Study of the fast ion confinement and current profile control on MAST
Study of the fast ion confinement and current profile control on MAST
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MAST 快离子约束和电流分布控制研究
DOI：
10.1088/0029-5515/49/6/065002
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发表时间：
2009
期刊：
影响因子：
3.3
通讯作者：
S. Pinches
中科院分区：
文献类型：
--
作者：
M. Turnyanskiy;D. Keeling;R. Akers;G. Cunningham;N. Conway;H. Meyer;Clive Michael;S. Pinches
MAST实验的主要操作目标之一（Darke等人1994 Proc.18th Symp. on Fusion Technology（Karlsruhe，德国，1994）第799页），提出的MAST升级是为了研究控制q分布和驱动离轴电流的可能机制。进行了实验，以确定在何种程度上的q分布可以修改使用两种不同的方法，瞬态和稳态。在等离子体电流斜升阶段的瞬态效应进行了研究，其目的是开发一个启动制度，以后可以用作目标等离子体的非感应电流驱动器或访问先进的操作模式，如混合或改进的H模式。在这种情况下，观察到最显着的效果时，早期中性束注入（NBI）施加到快速电流斜坡率启动等离子体造成反向磁剪切和等离子体电流“堆积”离轴。在稳态实验中，其中离轴NBI进行了研究，结果表明，拓宽快离子沉积轮廓离轴中性束（NB）注入有助于避免有害的等离子体不稳定性，并显着扩展MAST的操作窗口。长脉冲（>0.65 s）H模式等离子体的等离子体持续时间仅受当前机器和NBI工程限制的限制。为了匹配实验观察到的中子速率和储存的能量，需要低水平的反常快离子扩散离子（Db <$0.5 m2 s−1）。快速离子扩散的引入拓宽了中性束流驱动剖面，并将NB驱动电流的相对贡献从约40%降低到约30%。为了获得电流分布的直接测量值，MAST已委托进行多弦动斯塔克效应诊断，目前正在提供第一批结果，以确认NB驱动电流的离轴位置。
One of the main operational aims of the MAST experiment (Darke et al 1994 Proc. 18th Symp. on Fusion Technology (Karlsruhe, Germany, 1994) p 799) and the proposed MAST upgrade is to investigate possible mechanisms to control the q-profile and drive off-axis current. Experiments were carried out to determine the extent to which the q-profile may be modified using two different approaches, transient and steady-state. Transient effects during the plasma current ramp-up phase were investigated with the aim of developing a start-up regime that can later be used as a target plasma for non-inductive current drive or to access advanced modes of operation such as the hybrid or improved H-mode. The most significant effect in this case was observed when early neutral beam injection (NBI) was applied to the fast current ramp-rate start-up plasmas causing reversed magnetic shear and the plasma current to ‘pile-up’ off-axis. In steady-state experiments, in which off-axis NBI was studied, results indicate that broadening the fast ion deposition profile by off-axis neutral beam (NB) injection helps to avoid harmful plasma instabilities and significantly extends the operational window of MAST. Long pulse (>0.65 s) H-mode plasmas were achieved with plasma duration limited only by present machine and NBI engineering limits. In order to match the experimentally observed neutron rate and stored energy a low level of anomalous fast ion diffuse ion (Db ∼ 0.5 m2 s−1) is required. The introduction of the fast ion diffusion broadens the neutral beam current drive profile and degrades the relative contribution of NB driven current from ∼40% to ∼30%. To obtain direct measurements of the current profile, a multi-chord motional stark effect diagnostic has been commissioned on MAST and is currently delivering first results in order to confirm the off-axis location of the NB driven current.