Upward-facing lithium flash evaporator for NSTX-U

A. L. Roquemore, D. Andruczyk, R. Majeski, D. K. Mansfield, C. H. Skinner, D. Rodgers

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

NSTX plasma performance has been significantly enhanced by lithium conditioning [1]. To date, the lower divertor and passive plates have been conditioned by downward facing lithium evaporators (LITER) as appropriate for lower null plasmas. The higher power operation expected from NSTX-U requires double null plasma operation in order to distribute the heat flux between the upper and lower divertors making it desirable to coat the upper divertor region with Li as well. An upward aiming LITER (U-LITER) is presently under development and will be inserted into NSTX-U using a horizontal probe drive located in a 6 upper midplane port. In the retracted position the evaporator will be loaded with up to 300 mg of Li granules utilizing one of the calibrated NSTX Li powder droppers[2]. The evaporator will then be inserted into the vessel in a location within the shadow of the RF limiters and will remain in the vessel during the discharge. About 10 seconds before a discharge, it will be rapidly heated and the lithium completely evaporated onto the upper divertor, thus avoiding the complication of a shutter that prevents evaporation during the shot when the diagnostic shutters are open. The minimal time interval between the evaporation and the start of the discharge will avoid the passivation of the lithium by residual gases and enable the study of the conditioning effects of un-passivated Li surfaces [3]. Two methods are being investigated to accomplish the rapid (few second) heating of the lithium. A resistive method relies on passing a large current through a Li filled crucible. A second method requires using a 3 kW e-beam gun to heat the Li. In this paper the evaporator systems will be described and the pros and cons of each heating method will be discussed.

Original languageEnglish (US)
Title of host publication2013 IEEE 25th Symposium on Fusion Engineering, SOFE 2013
DOIs
StatePublished - 2013
Externally publishedYes
Event2013 IEEE 25th Symposium on Fusion Engineering, SOFE 2013 - San Francisco, CA, United States
Duration: Jun 10 2013Jun 14 2013

Publication series

Name2013 IEEE 25th Symposium on Fusion Engineering, SOFE 2013

Other

Other2013 IEEE 25th Symposium on Fusion Engineering, SOFE 2013
CountryUnited States
CitySan Francisco, CA
Period6/10/136/14/13

Keywords

  • Lithium evaporator
  • e-beam heating
  • spherical tokamak

ASJC Scopus subject areas

  • Software

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