学方程中，得到了等离子体旋转退稳的判别式.结果表明现有的电子回旋波加热功率水平可以驱动芯部等离子体的极向旋转. 关键词：     

托卡马克等离子体不同平衡位形下的电子回旋波电流驱动

在给定的等离子体总电流和中心电流密度条件下,数值求解平衡方程,求出不同拉长比和三角形变因子的托卡马克等离子体温度、密度、磁场分布,然后通过求解波迹方程和Fokker-Planck方程,分别计算这些位形下的电子回旋波波迹和电流驱动.结果表明：电子回旋波X模从顶部发射时,随着拉长比的增大,波迹会向弱场侧偏移.电子回旋波X模从弱场侧发射时,电子回旋波在等离子体中传播沉积的功率份额随着拉长比的增大而增加,驱动电流位置随着三角形变因子的增大向等离子体中心移动.驱动电流位置随环向和极向发射角的减小向中心移动,对应的电流密度峰值也变大.     

托卡马克等离子体不同运行模式下的电子回旋波电流驱动

在给定等离子体密度分布下，从电子、离子的能量方程出发，根据不同运行模式下等离子体的热传导率不同，分别求出了中心负剪切模式，常规剪切H模式和L模式下的等离子体温度分布，然后通过求解波迹方程与相对论情况下的Fokker-Planck方程，分别计算了这些模式下的电子回旋波电流驱动和波功率沉积.得到在中心负剪切下，驱动电流最大，驱动效率最高，功率沉积和电流分布区间跨度大；在常规剪切H模式下，驱动电流较小，分布区间跨度比较窄，驱动效率相对较低；在常规剪切L模式，驱动电流效率最低，分布区间跨度也非常集中. 关键词： 托卡马克 电子回旋波电流驱动 中心负剪切 常规剪切     

托卡马克等离子体中的电子回旋波电流驱动

通过将波迹方程与相对论情况下的完全Fokker-Planck方程联合进行求解,研究了寻常波基频电子回旋波从托卡马克等离子体中平面弱场侧发射时的电流驱动。数值结果表明:随着等离子体电子密度、温度的提高, 功率沉积和电流分布的位置将向等离子体的边缘方向偏移,并且产生的总的驱动电流随之减小;入射波极向发射角和环向发射角度的改变对功率沉积、电流分布及其大小产生明显的影响。     

环形系统双成份等离子体中快波离子回旋共振加热

本文考虑环形系统双成份等离子体中快波电场与少数成份离子共振时,快波经回旋阻尼以加热等离子体。假定粒子间接近无碰撞,沿特征线积分Vlasov方程的方法求一级分布函数及各类粒子贡献的电流。因为少数成份粒子密度与多数成份粒子密度之比为小量,不难求解等离子体内精确到一级的电场。从而求得快波回旋阻尼功率。对于一个具体的激发系统,由边条件求解场系数,得到了通过快波回旋阻尼加热等离子体的功率。     

HT-7托卡马克中低杂波和离子波恩斯坦波协同作用的数值研究

用隐含5点模式对二维Fokker-Planck方程进行离散化,调用NAG程序库中子函数D03UAF求解该方程,并将求解二维Fokker-Planck方程的code与波的射线轨迹code相结合,根据HT-7托卡马克装置参数,分别对有或没有IBW情况下的等离子体电流的全波驱动和在低杂波和离子伯恩斯坦波协同作用下低杂波的功率沉积分布、驱动电流分布等进行数值模拟研究.结果显示:有IBW情况下的全波驱动电流分布比没有IBW时全波驱动的电流分布区域要广一些,而且驱动的总电流也大一点;在双波协同作用下,全波驱动的等离子体电流空间分布随IBW的频率和n_//谱的变化而变化;在两波协同作用下低杂波驱动非感应电流的效率得到了很大的改善.     

ICRF快波模转换及快波传播

本文通过分析离子回旋频段(ICRF)快波在模转换区传播的物理过程,导出了一个新的快波近似——完全快波近似二阶波方程。数值计算表明,它能给出与求解高阶方程非常一致的结果,尤其是在弱回旋阻尼(k_1较小)情况下,完全快波近似比快波近似有更满意的结果。最后讨论了二次谐波加热和少数成份离子加热的实例。     

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用TSC程序模拟了EAST装置等离子体放电的全过程。模拟中考虑了自举电流，并加入了离子回旋共振加热ICRH和快波电流驱动FWCD，得到了中心电子温度4.5keV、中心离子温度3.8keV、中心电子密度1.2×1020m–3的D形截面的等离子体。根据模拟结果对EAST装置进行了伏秒数分析，并研究了不同等离子体电流上升时间、有效电荷数Zeff对放电的影响。     

低频Alfvén波对等离子体非共振加热与随机加热的粒子模拟

采用粒子模拟方法,研究沿背景磁场方向传播的低频Alfvén波对磁化等离子体加热的物理过程.模拟结果表明:离子在垂直和平行于背景磁场的方向都得到明显的加热,在非共振加热阶段,垂直方向比平行方向的加热效果更加显著,形成温度各向异性;在随机加热阶段,垂直和平行方向的温度最终达到饱和且趋于一致.加热过程中,离子所获得动力学温度的最大值由外加磁场能量密度与等离子体密度的比值决定,与Alfvén波的频率及振幅无关;离子在平行于背景磁场方向上被加速,并最终获得相当于Alfvén波相速度大小的流速.     

低混杂波高N‖分量对EAST等离子体电流驱动的影响

EAST等离子体高约束模运行条件下，在等离子体边缘区域观测到明显的等离子体电流带.在EAST托卡马克装置非圆截面平衡位形下，使用射线追踪方法研究低混杂波高平行折射率N_‖分量对电流驱动的影响.结果表明：当-8≤N_‖≤-6时，平行折射率分量能够在小半径（0.7 < r/a < 1）区域驱动kA量级的等离子体电流.对于具有台基区、等离子体边缘温度更高的电子温度剖面，驱动电流的位置r/a>0.9.低混杂波朗道阻尼的理论分析与数值模拟结果一致.另外，高N_‖低混杂波在等离子体边缘的功率沉积和电流驱动与电子温度分布和发射谱分布相关.     

Effects of trapped electrons on off-axis lower hybrid current drive in tokamaks

The effects of trapped electrons on off-axis lower hybrid current drive （LHCD） in tokamaks are studied, A computer code for solving the Fokker-Planck equation in a toroidal geometry is developed and employed. The code is suitable for various auxiliary heating and current drive schemes in tokamak plasmas. The influence of the resonance regime on the current drive efficiency as well as the influence of trapped particle fraction on the current drive efficiency are emphasized. It is shown that, as an electrostatic force, the lower hybrid wave causes some of the trapped electrons to be untrapped and lose their energy, which can cut the LHCD efficiency by about 30%. The ITER scaling law is also used to estimate the trapped electron effects.[第一段]     

EAST低混杂波功率沉积和电流驱动剖面控制的数值模拟

对原有的低混杂波电流驱动模拟程序进行改进,使之能够研究EAST上如何控制低混杂波功率沉积和电流驱动分布.在EAST非圆截面的平衡位形下,应用改进后的程序详细计算不同低混杂波功率谱、等离子体密度和温度分布对低混杂波功率沉积位置和电流驱动剖面分布的影响.通过计算发现,选取合适的低混杂波功率谱,等离子体温度分布和密度分布可以对功率沉积位置和电流驱动分布的剖面进行控制;调节等离子体温度分布可以很好的控制低混杂波近轴电流驱动分布和离轴电流驱动分布.     

Generation of Uniform Plasmas for Beat Wave Experiments

The laser plasma "beat wave" mechanism for the generation of ultrahigh electric fields requires plasmas of several meters length with density uniformity of about 1 percent. Multiphoton ionization of molecular hydrogen gas at a pressure of a few torr provides a scalable mechanism for generating these plasmas using the same laser beams that drive the beat wave. We describe measurements of electron density, temperature, and uniformity of plasmas generated by a frequency doubled Neodymium glass laser, at an irradiance of about 1014 W · cm-2. The plasma density corresponds to 100-percent ionization and is measured to be uniform to within the measurement errors over a length of 8 mm.     

Dynamics of fast electrons driven by the lower hybrid wave in giant sawtoothing plasmas

By hard x-ray tomography of the nonthermal bremsstrahlung emission, a detailed investigation of the dynamics of the fast electrons driven by the lower hybrid wave in the presence of giant sawteeth is carried out. While sawtooth activity is clearly observed on the bulk contribution, no modulation is detected on radiations emitted by the suprathermal population. This original effect is interpreted as the consequence of a poor penetration of the wave in the core of the plasma due to reduced accessibility conditions. Implications for current drive in sawtoothing plasmas are discussed.     

Observation of odd toroidal Alfvén eigenmodes

Experimental evidence is presented for the existence of the theoretically predicted odd toroidicity induced Alfvén eigenmode (TAE) from the simultaneous appearance of odd and even TAEs in a normal shear discharge of the joint European torus. The modes are observed in low central magnetic shear plasmas created by injecting lower hybrid current drive. A fast ion population was created by applying ion cyclotron heating at the high-field side to excite the TAEs. The odd TAEs were identified from their frequency, mode number, and timing relative to the even TAEs.     

Taming Drift Wave Turbulence

Drift waves in magnetized plasmas often occur in a turbulent form and are often considered as being responsible for anomalous cross‐field particle transport. It is thus very appealing to achieve active control of the drift wave dynamics. A control scheme acting both in space and in time is developed to synchronize drift wave turbulence. It consists of an arrangement of eight electrodes (octupole exciter) in flush‐mounted geometry in the edge region of the magnetized plasma column. The electrodes of the octupole exciter are driven by sinusoidal signals. Between each two neighbouring electrodes, the phase shift of the exciter signal is kept fixed. It is demonstrated experimentally that the exciter signals have strong influence on the different drift wave states, i.e. the turbulent states can be synchronized to a single preselected drift wave mode. The efficiency of the spatiotemporal synchronization is sensitively dependent on both driver frequency and phase shift.     

Sheared poloidal flow driven by mode conversion in tokamak plasmas

A two-dimensional integral full-wave model is used to calculate poloidal forces driven by mode conversion in tokamak plasmas. In the presence of a poloidal magnetic field, mode conversion near the ion-ion hybrid resonance is dominated by a transition from the fast magnetosonic wave to the slow ion cyclotron wave. The poloidal field generates strong variations in the parallel wave spectrum that cause wave damping in a narrow layer near the mode conversion surface. The resulting poloidal forces in this layer drive sheared poloidal flows comparable to those in direct launch ion Bernstein wave experiments.     

A Fast Computation of the Start-Oscillation Current of Backward Wave in MMW HTWT's

Backward wave oscillation can be troublesome in high power helix TWT, especially millimeter wave helix traveling wave tubes (MMW HTWT's). To suppress these oscillations, start-oscillation current of backward wave has to know when MMW HTWT's are designed.A fast computation of the start-oscillation current for MMW HTWT's is presented. It is shown that the computed values are agreed with the experimental results in Ka band.     

Wave Trajectory and Electron Cyclotron Heating in Tokamak Plasmas

Wave trajectories in high density tokamak plasmas are studied numerically. Results show that the ordinary wave injected at an appropriate incident angle can propagate into the dense plasmas and is mode-converted to the extraordinary wave at the plasma cutoff, is further converted to the electron Bernstein wave during passing a loop or a folded curve near the upper hybrid resonance (UHR) layer, and is cyclotron damped away, resulting in local electron heating before arriving at the cyclotron resonance layer. Similar trajectory and damping are obtained when a microwave in a form of extraordinary wave is injected quasi-perpendicularly in the direction of decreasing toroidal field.