Edge and core impurity behavior and transport in EAST H-mode plasma with internal transport barrier
After installation of tungsten divertor in EAST, impurity accumulation of tungsten ions has been frequently observed in H-mode discharge with internal transport barrier (ITB) due to an enhancement of the impurity confinement inside the ITB. A strong plasma cooling induced by the tungsten impurity io...
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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | Nuclear Fusion |
| Subjects: | |
| Online Access: | https://doi.org/10.1088/1741-4326/adcbc1 |
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| Summary: | After installation of tungsten divertor in EAST, impurity accumulation of tungsten ions has been frequently observed in H-mode discharge with internal transport barrier (ITB) due to an enhancement of the impurity confinement inside the ITB. A strong plasma cooling induced by the tungsten impurity ions caused a collapse of the ITB formation. To study the impurity transport in high β _N discharges with ITB, temporal behaviors and radial profiles of spectral lines emitted from low- and high-Z impurity ions were analyzed. Line emissions from moderately ionized ions, e.g. O ^6+ , Fe ^17+ and Mo ^25+ locating outside the ITB ( ρ ⩾ 0.4), maintain low intensities and remain unchanged during the ITB formation. However, line emissions from highly ionized high-Z impurity ions such as Fe ^22+ , Cu ^21+ , Cu ^25+ , Mo ^30+ and W ^26+ -W ^37+ locating inside the ITB ( ρ < 0.4) are strongly influenced by peaking effects of electron density and ion temperature profiles. The impurity screening effect due to the ion temperature peaking is dominant during T _i -ITB phase because the line intensities of high-Z impurity ions are reduced and the radial high-Z impurity profiles are flattened. In contrast, during n _e -ITB phase accompanied by electron and ion temperature ITB, an increase in the electron density gradient from R / L _n _e = 3.4–4.9 results in a significant increase in the high-Z impurity density, and leads to the impurity accumulation. Statistical analysis on the tungsten impurity density ( I _W-UTA / n _e ) with toroidal rotation velocity ( V _t0 ) and ion temperature gradient ( R / L _T _i ) suggests that the tungsten impurity accumulation can be effectively mitigated and the I _W-UTA / n _e can be reduced to below 18 (phs·m·s ^−1 ·Sr ^−1 ), when R / L _n _e < 3.4, V _t0 < 150 km·s ^−1 and R / L _T _i > 2.5. During two ITB phases, however, low-Z impurity ions like O ^7+ locating at edge of the ITB appear to be sensitive to only the electron density gradient. |
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| ISSN: | 0029-5515 |