Turbulence in the I-mode regime of confinement

I-mode is an ELM-free improved confinement regime with low impurity content. It appears in unfavorable configuration with the ion grad B drift poiting away from the active X-point. The I-mode exhibits temperature pedestal, but no density pedestal. Therefore, it is thought that the heat transport is suppressed, but the particle transport not. Turbulence in I-mode is not broadband as in L-mode. A prominent feature of turbulence in I-mode is the weakly coherent mode (WCM)

Here we can explain

  • How can heat and particle transport be decoupled? Density and electron temperature fluctuations can be decoupled by conduction. 
  • Why is the turbulence not broadband? The WCM is a drift-Alfven wave. Larger scales (low wavenumbers) are stabilized by phase randomization.  
  • Why is the operational window wider at higher magnetic field strength? An operation area in plasma beta automatically leads to this. 


relevant publications of the group

P. Manz et al. 'Physical mechanism behind and access to the I-mode confinement regime in tokamaks' Nucl. Fusion 60 096011 (2020)

P. Manz et al. 'Geodesic oscillations and the weakly coherent mode in the I-mode of ASDEX Upgrade'  Nucl. Fusion 55 083004 (2015)

I. Cziegler et al. 'Fluctuating zonal flows in the I-mode regime in Alcator C-Mod' Physics of Plasmas 20, 055904 (2013)

M. Herschel et al. 'Experimental evidence for the drift wave nature of the weakly coherent mode in ASDEX Upgrade I-mode plasmas', Nuclear Fusion 64, 076052 (2024)

T. Happel, P. Manz et al. 'Turbulence intermittency linked to the weakly coherent mode in ASDEX Upgrade I-mode plasmas' Nucl. Fusion 56 064004 (2016)

A.E. Hubbard et al. 'Multi-device studies of pedestal physics and confinement in the I-mode regime' Nucl. Fusion 56 086003 (2016)

T Happel et al. 'The I-mode confinement regime at ASDEX Upgrade: global properties and characterization of strongly intermittent density fluctuations'  Plasma Phys. Control. Fusion 59 014004 (2017)

P. Manz et al. 'Turbulence characteristics of the I-mode confinement regime in ASDEX Upgrade' Nucl. Fusion 57 086022 (2017)

T. Happel et al. 'Stationarity of I-mode operation and I-mode divertor heat fluxes on the ASDEX Upgrade tokamak' Nuclear Materials and Energy 18, 159 (2019)

D. Silvagni et al. 'I-mode pedestal relaxation events at ASDEX Upgrade' Nucl. Fusion 60 126028 (2020)

T. Happel et al. 'Approaching detachment in I-mode—response of core confinement and the edge pedestal in the ASDEX Upgrade tokamak'  Nucl. Fusion 61 036026 (2021)