Lithium Evaporation Research Articles

Wall Conditioning Systems for the NSTX-U Fusion Device

The National Spherical Torus eXperiment (NSTX) has undergone a major upgrade to NSTX-U at Princeton Plasma Physics Laboratory (PPPL). NSTX-U will double the toroidal field, plasma current, and neutral beam injection heating power, as well as significantly increase the pulse duration. Control of the influx of impurity gases and fuel recycling from plasma facing components (PFCs) are critical for further improving NSTX-U plasma performance. To achieve high quality plasmas during operations, wall conditioning technologies are needed to limit impurities in the plasma by removing the impurities from PFCs before plasma operation, and reducing recycling and outgassing during discharges via reactive coating materials. In this article, the design of a bakeout system, a glow discharge cleaning (GDC) system, a deuterated trimethylboron (dTMB) boron coating system, and a lithium evaporation (LITER) coating system for NSTX-U will be briefly described. Designed for enhanced operational safety, fully automated process control, and easy equipment maintenance and serviceability, these systems have been successfully used to condition the PFCs for NSTX and NSTX-U. Operational sequence and procedure of using these wall conditioning methods for NSTX-U will be covered in this article. Wall conditioning results will also be briefly discussed at the end of this article.

High-Temperature Treatment to Improve the Capacity of LiBC Anode Material in Li-ion Battery

As a graphite-like material, the LiBC can deliver a high capacity as an anode material in Li-ion batteries, which was strongly dependent on the carbon precursor. Developing a method to improve the capacity would be significant to study and utilize the LiBC anode material. Here we treated a pristine LiBC material with a high temperature to obtain four modified LiBC samples, and a reversible capacity of 353 mAh/g was delivered by a modified LiBC sample that was treated at 600 °C for 10h in a powder form wrapped with an Al foil, which was only 218 mAh/g for the pristine LiBC in Li-ion batteries. According to the XRD result, the layer structure of LiBC was maintained after the high-temperature treatment, while the lattice parameters were changed slightly, especially for the interlayer distance. And the modified LiBC samples showed the similar Raman spectra as the pristine LiBC except for the peak intensity, which indicates the lithium evaporation during the high-temperature treatment. Thereby, the high-temperature treatment can improve the capacity of LiBC through reducing the lithium content and modifying the crystal structure, and this method would make the LiBC material become a more promising anode materials in Li-ion batteries.

Real-time gas cooling of flowing liquid lithium limiter for the EAST

Abstract A novel continuously flowing liquid lithium limiter (FLiLi) which employs an in-vessel electro-magnetic pump to drive liquid Li flowing on the surface of limiter has been successfully designed and tested in the experimental advanced superconducting tokamak (EAST) device in 2014. In order to better control the surface temperature, an upgraded design and the real-time gas cooling were performed in 2016. Two kinds of cooling gas, helium (He) and argon (Ar) were tested on the FLiLi system prior to the experiment. It was found that the cooling rates of He and Ar at 2.5 MPa are 34.2 ℃/min, 10.2 ℃/min or 31.7 ℃/kL and 28.1 ℃/kL, respectively. The cooling performance of He is more effective than Ar. Experimental results show that the real-time He cooling could effectively contain the FLiLi surface temperature increase and prevent the strong passive evaporation of lithium during plasma discharges. Limiter heat flux up to 0.2 MW/m2 was removed during ohmic discharge with 2.5 MPa He gas. Finally, Because of the upgraded design and real-time gas cooling, the surface of FLiLi was not damaged by heat flux after entire plasma discharge.

Submicron-Sized Nb-Doped Lithium Garnet for High Ionic Conductivity Solid Electrolyte and Performance of Quasi-Solid-State Lithium Battery.

The garnet Li7La3Zr2O12 (LLZO) has been widely investigated because of its high conductivity, wide electrochemical window, and chemical stability with regards to lithium metal. However, the usual preparation process of LLZO requires high-temperature sintering for a long time and a lot of mother powder to compensate for lithium evaporation. In this study submicron Li6.6La3Zr1.6Nb0.4O12 (LLZNO) powder―which has a stable cubic phase and high sintering activity―was prepared using the conventional solid-state reaction and the attrition milling process, and Li stoichiometric LLZNO ceramics were obtained by sintering this powder―which is difficult to control under high sintering temperatures and when sintered for a long time―at a relatively low temperature or for a short amount of time. The particle-size distribution, phase structure, microstructure, distribution of elements, total ionic conductivity, relative density, and activation energy of the submicron LLZNO powder and the LLZNO ceramics were tested and analyzed using laser diffraction particle-size analyzer (LD), X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Electrochemical Impedance Spectroscopy (EIS), and the Archimedean method. The total ionic conductivity of samples sintered at 1200 °C for 30 min was 5.09 × 10−4 S·cm−1, the activation energy was 0.311 eV, and the relative density was 87.3%. When the samples were sintered at 1150 °C for 60 min the total ionic conductivity was 3.49 × 10−4 S·cm−1, the activation energy was 0.316 eV, and the relative density was 90.4%. At the same time, quasi-solid-state batteries were assembled with LiMn2O4 as the positive electrode and submicron LLZNO powder as the solid-state electrolyte. After 50 cycles, the discharge specific capacity was 105.5 mAh/g and the columbic efficiency was above 95%.

Optical radiation from the sputtered species under gas excitation by the products of the 6Li(n,α)3H nuclear reaction

The emission spectra during alkali metal sputtering into noble gases excited by the products of 6Li(n,α)3H nuclear reaction were studied. Lithium in the form of a capillary-porous structure (CPS) was heated up to a temperature of 730 K. At a temperature in the 520–620 K range, depending on a type of gas medium, intense radiation was observed for lines of lithium and lines of sodium and potassium found as impurities in lithium. The process activation energy (155–161 kJ/mol) obtained from the dependence of the optical radiation intensity on the lithium layer temperature is in good agreement with the lithium evaporation energy values. The vapour density that is significantly higher than that saturated lithium vapour under normal thermal heating was created by the α-particles and tritium nuclei released from the lithium layer and when the opposite wall was bombarded. Excitation of the sputtered lithium atoms occurs as the result of the plasma-chemical reactions in the gas. The Penning process for the lithium atoms is suggested to be the main channel for the excitation transmission from the noble gases to the lithium atoms.

Influence of Pulsed Beams of Deuterium Ions and Deuterium Plasma on the Aluminum Alloy of Al–Mg–Li System

The damage and structural state of the surface layer of Al–Li–Mg samples composed of Al–5% Mg–2% Li (wt %) under pulsed action of power streams of high-temperature deuterium plasma and high-energy deuterium ions in the Plasma Focus (PF) device have been investigated. The radiation power density was q ~ 106 W/cm2; the pulse duration was 50–100 ns. Pulsed thermal heating and rapid cooling is established to lead to the melting and solidification of a thin surface layer of the alloy for several tens of nanoseconds. At the same time, in the superheated surface layer of the alloy, microcavities of a spherical shape are formed which is associated with intense evaporation of lithium into micropores within the heated layer. Thermal stresses caused by abrupt heating, melting, and cooling of a thin surface layer of metal result in formation of microcracks in the near-surface zone of the samples. The evaporation by the power electron beam of the elements of the anode material of the PF device (copper and tungsten) and their subsequent deposition onto the irradiated surface of the investigated samples in the form of droplets of submicron size are noted. It is shown that the thermal and radiation-stimulated processes generated in the alloy under the action of pulsed energy fluxes in the implemented irradiation regime lead to the redistribution of elements in the surface layer of the aluminum solution, contributing to an increase in magnesium content and the formation of magnesium oxide on the surface.

Formulized average surface binding energy elevation and lithium vaporization and redeposition investigations in capillary pore systems

An investigation into lithium evaporation and redeposition with multi-mesh capillary pore systems (CPS) has been performed on a one-cathode linear plasma device. A diagnostic system has been used to monitor the lithium evaporation process in the vicinity of the specimen surface, with the adjustable plasma parameters of electron temperature ranging from 0.4–0.9 eV and electron density from 0.8–3.2 × 1019 m−3. The experimental results show that the lithium evaporation rate follows the reduction scaling ratio of 1.94:1.69:1.00 as the number of mesh layers is increased from two to four, which is closely related to the time-dependent fraction weighted average surface binding energy (i.e. evaporation heat) elevation because a fraction of lithium atoms is adhered to the mesh surface. From the viewpoint of nanoscale physics, a new formula is derived for the first time to qualitatively explain the physical mechanism of evaporation heat, or of time-dependent fraction weighted dual average surface binding energy with minor elevation in this special concomitant configuration CPS, which consists of liquid lithium and multi-meshes. The reason for this phenomenon is that the mesh surface binding force acts on a fraction of the adhered lithium atoms, leading to a minor elevation in the evaporation heat. The lithium vapor plays a modest shielding role from the incident heat flux dumping by stopping power plus lithium impurity radiation enhancement, as in the impurity radiation divertor, otherwise the thermal equilibrium of the system could not be attained. In addition, an experimental comparison with a nonactive target and a semi-empirical temperature-dependent model calculation have been applied to further verify the shielding effect. It has been observed that the redeposition rate increases with the applied discharge current.

Sputtering of lithium and lithium compound films under deuterium and helium ion bombardment

Abstract Conditioning of plasma facing components (PFCs) using lithium (Li) evaporation has shown to improve plasma performance in fusion devices by imposing low recycling boundary conditions. It is important to understand the retention and sputtering dynamics of deuterium (D) in Li and Li compound (Li O and Li C O) films to most efficiently make predictions on plasma performance. Energetic D2+ incident on thin Li films is shown to readily form LiD leading to a lower Li sputtering yield than the sputtering yield of pure Li. Measured sputtering yields for thin LiD films agree with previous simulations and bulk erosion measurements. The He+ sputtering yield of pure Li was 2–3 times higher than the sputtering yield of D2+ on LiD. Incident 1000–1200 eV/D2+ sputtered Li O films at a slower rate than D2+ on LiD and Li C O films.

Effect of sintering regimes on the microstructure and magnetic properties of LiTiZn ferrite ceramics

In present work, the influence of sintering regimes on the microstructure, saturation magnetization, density and porosity, the grain size, the Curie point, and the temperature dependence of the initial permeability of LiTiZn ferrite ceramics was investigated. Ceramics was prepared by a standard ceramic technique. The formation of a single-phase cubic spinel structure was confirmed by XRD analysis. The Curie point was determined from both the temperature dependences of the initial permeability and the method of thermogravimetric measurements in a magnetic field. Density/porosity and the grain size, the Curie point and magnetization are sensitive to the sintering regime. The initial permeability of ferrite decreases with sintering temperature (in the range of 1010–1150 °С) and grain size increasing that contradicts the generally accepted Globus and Smith-Wijn theories. A possible reason of such behavior is the formation of intragranular pores growing with the increase in the sintering temperature and inhibiting the domain wall motion inside the grain. These results correspond to the porosity of the investigated ferrite ceramic samples, which grows with sintering temperature increasing.The non-stoichiometry arising due to evaporation of lithium and zinc oxides at temperature above 1010 °C affects the initial permeability. In this work, a qualitative assessment of the defective state of ferrite samples obtained under various sintering regimes was given.

Magnetic perturbation diagnostics in the high-temperature lithiated environment of LTX-β.

Magnetic perturbation measurements will be invaluable for characterizing Lithium Tokamak Experiment Beta (LTX-β) plasmas due to the time-evolving 3D nature of the magnetic fields generated by eddy currents in the vessel and copper shell segments, as well as enhanced MHD instability drive due to newly introduced neutral beam heating. The LTX-β upgrade includes two new arrays of Mirnov coils: a shell eddy sensor array of two-axis coils distributed over the back surface of one shell segment and a toroidal array of poloidal field coils at the low-field side midplane gap. Evaporative lithium wall-coating and the high temperatures required for liquid lithium wall operation both complicate the implementation of in-vessel diagnostics. While the shell array is protected from lithium exposure, the shell segment to which it is mounted will at times exceed 300 °C. The toroidal array, however, will experience direct line-of-sight exposure to the lithium evaporator as well as close proximity to the hot shell and may also be subject to poorly confined beam-driven fast ions. We describe how the two new Mirnov coil arrays meet these environmental challenges and enhance the LTX-β diagnostic suite.

Ar + H2 Plasma Interacting with Lithium-Filled Capillary Porous Structure

Ar + H2 plasma interacting with liquid lithium was carried out on a one-cathode linear plasma device (SCU-PSI). The lithium sample was covered with capillary porous structure (CPS). It is found that the electron temperature of applied plasma ranged from ~0–1 eV and electron density ranged from 0.1 × 1020 to 1 × 1020 m−3. The experimental results indicate that a reduction in the electron temperature and the lithium evaporation is found as the percentage of H2 increases When the ratio of argon and hydrogen keeps constant, the electron temperature and lithium evaporation increase with applied input power, respectively. The retention of hydrogen atoms in lithium surface results in reducing the lithium evaporation. The XRD analysis result shows that during plasma radiation no LiH is formed.

A new developed in-between shots lithium evaporation coating system for improving plasma performance in EAST

A new in-between shots evaporative lithium coating system has been successfully developed and implemented on the Experimental Advanced Superconducting Tokamak (EAST) for the 2017 campaign. This paper describes a novel technique for the introduction of lithium into the EAST vessel allowing evaporative coatings to be applied between discharges without requiring a significant amount of time to insert and retract the lithium source. This newly designed system utilizes a rotating axis driven by a vacuum dynamic sealing feedthough under remote control to open and close a shutter. A compression bellows, which drives the delivery tube, guarantees accurate position of the oven thus avoiding possible direct contact with the plasma. This allows the new evaporation system to be operated in two distinct modes. One mode is operated in-between shots to refresh pre-coated lithium film, the other is a real-time lithium vapor injection during plasma operations to provide active wall conditioning during long pulse plasma discharges. In this paper, operation of this new lithium deposition system in the in-between shots replenishment mode is described. Initial experiments show that this system worked well during the interval of discharges in EAST, and the in-between shots lithium coating effectively reduced the wall recycling and impurity concentrations. Moreover, the application of fresh lithium coating lead to sustain the plasma stored energy and confinement, as well as a reduction of impurity radiation.

Process Development for Thin Film Solid State Battery on Four Inch Wafer Using Glove Box Attached Custom Built Single Chamber PVD System

A process for fabricating thin film solid state battery on four-inch silicon wafer has been developed in a custom built hybrid PVD configuration in a single chamber attached to a glove box. In this work, we have performed six layer deposition, which includes Lithium evaporation in the same chamber. As the cathode current collector, Aluminum of 2-5 microns thick, was deposited using specially designed compact thermal evaporation sources, after aluminium deposition thin layer metallic nickel or cobalt was used as the barrier for Lithium cobalt oxide cathode. The total thickness of the thin film solid state battery is 15-18 micron, with a specific capacity between 50-80 µAh-Cm2. The capacity of the batteries reduced to 20-30 percent from the initial capacity after 100 cycles. Some batteries were cycled up to 15,000 cycles and the capacity fading is about 50-60 percent. Based on different studies, we have established the protocol to make reliable thin film battery processing using custom built PVD system in the laboratory scale. The investigations have shown degradation due to the intrinsic material limitations rather than process induced degradation.

Vaporization of liquid Pb-Li eutectic alloy from 1000K to 1200K - A high temperature mass spectrometric study

Liquid lead-lithium eutectic will be used as a coolant in fusion reactor blanket loop. Vapor pressure of the eutectic is an important parameter to accurately predict its in-loop behavior. Past measurements of vapor pressure of the eutectic relied on indirect methods. In this paper, we report for the first time the in-situ vaporization behavior of the liquid alloy between 1042 and 1176 K by Knudsen effusion mass spectrometry (KEMS). It was seen that the vaporization occurred by independent evaporation of lead and lithium. No complex intermetallic vapor was seen in the mass spectra. The partial pressures and enthalpy of vaporization of Pb and Li were evaluated directly from the measured ion intensities formed from the equilibrium vapor over the alloy. The activity of Li over a temperature range of 1042–1176 K was found to be 4.8 × 10−5 to that of pure Li, indicating its very low activity in the alloy.

Flowing liquid lithium plasma-facing components – Physics, technology and system analysis of the LiMIT system

The use of low atomic number liquid metals has been shown to have the potential to solve many of the prevalent problems like erosion and radiation losses associated with the interaction of fusion plasma with the plasma facing component (PFC) structures in tokamaks. Since the first evidence of lithium increasing plasma performance in TFTR [1], the benefits of using lithium in fusion environments have been seen in many devices, including CDX-U [2], NSTX [3], LTX [4], and DIII-D [5]. While both fast flow and slow flow concepts have been studied with regards to liquid lithium first wall alternatives, this report will focus on efforts placed on fast flow research and will mainly focus on advancements in the LiMIT device that help to eliminate concerns over the broad use of liquid lithium. Due to the promising TFTR results along with results obtained at the University of Illinois at Urbana-Champaign [6], suitably designed trench structures holding liquid lithium could be an appropriate fast flow candidate for PFC modules in future fusion devices. There are four potential shortcomings of this approach: (1) Droplet ejection, (2) Wetting control, (3) Tritium retention, and (4) Limited heat flux handling. Droplet ejection is discussed in a companion publication [7], while this paper addresses the topics of wetting control and heat flux handling. Limitations in wetting and prevention of lithium creep (i.e. getting and keeping the lithium only where it should be) have been solved by laser-texturing the base material with extreme short laser pulses (pico – femto second) of high power (several 10s of W). Micro- and nano-structuring results indicate that the textured substrates displayed significant change in their wetting properties, increasing the temperature needed to wet from 310 °C to 390 °C. Lastly, initial designs for the Lithium Metal Infused Trenches (LiMIT) [6] showed dryout above 3 MW/m2, but new designs of the trench shaping show potential to be able to handle up to 10MW/m2. Dryout is accompanied by lithium evaporation which is shown to mitigate the incident heat flux, which may be viewed as beneficial [8]. The advances shown here will increase the viability of the LiMIT system in large-scale testing, and allow for extensive design iteration to begin tackling the large powers and heat fluxes present in reactor-relevant systems.

Phase formation and microstructure in lithium-carbon intercalation compounds during lithium uptake and release

Abstract The intercalation and de-intercalation behavior of lithium in graphite was investigated with respect to the formation of lithium graphite intercalation compounds (Li-GICs) using a combination of XRD measurements and metallography. Microstructural features and the evolution of phases and structural details of Li-GICs during Li uptake and release are correlated for the first time, giving new insight into the formation of Li-GICs. Lithium evaporation loss during annealing was exploited for studying the phase evolution during lithium de-intercalation, whereas phase formation during lithium uptake was studied in a sample exhibiting a lithium concentration gradient. The experiments indicate that growth and dissolution of the compound LiC6 do not occur by an inverse mechanism, as shown by the formation of different intermediate phases. The compound LiC12 was found to be a non-stoichiometric solid solution. LiC6 can be clearly identified in micrographs by the color and distinct phase boundaries, while LiC12 is situated in the vicinity of the LiC6 phase with varying coloration depending on the Li content.

Elimination of inter-discharge helium glow discharge cleaning with lithium evaporation in NSTX

Operation in the National Spherical Torus Experiment (NSTX) typically used either periodic boronization and inter-shot helium glow discharge cleaning (HeGDC), or inter-shot lithium evaporation without boronization, and initially with inter-shot HeGDC. To assess the viability of operation without HeGDC, dedicated experiments were conducted in which Li evaporation was used while systematically shrinking the HeGDC between shots from the standard 10min to zero (10→6.5→4→0). Good shot reproducibility without HeGDC was achieved with lithium evaporations of 100mg or higher; evaporations of 200–300mg typically resulted in very low ELM frequency or ELM-free operation, reduced wall fueling, and improved energy confinement. The use of HeGDC before lithium evaporation modestly reduced Dα in the outer scrape-off layer, but not at the strike point. Pedestal electron and ion temperature also improved modestly, suggesting that HeGDC prior to lithium evaporation is a useful tool for experiments that seek to maximize plasma performance.

Influence of Li conditioning on Lower Hybrid Current Drive efficiency in H-mode and L- mode plasmas on EAST

The lower hybrid current drive efficiency on the EAST tokamak is estimated on a large database of low loop voltage discharges (VL A.W-1 .m-2 . No deleterious effect of the density on the efficiency is found between 2.3 and 3.2×1019 m-3 . The high efficiency occurs after strong lithium evaporation. The low effective charge Zeff and the higher temperature > of these discharges, can account for the high efficiency according to the expected scaling with Zeff and >. Modelling with a ray-tracing code coupled to a Fokker-Planck solver supports this result, assuming that the fast electron transport is reduced in the zero loop voltage discharge with high efficiency.

An assessment of the evaporation and condensation phenomena of lithium during the operation of a Li(d,xn) fusion relevant neutron source.

The flowing lithium target of a Li(d,xn) fusion relevant neutron source must evacuate the deuteron beam power and generate in a stable manner a flux of neutrons with a broad peak at 14 MeV capable to cause similar phenomena as would undergo the structural materials of plasma facing components of a DEMO like reactors. Whereas the physics of the beam-target interaction are understood and the stability of the lithium screen flowing at the nominal conditions of IFMIF (25 mm thick screen with +/–1 mm surface amplitudes flowing at 15 m/s and 523 K) has been demonstrated, a conclusive assessment of the evaporation and condensation of lithium during operation was missing. First attempts to determine evaporation rates started by Hertz in 1882 and have since been subject of continuous efforts driven by its practical importance; however intense surface evaporation is essentially a non-equilibrium process with its inherent theoretical difficulties. Hertz-Knudsen-Langmuir (HKL) equation with Schrage’s ‘accommodation factor’ η = 1.66 provide excellent agreement with experiments for weak evaporation under certain conditions, which are present during a Li(d,xn) facility operation. An assessment of the impact under the known operational conditions for IFMIF (574 K and 10−3Pa on the free surface), with the sticking probability of 1 inherent to a hot lithium gas contained in room temperature steel walls, is carried out. An explanation of the main physical concepts to adequately place needed assumptions is included.

Effect of Sintering Additives on Relative Density and Li‐ion Conductivity of Nb‐Doped Li7La3ZrO12 Solid Electrolyte

Lithium ion conductors with garnet‐type structure are promising candidates for applications in all solid‐state lithium ion batteries, because these materials present a high chemical stability against Li metal and a rather high Li+ conductivity (10−3–10−4 S/cm). Producing densified Li‐ion conductors by lowering sintering temperature is an important issue, which can achieve high Li conductivity in garnet oxide by preventing the evaporation of lithium and a good Li‐ion conduction in grain boundary between garnet oxides. In this study, we concentrate on the use of sintering additives to enhance densification and microstructure of Li7La3ZrNbO12 at sintering temperature of 900°C. Glasses in the LiO2‐B2O3‐SiO2‐CaO‐Al2O3 (LBSCA) and BaO‐B2O3‐SiO2‐CaO‐Al2O3 (BBSCA) system with low softening temperature (<700°C) were used to modify the grain‐boundary resistance during sintering process. Lithium compounds with low melting point (<850°C) such as LiF, Li2CO3, and LiOH were also studied to improve the rearrangement of grains during the initial and middle stages of sintering. Among these sintering additives, LBSCA and BBSCA were proved to be better sintering additives at reducing the porosity of the pellets and improving connectivity between the grains. Glass additives produced relative densities of 85–92%, whereas those of lithium compounds were 62–77%. Li7La3ZrNbO12 sintered with 4 wt% of LBSCA at 900°C for 10 h achieved a rather high relative density of 85% and total Li‐ion conductivity of 0.8 × 10−4 S/cm at room temperature (30°C).