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The Lithium Tokamak – Results from CDX-U and the Design of LTX
| Author: | Majeski R. |
| Coauthor: | T. Gray, D. Hoffman, S. Jardin, R. Kaita, H. Kugel, P. Marfuta, G. Schmidt, J. Spaleta, J. Timberlak |
| Institution : | Princeton Plasma Physics Laboratory |
| Abstract text: | A fully nonrecycling first wall is predicted to fundamentally alter the nature of a tokamak plasma. Recent experiments in the Current Drive eXperiment – Upgrade (CDX-U) provide a first-ever test of large area liquid lithium surfaces as a tokamak PFC, to investigate whether very low recycling plasma regimes can be accessed with lithium walls. The CDX-U is a compact (R=34 cm, a=22 cm, B(toroidal) = 2 kG, IP =100 kA, Te(0)~100 eV, ne(0)~ 5 x 10^19 m^-3) spherical tokamak at the Princeton Plasma Physics Laboratory. A toroidal liquid lithium tray limiter of area 2000 cm^2 (half the total plasma limiting surface) is installed in CDX-U. Tokamak discharges with the liquid lithium limiter required a fourfold lower loop voltage to sustain the plasma current, and a factor of eight increase in gas fueling to achieve a comparable density, indicating that recycling is strongly reduced. Modeling of the evolution of the lithium-limited discharges is consistent with a low Z(effective) <1.2 (compared to 2.4 for the pre-lithium discharges), a broadened current channel, and a 25% increase in core Te. Spectroscopic measurements show that edge oxygen and carbon radiation are strongly reduced. These results support a new program to construct a tokamak with a fully nonrecycling wall. Next year, CDX-U will be upgraded to the Lithium Tokamak eXperiment (LTX), which will test transport and profile modification with fully nonrecycling walls. The theoretically-predicted development of an electron temperature profile with Te(a)/ >= 1 will be demonstrated for the first time in LTX. LTX will be a critical step in the development of the lithium wall tokamak, which may provide the shortest, lowest cost, and most environmentally attractive path to the implementation of fusion energy. Results of the CDX-U experiments will be presented, as well as modeling of the expected performance of LTX. |
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