{"id":"doi:10.1088/1741-4326/ac1653","kind":"article","title":"Ion temperature clamping in Wendelstein 7-X electron cyclotron heated plasmas","authors":["M. Beurskens","S. Bozhenkov","Oliver P. Ford","P. Xanthopoulos","A. Zocco","Yuriy Turkin","Arturo Alonso","C. D. Beidler","Iván Calvo","D. Carralero","T. Estrada","G. Fuchert","O. Grulke","M. Hirsch","K. Ida","M. Jakubowski","C. Killer","M. Krychowiak","Sehyun Kwak","S. Lazerson","Andreas Langenberg","R. Lunsford","N. Pablant","Ekkehard Pasch","A. Pavone"],"author_count":34,"year":2021,"published":"2021-07-21","venue":"Nuclear Fusion","cited_by":91,"doi":"10.1088/1741-4326/ac1653","arxiv_id":null,"nct_id":null,"source_url":"https://doi.org/10.1088/1741-4326/ac1653","archive_url":"https://space-kitty.com/papers/doi:10.1088/1741-4326/ac1653","updated":null,"pmid":null,"pmcid":null,"openalex_id":"W3184369425","pdf_url":"https://iopscience.iop.org/article/10.1088/1741-4326/ac1653/pdf","abstract":"The neoclassical transport optimization of the Wendelstein 7-X stellarator has not resulted in the predicted high energy confinement of gas fueled electron-cyclotron-resonance-heated (ECRH) plasmas as modelled in (Turkin et al 2011 Phys. Plasmas 18 022505) due to high levels of turbulent heat transport observed in the experiments. The electron -turbulent-heat transport appears non-stiff and is of the electron temperature gradient (ETG)/ion temperature gradient (ITG) type (Weir et al 2021 Nucl. Fusion 61 056001). As a result, the electron temperature T e can be varied freely from 1 keV–10 keV within the range of P ECRH = 1–7 MW, with electron density n e values from 0.1–1.5 × 10 20 m −3 . By contrast, in combination with the broad electron-to-ion energy-exchange heating profile in ECRH plasmas, ion -turbulent-heat transport leads to clamping of the central ion temperature at T i ∼ 1.5 keV ± 0.2 keV. In a dedicated ECRH power scan at a constant density of 〈 n e 〉 = 7 × 10 19 m −3 , an apparent 'negative ion temperature profile stiffness' was found in the central plasma for ( r / a < 0.5), in which the normalized gradient ∇ T i / T i decreases with increasing ion heat flux. The experiment was conducted in helium, which has a higher radiative density limit compared to hydrogen, allowing a broader power scan. This 'negative stiffness' is due to a strong exacerbation of turbulent transport with an increasing ratio of T e / T i in this electron-heated plasma. This finding is consistent with electrostatic microinstabilities, such as ITG-driven turbulence. Theoretical calculations made by both linear and nonlinear gyro-kinetic simulations performed by the GENE code in the W7-X three-dimensional geometry show a strong enhancement of turbulence with an increasing ratio of T e / T i . The exacerbation of turbulence with increasing T e / T i is also found in tokamaks and inherently enhances ion heat transport in electron-heated plasmas. This finding strongly affects the prospects of future high-performance gas-fueled ECRH scenarios in W7-X and imposes a requirement for turbulence-suppression techniques.","abstract_license":"CC-BY (publisher license, via OpenAlex)","license":"cc-by","is_open_access":true,"retracted":false,"peer_reviewed":null,"categories":["Magnetic confinement fusion research"],"details":null,"provenance":"openalex","attribution":"Abstract of \"Ion temperature clamping in Wendelstein 7-X electron cyclotron heated plasmas\" by M. Beurskens, S. Bozhenkov, Oliver P. Ford et al., https://doi.org/10.1088/1741-4326/ac1653, used under its Creative Commons Attribution license (CC-BY); markup removed, otherwise unmodified.","topics":[{"slug":"magnetic-fusion","name":"Magnetic Confinement Fusion","domain_slug":"energy"}],"cited_in_dossiers":[]}