Continuous Pellet Injector Begins to Operate in JT-60U
In order to achieve a high confinement near or above Greenwald density limit where ITER will be operated, the pellet injector of JT-60U has been modified to inject multipellets during a discharge (solid deuterium ices of 2 mm cube, 5 Hz x 7 s).
The pellet injection can fuel with higher efficiency than gas puffing. The individual pellet is accelerated to 300 ~ 1000 m/s and injected into the plasma either from outside or from top inside as shown in Fig. 1. The ablation cloud of a pellet injected into a plasma was clearly observed (Fig. 2) and significant increases in plasma density were confirmed as shown in Fig. 3.
Researches on improved confinement modes at an ITER relevant high-density regime are planned in JT-60U with maximum utilization of the continuous pellet injector.
The modification of the pellet injector has been carried out in collaboration with the IPP Garching (Max Planck institute).
Fig. 1 Schematic of fueling by pellet injection.
Fig. 2 A visible-TV image of an ablating pellet in a plasma (upper pellet injection).
Fig. 3 Increases in electron density by horizontal pellet injection.