Measurements of impurity mixing efficiency during massive gas injection in J-TEXT

Abstract

Experiments of disruption mitigation with massive gas injection have been conducted in J-TEXT tokamak with various impurities (He, Ne, Ar and He&Ar (90%:10%) mixtures) injection. A 17channels polarimeter-interferometer (POLARIS) has been used to analyze the evolution of the electron density profile during pre-TQ and TQ phases. Experiments show that both the impurity species and applied high voltage of the valve have an obvious influence on the impurities deposition location and electron density profile. Moreover, with the high spatial resolution of POLARIS, a rather accurate impurity mixing efficiency has been obtained. The results show that Ar, the high atomic number (high-Z) impurity, has high cooling efficiency and evident mitigation effects, but the mixing efficiency for Ar is only of order 5%-8%. As for the low-Z impurity, He has fast propagation velocity and can reach high mixing efficiency, which is found to be of order 20%-40%. The use of the mixtures of high-Z and low-Z impurities (He&Ar (90%:10%)) can combine the fast penetration of He and high cooling efficiency of Ar, and the mixing efficiency is up to the order 20%-40%, improving the disruption mitigation efficiency and time response of disruption mitigation system.

Magnetic island formation and rotation braking induced by low-Z impurity penetration in an EAST plasma

“…This simulation results agree the experimental observation that the modes can be locked following the redistribution of the low-Z impurity concentration [14], despite the fact that there is no error or external magnetic field at the perfectly conducting wall boundary in simulations. Similarly, Joint TEXT tokamak (J-TEXT) experiments demonstrate strong correlation between the 2/1 TM rotation and impurity distribution as well [30,31].…”

Comparison of different noble gas injections by massive gas injection on plasma disruption mitigation on Experimental Advanced Superconducting Tokamak

“…The observed durations of pre-TQ, TQ, and CQ in MGI plasma shutdown experiments measured on the EAST device were longer than that measured on the J-TEXT device. [22] However, they showed similar trends. The difference in timescales was possible mainly because of the EAST device's larger vessel structure size and some larger basic discharge parameters, including plasma current and heating powder.…”

“…However, slight impurity gas moves more quickly to the plasma, which results in a short pre-TQ duration and requires less time to accumulate impurities before TQ. [22] -0. The effect of different impurity gas species, including Ar, Ne, and He, on the CQ, can be estimated by the plasma current decay time analysis.…”

Magnetic island formation and rotation braking induced by low-Z impurity penetration in an EAST plasma

“…This simulation results agree the experimental observation that the modes can be locked following the redistribution of the low-Z impurity concentration [11], despite the fact that there is no error or external magnetic field at the perfectly conducting wall boundary in simulations. Similarly, J-TEXT experiments demonstrate strong correlation between the 2/1 tearing mode rotation and impurity distribution as well [26,27].…”