Auxiliary Plant – Pellet Launching System
In order to provide fuel to the plasma a Pellet Launching System (PLS) will be installed. The system produces frozen pellets of deuterium or hydrogen at a diameter of 2.4 mm. The pellets are dropped into a centrifuge which accelerates them to a velocity of 600 m·s-1 at a rate of 50 Hz. The pellets then enter a guide tube which delivers the pellets to the inboard side of the tokamak where they enter the plasma.
The Pellet Source freezes the chosen fuel on demand, slices the pellets to length and delivers them to the centre of the centrifuge.
In order to minimise impact forces on the fragile pellets, the centrifuge accelerates the pellets in two stages. The first stage (inner arm) takes the pellets from a point at approximately 40 mm radius relatively slowly to a point at approximately 80 mm radius where they enter the outer arm. The outer arm has a radius of 560 mm, and the pellets leave the outer arm with a nominal velocity of 600 m·s-1 at the nominal operating frequency of 100 Hz.
Since the pellets enter the guide tube at a high velocity care must be taken to ensure they do not disintegrate on first contact with the wall. The speed perpendicular to the impact surface must be limited to less than 35 m·s-1, hence the angle of impact must always remain less than 3 o. In order to control this normal impact velocity, a funnel is provided at the exit of the centrifuge.