Time: Wednesday, March 9, 4:00pm
Venue: Room 413, Buil. 11th, YuQuan Campus
Title: Toroidal Alfvén eigenmode excited by barely circulating energetic electrons in low density plasmas
Abstract:
Dynamics associated with shear Alfvén wave and energetic particles is intriguing but complicated. Recently, in EAST ohmic discharges which were initiated for disruption analysis, rather unexpectedly, toroidal Alfvén eigenmodes (TAEs) were observed during the current flat-top stage. Numerical simulations are applied to analyze the excitation mechanism of the TAE. It is suggested that barely circulating energetic electrons, potentially generated by the parallel electric field, could resonate with the TAE in low density plasmas. The resonance condition and drive mechanism are also verified by test particle orbit tracing. This work enriches our present understanding on energetic electron driven instabilities, it could also suggest a possible mechanism for runaway electron detection prior to disruption.
题目:回旋动理学-磁流体混杂模型求解阿尔芬波程序(GMAC)开发进展
摘要:
基于回旋动理学-磁流体混杂模型开发可模拟聚变等离子体中alpha粒子驱动阿尔芬本征模和alpha粒子输运过程的混杂数值模拟程序(以下简称GMAC)。在GAMC使用的回旋动理学-磁流体混杂模型中,电子用流体描述,而高能量离子和热离子用回旋动理学模型描述,相应的混合方程组被当作初值问题求解。因为阿尔芬本征模在沿着平行磁力线方向的波长远大于垂直磁力线方向的波长,为了高效地数值表达高模数的阿尔芬本征模结构,采用沿着磁力线的坐标系。在磁力线坐标系下,采用三维5点有限差分法,具有4阶精度。时间推进采用2阶或4阶有限差分法。回旋动理学方程的求解采用标准的particle-in-cell方法,同样在磁力线坐标系下,采用4阶Runge-Kutta积分方法推进粒子轨道。采用delta-f方法计算粒子分布函数的演化。本次报告我将介绍GMAC程序开发进展,包含(1)在有Shafranov位移的平衡位形下,雅可比和度规张量的解析计算;(2)在磁力线坐标系下求解约化磁流体方程用到导数算子,及其5点有限差分的数值收敛性证明;(3)采用解析的平衡场,4阶Runge-Kutta方法推进粒子轨道,在低能量和大环状比近似下与解析解相符,与蒋沛攸的三维笛卡尔坐标系下的粒子轨道程序结果一致,采用线性插值方法推进粒子轨道,并证明数值收敛性。
题目:三维磁流体平衡代码的调研与开发设计--托卡马克3维扰动场平衡
摘要:
等离子体平衡是物理问题,也是工程问题。3维平衡一般指仿星器的平衡,而托卡马克平衡一般是环向对称的2维平衡。随着国内近几年托卡马克装置实验的不断深入,3维物理已经成为一个重要的课题。尤其是在托卡马克上,共振磁扰动(RMP)控制边缘局域模(ELM)成功得应用,促使更多实验和模拟人员关注RMP下3维扰动场的物理。另外,离散的环向场线圈设计和装置机械安装误差也会引入3维效应,这些3维效应破坏了原有托卡马克的环向对称性,对粒子约束带来非常不利的影响。这些都是可以值得深入研究。
目前,国际上著名的3维平衡包括美国的VMEC和日本NIFS的HINT2等。开源的VMEC只能用于完整磁面;HINT2可用于具有磁岛和随机场情况,但是它主要针对仿星器,较少得应用于托卡马克。同时,国内还没有自主的3维平衡代码。报告人在调研基础之上,在CLT框架下,探讨设计托卡马克3维扰动场平衡的方法和可行性。