Edge fluid?plasma/kinetic?neutral SOLPS [1, 2] modeling of lithium (Li) transport and its effect on the edge plasma during real-time Li injection H-mode discharge on the EAST tokamak are analysed in this work. Since Li has strong chemical activity, deuterium (D) recycling is suppressed by a Li coated plasma-facing wall. By comparing the simulated edge plasma parameters between the no Li case and the Li injection case, it is found that both of the D atom and molecule densities in the divertor region are reduced with the Li injection. It is also found that most of the radiated power is radiated in the divertor. The simulation provides and analyzes the distributions of each Li ion charge state, and the evolution of Li impurity distribution. The simulation shows that the Li+ prefers to accumulate on the high-field side than on the low-field side, which is in qualitative agreement with the experimental measurements on EAST. The possible reason for the Li+ preferential accumulation is discussed in this study.

https://iopscience.iop.org/article/10.1088/0029-5515/56/10/106018/pdf

SOLPS modeling of lithium transport in the scrape-off layer during real-time lithium injection on EAST

Tungsten (W) and Carbon (C) are, respectively, used as the plasma-facing materials for upper and lower divertors in EAST. This provides an opportunity to study the plasma performance with both W and C divertors simultaneously. In this work, simulations are carried out by using the edge fluid-plasma/kinetic-neutral code SOLPS5.0-EIRENE99, with emphasis on the C impurity transport and its effect on the power radiation and erosion of the upper W divertor target. Three typical magnetic field equilibrium configurations, i.e., lower single null, upper single null (USN), and double null (DN), are studied. The main deuterium (D) plasma and C impurities at each ionization state and their neutrals are considered in the simulation. The SOLPS output such as averaged incident ion energy and particle flux density of each species are used to calculate the erosion rate of W walls using the empirical formula for physical sputtering yield. The transport and performance of C impurities on different plasma conditions of each configuration are investigated by changing the C source strength and upstream plasma density. The upper W target erosion by C ions under different conditions is also evaluated. The simulation results indicate that (1) carbon is a strong radiator in EAST divertor temperatures of 10–20 eV; (2) the amount of carbon transported from the lower carbon divertor to the upper tungsten divertor in both USN and DN configurations is predicted to be too small to cause significant W sputtering; and (3) C6+ dominates upper W erosion in the DN case.

/pdf/effects-of-carbon-impurities-on-the-power-radiation-and-7n4uopy93f.pdf

Effects of carbon impurities on the power radiation and tungsten target erosion in EAST

The application of liquid metal, especially liquid lithium, as a plasma facing component (PFC) has the capacity to offer a strong alternative to solid PFCs by reducing damage concerns and enhancing plasma performance. The liquid-metal infused trenches (LiMIT) concept is a liquid metal divertor alternative which employs thermoelectric current from either plasma or external heating in tandem with the toroidal field to self-propel liquid lithium through a series of trenches. LiMIT was tested in the linear plasma simulator, Magnum PSI, at heat fluxes of up to 3 MW m−2. Results of these experiments, including velocity and temperature measurements, as well as power handling considerations are discussed, focusing on the 80 shots performed at Magnum scanning magnetic fields and heat fluxes up to ~0.3 T and 3 MW m−2. Comparisons to predictions, both analytical and modelled, are made and show good agreement. Concerns over MHD droplet ejection are additionally addressed.

/pdf/performance-of-the-lithium-metal-infused-trenches-in-the-3unv48boct.pdf

Performance of the lithium metal infused trenches in the magnum PSI linear plasma simulator

https://iopscience.iop.org/article/10.1088/1741-4326/ab2d60/pdf

Modeling and advances in the high bootstrap fraction regime on EAST towards the steady-state operation

A radiation-driven m  =  2 island was observed in the experimental advanced superconducting tokamak (EAST) ohmic plasma, near the density limit. The mode onset occurs when the the ohmic heating input is less than the radiative cooling loss, which agrees with the mode onset behavior of the thermo-resistive model. The evolution of the equilibrium during the mode process was obtained using the ONETWO transport code, with inputs comprising the experimental electron temperature and density profiles. A large m  =  2 island can drive an m  =  1 sideband mode, which leads to an internal crash that appears as a large change in temperature that occurs not only in the q  =  2 region but also in the core.

https://iopscience.iop.org/article/10.1088/1741-4326/aa7f91/pdf

Radiation-driven m = 2 island formation and dynamics near density limit in experimental advanced superconducting tokamak ohmic plasma

Effective ion charge (Zeff) is an important parameter in fusion research and can be used to quantify impurity levels. Investigation into Zeff helps us to understand the impurity generation and transport mechanisms in order to find an effective way to control impurity levels. This key parameter Zeff is measured by the visible bremsstrahlung diagnostic in the EAST tokamak. In this report, Zeff and impurity behavior in siliconization and lithium coating experiments have been investigated. Comparisons of averaged Zeff and Zeff profiles have been made between L-mode and H-mode discharges. It is found that the dependence of Zeff on averaged electron density complies with the hyperbolic scaling. Finally, Zeff behavior in auxiliary heating experiments is analyzed in detail. The relationship between Zeff and external power injected into plasma in lower hybrid wave and ion cyclotron resonance frequency heating has been summarized and analyzed.

http://iopscience.iop.org/article/10.1088/0741-3335/56/10/105006/pdf

Measurement and analysis of Z(eff) in EAST tokamak

The control of the impurity level in magnetically confined plasmas is a critical issue for future fusion devices. All the graphite tiles have been replaced by molybdenum tiles as limiter materials in the 2011 spring campaign in order to further reduce the recycling and hydrogen content of the plasma. A lithium coating technique has been applied as an important wall conditioning method to the HT-7 tokamak. The effective ion charge Zeff and impurity behavior with full metallic first walls of high-Z materials and lower hydrogen recycling have been investigated in a series of lithium coating experiments in this paper. Plasma performance and impurity behavior without wall coatings are studied in the early stage of the campaign. Comparison of Zeff with different plasma-facing components has been made. A typical lithium coating experiment has been analyzed in order to understand the effect of lithium coating. The evolution of main impurity line radiation, Zeff and the H/(H + D) ratio is analyzed in detail as lithium coating is repeated, indicating that lithium coating is a very effective tool to control impurity level and reduce hydrogen recycling. Furthermore, a boronization is conducted at the end of this campaign in order to make comparison with lithium coating. Experimental results show that lithium coating has much more advantages in edge recycling control, though it does not reduce impurity level as effectively as boronization.

Investigation of Z eff and impurity behaviour in lithium coating experiments with full metallic first wall in HT-7 tokamak

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Measurement and analysis of Z(eff) in EAST tokamak

Investigation of Z eff and impurity behaviour in lithium coating experiments with full metallic first wall in HT-7 tokamak