Overview of recent results from LTX-β

LTX-β has resumed operations after a vent for modifications and modest upgrades. Modifications made during the vent include new porting for the neutral beam to increase the tangency radius by 50%, to significantly reduce the first orbit fast ion loss fraction, and increase beam coupling at higher power and injection energy. A new neutral particle analyzer diagnoses fast ion losses. Improvements have been made to the Thomson scattering system to increase signal to noise, especially for the separate APD-based high field side view. An additional Thomson scattering view of the scrape-off layer plasma has been installed. A new high-field side limiter is imaged by a two-color IR camera to diagnose the scrape-off layer (SOL) power deposition width. In a collaboration with Penn State University, a new remotely actuated liquid-filled lithium deposition system, which can be operated between shots, has been developed. LTX-β is fueled by a combination of high and low field side gas puffing, and a supersonic gas injector, as well as the neutral beam. An additional high field side gas nozzle surrounded by a small gas box has been installed. A new diagnostic, Doppler Free Saturation Spectroscopy (DFSS), is being tested to diagnose the electric field which is expected to develop in the low collisionality SOL. Operation has begun with bare stainless steel high-Z walls to provide a high recycling performance baseline. This phase will be followed by an emphasis on operation with low recycling liquid lithium walls. Results from the reconfigured device will be discussed. The effect of a lithium impurity on neutral beam fueling and heating will be discussed, with emphasis on the very low collisionality SOL expected to result.

This work supported by US DOE contracts DE-AC02-09CH11466, DE-AC05-00OR22725 and DE-AC52-07NA27344.