DIII-D Research to Prepare for Steady State Advanced Tokamak Power Plants

Steady-state burning plasma: a new stage in the development of magnetic confinement fusion energy

Over the past 20 years, advances in tokamak physics and technology have prepared the field of magnetic confinement fusion research for the next step toward a steady-state burning plasma.

Recent advances in high- β N experiments and magnetohydrodynamic instabilities with hybrid scenarios in the HL-2A Tokamak

Over the past several years, high- β N experiments have been carried out on HL-2A. The high- β N is realized using double transport barriers (DTBs) with hybrid scenarios. A stationary high- β N ( > 2 ) scenario was obtained by pure neutral-beam injection (NBI) heating. Transient high performance was also achieved, corresponding toβ N ≥ 3 , n e / n e G ∼ 0.6 ,H 98 ∼ 1.5 ,f b s ∼ 30 % ,q 95 ∼ 4.0 , and G ∼ 0.4 . The high- β N scenario was successfully modeled using integrated simulation codes, that is, the one modeling framework for integrated tasks (OMFIT). In high- β N plasmas, magnetohydrodynamic (MHD) instabilities are abundant, including low-frequency global MHD oscillation with n = 1, high-frequency coherent mode (HCM) at the edge, and neoclassical tearing mode (NTM) and Alfvénic modes in the core. In some high- β N discharges, it is observed that the NTMs with m / n = 3 / 2 limit the growth of the plasma energy and decrease β N . The low-n global MHD oscillation is consistent with the coupling of destabilized internal (m/n = 1/1) and external (m/n = 3/1 or 4/1) modes, and plays a crucial role in triggering the onset of ELMs. Achieving high- β N on HL-2A suggests that core-edge interplay is key to the plasma confinement enhancement mechanism. Experiments to enhance β N will contribute to future plasma operation, such as international thermonuclear experimental reactor .

Effects of plasma turbulence on the nonlinear evolution of magnetic island in tokamak

Magnetic islands (MIs), resulting from a magnetic field reconnection, are ubiquitous structures in magnetized plasmas. In tokamak plasmas, recent researches suggested that the interaction between an MI and ambient turbulence can be important for the nonlinear MI evolution, but a lack of detailed experimental observations and analyses has prevented further understanding. Here, we provide comprehensive observations such as turbulence spreading into an MI and turbulence enhancement at the reconnection site, elucidating intricate effects of plasma turbulence on the nonlinear MI evolution.

Magnetic reconnection and plasma turbulence occur in atmospheric and magnetized laboratory plasmas. Here the authors report evolution of magnetic islands and plasma turbulence in tokamak plasmas using high resolution 2D electron cyclotron emission diagnostics.