LNF: LIMPLASH, Liquid Metal Plasma Shields as new generation power exhaust solutions for magnetic fusion devices (2025-2028): Difference between revisions
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*Recent analyses have also investigated the physics of these local Sn plasmas in terms of sheath potential and Sn–Sn⁺ collisionality. Experimental values of the sheath potential were compared to theoretical calculation of the considering collisionless Bohm sheath (cold ion approximation), generalized to a plasma with Sn+, Sn2+ and H+ populations and cold ion approximation. The results shown no significant deviations between theory and measurements in the studied range restricted to Ttarget≤1300 K, Sn+ density≤5∙1018 m-3 and Sn plasma fraction ≤90 % (this latter condition corresponds to a proton one xH+>10%). This experimental range was limited due to problems related to the overlapping of the electron saturation current branch with the Langmuir probe diagnostic limits (circuit, biasing power source and amplifier) System upgrade and future experiments to study denser, almost pure Sn plasmas in further vapor shielding regimes deployed at Ttarget>1700 K are ongoing. | *Recent analyses have also investigated the physics of these local Sn plasmas in terms of sheath potential and Sn–Sn⁺ collisionality. Experimental values of the sheath potential were compared to theoretical calculation of the considering collisionless Bohm sheath (cold ion approximation), generalized to a plasma with Sn+, Sn2+ and H+ populations and cold ion approximation. The results shown no significant deviations between theory and measurements in the studied range restricted to Ttarget≤1300 K, Sn+ density≤5∙1018 m-3 and Sn plasma fraction ≤90 % (this latter condition corresponds to a proton one xH+>10%). This experimental range was limited due to problems related to the overlapping of the electron saturation current branch with the Langmuir probe diagnostic limits (circuit, biasing power source and amplifier) System upgrade and future experiments to study denser, almost pure Sn plasmas in further vapor shielding regimes deployed at Ttarget>1700 K are ongoing. | ||
*On the other hand, Sn–Sn⁺ collisions have been identified as plausible mechanism contributing to the partial detachment of the incoming heat flux from the target surface. Sn-Sn+ rate coefficients, cross sections and mean free paths were estimated using a Langevin capture model.This mean free path was compared to the Sn+ plasma characteristic length (obtained from the measures with a 16 channel SnII -645.3 nm- spatial array emission) in order to get a collisionality metric Estimation of Sn+ plasma characteristic length defined as: ξ_(Sn-Sn+)=(2R_p)/λ_(Sn-Sn+) that also varies exponentially with radius (same Sn plasma characteristic length, 2Rp ) | *On the other hand, Sn–Sn⁺ collisions have been identified as plausible mechanism contributing to the partial detachment of the incoming heat flux from the target surface. Sn-Sn+ rate coefficients, cross sections and mean free paths were estimated using a Langevin capture model.This mean free path was compared to the Sn+ plasma characteristic length (obtained from the measures with a 16 channel SnII -645.3 nm- spatial array emission) in order to get a collisionality metric Estimation of Sn+ plasma characteristic length defined as: ξ_(Sn-Sn+)=(2R_p)/λ_(Sn-Sn+) that also varies exponentially with radius (same Sn plasma characteristic length, 2Rp). This analysis has shown that the entire plasmoid volume would get moderately collisional (ξ_(Sn-Sn+)>1) and the surface boundary fully collisional (ξ_(Sn-Sn+)>5) at Ttarget>1650 K and nSn+ >1.35∙1029 m-3. These are the conditions previously identified as vapor shielding onset (A. de Castro et al. Nucl. Fusion 2025 65 056034). At Ttarget>1760 K the entire characteristic plasmoid is predicted (extrapolation from measurements limited to 1700 K due to commented LP issues) to become fully collisional which approximately coincides with the experimentally observed steady-state regime (≈1775 K). | ||
This analysis has shown that | |||