A compact W-shaped pumped divertor concept for JT-60U

In JT-60U, the open divertor was modified to the pumped W-shaped divertor in February to May, 1997. The new divertor consists of inclined divertor plates and a dome in the private flux region. The performance of this divertor was assessed by numerical simulations. A sufficient reduction in the backflow of neutral particles is found by the baffling effect of the inclined divertor plates. The dome is expected to increase the pumping efficiency from the private region; this is to be used for controlling the pumping speed and to reduce the influx of methane gas to the X point region. However, the particle flux ionized around the X point region will increase, because of the shallow divertor. (author)