Edge properties with the liquid lithium limiter in FTU—experiment and transport modelling

Abstract

Liquid lithium as a plasma-facing material was tested for the first time on a high field medium size tokamak, FTU. A liquid Li reservoir supplies a mesh of capillaries that is movable from shot to shot in the scrape-off layer (SOL) plasma to act as a secondary limiter. An almost complete lithization of the vacuum vessel walls is obtained in about three discharges. Plasmas cleaner than boronization and titanization, with lower radiation losses and smaller impurity content are produced. The SOL electron temperature increases, T e ∼ 10 eV, while density (n e ) is less affected. The 2D multifluid code TECXY explains this only if a strong reduction of plasma recycling on the walls and main limiter occurs, consistent with the high Li hydrogen pumping capability. This property also permits a much tighter control of the plasma density. With the Li limiter inserted inside the vessel poloidal asymmetries develop in the SOL that TECXY explains with a local increase of radiation, caused by enhanced evaporation/sputtering of Li. New regimes can be produced in such conditions with a clear increase in |∇n e /n e | and of the peaking factor n e0 / < n e 2 at the Greenwald density limit ( ne ∼ 2 × 10 20 m −3 ), without any direct central particle fuelling.

Liquid Metal Walls, Lithium, And Low Recycling Boundary Conditions In Tokamaks

“…A system based on the T11-M development, but larger and more extensive, has been more recently employed in the FTU tokamak, starting in 2006. 14,29 A photograph of the FTU liquid lithium limiter system, prior to installation, is shown in Figure 7. In FTU, the lithium limiter system has mainly been used as a lithium source for wall coatings, rather than as the primary plasma limiting surface.…”

Molecular dynamics study on diffusion behavior of Li in α-Fe

“…For instance, plus its tritium-breeding effect, it has long been considered as an attractive material for tritium breeder and cooling media for the blanket. Besides, recent experimental researches show that flowing liquid lithium using as plasma facing material can effectively reduce hydrogen recycling, suppress impurities and remove high heat flux [1][2][3][4], which makes liquid lithium first wall a popular concept for tokamak.…”

Particle Control and Plasma Performance in the Lithium Tokamak Experiment (LTX)

“…3 Of these candidates, virtually no experimental tests of gallium or tin have been conducted in confinement devices, whereas lithium wall coatings and wall conditioning have been tested in a number of devices, and observed to strongly affect tokamak performance, since the experiments on the Tokamak Fusion Test Reactor (TFTR). 4 Several, more recent, experiments 5,6,7,8 have employed localized limiters of liquid lithium, but the liquid lithium surface area in these systems has never exceeded a few percent of the total plasma surface. Evaporation from a liquid lithium limiter at a temperature of 350 -400 °C will coat lineof-sight PFCs with lithium, but the coating will remain solid if the PFCs are not heated to the melting point of lithium (182 °C).…”