The transport of impurities is very important for burning plasma; in particular, the accumulation of highly charged impurities will lead to the deterioration of plasma performance and trigger disruption by radiation losses. In order to study impurity transport in Joint Texas EXperimental Tokamak electron cyclotron resonance heating (ECRH) plasmas, argon has been injected at the discharge flattop in an amount approximately 1% that of fuelling hydrogen gas to ensure no significant effect on the discharge. Experimental results show that precursor oscillations with a sawtooth appearance are beneficial for argon ion transport to the wall. The argon behaviour has been modulated by ECRH, with the power deposited inside/outside the sawtooth inverse radius. The ECRH power deposited outside the sawtooth inverse radius can induce larger precursor oscillations in the end of sawtooth and promote the argon transport. The ECRH power deposited inside the sawtooth inverse radius can induce oscillations in the mid-phase of the sawtooth and decrease the core toroidal rotation velocity, which can enhance argon transport. The results of the analysis that these oscillations can lead to an outward convection velocity, which means that the argon ions are transported to the wall. In addition, the oscillations in the mid-phase of the sawtooth can strongly enhance the argon transport.
Effects of localized electron heating and current drive on the sawtooth period