Investigation of the bifurcation character of the H-mode in ASDEX Upgrade

Zohm, H.; Suttrop, W.; Büchl, K.; Blank, H. J. de; Gruber, O.; Kallenbach, A.; Mertens, V.; Ryter, F.; Schittenhelm, M.

doi:10.1088/0741-3335/37/4/005

Cited by 52 publications

(60 citation statements)

References 10 publications

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“…Although the appearance of the two types of L-H transitions shows no significant dependence on heating power, the duration of the dithering phase of the dithering L-H transition directly relates to it [34]. In EAST, dithering L-H transitions, dominantly heated by radio-frequency power, i.e.…”

Section: Influences Of Divertor Configuration On the L-h Power Threshmentioning

confidence: 98%

Study on the L–H transition power threshold with RF heating and lithium-wall coating on EAST

Chen

Nielsen

et al. 2016

Nucl. Fusion

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The power threshold for low (L) to high (H) confinement mode transition achieved by radio-frequency (RF) heating and lithium-wall coating is investigated experimentally on EAST for two sets of walls: an all carbon wall (C) and molybdenum chamber and a carbon divertor (Mo/C). For both sets of walls, a minimum power threshold P thr of ~0.6 MW was found when the EAST operates in a double null (DN) divertor configuration with intensive lithium-wall coating. When operating in upper single null (USN) or lower single null (LSN), the power threshold depends on the ion ∇B drift direction. The low density dependence of the L-H power threshold, namely an increase below a minimum density, was identified in the Mo/C wall for the first time. For the C wall only the single-step L-H transition with limited injection power is observed whereas also the so-called dithering L-H transition is observed in the Mo/C wall. The dithering behaves distinctively in a USN, DN and LSN configuration, suggesting the divertor pumping capability is an important ingredient in this transition since the internal cryopump is located underneath the lower divertor. Depending on the chosen divertor configuration, the power across the separatrix P loss increases with neutral density near the lower X-point in EAST with the Mo/C wall, consistent with previous results in the C wall (Xu et al 2011 Nucl. Fusion 51 072001). These findings suggest that the edge neutral density, the ion ∇B drift as well as the divertor pumping capability play important roles in the L-H power threshold and transition behaviour.

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Section: Influences Of Divertor Configuration On the L-h Power Threshmentioning

confidence: 98%

Study on the L–H transition power threshold with RF heating and lithium-wall coating on EAST

Chen

Nielsen

et al. 2016

Nucl. Fusion

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“…So-called 'dithering' L-H transitions were observed early on the ASDEX [42,43] and JET [45] tokamaks and, in ASDEX, interpreted as successive L-H and H-L transitions within a bifurcation model. In 2010, experiments at the TJ-II stellarator revealed periodic oscillations of the turbulence intensity and the edge electric field preceding the L to H-mode transition [28], with the radial electric field and E × B drift lagging the normalized density-fluctuation amplitude by π/2 (figures 1(a) and (b)).…”

Section: L-h Transitions Initiated Via Lcomentioning

confidence: 99%

The role of turbulence–flow interactions in L- to H-mode transition dynamics: recent progress

Schmitz

2017

Nucl. Fusion

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This scaling reflects only the dependence of the L-H transition power threshold on plasma density ) − n (10 m e 203 , toroidal magnetic field φ B (T), and the plasma surface area S (m 2 ). However, the threshold power has been shown to depend on additional parameters such as isotopic plasma composition, plasma shape, divertor geometry, and the beam-induced and intrinsic torque [4][5][6][7][8]. A physics-based model of the L-H transition threshold power is therefore needed to confidently extrapolate to auxiliary heating requirements for ITER and future burning plasma experiments. It was recognized early on that the H-mode edge barrier forms as fluctuations are suppressed due to E × B flow shear [9][10][11] in a narrow (few cm wide) radial layer just inside the last closed flux surface (LCFS) [12][13][14][15]. While the paradigm of Nuclear Fusion

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“…Figure 6a shows the frequency spectrogram for shot #26615 detected with Mirnov coils [16] between 1 and 3 seconds (the spectrogram for shot #26616 is very similar and is not shown).…”

Section: Results From the Fast Proton Scenariomentioning

confidence: 99%

Gamma-ray spectroscopy measurements of confined fast ions on ASDEX Upgrade

et al. 2012

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Evidence of -ray emission from fast ions in ASDEX Upgrade (AUG) is presented. The plasma scenarios developed for the experiments involve deuteron or proton acceleration. The observed -ray emission level induced by energetic protons is used to determine an effective tail temperature of the proton distribution function that can be compared with Neutral Particle Analyzer measurements. More generally the measured emission rate is used to assess the confinement of protons with energies < 400 keV in discharges affected by Toroidal Alfvén Eigenmode instabilities. The derived information on confined ions is combined with observations made with the AUG Fast Ion Loss Detector.

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Investigation of the bifurcation character of the H-mode in ASDEX Upgrade

Cited by 52 publications

References 10 publications

Study on the L–H transition power threshold with RF heating and lithium-wall coating on EAST

Study on the L–H transition power threshold with RF heating and lithium-wall coating on EAST

The role of turbulence–flow interactions in L- to H-mode transition dynamics: recent progress

Gamma-ray spectroscopy measurements of confined fast ions on ASDEX Upgrade

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