Operation of TFTR neutral beams and heavy ions

Moderate atomic number neutral atoms have been injected into TFTR (Tokamak Fusion Test Reactor) plasma in an attempt to enhance plasma confinement through modification of the edge electric field. TFTR ion sources have extracted 9 A of 62-keV Ne⁺ for up to 0.2 s during injection into deuterium plasmas, and for 0.5 s during conditioning pulses. Approximately 400 kW of Ne⁰ have been injected from each of two ion sources. Operation under these conditions was at full bending magnet current, with the Ne⁺ just contained on the ion dump. Modifications to permit operation up to 120 keV with krypton and/or xenon are described. Such ions are too massive to be deflected up to the ion dump with the beamlines as designed. The plan is to procure a 3600-A power supply and pulse it into the magnet for initial Kr/Xe experiments. Information relevant to heavy ion operation was acquired during the course of ion source operation with small water leaks. Spectroscopic analysis of certain pathological pulses indicates that up to 6% of the extracted ions were water. After dissociation in the neutralizer, water produces oxygen ions which, as with Ne⁺, Kr⁺, and Xe⁺, are underdeflected by the magnet. Damage to a calorimeter scraper, due to the focal properties of the magnet, resulted. A power density of 6 kW/cm ² for 2 s, from ~90 kW of O⁺, is the probable cause