Physics:Edge-localized mode
An edge-localized mode (ELM) is a plasma instability occurring in the edge region of a tokamak plasma due to periodic relaxations of the edge transport barrier in high-confinement mode. Each ELM burst is associated with expulsion of particles and energy from the confined plasma into the scrape-off layer. This phenomenon was first observed in the ASDEX tokamak in 1981.[1] Diamagnetic effects in the model equations expand the size of the parameter space in which solutions of repeated sawteeth can be recovered compared to a resistive MHD model.[2] An ELM can expel up to 20 percent of the reactor's energy.[3]
Issues
ELM is a major challenge in magnetic fusion research with tokamaks, as these instabilities can:
- Damage wall components (in particular divertor plates) by ablating them away due to their extremely high energy transfer rate (GW/m2);[4]
- Potentially couple or trigger other instabilities, such as the resistive wall mode (RWM) or the neoclassical tearing mode (NTM).[5]
Prevention and control
A variety of experiments/simulations have attempted to mitigate damage from ELM. Techniques include:
- Application of resonant magnetic perturbations (RMPs) with in-vessel current carrying coils can eliminate or weaken ELMs.[6]
- Injecting pellets to increase the frequency and thereby decrease the severity of ELM bursts (ASDEX Upgrade).[citation needed]
- Multiple small-scale ELMs (000s/s) in tokamaks to prevent the creation of large ones, spreading the associated heat over a larger area and interval[7]
- Increase the plasma density and, at high densities, adjusting the topology of the magnetic field lines confining the plasma.[8]
History
In 2003 DIII-D begn experimenting with resonant magnetic perturbations to control ELMs.[9]
In 2006 an initiative (Project Aster) was started to simulate a full ELM cycle including its onset, the highly non-linear phase, and its decay. However, this did not constitute a “true” ELM cycle, since a true ELM cycle would require modeling the slow growth after the crash, in order to produce a second ELM.
As of late 2011, several research facilities had demonstrated active control or suppression of ELMs in tokamak plasmas. For example, the KSTAR tokamak used specific asymmetric three-dimensional magnetic field configurations to achieve this goal.[10][11]
In 2015, results of the first simulation to demonstrate repeated ELM cycling was published.[12]
In 2022, researchers began testing the small ELM hypothesis at JET to assess the utility of the technique.[7][3]
See also
- Resonant magnetic perturbations, used to control ELMs
- Plasma instability
- Tokamak
References
- ↑ F., Wagner; A.R., Field; G., Fussmann; J.V., Hofmann; M.E., Manso; O., Vollmer; José, Matias (1990). "Recent results of H-mode studies on ASDEX". 13th International Conference on Plasma Physics and Controlled Nuclear Fusion: 277–290.
- ↑ Halpern, F D; Leblond, D; Lütjens, H; Luciani, J-F (2010-11-30). "Oscillation regimes of the internal kink mode in tokamak plasmas". Plasma Physics and Controlled Fusion 53 (1): 015011. doi:10.1088/0741-3335/53/1/015011. ISSN 0741-3335.
- ↑ 3.0 3.1 Choi, Charles Q. (20 October 2022). "Controlled chaos may be the key to unlimited clean energy" (in en). https://www.inverse.com/innovation/nuclear-fusion-instabilities.
- ↑ Lee, Chris (13 September 2018). "A third dimension helps Tokamak fusion reactor avoid wall-destroying instability" (in en-us). Ars Technica. https://arstechnica.com/science/2018/09/a-third-dimension-helps-tokamak-fusion-reactor-avoid-wall-destroying-instability/.
- ↑ Leonard, A.W. (11 September 2014). "Edge-localized modes in tokamaks". Physics of Plasmas 21 (9): 090501. doi:10.1063/1.4894742. Bibcode: 2014PhPl...21i0501L.
- ↑ T.E. Evans (2008). "RMP ELM suppression in DIII-D plasmas with ITER similar shapes and collisionalities". Nucl. Fusion 92 (48): 024002. doi:10.1088/0029-5515/48/2/024002. Bibcode: 2008NucFu..48b4002E. https://iopscience.iop.org/article/10.1088/0029-5515/48/2/024002.
- ↑ 7.0 7.1 Harrer, G. F.; Faitsch, M.; Radovanovic, L.; Wolfrum, E.; Albert, C.; Cathey, A.; Cavedon, M.; Dunne, M. et al. (2022-10-10). "Quasicontinuous Exhaust Scenario for a Fusion Reactor: The Renaissance of Small Edge Localized Modes". Physical Review Letters 129 (16): 165001. doi:10.1103/PhysRevLett.129.165001. PMID 36306746. Bibcode: 2022PhRvL.129p5001H. https://link.aps.org/doi/10.1103/PhysRevLett.129.165001.
- ↑ "Fusion-reactor instabilities can be optimized by adjusting plasma density and magnetic fields". Physics World. Nov 4, 2022. https://physicsworld.com/a/fusion-reactor-instabilities-can-be-optimized-by-adjusting-plasma-density-and-magnetic-fields/.
- ↑ T.E. Evans (2004). "Suppression of Large Edge-Localized Modes in High-Confinement DIII-D Plasmas with a Stochastic Magnetic Boundary". Physical Review Letters 92 (23): 235003. doi:10.1103/PhysRevLett.92.235003. PMID 15245164. Bibcode: 2004PhRvL..92w5003E. http://juser.fz-juelich.de/search?p=id:%22PreJuSER-38026%22.
- ↑ Kwon, Eunhee (2011-11-10). "KSTAR announces successful ELM suppression". http://www.iter.org/newsline/198/950.
- ↑ Park, Jong-Kyu; Jeon, YoungMu; In, Yongkyoon; Ahn, Joon-Wook; Nazikian, Raffi; Park, Gunyoung; Kim, Jaehyun; Lee, HyungHo et al. (2018-09-10). "3D field phase-space control in tokamak plasmas" (in En). Nature Physics 14 (12): 1223–1228. doi:10.1038/s41567-018-0268-8. ISSN 1745-2473. Bibcode: 2018NatPh..14.1223P.
- ↑ Orain, François; Bécoulet, M; Morales, J; Huijsmans, G T A; Dif-Pradalier, G; Hoelzl, M; Garbet, X; Pamela, S et al. (2014-11-28). "Non-linear MHD modeling of edge localized mode cycles and mitigation by resonant magnetic perturbations". Plasma Physics and Controlled Fusion 57 (1): 014020. doi:10.1088/0741-3335/57/1/014020. ISSN 0741-3335. https://hal.archives-ouvertes.fr/hal-02184569/file/Orain_F_PPCF_2014%20%281%29.pdf.
Further reading
- Kirk, A; Liu, Yueqiang; Chapman, I T; Harrison, J; Nardon, E; Scannell, R; Thornton, A J (2013-03-06). "Effect of resonant magnetic perturbations on ELMs in connected double null plasmas in MAST". Plasma Physics and Controlled Fusion 55 (4): 045007. doi:10.1088/0741-3335/55/4/045007. ISSN 0741-3335. Bibcode: 2013PPCF...55d5007K.
- Tala, Tuomas; Garbet, Xavier (2006). "Physics of Internal Transport Barriers". Comptes Rendus Physique 7 (6): 622–633. doi:10.1016/j.crhy.2006.06.005. Bibcode: 2006CRPhy...7..622T. https://comptes-rendus.academie-sciences.fr/physique/item/10.1016/j.crhy.2006.06.005.pdf.
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