Particle exhaust studies in ASDEX Upgrade

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