On April 8, 2018, the paper “Effect of electrode biasing on m/n=2/1 tearing modes in J-TEXT experiments”, written by Hai Liu, et. al. from the Institute of Fusion and Plasma Research (IFPR), was selected as a Highlight article by the Nuclear Fusion, an international journal in plasma field.
In the paper, authors noticed that macro-magnetohydrodynamic instabilities, such as tearing mode (TM) or neoclassical tearing mode (NTM), would reduce the confinement of tokamak plasmas and even cause ending of discharges. In experiments, a biased graphite electrode was inserted into the plasma (several centimeters inside the last closed flux surface). It was found that the TM was stabilized by the negative bias voltage, while destabilized by the positive bias voltage, as shown in figure 1. Based on the voltage-scanning experiments, it was found that the variations of toroidal rotation, frequency of 1/2 TM and amplitude of perturbation magnetic field is proportional to the values of bias voltage. When the bias voltage reached to a certain threshold, the TM could be suppressed entirely (negative bias threshold) or locked (positive bias threshold). And it was also found that the thresholds were related to the edge safety factor, as shown in figure 2. It was considered that the electrode biasing (EB) could generate a radial current between the flux surface of the EB location and the last closed flux surface (ground) and then yield toroidal and poloidal electromagnetic force moment to drive plasma rotation. Furtherly, the frequency and amplitude of TM could be impacted by this process. This study was expected to provide a possible method for the avoidance of mode locking and subsequent disruption.
Fig.1 electrode biasing effect on tearing modes
Fig.2 Scaning of the EB voltage
This paper was selected as a Featured article and LabTalk.
In 2017, 16 papers are selected as Highlight articles by Nuclear Fusion. There are only from China were selected. This paper is the second Highlight article of Nuclear Fusion for IFPR. Since 2015, 6 papers from IFPR have been selected as Highlight Article, Cover article or LabTalk of the top journals in fusion field, such as Plasma Physics and Controlled Fusion, Nuclear Fusion. It shows the influence of IFPR and J-TEXT device in international fusion field and confirms the research findings of IFPR.
Paper link: http://iopscience.iop.org/article/10.1088/0029-5515/57/1/016003
LabTalk link: http://iopscience.iop.org/journal/0029-5515/labtalk/article/66595
Highlight link: http://iopscience.iop.org/journal/0029-5515/page/Highlights-of-2017