Modification of H-mode pedestal structure with lower hybrid waves on Alcator C-Mod
Modification of H-mode pedestal structure with lower hybrid waves on Alcator C-Mod
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DOI：
10.1088/0029-5515/50/6/064001
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发表时间：
2010-05
期刊：
影响因子：
3.3
通讯作者：
J. Hughes;A. Hubbard;G. Wallace;M. Greenwald;B. LaBombard;L. Lin;R. McDermott;R. Parker;M. Reinke;J. Rice;J. Wilson
中科院分区：
文献类型：
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作者：
J. Hughes;A. Hubbard;G. Wallace;M. Greenwald;B. LaBombard;L. Lin;R. McDermott;R. Parker;M. Reinke;J. Rice;J. Wilson
在 Alcator C-Mod 上的 H 模式等离子体中应用较低混合频率范围 (LHRF) 波可以显着减少核心粒子库存，而不会显着降低能量限制。这种现象已在稳定增强 Dα (EDA) H 模式目标中观察到，这些目标由离子回旋加速器 RF 辅助加热维持，其中基座密度 nped 通常与等离子体电流 IP 紧密相关，并且对边缘中性源的变化表现出很强的弹性。在应用高达 1 MW LHRF 功率时，nped 降低高达 30%，而温度曲线同时增加，使得压力基座保持恒定或略有增加。可以保持稳定的 EDA H 模式操作，没有边缘局部模式，同时边缘碰撞性减少了 2-4 倍。刮除层（SOL）密度和电流的升高伴随着LHRF（低至400 kW）的应用，具有快速时间响应（〜10−2 s），而全密度基座松弛和核心密度降低发生在较长的时间尺度（〜10−1 s）上。响应 LHRF，还观察到边缘环形速度中类似的快速反 IP 变化，随后在较长的时间尺度上观察到中心旋转的反 IP 变化。等离子体响应的时间尺度范围可能表明 LHRF 相互作用的径向位置（即 SOL 与核心）和功率沉积机制正在随时间演变。了解负责的物理机制并将其应用于广泛的放电可以为改进 H 模式密度控制提供工具。
The application of lower hybrid range of frequencies (LHRF) waves in H-mode plasmas on Alcator C-Mod can result in a significant reduction in core particle inventory, with no significant degradation of energy confinement. This phenomenon has been observed in steady enhanced Dα (EDA) H-mode targets, which are sustained by ion cyclotron RF auxiliary heating, in which pedestal density nped is usually tied firmly to plasma current IP and shows a strong resilience to changes in the edge neutral source. Upon application of up to 1 MW LHRF power, nped is reduced by up to 30%, while the temperature profile increases simultaneously such that the pressure pedestal remains constant or is slightly increased. Steady EDA H-mode operation with no edge-localized modes can be maintained while edge collisionality is reduced by factors of reduction of 2–4. Elevation of scrape-off layer (SOL) density and electric currents accompany the application of LHRF (at levels as low as 400 kW) with a fast time response (∼10−2 s), while full density pedestal relaxation and core density reduction occur on longer time scales (∼10−1 s). A similarly prompt counter-IP change in the edge toroidal velocity is also observed in response to LHRF, followed on longer time scales by a counter-IP change in the central rotation. The range of time scales of the plasma response may indicate that the radial locations of LHRF interactions (i.e. SOL versus core), and power deposition mechanisms, are evolving in time. Understanding the responsible physical mechanisms and applying them to a broad range of discharges could provide a tool for improved H-mode density control.