Improved neutral and plasma density control with increasing lithium wall coatings in the Lithium Tokamak Experiment-β (LTX-β)

Abstract

A comparison of three sets of Lithium Tokamak Experiment-β (LTX-β) discharges is presented, each with progressively more lithium evaporatively deposited on the stainless steel plasma facing components (PFCs). Multiple observations independently indicate a reduction in recycling with increasing lithium deposition - plasma current, discharge duration, density pumpout, and edge electron temperatures increase while plasma density and neutral influx decrease. These measurements make use of several new operational and diagnostics upgrades that have been installed on LTX-β to enable recycling analysis and quantification. Installation of an upgraded Supersonic Gas Injector (SGI) provides access to rapid density pumpout, enabling estimation of effective particle confinement times. Edge density and temperature are measured using a new, movable, low field side, off-midplane, swept single langmuir probe in addition to the LTX-β core Thomson scattering system. The neutral particle influx from the high field side limiter is measured using a hydrogen Lyman-α array. Prospects for future modeling and analysis integrating all of these measurements is discussed.

Keywords

• Lithium wall
• Plasma material interactions
• Recycling