"Enhanced understanding of the MHD dynamics and ELM control experiments in KSTAR," by Hyeon K. Park (UNIST, Ulsan, Korea)

Date: 
Thursday, November 7, 2013 - 1:00pm to 2:15pm
Series: 
Plasma Seminars

Plasma Seminar

Thursday, November 7, 2013
1-2PM
Physics & Astronomy Building (PAB) Room 4-330
Refreshments at 12:30

Guest Speaker: Hyeon K. Park (UNIST, Ulsan, Korea)

Talk Title: "Enhanced understanding of the MHD dynamics and ELM control experiments in KSTAR"

Abstract:

In KSTAR, H-mode discharges have been achieved reliably at toroidal fields from 1.4 to 3.5 T with a heating power of ~5 MW including 3.5 MW neutral beam injection. Using real-time plasma shape control [1], the flattop time in H-mode has been extended to over ~16 s at 600 kA in the 2012 campaign, and will be extended to 1 MA operation in 2013 campaign. The extended plasma operation boundary has surpassed the n=1 no-wall limit withbN/li up to 4.1. In order to achieve a high beta steady state operation, which is the prime mission of KSTAR, establishment of predictive MHD simulation and first-principle-based control of the harmful MHD are the first steps. Visualization of MHD dynamics via a 2-D Electron Cyclotron Emission Imaging (ECEI) [2] has significantly enhanced the level of understanding of the MHD dynamics in both linear and nonlinear regimes.Following the first successful 2-D ELM measurements in H-mode plasmas [3] in KSTAR, the measured 2-D ELM images were compared with synthetic images [4] based on the calculated mode structure from the BOUT++code. The physics of ELMs is characterized based on a wide range of measured mode numbers (nm), local magnetic shear, and pressure gradients. The observed ELM dynamics during controlled experiments have been enlightening and consistent with the stability models, including the Peeling/Ballooning mode model. Near the q~2surfaces, important physical parameters of the m=2 tearing mode such as the island width and D' have beenverified through the modified Rutherford model based on the 2-D images. With the aid of a second (toroidally separated) ECEI system installed in the 2012 KSTAR campaign, a 3-D reconstruction of the MHD instabilities has allowed further validation of the computed magnetic field pitch angles, rotation speeds, and toroidalasymmetries of the MHDs. Work supported by NRF of Korea under contract No. 20120005920 and the U.S. DoE under contract No. DE-FG-02-99ER54531

[1] Kwak, J.G. . 2012 24th IAEA Conference, San Diego, CA

[2] Park, H. 2004 Rev. Sci. Instrum. Vol. 74, 3787

[3] Yun, G.S. 2011 Phys. Rev. Lett. 107, 035001

[4] Park, H. 2012 24th IAEA Conference, San Diego, CA