Negative-potential operation of TMX-Upgrade

A tandem-mirror configuration can be created by combining hot electron end-cell plasmas with neutral-beam pumping. A region of large negative potential formed in each end cell confines electrons in the central cell. The requirement of charge neutrality causes the central-cell potential to become negative with respect to ground in order to equate ion loss to electron loss. Start-up and formation of the axial potential distribution, neutral-beam pumping, hot electron feed, electron-cyclotron-resonance heating (ECRH) power requirements, and stability are discussed in general terms. Each of these considerations impose constraints on the operation of TMX as a negative machine. The start-up requirements and scenario are also presented. Work on the design and analysis of negative tandems is continuing. The status of work to date is presented here with problem areas for future work identified