In the J-TEXT tokamak, the penetration of resonant magnetic perturbations (RMPs) has been studied by using a set of in-vessel RMP coils. It is found that, once the RMP amplitude exceeds a critical value, the applied RMP can lead to field penetration and excitation of a large locked mode in the tearing-stable plasma. The sawtooth oscillations disappear and the confinement deteriorates significantly accompanied by tearing mode excitation. For the plasma with an initial high frequency tearing mode, the RMP can suppress the tearing mode, and field penetration followed with a further increased RMP. The relationship between the RMP penetration threshold and the electron density has been investigated for tearing-stable plasmas. It is found that the penetration threshold increases with the density and scales proportionally to in the ranges of (0.7–2.7) × 1019 m−3. Using the experimental parameters as input, the numerical modelling based on two-fluid equations gives the scaling of , which approximately agrees with the experimental density scaling.

View the article online for updates and enhancements.

No abstract

Aqueous reactive species induced by gas plasmas play a dominant role in many plasma applications such as water purification and biomedicine, but their production mechanism is so far not well understood. In this paper, an experimental setup is designed to study the interaction between an AC helium plasma jet and PBS, which allows a decoupling analysis of the plasmaliquid processes on the production of aqueous reactive species. The processes include the dissolution of neutral reactive species, the electron absorption by dissolved oxygen, the deposition of positive ions, etc. Four aqueous reactive species including H 2 O 2 , O , 2 -OH and peroxynitrite (ONOOH/ONOO − ) are detected, among which the peroxynitrite should originate from the air impurity in helium. It is found that the aqueous H 2 O 2 and peroxynitrite are mainly dissolved from the gas phase, the aqueous O 2is mainly generated by the electron absorption by dissolved oxygen, and the aqueous OH is mainly generated by the deposition of positive ions.

Pulse direct current (dc) voltage with different pulse rising time trise have been used to generate atmospheric pressure non‐equilibrium plasmas. However, no quantitative investigation has been reported on how the trise will affect the plasma characteristics. In this paper, the effect of pulse rising time variable from 4 µs to 100 ns on plasma characteristics is investigated. The experimental results show that, when the trise is reduced from 4 µs to 140 ns, the length of the plasma plume increases from less than 20 mm to about 70 mm, the peak value of the discharge current increases from about 0.2 A to 1.3 A. The corresponding breakdown voltage increase from less than 4 kV to about 6 kV and the electron temperature increase from 1.25 eV to 1.55 eV. These results confirm that the shorter the pulse rising time is, the more reactive the plasma is. magnified image