Low temperature partly ionized plasma in magnetic fusion devices: Present status and prospects

Conference · Thu Dec 31 04:00:00 EST 1998

OSTI ID:346896

Krasheninnikov, S I ^[1]

---

1. Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Science and Fusion Center

The most striking achievement in magnetic fusion experiments during last few years was the discovery of plasma detachment from material targets, a much needed effect for plasmas with high power fusion parameters. Due to the very low heat loads on the targets observed in these regimes and potentially low erosion of the targets, detached regimes look attractive from the International Thermonuclear Experimental Reactor (ITER) design point of view. Thus the author has experimental proof for the possibility for a co-existence of fusion relevant hot plasma in the core and a low temperature partly ionized plasma at the edge of magnetic fusion device. Although somewhat similar behavior of edge plasma was considered theoretically even before plasma detachment was found experimentally, it was not clear in the beginning how these theoretical and experimental findings would fit together. Now, after a few years of intensive additional experimental and theoretical studies, a self-consistent physical picture of detached regimes has emerged and it has become clear that the most important processes are energy loss due to impurity radiation and plasma recycling which involve neutral gas ionization, ion-neutral interaction, and plasma volumetric recombination and neutralization at a target surface. Here the author reviews a modern physical picture of plasma detachment in fusion devices with magnetic confinement and in linear machines, and discuss new results on the stability of detached plasmas. Experimental observations and 2D modeling show that the impurity radiation, neutral gas ionization and plasma recombination regions (fronts) jump from the target towards the bulk plasma when detachment occurs. Simultaneously this affects core plasma confinement. This indicates that the localization of the fronts close to the targets is unstable. He shows analytically that detached plasma can be unstable with respect to both ionization-recombination instability and thermal bifurcations of impurity radiation front. He shows that this instability and bifurcation, driven by violation of the plasma energy balance at low power coming from core to the edge plasma, can restrict the achievable edge plasma density in magnetic fusion devices. He discusses implications of this theoretical insight for the interpretation of experimental data on detached plasmas and density limit.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• OSTI ID: 346896
• Report Number(s): CONF-980601--
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ENERGY LOSSES
HOT PLASMA
ITER TOKAMAK
PLASMA DENSITY
PLASMA IMPURITIES
PLASMA INSTABILITY
PLASMA SIMULATION
SPATIAL DISTRIBUTION