LNF: (2022-2024) Estudio experimental de flujos, turbulencia y modos MHD, y su impacto en confinamiento en los stellarators TJ-II y W7-X: Difference between revisions
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'''Project type''': Proyecto individual | '''Project type''': Proyecto individual | ||
'''Start-end dates''': 01/01/2022 - 31/12/ | '''Start-end dates''': 01/01/2022 - 31/12/2025 | ||
'''Financing granted (direct costs)''': 160.000,00 € | '''Financing granted (direct costs)''': 160.000,00 € | ||
== Description of the project == | == Description of the project == | ||
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At W7-X, upgraded Doppler Reflectometer (DR) systems were installed, commissioned, and successfully operated during the OP2 experimental campaigns. Two systems delivered optimal performance, providing high-resolution measurements of turbulence amplitude, perpendicular flows, and long-range correlations, while a third enabled correlation studies despite alignment limitations. A wide range of magnetic configurations—including reduced mirror, low rotational transform, low magnetic shear, and island-chain scenarios—was explored using standardized density and heating power scans. Turbulence levels were found to increase with plasma density and ECH power, while edge turbulence decreased with increasing rotational transform. A clear correlation emerged between reduced edge turbulence, enhanced radial electric field shear, and improved global energy confinement time. Post-pellet enhanced confinement regimes were successfully reproduced, showing turbulence stabilization and increased plasma flow. Dedicated correlation experiments enabled the first direct measurement of zonal flows in a large stellarator, confirming their dependence on density and heating power and validating gyrokinetic predictions. CXRS flow measurements, refined through improved self-calibration, showed significantly better agreement with neoclassical calculations. | At W7-X, upgraded Doppler Reflectometer (DR) systems were installed, commissioned, and successfully operated during the OP2 experimental campaigns. Two systems delivered optimal performance, providing high-resolution measurements of turbulence amplitude, perpendicular flows, and long-range correlations, while a third enabled correlation studies despite alignment limitations. A wide range of magnetic configurations—including reduced mirror, low rotational transform, low magnetic shear, and island-chain scenarios—was explored using standardized density and heating power scans. Turbulence levels were found to increase with plasma density and ECH power, while edge turbulence decreased with increasing rotational transform. A clear correlation emerged between reduced edge turbulence, enhanced radial electric field shear, and improved global energy confinement time. Post-pellet enhanced confinement regimes were successfully reproduced, showing turbulence stabilization and increased plasma flow. Dedicated correlation experiments enabled the first direct measurement of zonal flows in a large stellarator, confirming their dependence on density and heating power and validating gyrokinetic predictions. CXRS flow measurements, refined through improved self-calibration, showed significantly better agreement with neoclassical calculations. | ||
In TJ-II, three experimental campaigns ensured full operation of the DR and the helical Mirnov coil array. Dedicated calibration experiments and advanced numerical tools supported reliable magnetic fluctuation analysis. A comprehensive database of NBI-driven Alfvén Eigenmodes was obtained under varying heating and rotational transform conditions. Synthetic magnetic diagnostics and linear MHD simulations improved mode interpretation. While no direct impact of Alfvén activity on turbulence was confirmed, indirect effects linked to injection direction and fast-ion losses were identified. Pellet experiments reproduced enhanced confinement regimes similar to W7-X, though modeling suggests different underlying mechanisms. Overall, the project achieved near-complete fulfillment of its objectives and delivered substantial advances in stellarator turbulence and flow physics. | In TJ-II, three experimental campaigns ensured full operation of the DR and the helical Mirnov coil array. Dedicated calibration experiments and advanced numerical tools supported reliable magnetic fluctuation analysis. A comprehensive database of NBI-driven Alfvén Eigenmodes was obtained under varying heating and rotational transform conditions. Synthetic magnetic diagnostics and linear MHD simulations improved mode interpretation. While no direct impact of Alfvén activity on turbulence was confirmed, indirect effects linked to injection direction and fast-ion losses were identified. Pellet experiments reproduced enhanced confinement regimes similar to W7-X, though modeling suggests different underlying mechanisms. Overall, the project achieved near-complete fulfillment of its objectives and delivered substantial advances in stellarator turbulence and flow physics. | ||
== Collaborations with other research groups directly related to the project == | |||
A Collaboration Agreement between the Max-Planck Institute and CIEMAT for the development of Doppler reflectometry in the W7-X stellarator (Germany) was signed in 2013, renewed in 2021 and in force until 2025. | |||
A collaboration with the X-ray Imaging Chrystal Spectroscopy (XICS) team at W7-X (IPP, PPPL) was formalized to include the plasma flow model and assess the influence of fast parallel rotation in the XICS inversions. | |||
Under a more global framework within EUROfusion, the collaboration with the IPP group of the Max-Planck Institute of Greifswald has allowed us to participate in the experiments carried out in the W7-X stellarator. W7-X is the largest stellarator in the world whose objective is to demonstrate the viability of this type of magnetic configuration for a future fusion reactor. Our group has participated in all experimental campaigns since the beginning of the operation of this stellarator back in 2016, with our engagement being reflected in the co-authorship of many scientific publications of the W7-X group over the last decade. During the campaigns the direct part of this participation has included the manning of the Doppler reflectometer and CXRS systems. Besides, our group has adopted a very active stance in the design and supervision of the experimental program, directly participating in its design through the submission of experimental proposals, taking charge of some experimental sessions and generally taking part in the public discussion about the objectives and conduction of the campaigns. This last part was substantially enhanced by the appointment of D. Carralero and A. Alonso as Task Force Leaders of the experimental campaigns, which allowed them a much more direct access to the decision-making process. As well, D. Carralero was part of the team in charge of the supervision of the experimental program realization, its reorganizations as a response to different operational issues and the periodic communication of the campaign status to the W7-X team through a series of regular physics meetings. This work was partly summarized in an invited talk presented after the end of OP2.3, in which he summarized the main core physics results of the campaigns. | |||
The stays at Greifswald during the experimental campaigns have been funded by EUROfusion; only a short stay of P. Pons, needed to carry out preparatory work for the campaign, has been included in the expenses of the present project. | |||
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“First experimental observation of zonal flows in the optimized stellarator Wendelstein 7-X” 24th International Stellarator and Heliotron Workshop, Hiroshima, Japan, September 2024. | “First experimental observation of zonal flows in the optimized stellarator Wendelstein 7-X” 24th International Stellarator and Heliotron Workshop, Hiroshima, Japan, September 2024. | ||
[17] P. Pons et al, | [17] P. Pons et al, "Characterization of the spatial structure of NBI driven shear Alfven waves in the TJ-II stellarator". 18th Technical Meeting on Energetic Particles (TMEP2025), Seville, Spain, March 2025. | ||
[18] D. Carralero, on behalf of the W7-X team (invited) | [18] D. Carralero, on behalf of the W7-X team (invited) | ||
“Machine report: W7-X Core Transport after OP2.3” 25th Coordinated Working Group Meeting, Princeton, USA, June, 2025. | “Machine report: W7-X Core Transport after OP2.3” 25th Coordinated Working Group Meeting, Princeton, USA, June, 2025. | ||