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Dependence of the $n=1$ MHD $\beta$ Limits on the Aspect Ratio in Tokamaks
New Phys.: Sae Mulli 2019; 69: 309~316
Published online March 29, 2019;
© 2019 New Physics: Sae Mulli.

Ohjin KWON*

Department of Physics, Daegu University, Gyeongsan 38453, Korea
Correspondence to:
Received December 11, 2018; Revised January 1, 2019; Accepted January 2, 2019.
cc This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
We have numerically investigated the dependence of the $n=1$ global beta limit without wall stabilization on the aspect ratio in tokamaks. For all aspect ratios, the maximum stable $\beta$ values generally increase as the safety factor at the magnetic axis increases. The maximum $\beta_t$ and maximum $\beta_N$ increase considerably as the aspect ratio becomes tighter while the maximum $\beta_p$ does not change much. The maximum $\beta$ depends on the profile of the plasma current density such that it increases with increasing internal inductance. This behavior is dominant for large aspect ratios and for low plasma currents, but becomes negligible for tight aspect ratios. As the plasma current increases, the maximum $\beta_p$ and the maximum $\beta_N$ decrease, while the maximum $\beta_t$ increases.
PACS numbers: 52.55.Fa, 52.65.-y, 52.30.Cv, 52.35.Py
Keywords: Spherical tokamak, Aspect ratio, $\beta$ values, Internal inductance

March 2019, 69 (3)
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