The operation region and MHD modes on the J-TEXT tokamak. (11th October 2016)

• Record Type: Journal Article
• Authors: Huang, Mingxiang; Hu, Qiming; Shi, Peng; Zhang, Xiaolong; Zhu, Lizhi; Chen, Zhipeng; Zhuang, Ge
• Is Part Of: Plasma physics and controlled fusion. Volume 58:Number 12(2016:Dec.)
• Publication Date: 2016-10-11
• Subjects: operation region -- density limit -- low-q limit -- magnetohydrodynamic (MHD) modes -- resonant magnetic perturbations (RMPs); Plasma (Ionized gases) -- Periodicals; Controlled fusion -- Periodicals; 530.44
• DOI: 10.1088/0741-3335/58/12/125002
• Languages: English
• ISSNs: 0741-3335

Abstract

Abstract: The operation region and the parameter region of magnetohydrodynamic (MHD) modes are analyzed for J-TEXT Ohmic discharges. The operation region is described by the Hugill diagram, which combines low- q and high density limits. It is found that the operation region has expanded over the years on J-TEXT. In detail, the high density limit has increased from less than 0.5 n G to 0.7 n G and the low- q limit has lowered from 2.8 to 2.2; this is due to the reduced impurity content that results from coating graphite on the wall. Furthermore, the operation region has further expanded to 0.85 n G and q a ~ 2.0, respectively—a result of suppressing the disruptive precursor MHD by using externally-applied resonant magnetic perturbations (RMPs). Here, n G and q a are the Greenwald density limit and edge safety factor, respectively. Corresponding to the results of the operation region, the parameter regions of MHD modes are presented. It is found that a m / n = 2/1 tearing mode (TM) appears for a wide parameters region with 2.4 < q a < 4 and n e < 3 × 10 19 m −3 —here m and n are the poloidal and toroidal mode numbers. Furthermore, other MHD modes such as m / n = 5/2, 3/1, 4/1 and 7/2, appear only when their rational surfaces are close to the plasma edge or m / n ~ q a, and these MHD modes may transit to a 2/1 TM when changing the plasma parameters. In addition, correlation analysis between the amplitude and frequency of the dominant 2/1 TM for different plasma conditions reveals that there is a threshold between normal discharges and density-limit discharges, which would be a reference to predict density-limit disruptions.