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Title: Interaction of external n = 1 magnetic fields with the sawtooth instability in low- q RFX-mod and DIII-D tokamaks

Abstract

External n = 1 magnetic fields are applied in RFX-mod and DIII-D low safety factor Tokamak plasmas to investigate their interaction with the internal MHD dynamics and in particular with the sawtooth instability. In these experiments the applied magnetic fields cause a reduction of both the sawtooth amplitude and period, leading to an overall stabilizing effect on the oscillations. In RFX-mod sawteeth eventually disappear and are replaced by a stationary m = 1, n = 1 helical equilibrium without an increase in disruptivity. However toroidal rotation is significantly reduced in these plasmas, thus it is likely that the sawtooth mitigation in these experiments is due to the combination of the helically deformed core and the reduced rotation. The former effect is qualitatively well reproduced by nonlinear MHD simulations performed with the PIXIE3D code. The results obtained in these RFX-mod experiments motivated similar ones in DIII-D L-mode diverted Tokamak plasmas at low q 95. These experiments succeeded in reproducing the sawtooth mitigation with the approach developed in RFX-mod. In DIII-D this effect is correlated with a clear increase of the n = 1 plasma response, that indicates an enhancement of the coupling to the marginally stable n = 1 external kink,more » as simulations with the linear MHD code IPEC suggest. A significant rotation braking in the plasma core is also observed in DIII-D. Finally, numerical calculations of the neoclassical toroidal viscosity (NTV) carried out with PENT identify this torque as a possible contributor for this effect.« less

Authors:
 [1];  [1];  [1];  [2];  [3];  [4];  [1];  [2];  [2];  [1];  [4];  [4];  [2];  [3];  [4];  [1];  [4]
  1. Consorzio RFX (CNR, ENEA, INFN, Univ. di Padova, Acciaierie Venete SpA), Padova (Italy)
  2. Columbia Univ., New York, NY (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  4. General Atomics, San Diego, CA (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1335695
Grant/Contract Number:
FG02-04ER54761; AC02-09CH11466; FC02-04ER54698; 633053
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 56; Journal Issue: 10; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; sawtooth instability; 3D magnetic fields; low-q plasmas

Citation Formats

Piron, C., Martin, P., Bonfiglio, D., Hanson, J., Logan, N. C., Paz-Soldan, C., Piovesan, P., Turco, F., Bialek, J., Franz, P., Jackson, G., Lanctot, M. J., Navratil, G. A., Okabayashi, M., Strait, E., Terranova, D., and Turnbull, A. Interaction of external n = 1 magnetic fields with the sawtooth instability in low-q RFX-mod and DIII-D tokamaks. United States: N. p., 2016. Web. doi:10.1088/0029-5515/56/10/106012.
Piron, C., Martin, P., Bonfiglio, D., Hanson, J., Logan, N. C., Paz-Soldan, C., Piovesan, P., Turco, F., Bialek, J., Franz, P., Jackson, G., Lanctot, M. J., Navratil, G. A., Okabayashi, M., Strait, E., Terranova, D., & Turnbull, A. Interaction of external n = 1 magnetic fields with the sawtooth instability in low-q RFX-mod and DIII-D tokamaks. United States. doi:10.1088/0029-5515/56/10/106012.
Piron, C., Martin, P., Bonfiglio, D., Hanson, J., Logan, N. C., Paz-Soldan, C., Piovesan, P., Turco, F., Bialek, J., Franz, P., Jackson, G., Lanctot, M. J., Navratil, G. A., Okabayashi, M., Strait, E., Terranova, D., and Turnbull, A. 2016. "Interaction of external n = 1 magnetic fields with the sawtooth instability in low-q RFX-mod and DIII-D tokamaks". United States. doi:10.1088/0029-5515/56/10/106012. https://www.osti.gov/servlets/purl/1335695.
@article{osti_1335695,
title = {Interaction of external n = 1 magnetic fields with the sawtooth instability in low-q RFX-mod and DIII-D tokamaks},
author = {Piron, C. and Martin, P. and Bonfiglio, D. and Hanson, J. and Logan, N. C. and Paz-Soldan, C. and Piovesan, P. and Turco, F. and Bialek, J. and Franz, P. and Jackson, G. and Lanctot, M. J. and Navratil, G. A. and Okabayashi, M. and Strait, E. and Terranova, D. and Turnbull, A.},
abstractNote = {External n = 1 magnetic fields are applied in RFX-mod and DIII-D low safety factor Tokamak plasmas to investigate their interaction with the internal MHD dynamics and in particular with the sawtooth instability. In these experiments the applied magnetic fields cause a reduction of both the sawtooth amplitude and period, leading to an overall stabilizing effect on the oscillations. In RFX-mod sawteeth eventually disappear and are replaced by a stationary m = 1, n = 1 helical equilibrium without an increase in disruptivity. However toroidal rotation is significantly reduced in these plasmas, thus it is likely that the sawtooth mitigation in these experiments is due to the combination of the helically deformed core and the reduced rotation. The former effect is qualitatively well reproduced by nonlinear MHD simulations performed with the PIXIE3D code. The results obtained in these RFX-mod experiments motivated similar ones in DIII-D L-mode diverted Tokamak plasmas at low q 95. These experiments succeeded in reproducing the sawtooth mitigation with the approach developed in RFX-mod. In DIII-D this effect is correlated with a clear increase of the n = 1 plasma response, that indicates an enhancement of the coupling to the marginally stable n = 1 external kink, as simulations with the linear MHD code IPEC suggest. A significant rotation braking in the plasma core is also observed in DIII-D. Finally, numerical calculations of the neoclassical toroidal viscosity (NTV) carried out with PENT identify this torque as a possible contributor for this effect.},
doi = {10.1088/0029-5515/56/10/106012},
journal = {Nuclear Fusion},
number = 10,
volume = 56,
place = {United States},
year = 2016,
month = 8
}

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  • External n = 1 magnetic fields are applied in RFX-mod and DIII-D low safety factor Tokamak plasmas to investigate their interaction with the internal MHD dynamics and in particular with the sawtooth instability. In these experiments the applied magnetic fields cause a reduction of both the sawtooth amplitude and period, leading to an overall stabilizing effect on the oscillations. In RFX-mod sawteeth eventually disappear and are replaced by a stationary m = 1, n = 1 helical equilibrium without an increase in disruptivity. However toroidal rotation is significantly reduced in these plasmas, thus it is likely that the sawtooth mitigationmore » in these experiments is due to the combination of the helically deformed core and the reduced rotation. The former effect is qualitatively well reproduced by nonlinear MHD simulations performed with the PIXIE3D code. The results obtained in these RFXmod experiments motivated similar ones in DIII-D L-mode diverted Tokamak plasmas at low q 95. These experiments succeeded in reproducing the sawtooth mitigation with the approach developed in RFX-mod. In DIII-D this effect is correlated with a clear increase of the n = 1 plasma response, that indicates an enhancement of the coupling to the marginally stable n = 1 external kink, as simulations with the linear MHD code IPEC suggest. A significant rotation braking in the plasma core is also observed in DIII-D. Numerical calculations of the Neoclassical Toroidal Viscosity (NTV) carried out with PENT identify this torque as a possible contributor for this effect.« less
  • The effect of the sawtooth instability on the 2.5 MeV neutron emission in the PLT (Plasma Physics Controlled Nuclear Fusion Research, 1976 (IAEA, Vienna, 1977), Vol. I, p. 21), DIII-D (Plasma Physics Controlled Nuclear Fusion Research, 1986 (IAEA, Vienna, 1987), Vol. 1, p. 159), and TFTR (Plasma Physics Controlled Nuclear Fusion Research, 1984 (IAEA, Vienna, 1985), Vol. I, p. 29) tokamaks is studied.
  • We evaluate the accuracy of the Porcelli sawtooth model using more realistic numerical models from the ORBIT-RF and GATO codes in DIII-D fast wave heating experiments. Simulation results confirm that the fast wave-induced energetic trapped particles may stabilize the sawtooth instability. The crucial kinetic stabilizing contribution strongly depends on both the experimentally reconstructed magnetic shear at the q = 1 surface and the calculated poloidal beta of energetic trapped particles inside the q = 1 surface.
  • The sensitivity of the pitch angle profiles measured by the motional Stark effect (MSE) diagnostic to the evolution of the safety factor, q, profiles during the tokamak sawtooth events has been investigated for Korea Superconducting Tokamak Advanced Research (KSTAR). An analytic relation between the tokamak pitch angle, γ, and q estimates that Δγ ∼ 0.1° is required for detecting Δq ∼ 0.05 near the magnetic axis (not at the magnetic axis, though). The pitch angle becomes less sensitive to the same Δq for the middle and outer regions of the plasma (Δγ ∼ 0.5°). At the magnetic axis, it ismore » not straightforward to directly relate the γ sensitivity to Δq since the gradient of γ(R), where R is the major radius of the tokamak, is involved. Many of the MSE data obtained from the 2015 KSTAR campaign, when calibrated carefully, can meet these requirements with the time integration down to 10 ms. The analysis with the measured data shows that the pitch angle profiles and their gradients near the magnetic axis can resolve the change of the q profiles including the central safety factor, q{sub 0}, during the sawtooth events.« less