JT-60 DIVERTOR PUMPING SYSTEM AND ITS INITIAL OPERATION IN OHMICALLY HEATED DIVERTOR DISCHARGES

A pumping system was installed in the JT-60 machine to exhaust neutral particles from a divertor chamber. The objective of this system is an active particle control in neutral beam heated discharges. The pumps are composed of four Zr-Al getter pumps with a pumping speed of 5.3 m 3 /s in the diverter chamber. In addition, the particle flow from the divertor chamber to torus main pumps was enhanced by attaching augmentation plates inside the vacuum vessel. Baffle plates were also attached to reduce the conductance between the divertor and the main chambers. The pressure in the divertor chamber measured in ohmically heated divertor discharges increases approximately in proportion to the square of the line averaged electron density n e of the main plasma. A total gas exhaust rate of 2.4 Pam 3 /s is possible for n e = 1x10 20 m -3 , which is as large as the fueling rate by the neutral beam injection with a heating power of 20 MW.