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Title: On hybrid scenarios in KSTAR

Abstract

We report the status of hybrid scenario experiments in Korea Superconducting Tokamak Advanced Research (KSTAR). The hybrid scenario is defined as stationary discharges with $${\beta _{\rm{N}}}$$ $$ \geqslant $$ 2.4 and $${H_{89}}$$ $$ \geqslant $$ 2.0 at $${q_{95}}$$ < 6.5 without or with very mild sawtooth activities in KSTAR. It is being developed towards reactor-relevant conditions. High performance of $${\beta _{\rm{N}}} \lesssim 3.0$$, $${H_{89}} \lesssim 2.4$$ and G-factor ($$ \equiv {\beta _{\rm{N}}}{H_{89}}/q_{95}^2$$) $$ \lesssim 0.4$$6 has been achieved and sustained for $$ \gtrsim 40{{\tau }_{\text{E}}}$$ at ne/nGW ~ 0.7 with heating power of $$ \lesssim $$5 MW. Some KSTAR hybrid discharges exhibit a unique feature of a slow transition from conventional H-mode to hybrid mode after the third neutral beam injection. The reason for the confinement enhancement is extensively studied in this transition period of a representative discharge exhibiting a common feature of KSTAR hybrid scenarios. 0D performance analysis with magnetohydrodynamic activities, 1D kinetic profile dynamics, power balance analysis, linear gyro-kinetic analysis and edge pedestal stability analysis were conducted. The enhancement is thought to be from both the core and the pedestal. The improvement in the core region of the ion energy channel is observed from the linear gyro-kinetic analysis considering the electromagnetic, the fast ion, the Shafranov shift, $${\it{\omega }_{E \times B}}$$, and the magnetic shear effect. The electromagnetic finite $$\beta $$ stabilisation plays a role in the inner core region at $${\rho _{\rm{tor}}}\sim0.35$$ together with the fast ion effect. The alpha stabilisation effect is also found at $${\rho _{\rm{tor}}}\sim0.5$$. $${\omega _{E \times B}}$$, which could reduce the linear growth of the ion temperature gradient mode in the outer core region at $${\rho _{\rm{tor}}}\sim0.5 - 0.7$$ with the highest contribution from the toroidal rotation. Furthermore, regarding the improvement in the pedestal, Shafranov shift broadens the stability boundary of the pedestal in support of the diamagnetic effect. The pedestal height and width could be reproduced by the EPED model, while a realistic current profile is used to calculate the internal inductance for Shafranov shift. Based on these findings, a comprehensive confinement enhancement mechanism has been proposed by considering the core-edge interplay.

Authors:
 [1];  [2];  [1];  [1];  [1];  [1];  [3];  [1];  [4]; ORCiD logo [5];  [6];  [4]; ORCiD logo [4];  [4]; ORCiD logo [4];  [4];  [4]; ORCiD logo [4];  [4];  [4] more »;  [4]; ORCiD logo [7] « less
  1. Seoul National Univ. (South Korea)
  2. Seoul National Univ. (South Korea); National Fusion Research Inst., Daejeon (South Korea)
  3. Seoul National Univ. (South Korea); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  4. National Fusion Research Inst., Daejeon (South Korea)
  5. Seoul National Univ. (South Korea); Univ. of California, Irvine, CA (United States)
  6. Dutch Inst. for Fundamental Energy Research (DIFFER), Eindhoven (Nethernalnds)
  7. Pohang Univ. of Science and Technology (South Korea)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE; National Research Foundation of Korea (NRF)
Contributing Org.:
KSTAR Team
OSTI Identifier:
1668288
Grant/Contract Number:  
AC02-09CH11466; NRF-2019R1A2C1010757
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 60; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English

Citation Formats

Na, Yong-Su, Lee, Y. H., Byun, C. S., Kim, S. K., Lee, C. Y., Park, M. S., Yang, S. M., Kim, B., Jeon, Y. -M., Choi, G. J., Citrin, J., Juhn, J. W., Kang, J. S., Kim, H. -S., Kim, J. H., Ko, W. H., Kwon, J. -M., Lee, W. C., Woo, M. H., Yi, S., Yoon, S. W., and Yun, G. S. On hybrid scenarios in KSTAR. United States: N. p., 2020. Web. doi:10.1088/1741-4326/ab8b7a.
Na, Yong-Su, Lee, Y. H., Byun, C. S., Kim, S. K., Lee, C. Y., Park, M. S., Yang, S. M., Kim, B., Jeon, Y. -M., Choi, G. J., Citrin, J., Juhn, J. W., Kang, J. S., Kim, H. -S., Kim, J. H., Ko, W. H., Kwon, J. -M., Lee, W. C., Woo, M. H., Yi, S., Yoon, S. W., & Yun, G. S. On hybrid scenarios in KSTAR. United States. doi:10.1088/1741-4326/ab8b7a.
Na, Yong-Su, Lee, Y. H., Byun, C. S., Kim, S. K., Lee, C. Y., Park, M. S., Yang, S. M., Kim, B., Jeon, Y. -M., Choi, G. J., Citrin, J., Juhn, J. W., Kang, J. S., Kim, H. -S., Kim, J. H., Ko, W. H., Kwon, J. -M., Lee, W. C., Woo, M. H., Yi, S., Yoon, S. W., and Yun, G. S. Fri . "On hybrid scenarios in KSTAR". United States. doi:10.1088/1741-4326/ab8b7a.
@article{osti_1668288,
title = {On hybrid scenarios in KSTAR},
author = {Na, Yong-Su and Lee, Y. H. and Byun, C. S. and Kim, S. K. and Lee, C. Y. and Park, M. S. and Yang, S. M. and Kim, B. and Jeon, Y. -M. and Choi, G. J. and Citrin, J. and Juhn, J. W. and Kang, J. S. and Kim, H. -S. and Kim, J. H. and Ko, W. H. and Kwon, J. -M. and Lee, W. C. and Woo, M. H. and Yi, S. and Yoon, S. W. and Yun, G. S.},
abstractNote = {We report the status of hybrid scenario experiments in Korea Superconducting Tokamak Advanced Research (KSTAR). The hybrid scenario is defined as stationary discharges with ${\beta _{\rm{N}}}$ $ \geqslant $ 2.4 and ${H_{89}}$ $ \geqslant $ 2.0 at ${q_{95}}$ < 6.5 without or with very mild sawtooth activities in KSTAR. It is being developed towards reactor-relevant conditions. High performance of ${\beta _{\rm{N}}} \lesssim 3.0$, ${H_{89}} \lesssim 2.4$ and G-factor ($ \equiv {\beta _{\rm{N}}}{H_{89}}/q_{95}^2$) $ \lesssim 0.4$6 has been achieved and sustained for $ \gtrsim 40{{\tau }_{\text{E}}}$ at ne/nGW ~ 0.7 with heating power of $ \lesssim $5 MW. Some KSTAR hybrid discharges exhibit a unique feature of a slow transition from conventional H-mode to hybrid mode after the third neutral beam injection. The reason for the confinement enhancement is extensively studied in this transition period of a representative discharge exhibiting a common feature of KSTAR hybrid scenarios. 0D performance analysis with magnetohydrodynamic activities, 1D kinetic profile dynamics, power balance analysis, linear gyro-kinetic analysis and edge pedestal stability analysis were conducted. The enhancement is thought to be from both the core and the pedestal. The improvement in the core region of the ion energy channel is observed from the linear gyro-kinetic analysis considering the electromagnetic, the fast ion, the Shafranov shift, ${\it{\omega }_{E \times B}}$, and the magnetic shear effect. The electromagnetic finite $\beta $ stabilisation plays a role in the inner core region at ${\rho _{\rm{tor}}}\sim0.35$ together with the fast ion effect. The alpha stabilisation effect is also found at ${\rho _{\rm{tor}}}\sim0.5$. ${\omega _{E \times B}}$, which could reduce the linear growth of the ion temperature gradient mode in the outer core region at ${\rho _{\rm{tor}}}\sim0.5 - 0.7$ with the highest contribution from the toroidal rotation. Furthermore, regarding the improvement in the pedestal, Shafranov shift broadens the stability boundary of the pedestal in support of the diamagnetic effect. The pedestal height and width could be reproduced by the EPED model, while a realistic current profile is used to calculate the internal inductance for Shafranov shift. Based on these findings, a comprehensive confinement enhancement mechanism has been proposed by considering the core-edge interplay.},
doi = {10.1088/1741-4326/ab8b7a},
journal = {Nuclear Fusion},
number = 8,
volume = 60,
place = {United States},
year = {2020},
month = {7}
}

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