Lithium As Plasma Facing Component for Magnetic Fusion Research

Abstract

The use of lithium in magnetic fusion confinement experiments started in the 1990's in order to improve tokamak plasma performance as a low-recycling plasma-facing component (PFC). Lithium is the lightest alkali metal and it is highly chemically reactive with relevant ion species in fusion plasmas including hydrogen, deuterium, tritium, carbon, and oxygen. Because of the reactive properties, lithium can provide strong pumping for those ions. It was indeed a spectacular success in TFTR where a very small amount (~ 0.02 gram) of lithium coating of the PFCs resulted in the fusion power output to improve by nearly a factor of two. The plasma confinement also improved by a factor of two. This success was attributed to the reduced recycling of cold gas surrounding the fusion plasma due to highly reactive lithium on the wall. The plasma confinement and performance improvements have since been confirmed in a large number of fusion devices with various magnetic configurations including CDX-U/LTX (US), CPD (Japan), HT-7 (China), EAST (China), FTU (Italy), NSTX (US), T-10, T-11M (Russia), TJ-II (Spain), and RFX (Italy). Additionally, lithium was shown to broaden the plasma pressure profile in NSTX, which is advantageous in achieving high performance H-mode operation for tokamak reactors. It is also noted that even with significant applications (up to 1,000 grams in NSTX) of lithium on PFCs, very little contamination (< 0.1%) of lithium fraction in main fusion plasma core was observed even during high confinement modes. The lithium therefore appears to be a highly desirable material to be used as a plasma PFC material from the magnetic fusion plasma performance and operational point of view. An exciting development in recent years is the growing realization of lithium as a potential solution to solve the exceptionally challenging need to handle the fusion reactor divertor heat flux, which could reach 60 MW/m 2. By placing the liquid lithium (LL) surface in the path of the main divertor heat flux (divertor strike point), the lithium is evaporated from the surface. The evaporated lithium is quickly ionized by the plasma and the ionized lithium ions can provide a strongly radiative layer of plasma ("radiative mantle"), thus could significantly reduce the heat flux to the divertor strike point surfaces, thus protecting the divertor surface. The protective effects of LL have been observed in many experiments and test stands. As a possible reactor divertor candidate, a closed LL divertor system is described. Finally, it is noted that the lithium applications as a PFC can be quite flexible and broad. The lithium application should be quite compatible with various divertor configurations, and it can be also applied to protecting the presently envisioned tungsten based solid PFC surfaces such as the ones for ITER. Lithium based PFCs therefore have the exciting prospect of providing a cost effective

Cross Sections for Electron Stripping, Electron Capture, and System Breakdown of C5+ and Li2+ Ions with Atomic Hydrogen

“…It has been found that the energy confinement duration of the discharge in [22,23] a keV temperature plasma edge was significantly enhanced by the pulses that were preceded by lithium pellet injections [22,24]. In addition, lithium has become increasingly recognized as a potential solution to combating divertor heat flux issues within fusion reactors, as ionized lithium atoms form highly radiative plasma layers which could significantly decrease heat flow into divertors surfaces [25][26][27][28][29][30]. As it happens, evaporated lithium in its ionic form (partially stripped ions) combined with hydrogen, carbon, and oxygen atoms increased the possibility for inelastic collisions between multiply charged ions and neutral atoms -stimulating inelastic collision research not only out of general scientific curiosity but also as essential tools in fusion-related research [5].…”

Social participation in English classes of students with Asperger syndrome at Picoaza public school

“…This approach is difficult for the person with Asperger's syndrome because of the bad social interpretations and a maturity that is not consistent with his age. Masayuki, (2012) The lack of preparation and experience in terms of social interactions leads to these children or adults to a situation of failure. Adequate support, before or during schooling, would therefore allow them to experience fewer difficulties.…”

Magnetic field modeling for non-axisymmetric tokamak discharges

“…Thermonuclear fusion stands out among other concepts due to the large energy/volume ratio of its fuels and to the natural abundance of the deuterium isotope (D or 2 H), which can be found naturally on sea-water and corresponds to one on every 6700 atoms of Hydrogen [Freidberg (2007)]. On the other hand, tritium (T or 3 H), is quite scarce in nature, but the neutron released by the D-T reaction can be used to produce more tritium, in situ, by means of its reaction with lithium (Li), also abundant in nature [Freidberg (2007); Mazayuki (2012)].…”