Physical Sputtering of Liquid Metal Surfaces

Lithium is the other primary liquid metal being considered as a plasmafacing material. Lithium has the intriguing property that its melting temperature is 181°C, which means that it can be studied in either its solid or liquid state. Measurements of the physical sputtering yield of lithium across the phase transition (Fig. 14.7 [22]) have verified that no modifications to sputtering theory are needed to predict sputtering from liquid surfaces. One 

One serious constraint involved with the use of lithium as a plasma-facing material is its relatively high vapor pressure [21]. This restricted maximum permissible operating temperature coupled to its transition to a solid state below 181°C, means that lithium has a narrow temperature window in operational space. As will be discussed in the next section, enhanced erosion at elevated temperature will further restrict the size of this window. 

In summary, the sputtering properties of liquid surfaces are fairly well understood and do not preclude their use as plasma facing materials. There are, however, other mechanisms that can remove material from a liquid surface 

O He ion beam bombardment of solid Li He ion beam bombardment of liquid Li 

One innovative technique that has been developed to limit the mobility of a liquid plasma-facing surface is the capillary pore system [27]. This system has been successfully deployed in a tokamak environment [28]. Although this system addresses many of the mobility and erosion issues of a liquid plasmafacing surface, as will be discussed later in this chapter in order to achieve the full benefits from a low-recycling boundary a larger scaled-up version of this system will need to be developed. 

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