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Liquid metal PFC development and the Lithium Tokamak eXperiment (LTX) *

Author: Richard Majeski
Requested Type: Consider for Invited
Submitted: 2009-12-04 10:26:12

Co-authors: L. Berzak, D. Boyle, S. Gershman, E. Granstedt, C. M. Jacobson, A.D. Jones, R. Kaita, T. Kozub, B. LeBlanc, N. Logan, M. Lucia, D. P. Lundberg, K. Snieckus, T. Strickler, J. Timberlake, L. Zakharov, PPPL, G. V. Pereverzev, IPP-Garching, V. Soukhanovskii,

Contact Info:
Princeton Plasma Physics Lab
PO Box 451
Princeton, NJ   08543
USA

Abstract Text:
LTX is progressing through the shakedown phase, with first operation with a liquid lithium film wall expected early in 2010. LTX is a modest spherical tokamak with R=0.4 m, a=0.26 m, and an elongation of 1.5. Design targets are a toroidal field of 3.4 kG, plasma current < 400 kA, and a current flattop ~ 100 msec, although during initial operation the device will be limited to a toroidal field of 2.1 kG, plasma current < 150 kA, and a flattop of ~ 25 msec. The primary LTX research objective is to investigate modifications to equilibria and transport when global recycling is reduced to very low values (<50%). In addition, LTX will be the first plasma device ever operated with a full liquid metal wall. The development of liquid metal walls is essential to any approach to a more compact fusion reactor, since there is no solid wall solution which shows promise for withstanding high power density and plasma fluence, even in the absence of neutrons. Although lithium is the liquid metal deployed in LTX, the techniques employed for retention and control of the liquid on the wall, control of the interaction of the plasma with the liquid metal, etc. are applicable to other liquid metals, including the high recycling choices, such as gallium or tin. We will briefly discuss general issues for, and approaches to, liquid metal walls. In particular, in LTX, the plasma facing surface is composed of a conformal 3/8” thick heated copper wall, constructed in four electrically and thermally isolated sections, and clad on the plasma side with 1/16” 304 stainless steel. The stainless steel plasma-facing surface will be coated with liquid lithium by an evaporative system. The lithium evaporation system is simple, and suited to usage in other experiments. The shell system is designed to operate at very high temperatures, up to 550 °C, with uniform surface temperature due to the high thermal conductivity of the underlying copper. Although the heated shell has two poloidal and two toroidal breaks or gaps, the high electrical conductivity of the copper shell segments, combined with the low aspect ratio (A=1.6) geometry introduce significant eddy current shielding during startup. Pulsed fueling with supersonic gas jets, and a newly tested H2 cluster injector, will be employed to transiently eliminate edge gas. Diagnostics include single-pulse multipoint Thomson scattering at up to 16 radial locations, multiple Lyman alpha arrays for recycling determinations, a fixed 1mm and a movable 2 mm microwave interferometer, a VUV survey spectrometer, visible spectrometers, and an edge Langmuir probe. In 2010 a new diagnostic (Digital Holography) for core density fluctuations will be tested on LTX. Machine status and initial operation during the shakedown period will be discussed.

*Supported by US DOE contracts DE-AC02-09CH11466.

Characterization: A4

Comments:
Please group (1)R. Majeski, (2)L. Berzak, (3)D. Lundberg together, all in A4.