Stationarity of I-mode operation and I-mode divertor heat fluxes on the ASDEX Upgrade tokamak

Happel, T.; Griener, M.; Silvagni, D.; Freethy, S. J.; Hennequin, Pascale; Janky, F.; Mänz, P.; Prisiazhniuk, D.; Ryter, F.; Bernert, M.; Brida, D.; Eich, T.; Faitsch, M.; Gil, L.; Guimarãis, L.; Merle, A.; Nille, D.; Pinzon, J. R.; Sieglin, B.; Stroth, U.

doi:10.1016/j.nme.2018.12.022

Cited by 29 publications

(39 citation statements)

References 42 publications

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“…The right panels of figure 1 show a typical AUG I-mode discharge with PREs. The plasma is heated with constant electron cyclotron resonance heating (ECRH) and neutral beam injection, the latter being feedback controlled on the value of the β pol , similarly to [7,18]. The β pol is defined as 2μ 0 p/B 2 pol , where p is the average plasma pressure and B pol is the average poloidal magnetic field strength.…”

Section: Typical Discharge In C-mod and Augmentioning

confidence: 99%

I-mode pedestal relaxation events in the Alcator C-Mod and ASDEX Upgrade tokamaks

et al. 2022

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In some conditions, I-mode plasmas can feature pedestal relaxation events (PREs) that transiently enhance the energy reaching the divertor target plates. To shed light on their appearance, characteristics and energy reaching the divertor targets, a comparative study between two tokamaks – Alcator C-Mod and ASDEX Upgrade – is carried out. It is found that PREs appear only in a subset of I-mode discharges, mainly when the plasma is close to the H-mode transition. Also, a growing oscillating precursor before the PRE onset is observed in the region close to the separatrix in both devices, and a discussion on a possible triggering mechanism is outlined. The PRE relative energy loss from the confined region is found to increase with decreasing pedestal top collisionality ν* ped. Similarly, also the relative electron temperature drop at the pedestal top, which is related to the conductive energy loss, rises with decreasing ν* ped. Based on these relations, the PRE relative energy loss in future devices such as DEMO and ARC is estimated. Finally, the divertor peak energy fluence due to the PRE is measured on each device. Those values are then compared to the model introduced in [1] for type-I ELMs. The model is shown to provide an upper boundary for PRE energy fluence data, while a lower boundary is found by dividing the model by three. These two boundaries are used to make projections of the PRE divertor energy fluence to DEMO and ARC.

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Section: Typical Discharge In C-mod and Augmentioning

confidence: 99%

I-mode pedestal relaxation events in the Alcator C-Mod and ASDEX Upgrade tokamaks

et al. 2022

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“…1 show a typical AUG Imode discharge with PREs. The plasma is heated with constant electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI), the latter being feedback controlled on the value of the β pol , similarly to [17,7]. The β pol is defined as 2µ 0 p/B 2 pol , where p is the average plasma pressure and B pol is the average poloidal magnetic field strength.…”

Section: Typical Discharge In C-mod and Augmentioning

confidence: 99%

I-mode pedestal relaxation events at ASDEX Upgrade

et al. 2020

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In some conditions, I-mode plasmas can feature pedestal relaxation events (PREs) that transiently enhance the energy reaching the divertor target plates. To shed light into their appearance, characteristics and energy reaching the divertor targets, a comparative study between two tokamaks -Alcator C-Mod and ASDEX Upgrade -is carried out. It is found that PREs appear only in a subset of I-mode discharges, mainly when the plasma is close to the H-mode transition. Also, the nature of the triggering instability is discussed by comparing measurements close to the separatrix in both devices. The PRE relative energy loss from the confined region increases with decreasing pedestal top collisionality ν * ped . In addition, the relative electron temperature drop at the pedestal top, which is related to the conductive energy loss, rises with decreasing ν * ped . Finally, the peak parallel energy fluence due to the PRE measured on the divertor in both devices is compared to the model introduced in [1] for type-I ELMs. The model is shown to provide an upper boundary for PRE energy fluence data, while a lower boundary is found by dividing the model by three. These two boundaries are used to make projections to future devices such as DEMO and ARC.

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“…-12 Stationary operation on different machines makes the I-mode an appealing regime for tokamaks. 13,14 The mechanisms which allow for the decoupling of density and temperature profiles in the I-mode have not yet been fully understood, although common characteristics in a) Electronic mail: karl.stimmel@ipp.mpg.de both C-Mod and ASDEX-Upgrade I-mode discharges include heightened temperature profiles simultaneous with low density profiles, and the weakly coherent mode (WCM), a pedestal mode that is observed to be electrostatic in ASDEX-Upgrade I-mode plasmas. 10 While experimental diagnostics have given much insight into the nature of the I-mode, and other gyrokinetic simulations have expanded theoretical understanding of turbulent transport in I-mode scenarios, a clear understanding of turbulent transport in the tokamak pedestal has not yet been developed for the I-mode.…”

Section: Introductionmentioning

confidence: 99%

Gyrokinetic investigation of the ASDEX Upgrade I-mode pedestal

et al. 2019

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Characterizing pedestal turbulence in the tokamak I-mode is a crucial step in understanding how particle and heat transport decouple during I-mode operation. This work models an ASDEX Upgrade I-mode discharge for the first time via linear and nonlinear gyrokinetic simulations with the GENE code. L-mode and I-mode regimes at two different pedestal locations are investigated. A microtearing mode which is not apparent in initial value linear L-mode simulations is found to dominate in I-mode simulations at both radial positions, and ion-scale instabilities are characterized for all four scenarios linearly. Computed nonlinear heat flux values approach experimental measurements with nominal input parameters in three of the four cases, and heat transport is found to be dominated by ion-scale electrostatic turbulence. Electrostatic potential oscillation frequencies, as well as potential-temperature and potential-density crossphases are compared linearly and nonlinearly, and agreement is found at wavenumber ranges corresponding with peaks in the simulated heat flux spectra at one radial position for L-mode and I-mode.

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Stationarity of I-mode operation and I-mode divertor heat fluxes on the ASDEX Upgrade tokamak

Cited by 29 publications

References 42 publications

I-mode pedestal relaxation events in the Alcator C-Mod and ASDEX Upgrade tokamaks

I-mode pedestal relaxation events in the Alcator C-Mod and ASDEX Upgrade tokamaks

I-mode pedestal relaxation events at ASDEX Upgrade

Gyrokinetic investigation of the ASDEX Upgrade I-mode pedestal

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