Investigation of inter-ELM pedestal profiles in ASDEX Upgrade

Wolfrum, E.; Burckhart, A.; Fischer, R.; Hicks, N.; Konz, C.; Kurzan, B.; Langer, Burkhard; Pütterich, T.; Zohm, H.

doi:10.1088/0741-3335/51/12/124057

Cited by 27 publications

(34 citation statements)

References 16 publications

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“…Each reconstruction is averaged over ∼ 2 ms and separated by ∼ 5 ms. Additional details can be found in Refs. [23,24]. In the following analysis, we focus largely on the segments at t = 3.5, 7.5, −2.5 ms with respect to the ELM crash, which will be denoted S3, S4, and S1, respectively, consistent with the labels in Fig.…”

Section: Methodsmentioning

confidence: 99%

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Gyrokinetic study of ASDEX Upgrade inter-ELM pedestal profile evolution

et al. 2015

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The gyrokinetic GENE code is used to study inter-ELM H-mode pedestal profile evolution for an ASDEX Upgrade discharge. Density gradient driven trapped electron modes (TEM) are the dominant pedestal instability during the early density-buildup phase. Nonlinear simulations produce particle transport levels consistent with experimental expectations. Later inter-ELM phases appear to be simultaneously constrained by electron temperature gradient (ETG) and kinetic ballooning mode (KBM) turbulence. The electron temperature gradient achieves a critical value early in the ELM cycle, concurrent with the appearance of both microtearing modes (MTM) and ETG modes. Nonlinear ETG simulations demonstrate that the profiles lie at a nonlinear critical gradient. The nominal profiles are stable to KBM, but moderate increases in β are sufficient to surpass the KBM threshold. Certain aspects of the dynamics support the premise of KBM-constrained pedestal evolution; the density and temperature profiles separately undergo large changes, but in a manner that keeps the pressure profile constant and near the KBM limit.

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Section: Methodsmentioning

confidence: 99%

“…[23,24]. The profile evolution is characterized by an early density-buildup phase during which TEM dominates, and later phases during which the profile evolution appears to be simultaneously constrained by ETG and KBM turbulence.…”

Section: Introductionmentioning

confidence: 99%

Gyrokinetic study of ASDEX Upgrade inter-ELM pedestal profile evolution

et al. 2015

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“…The high resolution of these diagnostics allows the pedestal structure (of the order of 2 cm in ASDEX Upgrade) to be determined. Ion temperatures were taken to be equal to electron temperatures, as shown for this case by Wolfrum et al [5], and the ion density to be 0.85 that of the electron density, as derived from a typical value for Z ef f ≈ 1.8 and the main impurities being Boron and Oxygen.…”

Section: Pressure Measurementsmentioning

confidence: 99%

“…by comparing the locations of the peak edge electron density and temperature drives from [5] (figure 5); in discharge #23225(#23226) the T e (n e ) profile has a lower value at ρ poloidal = 0.99, due to the higher (lower) fuelling at the edge. The implication of this is that one gradient term peaks further inside, thus driving the peak current further in, while discharge #23221 has a fuelling/heating balance which creates gradients, and hence currents, closer towards the separatrix.…”

Section: Fuelling Studymentioning

confidence: 99%

Measurement of neoclassically predicted edge current density at ASDEX Upgrade

et al. 2012

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Abstract. Experimental confirmation of neoclassically predicted edge current density in an ELMy H-mode plasma is presented. Current density analysis using the CLISTE equilibrium code is outlined and the rationale for accuracy of the reconstructions is explained. Sample profiles and time traces from analysis of data at ASDEX Upgrade are presented. A high time resolution is possible due to the use of an ELM-synchronisation technique. Additionally, the flux surface averaged current density is calculated using a neoclassical approach. Results from these two separate methods are then compared and are found to validate the theoretical formula. Finally, several discharges are compared as part of a fuelling study, showing that the size and width of the edge current density peak at the low field side can be explained by the electron density and temperature drives and their respective collisionality modifications.

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“…In particular, the dynamic behaviour of the profiles of plasma density and temperature in the edge region, influenced by edge-localized modes (ELMs), deserves further attention. With improved diagnostic capabilities, some of these subjects may now be addressed [6][7][8][9][10][11][12] and the experimental results can be compared with the predictions of theoretical models [13][14][15][16][17] . For this study, profiles of electron density and temperature were measured using Thomson scattering with high spatial resolution near the plasma edge 12 .…”

mentioning

confidence: 99%

Electron temperature and density profile evolution during the edge-localized mode cycle in ohmic and electron cyclotron-heated H-mode plasmas in TCV

Pitzschke

Behn

Sauter

et al. 2011

Plasma Phys. Control. Fusion

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The dynamics of electron temperature and density profiles during quasi-stationary H-mode phases in the TCV tokamak has been investigated for type III and type I ELMs using electron cyclotron heating (ECH) to vary the collisionality. At heating power levels close to the threshold for the L-H transition, ELMs of type III were observed, with an energy loss per ELM below 10% of the total plasma energy. Electron temperature and pressure showed no significant increase during the phase before the ELM crash. ELMs of type I were characterized by a lower repetition rate, but caused fractional energy losses reaching 20%. For this ELM type, a clear increase in pedestal pressure and pressure gradient was observed before the collapse associated with the ELM event. The rapid drop in electron temperature also affected the plasma core explaining the rather large energy losses per ELM. Ideal MHD stability calculations of the edge pedestal with the KINX code showed that high-n ballooning modes restricted the achievable pressure gradient at high collisionality and ELMs of type III. With additional heating and type I ELMs, stability limits were set by medium-n kink-ballooning modes. Comparing the values of the pressure gradients and current densities obtained from experimental data with those of ideal MHD stability calculations showed good agreement. The model, however, needs to account for the radial displacement of the location of maximum pressure gradient during the ELM cycle.

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Investigation of inter-ELM pedestal profiles in ASDEX Upgrade

Cited by 27 publications

References 16 publications

Gyrokinetic study of ASDEX Upgrade inter-ELM pedestal profile evolution

Gyrokinetic study of ASDEX Upgrade inter-ELM pedestal profile evolution

Measurement of neoclassically predicted edge current density at ASDEX Upgrade

Electron temperature and density profile evolution during the edge-localized mode cycle in ohmic and electron cyclotron-heated H-mode plasmas in TCV

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