2019年6月21日 五室第109期研讨会

2019621 五室第109期研讨会

题  目:回旋动理学粒子模拟与全轨道粒子模拟的比较

报告人胡友俊

 时  间:2019年6月21日(星期五)  14:30—15:30

地  点:6楼中间办公室

摘  要:

从上个世纪90年代开始, 回旋动理学模拟逐渐成为研究托卡马克湍流输运的标准方法。 传统的包含回旋运动的粒子模拟方法对研究高频波现象是常用的方法, 但对研究低频湍流现象, 仍然面临时间步长与数值稳定性等限制,因而未能在这一领域广泛应用。我同时尝试过这两种模拟手段,对二者的区别有一点体会。我想借周五讨论的机会,梳理一些这两种模拟方法。对回旋动理学模拟, 从基本的麦克斯韦方程组出发,采用矢势与标势描述,导出回旋动理学模拟中要求解的场方程的具体形式。 然后定义导心变换,并讨论一下Frieman-Chen的非线性回旋动理学方程的推导步骤,以及回旋动理学模拟中非常重要的极化密度,回旋平均的数值处理及场方程的数值求解。给出回旋动理学模拟出的离子温度梯度模(ITG)与电子温度梯度模(ETG)的结果。讨论绝热电子与动理学电子, 静电模型与电磁模型所带来的处理方法的区别, 以及电磁模拟中的数值抵销误差问题。 对全轨道模拟方法,介绍计算全轨道的Boris算法及其相对于Runge-Kutta方法的优越性。由于没有回旋平均,全轨道粒子模拟的噪声比回旋动理学粒子模拟的噪声大。与回旋动理学模拟不同, 在全轨道模拟中,等离子体温与度密度的空间梯度不显式出现在模型中,如何把梯度效应包含到模拟中的是一个很微妙且很关键的问题。最后给出用全轨道粒子模拟给出的ITG与ETG的结果及仍然面临的一些数值困难。

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2019年6月14日 五室第108期研讨会

2019614 五室第108期研讨会

题  目:1.Nonlinear interaction between toroidal Alfven eigenmodes

and tearing modes

2. Sawtooth Oscillation and Fast Core-Crash in Tokamak

报告人 马志为 教授 (浙江大学)

时  间:2019年6月14日(星期五)  10:00—11:30

地  点:4楼中间办公室

摘  要:

  1. Nonlinear interaction between toroidal Alfven eigenmodes and tearing modes

Nonlinear interaction between toroidal Alfven eigenmodes (TAEs) and tearing modes is investigated by using the MHD-Particle hybrid code CLT-K. It is found that the n=1 TAE is first excited by isotropic energetic particles at the linear stage and reaches the first steady state due to wave-particle interaction. After the saturation of the n=1 TAE, the m/n=2/1 tearing mode grows continuously and reaches its steady state due to nonlinear mode-mode coupling. The development of the tearing mode activity could weaken the TAE frequency chirping through the interaction between the p=1 TAE resonance and the p=2 tearing mode resonance for passing particles in the phase space, which is opposite to the classical physical picture of the TAE frequency chirping that is enhanced with increase of dissipation. The tearing mode activity can also cause strong increase of the n=0 zonal component and large decrease of the n=1 TAE mode due to redistribution of energetic particles associated with formation of magnetic islands.  

  • Sawtooth Oscillation and Fast Core-Crash in Tokamak

Sawtooth oscillation and fast core-crash are investigated using a three-dimensional toroidal and nonlinear MHD code CLT. It is found that the behavior of sawtooth oscillations significantly depends on the viscosity of plasma. With a high viscosity, a normal sawtooth oscillation is observed. With low viscosity, the system quickly turns into a small sawtooth after the first pressure crash. When the viscosity falls below the critical value, the system reaches a stationary state, in which the magnetic field, plasma pressure, and q profile remain unchanged. The mode-mode coupling effect plays an crucial role on fast core-crash associated with double tearing mode. The zonal component and all other high n harmonics generated by the mode-mode coupling of the n=1 mode gain more than 40% of the total kinetic energy and become unneglectable at the nonlinear phase. The time scale of the fast core crash is nearly independence of the resistivity.  ��c*

2019年度 五室研讨会人员顺序表

顺序 人员
  1 胡友俊
  2 夏天阳
  3 胡业民
  4 周登
  5 郭文峰
  6 肖小涛
  7 马骏
  8 于治
  9 李德徽
  10 徐颖峰
  11 潘成康
  12 叶磊
  13 甘春芸
  14 申伟
  15 桂彬
  16 杨程
  17 贾国章
  18 杨小庆
  19 陈佳乐
  20 刘晓娟
  21 黄跃恒
  22 欧靖
  23 项农

2019年5月30日 五室第107期研讨会

2019530 五室第107期研讨会

题  目:23rd  RFPPC 会议相关内容介绍

报告人胡业民 欧靖 陈佳乐 甘春芸

 时  间:2019年5月30日(星期四)  9:30—11:00

地  点:4楼中间办公室

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2019年5月24日 五室第106期研讨会

2019524 五室第106期研讨会

题  目:低杂波电流驱动物理和应用

报告人项农

 时  间:2019年5月24日(星期五)  14:30—15:10

地  点:506办公室

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2019年5月10日 五室第105期研讨会

2019510 五室第105期研讨会

题  目:Dynamics of the radio-frequency sheath of plasma containing energetic electrons

报告人欧靖

 时  间:2019年5月10日(星期五)  15:00—16:00

地  点:6楼中间会议室

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2019年4月19日 五室第105期研讨会

2019419 五室第105期研讨会

题  目:5th UNIST-Kyoto university workshop总结和讨论

报告人夏天阳和叶磊

时  间:2019年4月26日(星期五)  2:30—3:30地  点:506室

2019年4月19日 五室第104期研讨会

2019419 五室第104期研讨会

题  目:Open Discussion on Kinetic Simulation of Magnetic Confinement Fusion Plasmas

报告人Chen Yang( University of Colorado)

 时  间:2019年4月19日(星期五)  2:30—3:30

地  点:4楼中间会议室

  摘  要:This is an open discussion. Any question concerning kinetic simulation (Particle-in-Cell or Eulerian) of magnetic fusion devices (tokamak, stellarator,…) can be brought up for discussion. Including kinetic effects has become a high priority in the modeling of many low-frequency phenomena such as sawtooth, tearing mode, the neoclassical tearing mode, the edge-localized mode, etc. These problems are traditionally modeled with resistive MHD, but major efforts have been put in extending MHD codes, such as NIMROD or M3D, to include kinetic effects. At the same time, gyrokinetic codes (GEM, GTC, GYRO …) that are originally  developed for the study of anomalous transport, are being used to study these same “MHD” phenomena. What are the advantages and disadvantages of each of these two major approaches? What experimental phenomena can be directly simulated and what phenomena are beyond the capability of direct simulation in the foreseeable  future? Plasma  physics is a subject of vast complexity. One has to wonder if there is ever a problem that has been really solved. For example, is the neoclassical transport a solved problem? These are but a few possible questions that might be used to motivate the free discussion.

我室举行塘西河公园环湖健身走活动

正值最美人间四月天的时节,在所工会的支持下,五室于4月11日上午举行塘西河公园环湖健身走活动。此次活动旨在丰富职工的文化生活,缓解繁重的科研工作,增进同事之间相互的交流。

蓝天白云映衬下的滨湖塘西河公园格外美丽,沿途的春林一片生机盎然、欣欣向荣的景象。道路两旁的树木抽出了嫩绿的新叶,樱花、垂丝海棠、牡丹竞相开放点缀着美丽的塘西河公园。一路上,伴随着柔和的春风,踏着轻快的脚步,伙伴们三五成群有说有笑,感受着春天的气息,接受大自然美丽的馈赠,工作和生活上的压力已然在大自然的美景和轻松的心情中释放。

紧张的科研工作之余需要丰富的文化生活来调剂,此次健身走活动不仅锻炼了大家的身体,加强了同事之间的沟通与交流,同时也进一步增强了科研团队的协作意识和集体意识。

2019年2月20日 五室第103期研讨会

 

2019220 五室第103期研讨会

 

题  目:Resistive Axisymmetric X-Point (RAXP) Modes and ELMs control by Vertical Kicks: an informal discussion

报告人Prof.Franco Porcelli (Polytechnic University of Turin, Italy)

时  间:2019年2月20日(星期三)  9:30—10:30

地  点:4楼中间会议室

 摘  要:

The magnetic field line going through to the X-point of a magnetic divertor separatrix is resonant to axisymmetric MHD perturbation with toroidal mode number n=0 and any poloidal mode number. For this reason, the magnetic X-point region may be strongly influenced by axisymmetric MHD perturbations. Yet, it appears that a detailed theoretical study of resistive axisymmetric X-point modes has not been carried out. In this seminar, I will discuss the analytical and numerical difficulties that may have prevented so far a detailed theoretical study of this problem.

The stability of the magnetic separatrix region of tokamak plasmas with divertor configurations takes on great importance in the realization of sustainable H-mode regimes at high performance. In particular, instabilities like ELMs modulate the heat flux across the separatrix and can give rise to very high peak heat loads on the divertor plates. Exploiting the intrinsic dynamics of the X-point configuration can ease ELM mitigation and control.

As a case in point, experiments on JET have demonstrated the efficacy of using an externally induced fast vertical motion (referred to as “vertical kicks” by the JET team) for active ELM control [1]. Vertical kicks are controlled plasma and magnetic field perturbations driven by the JET vertical stabilization system, which result in rapid upward or downward displacements of the plasma column. Preliminary modeling and stability considerations reported in [2] suggest that the edge localized plasma currents driven by the vertical kicks play the major role in controlling the ELMs. The HL-2A team also reported similar results [3].

From a theoretical point of view, radially localized low-m, n=0 perturbations can cause a compression of the plasma in the X-point region, resulting in transient current spikes localized near the X-point, possibly associated with the generation of energetic electrons. The correct theoretical treatment of these modes requires considerations of the full two-dimensional nature of the X-point divertor equilibrium and of the oscillating external currents associated with the control of the vertical instability.

Please note: Since the development of a model for RAXP modes is still underway, the discussion will be kept at a very informal level.

[1] E. R. Solano et al, ELMs and strike point movements, 2008 Nucl. Fusion 48 065005.

[2] E. de la Luna et al, Understanding the physics of ELM pacing via vertical kicks in JET in view of ITER, Nucl. Fusion 56 (2016) 026001 (22pp).

[3] N. Wu et al, Study on edge localized modes during plasma vertical swing in HL-2A tokamak, Physics of Plasmas 25, 102505 (2018).

 

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