Identification of slow-wave ion cyclotron emission on JT-60U
Identification of slow-wave ion cyclotron emission on JT-60U
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DOI：
10.1088/1741-4326/ac2777
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发表时间：
2021-10
期刊：
影响因子：
3.3
通讯作者：
S. Sumida;K. Shinohara;M. Ichimura;T. Bando;A. Bierwage;S. Ide
中科院分区：
文献类型：
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作者：
S. Sumida;K. Shinohara;M. Ichimura;T. Bando;A. Bierwage;S. Ide
离子回旋辐射通常被认为是由快离子引起的速度-空间不稳定性驱动的快波辐射。然而，在JT-60 U上，在低于体离子回旋频率（L-ICE）的频率下观察到的ICE的测量特性与快波色散关系不匹配，表明L-ICE可能是慢波发射。在本文中，我们表明JT-60 U上的L-ICE观察可以用快离子驱动的慢波发射（即慢波ICE）来解释。为了研究慢波是否可以被快离子驱动，在一个典型的放电使用波色散代码计算其线性增长率。该波频散代码能够执行具有任意空间局部化速度分布的计算。对于生长率的计算，我们直接使用快速离子速度分布评估的轨道以下蒙特-卡罗模拟。研究发现，负离子源中性束注入快离子会使慢波不稳定。其频率和波数在高线性增长率接近L-ICE的实验观察。此外，所观察到的L-ICE频率同意合理的慢波色散关系的基础上在几个放电测量的环形波数的频率。此外，所观察到的频率也同意的多普勒频移回旋共振频率的N-NB注入离子。因此，JT-60 U中的L-ICE被确定为由N-NB注入的快离子驱动的慢波ICE，并且通过测量其频率和波数来与其他ICE区分。
Ion cyclotron emissions (ICEs) are generally considered to be emissions of fast waves driven by velocity-space instabilities due to fast ions. However, on JT-60U, measured properties of ICEs observed at frequencies lower than the bulk ion cyclotron frequency (L-ICEs) do not match the fast-wave dispersion relation, indicating the possibility of L-ICEs being slow-wave emissions. In this paper, we show that L-ICE observation on JT-60U can be explained in terms of a slow-wave emission driven by fast ions, i.e. a slow-wave ICE. To investigate whether the slow wave can be driven by fast ions, its linear growth rate has been calculated in a typical discharge using a wave dispersion code. This wave dispersion code is capable of performing calculations with an arbitrary spatially-localized velocity distribution. For the growth rate calculation, we have directly used fast ion velocity distributions evaluated by an orbit following Monte-Carlo simulation. It is found that negative-ion-source neutral beam (N-NB) injected fast ions can destabilize the slow wave. Its frequency and wavenumber at high linear growth rates are close to experimental observations of L-ICE. In addition, observed L-ICE frequencies agree reasonably well with frequencies based on the slow-wave dispersion relation at measured toroidal wavenumbers in several discharges. Moreover, the observed frequencies also agree with the Doppler-shifted cyclotron resonance frequencies for the N-NB injected ion. Therefore, L-ICE in JT-60U is identified as a slow-wave ICE driven by the N-NB injected fast ions and distinguished from other ICEs through a measurement of its frequency and wavenumber.