Radiative heat exhaust in Alcator C-Mod I-mode plasmas

Reinke, M.L.; Brunner, D.; Golfinopoulos, T.; Hubbard, A.; Hughes, J.W.; Kuang, Adam; LaBombard, B.; Marmar, E.; Mumgaard, R.; Terry, J. L.; Lore, J.; Canik, J.; Cziegler, I.; Team, Alcator C‐Mod

doi:10.1088/1741-4326/ab04cf

Cited by 16 publications

(21 citation statements)

References 42 publications

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“…The use such a diagnostic for control purposes has some advantages over existing methods. Firstly, our approach yields a 2D spatial measurement of the temperature in the divertor, which is compatible with other heat load mitigation techniques like strike-point sweeping 47 . In addition, a full 2D view is relevant as it has become clear that the onset of detachment is driven from a high density, low temperature region in the private flux region 48 .…”

Section: Discussionmentioning

confidence: 93%

Real-time feedback control of the impurity emission front in tokamak divertor plasmas

et al. 2021

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In magnetic confinement thermonuclear fusion the exhaust of heat and particles from the core remains a major challenge. Heat and particles leaving the core are transported via open magnetic field lines to a region of the reactor wall, called the divertor. Unabated, the heat and particle fluxes may become intolerable and damage the divertor. Controlled ‘plasma detachment’, a regime characterized by both a large reduction in plasma pressure and temperature at the divertor target, is required to reduce fluxes onto the divertor. Here we report a systematic approach towards achieving this critical need through feedback control of impurity emission front locations and its experimental demonstration. Our approach comprises a combination of real-time plasma diagnostic utilization, dynamic characterization of the plasma in proximity to the divertor, and efficient, reliable offline feedback controller design.

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Section: Discussionmentioning

confidence: 93%

Real-time feedback control of the impurity emission front in tokamak divertor plasmas

et al. 2021

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“…The associated reduction in the electrostatic particle flux can be compensated by the electromagnetic particle transport as demonstrated in the simulations. iv) Detachment: The I-mode regime is difficult to detach, usually an I-L back-transition (not linked to bulk-plasma impurity radiation) is triggered prior to meaningful reductions in parallel heat flux to the divertor [39]. In the present model, the back transition might be explained as follows: If the plasma starts to detach, a large source of cold ions is created in the scrape-off layer from ionization of recycled neutrals from the first wall [16].…”

Section: Discussionmentioning

confidence: 99%

Physical mechanism behind and access to the I-mode confinement regime in tokamaks

et al. 2020

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The I-mode is an attractive confinement regime for future tokamak based fusion reactors. A model is presented which explains the I-mode regime by the reduction of ITG turbulence near the separatrix at low collisionality, where the separatrix ion temperature can exceed the electron temperature. Drift-Alfvénturbulence develops, with large and small-scale fluctuations being suppressed by phase randomization and finite-Larmor-radius effects, respectively. The intermediate scales form a broad peak in the frequency spectrum, which features the same properties as the characteristic weakly coherent mode. The model, which is studied by means of gyrofluid simulations, reproduces a number of other experimental I-mode observations, such as decoupled energy and particle transport, intermittent turbulent bursts with precursors, an operational window widening with magnetic field strength, and the challenges met when detaching the plasma.

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“…Alcator C-Mod experiments were not successful in demonstrating compatibility of the I-mode regime with divertor detachment [23]. These investigations are being continued in AUG [24].…”

Section: Ar Injection Into Intrinsically Elm-free and Close-to Elm Fr...mentioning

confidence: 99%

Developments towards an ELM-free pedestal radiative cooling scenario using noble gas seeding in ASDEX Upgrade

et al. 2020

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Integrated edge-localized-mode (ELM)-free or small ELM scenarios for the demonstration fusion power plant (DEMO) are investigated in ASDEX Upgrade using argon seeding for radiative power removal mainly in the pedestal region. An important aspect is the modification of the electron pressure in the pedestal by the additional radiative power losses. Full ELM suppression could be achieved in a no-ELM H-mode scenario featuring an edge electromagnetic quasicoherent mode up to a heating power of 5 MW, where argon radiation allowed the extension of the heating power operational space. At higher powers up to 12 MW (reaching the beta limit), ELMs of reduced size prevail and detachment is obtained by the argon seeding. Control of the position of a radiating zone localized inside the X-point was found to be favorable compared to the control of the separatrix power for low P s e p / P h e a t . Integration of pedestal cooling with Ar and ELM suppression by resonant magnetic perturbations (RMP) allowed an increase of the core radiation and a partial recovery of normalized confinement to H98 = 1. This favorable behavior is finally limited by the loss of the RMP density pump-out effect, followed by an ELM-free H-mode phase and re-occurrence of ELMs. For an active tailoring of the pedestal pressure profile, precise knowledge of the radiation profile is required. Modeling of the argon radiation profile with the STRAHL code showed good agreement with bolometry only if charge exchange of neutral deuterium with argon ions was taken into account, highlighting the importance of the neutral density in the pedestal region. In view of best integration of a no-ELM scenario with divertor detachment and high heating power, the divertor compression and enrichment of argon and neon were compared using dynamic gas puff experiments. Argon shows more than a factor of 3 higher divertor enrichment compared to neon, but the absolute values decrease with higher neutral deuterium pressure.

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Radiative heat exhaust in Alcator C-Mod I-mode plasmas

Cited by 16 publications

References 42 publications

Real-time feedback control of the impurity emission front in tokamak divertor plasmas

Real-time feedback control of the impurity emission front in tokamak divertor plasmas

Physical mechanism behind and access to the I-mode confinement regime in tokamaks

Developments towards an ELM-free pedestal radiative cooling scenario using noble gas seeding in ASDEX Upgrade

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