FTU results with a liquid lithium limiter

Abstract

Since the end of 2005 most of the plasma-wall interaction experiments on FTU have been focused on the possible use of liquid lithium as the plasma facing material. Liquid lithium limiter is an active method to deposit, during the plasma discharge, a lithium film on the walls with prolonged beneficial effects. Reliable operation with very clean plasmas, very low wall particle recycling, spontaneous peaking of the density profile for line-averaged density values n e > 1.0 × 10 20 m −3 have been obtained. These results have allowed us to extend the density limit to the highest value so far obtained (n e = 4.0 × 10 20 m −3 at I p = 0.7 MA and B T = 7.1 T, q a = 5.0, by gas puffing only) and to increase the energy confinement time by almost 50% with respect to the average value of 50 ms of the old ohmic FTU database. An accurate analysis of these plasmas has been carried out by means of a gyrokinetic code to establish the role of collisionality and density gradients on the observed phenomenology.

Development of and experiments with liquid lithium limiters on HT-7

“…These results were similar to those observed after the application of Li coating on EAST [22]. It should also be noted that, in the FTU experiments the walls were fully coated with Li after 2-3 discharges with LLL in place, and most of the improved performance (lower recycling, lower loop voltage, lower radiated power lower Z eff , lower H/ (H + D) ratio, but increased wall retention) are attributed to the fully 'Lithized' walls [23]. However, the HT-7 experiments started with walls that had been coated with Li, and we attributed further improvements after filling the LLL to direct interactions with the LLL, and not with additional or improved Li wall conditioning.…”

Liquid lithium divertor characteristics and plasma–material interactions in NSTX high-performance plasmas

“…There have, to date, been few examples of liquid metal PFCs in fusion plasma experiments (CDX-U [2], FTU [3], T11-M [4], ISTTOK [5]) and none in a diverted configuration (though KTM [6] is beginning such development). Liquid metal PFCs include a set of technical challenges that require development before implementation into large machines.…”

TECXY Study of a Liquid Lithium Divertor for DEMO

“…To prevent that, a metal 'sponge' (capillary porous system, CPS) through which liquid metal flows, was introduced in several machines e.g. tokamak FTU [13] and stellarator TJ-II [14]. Those experiments yielded promising results.…”