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.

CCFE Culham Science Centre Abingdon Oxon United Kingdom

Department ELEC Vrije Universiteit Brussel Brussels Belgium

Department of Electrical Engineering Control Systems Group Eindhoven University of Technology Eindhoven Netherlands

Department of Mechanical Engineering Control Systems Technology Group Eindhoven University of Technology Eindhoven Netherlands

DIFFER Dutch Institute for Fundamental Energy Research Eindhoven Netherlands

École Polytechnique Fédérale de Lausanne Lausanne Switzerland

Institute of Plasma Physics of the CAS Prague 8 Czech Republic

Max Planck Institut für Plasmaphysik Garching bei München Germany

Plasma Science and Fusion Center Massachusetts Institute of Technology Cambridge MA USA

Zobrazit více v PubMed

Zohm H, et al. On the physics guidelines for a tokamak DEMO. Nucl. Fusion. 2013;53:073019. doi: 10.1088/0029-5515/53/7/073019. DOI

Kallenbach A, et al. Impurity seeding for tokamak power exhaust: from present devices via ITER to DEMO. Plasma Phys. Controlled Fusion. 2013;55:124041. doi: 10.1088/0741-3335/55/12/124041. DOI

Loarte A, Neu R. Power exhaust in tokamaks and scenario integration issues. Fusion Eng. Des. 2017;122:256–273. doi: 10.1016/j.fusengdes.2017.06.024. DOI

Loarte A, et al. Progress in the ITER Physics Basis Chapter 4: power and particle control. Nucl. Fusion. 2007;47:S203–S263. doi: 10.1088/0029-5515/47/6/S04. DOI

Pitts RA, et al. Physics basis for the first ITER tungsten divertor. Nucl. Mater. Energy. 2019;20:100696. doi: 10.1016/j.nme.2019.100696. DOI

Lipschultz B, Parra FI, Hutchinson IH. Sensitivity of detachment extent to magnetic configuration and external parameters. Nucl. Fusion. 2016;56:056007. doi: 10.1088/0029-5515/56/5/056007. DOI

Goetz JA, et al. High confinement dissipative divertor operation on Alcator C-Mod. Phys. Plasmas. 1999;6:1899–1906. doi: 10.1063/1.873447. DOI

Gunn JP, et al. Surface heat loads on the ITER divertor vertical targets. Nucl. Fusion. 2017;57:046025. doi: 10.1088/1741-4326/aa5e2a. DOI

Wesson, J. Tokamaks (Oxford University Press, 2004).

Panek R, et al. Conceptual design of the COMPASS upgrade tokamak. Fusion Eng. Des. 2017;123:11–16. doi: 10.1016/j.fusengdes.2017.03.002. DOI

Albanese R, Pizzuto A. The DTT proposal. A tokamak facility to address exhaust challenges for DEMO: introduction and executive summary. Fusion Eng. Des. 2017;122:274–284. doi: 10.1016/j.fusengdes.2016.12.030. DOI

Romanelli, F. et al. Fusion Electricity: a roadmap to the realisation of fusion energy. EFDA. https://www.euro-fusion.org/wpcms/wp-content/uploads/2013/01/JG12.356-web.pdf (2012).

Kallenbach A, et al. Optimized tokamak power exhaust with double radiative feedback in ASDEX Upgrade. Nucl. Fusion. 2012;52:122003. doi: 10.1088/0029-5515/52/12/122003. DOI

Guillemaut C, et al. Real-time control of divertor detachment in H-mode with impurity seeding using Langmuir probe feedback in JET-ITER- like wall. Plasma Phys. Controlled Fusion. 2017;59:045001. doi: 10.1088/1361-6587/aa5951. DOI

Brunner D, et al. Feedback system for divertor impurity seeding based on real-time measurements of surface heat flux in the Alcator C-Mod tokamak. Rev. Sci. Instrum. 2016;87:023504. doi: 10.1063/1.4941047. PubMed DOI

Kolemen E, et al. Heat flux management via advanced magnetic divertor configurations and divertor detachment. J. Nucl. Mater. 2015;463:1186–1190. doi: 10.1016/j.jnucmat.2014.11.099. DOI

Kallenbach A, et al. Partial detachment of high power discharges in ASDEX Upgrade. Nucl. Fusion. 2015;55:053026. doi: 10.1088/0029-5515/55/5/053026. DOI

Eldon D, et al. Advances in radiated power control at DIII-D. Nucl. Mater. Energy. 2019;18:285–290. doi: 10.1016/j.nme.2019.01.010. DOI

Bernert M, et al. X-Point radiation, its control and an ELM suppressed radiating regime at the ASDEX Upgrade tokamak. Nucl. Fusion. 2020;61:024001. doi: 10.1088/1741-4326/abc936. DOI

Xu GS, et al. Divertor impurity seeding with a new feedback control scheme for maintaining good core confinement in grassy-ELM H-mode regime with tungsten monoblock divertor in EAST. Nucl. Fusion. 2020;60:086001. doi: 10.1088/1741-4326/ab91fa. DOI

Wu K, et al. Radiative feedback control on EAST. Fusion Eng. Des. 2018;129:291–293. doi: 10.1016/j.fusengdes.2017.12.033. DOI

Coda S, et al. Physics research on the TCV tokamak facility: from conventional to alternative scenarios and beyond. Nucl. Fusion. 2019;59:112023. doi: 10.1088/1741-4326/ab25cb. DOI

Perek A, et al. MANTIS: a real-time quantitative multispectral imaging system for fusion plasmas. Rev. Sci. Instrum. 2019;90:123514. doi: 10.1063/1.5115569. PubMed DOI

Doyle EJ, et al. Progress in the ITER physics basis chapter 2: plasma confinement and transport. Nucl. Fusion. 2007;47:S18–S127. doi: 10.1088/0029-5515/47/6/S02. DOI

Lipschultz B, Labombard B, Terry JL, Boswell C, Hutchinson IH. Divertor physics research on alcator C-Mod. Fusion Sci. Technol. 2007;51:369–389. doi: 10.13182/FST07-A1428. DOI

Reimerdes H, et al. TCV experiments towards the development of a plasma exhaust solution. Nucl. Fusion. 2017;57:126007. doi: 10.1088/1741-4326/aa82c2. DOI

Smolders A, et al. Comparison of high density and nitrogen seeded detachment using SOLPS-ITER simulations of the TCV tokamak. Plasma Phys. Controlled Fusion. 2020;62:125006. doi: 10.1088/1361-6587/abbcc5. DOI

Anand H, et al. Distributed digital real-time control system for the TCV tokamak and its applications. Nucl. Fusion. 2017;57:056005. doi: 10.1088/1741-4326/aa6120. DOI

Ravenbergen T, et al. Development of a real-time algorithm for detection of the divertor detachment radiation front using multi-spectral imaging. Nucl. Fusion. 2020;60:066017.

Theiler C, et al. Results from recent detachment experiments in alternative divertor configurations on TCV. Nucl. Fusion. 2017;57:072008. doi: 10.1088/1741-4326/aa5fb7. DOI

Harrison JR, et al. Detachment evolution on the TCV tokamak. Nucl. Mater. Energy. 2017;12:1071–1076. doi: 10.1016/j.nme.2016.10.020. DOI

Harrison JR, et al. Progress toward divertor detachment on TCV within H-mode operating parameters. Plasma Phys. Controlled Fusion. 2019;61:065024. doi: 10.1088/1361-6587/ab140e. DOI

Carr M, et al. Description of complex viewing geometries of fusion tomography diagnostics by ray-tracing. Rev. Sci. Instrum. 2018;89:083506. doi: 10.1063/1.5031087. PubMed DOI

Skogestad, S. & Postlethwaite, I. Multivariable Feedback Control 2nd edn, (Wiley, 2005).

Pintelon, R. & Schoukens, J. System Identification, a Frequency Domain Approach (IEEE Press, 2001).

Leonard A. Plasma detachment in divertor tokamaks. Plasma Phys. Controlled Fusion. 2018;60:044001. doi: 10.1088/1361-6587/aaa7a9. DOI

Krasheninnikov SI, Kukushkin AS. Physics of ultimate detachment of a tokamak divertor plasma. J. Plasma Phys. 2017;83:155830501. doi: 10.1017/S0022377817000654. DOI

Burell, K. H., Ahlgren, D. R. & Crosbie, J. General Atomics Fast Gas injection System Manuel. Tech. Rep., General Atomics, San Diego, USA (1997).

Mallat, S. A wavelet tour of signal processing: the sparse way 3rd edn, (Academic Press, Cambridge, 2008).

Schoukens J, Godfrey K, Schoukens M. Nonparametric Data-Driven Modeling of Linear Systems. IEEE Control Syst. Mag. 2018;38:49–88. doi: 10.1109/MCS.2018.2830080. DOI

Labit B, et al. Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade. Nucl. Fusion. 2019;59:086020. doi: 10.1088/1741-4326/ab2211. DOI

van Berkel M, et al. Correcting for non-periodic behaviour in perturbative experiments : application to heat pulse propagation and modulated gas-puff experiments. Plasma Phys. Controlled Fusion. 2020;62:094001. doi: 10.1088/1361-6587/ab9eaa. DOI

Ravenbergen T, et al. Density Control in ITER: an Iterative Learning Control and Robust Control approach. Nucl. Fusion. 2018;58:016048. doi: 10.1088/1741-4326/aa95ce. DOI

Söderström, T. & Bhikkaji, B. Reduced Order Models for Diffusion Systems via Collocation Methods. In 12th IFAC Symposium on System Identification 977–982 (Elsevier, 2000).

Curtain R, Morris K. Transfer functions of distributed parameter systems: a tutorial. Automatica. 2009;45:1101–1116. doi: 10.1016/j.automatica.2009.01.008. DOI

Hofmann F, Tonetti G. Tokamak equilibrium reconstruction using Faraday rotation measurements. Nucl. Fusion. 1988;28:1871. doi: 10.1088/0029-5515/28/10/014. DOI

Reinke ML, et al. Radiative heat exhaust in Alcator C-Mod I-mode plasmas. Nucl. Fusion. 2019;59:046018. doi: 10.1088/1741-4326/ab04cf. DOI

Lipschultz B, et al. The role of particle sinks and sources in Alcator C-Mod detached divertor discharges. Phys. Plasmas. 1999;6:1907–1916. doi: 10.1063/1.873448. DOI

Eldon D, et al. Controlling marginally detached divertor plasmas. Nucl. Fusion. 2017;57:066039. doi: 10.1088/1741-4326/aa6b16. DOI

Loarer T, et al. Gas balance and fuel retention in fusion devices. Nucl. Fusion. 2007;47:1112–1120. doi: 10.1088/0029-5515/47/9/007. DOI

Harrison JR, et al. Overview of new MAST physics in anticipation of first results from MAST Upgrade. Nucl. Fusion. 2019;59:112011. doi: 10.1088/1741-4326/ab121c. DOI

Silburn, S. et al. Calcam, Python tools for spatial calibration of camera diagnostics. Zenodo. 10.5281/zenodo.4308088 (2018)

Novel concept suppressing plasma heat pulses in a tokamak by fast divertor sweeping