The plasma fueling system is an indispensable component in current fusion devices and is required to compensate for continuous particle loss. Recently, a low-temperature supersonic molecular beam injection (LT-SMBI) system has been developed and implemented successfully to increase the fueling efficiency on the Experimental Advanced Superconducting Tokamak (EAST). The fueling gas in the reservoir tank is cryogenically cooled to a temperature lower than 120 K before injection to increase the size of the clusters and their formation probability in the beam. A series of LT-SMBI experiments were conducted on EAST, and the fueling characteristics, including the fueling efficiency, delay time, injection depth, and fuel consumption, were compared with those of room-temperature SMBI (RT-SMBI). The experimental results demonstrate that LT-SMBI results in greater plasma density enhancement with an equivalent number of injected particles. The fueling efficiency of both SMBI systems decreases with increasing plasma density. Compared with the RT-SMBI, the LT-SMBI results in about 5–7 cm deeper injection depth, as measured via microwave reflectometry. Furthermore, the fueling gas consumption is decreased by 33% in the feedback control experiments using the LT-SMBI. Although LT-SMBI has a longer delay time because of its low temperature, it is recognized as an efficient method for plasma fueling and other impurity injections, such as edge localized mode mitigation and divertor heat flux reduction, for EAST and future fusion devices.
Stimulated effect of SMBI on low-to-high confinement transition of tokamak plasmas