PARTICLE EXHAUST STUDIES IN ASDEX UPGRADE

An experimental overview on pumping and particle exhaust studies for d euterium as well as for helium and neon in the ASDEX Upgrade divertor tokamak is presented. Strong turbomolecular pumps connected to the div ertor region allow effective pumping of ail these Abstract. Deuterium, however, is pumped effectively by the carbon walls in ASDEX Upgrade w hich dominate over the external pumping. Noble gases are hardly pumped by the walls,and their pumping efficiency and exhaust rate depends st rongly on their respective density in the divertor chamber, i.e. on th e effectivity of scrape-off layer transport and divertor retention. Co mpression of helium and neon in the divertor chamber increases with th e divertor neutral gas density, and in high-power, high-density discha rges in H-or CDH-mo;de pumping is very efficient. Helium exhaust in th ese scenarios is sufficiently fast to fulfill the requirements for ITE R or a fusion reactor.