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MHD limit cycles on FTU

机译：FTU的MHD极限周期

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摘要

The development of low-order tearing modes during density ramp-up in the high density regime on the Frascati Tokamak Upgrade is characterized by an initial ordinary stage, with a 'one-to-one' relation between mode amplitude and frequency, followed by the formation, on the amplitude/frequency plane, of 'limit cycles' with increasing area up to disruption for density limit if the density continues to grow. A critical mode amplitude for transition from smooth to cyclic behavior has been observed in experiments performed changing the line-averaged density, and the existence of such a threshold has been confirmed in experiments of real time control of tearing mode in the high density regime by means of electron cyclotron resonance heating. The amplitude and frequency modulations of the observed m = 2/1 tearing mode (m and n are the poloidal and toroidal mode number, respectively) occur in few milliseconds, which is not in agreement with the diffusion resistive time of about two hundred milliseconds expected on the q = 2 resonance from the non-linear theory. The origin of such modulations has been investigated, taking into account that in the high amplitude stages of the mode temporal evolution it is difficult to discriminate between non-linear effects and mode coupling mechanisms. Our analysis suggests that the formation of limit cycles could be due to a recursive island fragmentation, with a sort of self-healing phenomenon; in fact the island distortion increases before amplitude drops. Concerning the interaction with modes of different helicity, our experiments seem to indicate that the presence of the q = 3 resonance in the plasma is necessary for the occurrence of deep and regular limit cycles for the 2/1 tearing mode.
机译：在Frascati Tokamak升级系统的高密度模式下，密度提升过程中低阶撕裂模式的发展，其特征在于初始的初始阶段，模式振幅与频率之间存在“一对一”的关系，随后是如果密度继续增长，则在幅度/频率平面上形成“极限循环”，并随着面积的增加而达到破坏密度极限的目的。在改变线平均密度的实验中观察到了从平滑行为到循环行为转变的临界模式振幅，并且在通过高密度方式实时控制撕裂模式的实验中已经确认了这种阈值的存在。电子回旋共振加热。观察到的m / n = 2/1撕裂模式的振幅和频率调制（m和n分别是倍数模和环形模数）在几毫秒内发生，这与约200的扩散阻滞时间不一致非线性理论在q = 2共振上期望的毫秒数。考虑到在模式时间演化的高幅度阶段很难区分非线性效应和模式耦合机制，已经研究了这种调制的起源。我们的分析表明，极限环的形成可能是由于递归岛断裂，带有某种自我修复现象。实际上，岛畸变在振幅下降之前就增加了。关于与不同螺旋度模式的相互作用，我们的实验似乎表明，在等离子体中存在q = 3共振对于2/1撕裂模式的深度和规则极限循环的发生是必要的。

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  • 来源
    《Nuclear fusion》 |2017年第11期|116037.1-116037.6|共6页
  • 作者

    Pucella Gianluca; Giovannozzi Edmondo; Buratti Paolo; Cianfarani Cesidio;

  • 作者单位

    ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, Frascati (Roma), Italy;

    ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, Frascati (Roma), Italy;

    ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, Frascati (Roma), Italy;

    ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, Frascati (Roma), Italy;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    limit cycle; magnetic island; tearing mode;

    机译：极限循环磁岛撕裂模式;

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