Speaker
Hyeon K. Park
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1051.pdf
Experimental validation of the reconnection model (full or partial) in the
sawtooth instability in KSTAR
H.K. Park1, J.S. Ko2, Y.B. Nam3, S. Jardin4
1, Ulsan National Institute of Science and Technology, Ulsan, Korea
2, National Fusion Research Institute, Daejeon, Korea
3, CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France.
4
Princeton Plasma Physics Laboratory, Princeton, NJ, United States
The long-standing issue whether the central safety factor (q0) goes back to above ~1.0 or not
after the crash of the sawtooth instability was revisited in this paper. In this study, it was
found that the “full reconnection model” in which the q0 goes back to above ~1.0 after the
crash, originally proposed by Kadomtsev, is likely to be the correct model [1]. This model
was discarded for a long time due to the first q0 measurements (Faraday rotation and
Motional Stark Effect (MSE)) where the measured q0 was remained well below ~1.0 (~0.8)
after the crash. Now we have learned that the unfolding techniques of these polarimetry
measurements are much more complex and understanding has evolved since the first
measurement. Some of the critical issues in unfolding techniques will be addressed in this
paper. Recent MSE measurement of the q0 for sawtoothing plasmas on KSTAR has been
~1.0 ± 0.03 and this value is consistent with the previous MSE measurements in DIII-D.
Since the change of the q0 (or core current density) is relatively small, the required absolute
accuracy of ~2% of the MSE system for a definitive proof of the model is too stringent. A
controlled supplementary experiment employing the higher order tearing modes that are
extremely sensitive to the background q0 in conjunction with the measured q0~1.0
successfully validated the full reconnection model [2]. Here, a resistive MHD code, M3D-C1
was employed to identify the growth rate of the excited modes and compared with the
experiment. The dynamics of the high m tearing modes in non-sawtoothing plasmas (hybrid
mode) are studied and the results are consistent with the conclusion from the sawtoothing
discharges. This work is supported by the NRF of Korea under Contract No
2014M1A7A1A03029865
[1] B.B. Kadomtsev, Sov. J. Plasma Phys. 1, 389 (1975).
[2] Y.B. Nam, et al., Validation of “full reconnection model” of the sawtooth oscillation, to
be published in Nuclear Fusion, 2018.
