Development of the pellet injection system on the J-TEXT tokamak

Abstract

Pellet injection is an attractive technology for core-fueling and MHD study on magnetic-confined fusion device like tokamak and stellarator. It can inject solid Hydrogen/Deuterium pellets into the plasma with deeper density deposition compared with other fueling methods, such as gas puffing. A set of three-barrel H2 pellet injection system has been installed on J-TEXT tokamak and some experiments have been carried out. The pellets are formed in three barrels cooled by a cryocooler and compressor system at around 9 K, and have 0.8 mm/1 mm diameter and 0.8 mm length. The pellet is launched by high-pressure helium propellant gas and injected from low field side of plasma. The range of pellet speed is 25-310 m/s for different propellant gas pressure. With the three-barrel structure, the number of pellets injected can be adjusted with 1-3, when launch over 2 pellets, pellets can be launched simultaneously or sequentially with arbitrary time interval, which enables flexible applications. From the experiment results, pellet fueling efficiency can reach 50%. The energy confinement time has increased by about 7.5-10 ms after pellet injection.