CDX-U operation with a large area liquid lithium limiter

The current drive experiment-upgrade (CDX-U) at the Princeton Plasma Physics Laboratory has begun experiments with a fully toroidal liquid lithium limiter. CDX-U is a compact (R ¼ 34 cm, a ¼ 22 cm, Btoroidal ¼ 2 kG, IP ¼ 100 kA, Teð0 Þ� 100 eV, neð0 Þ� 5 � 10 19 m � 3 ) short-pulse (<25 ms) spherical torus with extensive diagnostics. The limiter, which consists of a shallow circular stainless steel tray of radius 34 cm and width 10 cm, can be filled with lithium to a depth of a few millimeters, and forms the lower limiting surface for the discharge. Heating elements beneath the tray are used to liquefy the lithium prior to the experiment. Surface coatings are evident on part of the lithium. Despite the surface coatings, tokamak discharges operated in contact with the lithium-filled tray show evidence of reduced impurities and recycling. The reduction in recycling is largest when the lithium is liquefied. 2003 Elsevier Science B.V. All rights reserved.