Neutral pressures in JT-60 divertor discharges

Neutral Pressures in the divertor chamber (Pdiv) and around the main plasma (P main ) are measured by ionization gauges which have a delay time constant of 200 to 300 ms. The H-mode shots were observed mainly in the range of n e = 2 to 4 × 10 19 m 3 and P main = 0.8 to 3.5 × 10 −3 Pa in the outside X-point divertor discharges with graphite walls. After the H-mode transition, significant reduction in P div is observed. The compression ratio is around 20 although in the L-mode shots with TiC/Mo walls this value was around 45. Since p div is 1.5 to 13 × 10 −2 Pa during the H-mode phase, the total exhaust rate by divertor pumping system Q ex is 0.1 to 0.8 Pa m 3 /s. This value is 1 30 − 1 4 of the particle fueling rate (~ 3 Pa m 3 /s) by NB injection of 20 MW and 75 keV. Therefore, in the H-mode discharge, improvement of particle exhaust is one of the critical issues.