A new look at density limits in tokamaks
A new look at density limits in tokamaks
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DOI：
10.1088/0029-5515/28/12/009
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发表时间：
1988-12
期刊：
影响因子：
3.3
通讯作者：
Martin Greenwald;J. L. Terry;S. M. Wolfe;S. Ejima;M. Bell;S. Kaye;G. H. Neilson
中科院分区：
文献类型：
--
作者：
Martin Greenwald;J. L. Terry;S. M. Wolfe;S. Ejima;M. Bell;S. Kaye;G. H. Neilson
虽然 ORMAK 和 DITE 小组关于托卡马克密度极限的早期工作结果多年来一直很有用，但最近实验的结果以及外推到未来实验的要求促使人们对这一主题有了新的认识。有许多物理过程限制了托卡马克等离子体可达到的密度。这些过程包括：（1）低Z杂质的辐射、对流、电荷交换和等离子体边缘的其他损失； (2)等离子体核心中低Z或高Z杂质的辐射； (3) 等离子体核心内粒子限制的恶化； (4) 燃料供给不足，通常因墙壁、限制器或偏滤器的强烈泵送而加剧。根据具体情况，这些过程中的任何一个都可以主导并确定密度限制。一般来说，这些机制并不表现出对等离子体参数的相同依赖性。在比较不同机器的密度限制时，导致密度限制和各种缩放的过程的多样性导致了一些混乱。作者试图理清各种限制，并扩展其中一个的标度律，以包含等离子体成形的重要影响，即 n̄;e = kJ̄，其中 ne 是线平均电子密度 (1020 m−3)，κ 是等离子体伸长率，J̄(MA·m−2) 是平均等离子体电流密度，定义为总电流除以等离子体横截面积。从某种意义上说，这是最重要的密度极限，因为它与 q 极限一起产生了托卡马克等离子体的最大工作密度。结果表明，该极限可能是由于接近密度极限边界时发生的核心颗粒限制的急剧恶化引起的。这种机制可以帮助解释与密度限制相关的破坏和 Marfes。
While the results of early work on the density limit in tokamaks from the ORMAK and DITE groups have been useful over the years, results from recent experiments and the requirements for extrapolation to future experiments have prompted a new look at this subject. There are many physical processes which limit the attainable densities in tokamak plasmas. These processes include: (1) radiation from low Z impurities, convection, charge exchange and other losses at the plasma edge; (2) radiation from low or high Z impurities in the plasma core; (3) deterioration of particle confinement in the plasma core; and (4) inadequate fuelling, often exacerbated by strong pumping by walls, limiters or divertors. Depending upon the circumstances, any of these processes may dominate and determine a density limit. In general, these mechanisms do not show the same dependence on plasma parameters. The multiplicity of processes leading to density limits with a variety of scaling has led to some confusion when comparing density limits for different machines. The authors attempt to sort out the various limits and to extend the scaling law for one of them to include the important effects of plasma shaping, i.e. n̄;e = kJ̄, where ne is the line average electron density (1020 m−3), κ is the plasma elongation and J̄(MA·m−2) is the average plasma current density, defined as the total current divided by the plasma cross-sectional area. In a sense, this is the most important density limit since, together with the q-limit, it yields the maximum operating density for a tokamak plasma. It is shown that this limit may be caused by a dramatic deterioration in core particle confinement occurring as the density limit boundary is approached. This mechanism can help explain the disruptions and Marfes that are associated with the density limit.