Material Teststands

HIDRA Material Analysis Teststand (HIDRA-MAT)

The HIDRA Material Analysis Teststand (HIDRA-MAT) is a midplane materials probe that allows samples to be exposed to the HIDRA plasma. It has an in-vacuo analysis chamber with different surface diagnostics available to analyze the retention effects of plasma and gases into the surface. The Probe head has a heated surface that can go up to 800 ^oC. It is also able to be rotated ±90^o with respect to the horizontal. This is an important feature that allows drops of liquid lithium to be placed onto its surface via the lithium metals droplet injector (LMDI).

The analysis chamber is attached to HIDRA and allows for efficient transfer of samples to the HIDRA plasma. Also the placement of lithium on the surface is able to be done efficiently without air exposure and movement in and out of HIDRA. This means that HIDRA-MAT allows the capability of doing temporal resolution of surface changes.

Currently HIDRA-MAT has two surface techniques that can be applies, Thermal Desorption Spectroscopy (TDS) and Laser Induced Blowoff Spectroscopy (LIBS). The TDS system uses a dual Residual Gas Analyzer (RGA) set up that allows the distinction between helium (He) and deuterium (D₂) molecules which are both mass 4. This is important in being able to run realistic scenarios where isotopic plasma, involving hydrogen (H₂₎, D₂ and He are involved.

Lithium is inserted in HIDRA-MAT into a surface via the LMDI. Is uses a piston and plunder system with a computer control the size and mass of the lithium that is placed onto the surface. It also allows for the injector to touch the surface of the probe head so that the lithium is not just free-falling but is physically placed onto the surface.

HIDRA Flowing Lithium PFC (HIDRA-FLiP)

A new HIDRA Flowing Lithium PFC (HIDRA-FLiP) module is being designed and manufactured that will be able to be mounted where the HIDRA-MAT head is. This means there will be two types of material surfaces that can be used for material interactions and exposure in HIDRA.

HIDRA-FLiP will have an actively flowing liquid lithium and metal loop embedded within the head. It will provide cooling for thermoelectric magnetohydrodynamic drive (TEMHD) and have the ability to mount different surfaces to the probe head. It will utilize the magnetic field in HIDRA to help with an EM pump to drive flows and to also drive the TEMHD J×B forces. This will essentially be a smaller version of the FLiLi system that was deployed in the Experimental Advanced Superconducting Tokamak (EAST).

The main goal of HIDRA-FLiP is to be able to test porous structures with flowing lithium and expose them to a toroidal plasma in real conditions. In conjunction to this a two-wavelength IR camera diagnostic is also being developed to be able to measure the lithium surface temperature. This two-wavelength system is able to remove the dependence on emissivity, ɛ, of the surface and give a direct temperature measurement of the surface. Surface temperature is an important measurement particularly when the plasma and surface are interacting directly. Initially FLIR cameras will be used up to 500 ^oC and then upgrade to larger temperature ranges.

Ion-Gas-Neutral Interactions with Surfaces (IGNIS)

The IGNIS facility is a state-of-the art in-situ experimental surface science facility that is capable of surface characterization of materials under extreme conditions.  The acronym “ignis” means “fire” in Latin and encompasses the ability to expose surfaces to a collection of energetic particles under high-pressure and high-temperature environmental conditions during surface analysis measurements.  This unique facility allows x-ray photoelectron spectroscopy, ion-scattering spectroscopy, and Raman spectroscopy in a single chamber during the following conditions: High-intensity plasma irradiation using a hollow-cathode plasma source, neutral atom irradiation from a broad beam source with a neutralizer, photon irradiation with a UV source or laser, and electron irradiation using an e-beam source.  The charged particle spectroscopy will be done with the Specs PHOIBOS 150 NAP hemispherical analyzer.

Tungsten Fuzz Characterization by Helicon (TUFCON) & Hydrogen-plasma Experiment Radical-induced MEtal Spitting (HERMES)

The Tungsten Fuzz Characterization by Helicon (TUFCON) chamber was originally used to investigate the formation of tungsten fuzz after helium plasma exposure. This work performed parametric sweeps over ion energy and fluence to determine the causes of the fuzz formation. Recently, the device has been used to determine the effect of hydrogen plasma parameters and radical density on the spitting of microdroplets from liquid metals (tin, lithium, tin-lithium).Upon radical or plasma exposure, hydrogen bubbles form in the molten metal, which eventually migrate to the surface and burst, releasing microdroplets of liquid metals. This could be extremely detrimental to fusion plasma operation, as droplets entering the core plasma would reduce the plasma performance. In an effort to better understand these droplets, the plasma in TUFCON is being fully characterized by Langmuir probe and radical probe to determine plasma temperature, plasma density, and radical density. After the plasma is fully characterized, a microdroplet size distribution will be made as a function of liquid temperature and plasma parameters. Eventually, the aim is to implement techniques which can mitigate the droplet emission or prevent the droplets from entering the core plasma.

More recently the chamber has been used to look at hydrogen absorption and spitting in tin (Sn). Tin is being considered as an alternative liquid metal for fusion divertors since it has a lower evaporation rate and thus can be operated at higher temperatures than lithium. However, tin and tin eutectics such as lithium-tin (LiSn) still have their engineering challenges such as spitting which can contaminate a plasma and radiate energy away.

Materials Characterization and Analysis Test Stand (MCATS)

For proper functioning of lithium-based plasma-facing components (PFCs) control over the wettability of substrates must be known. The Materials Characterization and Analysis Test Stand (MCATS) chamber allows for rapid testing of lithium wetting on attractive materials over a large range of temperatures (200C – 750C). Material choice, surface roughness, and plasma treatment have all been shown to influence the lithium wettability. An understanding of these mechanisms and materials allows for the creation of components which can better control the flow of liquid lithium. For example, the nano-texturing of portions of a polished stainless steel plate may allow us to guide lithium flow on a flat plate with no need for physical walls. These techniques and experiences can be used to guide the fabrication of many lithium-based devices (PFCs, lithium injectors, lithium pumps, etc.).

Current work in MCATS is centered around ensuring that particular materials do no wet with lithium, such that if lithium is splashed on that surface, it will readily leave the surface. These tests are looking into many materials (metals, ceramics, polymers) that have application in fusion devices. Varying surface roughness and plasma treatment is being investigated to ensure that as a plasma cleans the surface or sputtering smooths the surface, a transition to wetting will not occur.

Materials Attacked by Liquid Lithium Corrosion Experiment (MALiCE)

A number of static lithium corrosion experiments have been performed over the last several decades. However, not many have been performed for extended periods of time at PFC relevant temperatures or utilizing modern analysis techniques. Materials Attacked by Lithium Corrosion Experiment (MALICE) aims to perform extend (>2000 hr) static lithium corrosion tests at a temperature of 300 ^oC. A variety of materials are to be tested, including stainless steels, refractory metals, and incoloys, each possessing some use in fusion applications. Samples are characterized using a variety of optical and chemical techniques, including surface profilometry, ICP-OES, SIMS, FIB, and EDS.

Spinning Lithium Attacking Potential Substrates (SLAPS)

In order to be able to fully utilize liquid metals in fusion devices, their corrosive attack on a variety of materials needs to be known. Particularly, lithium attack on the structural components of a device are of concern.

Previous work has looked at static lithium corrosion, often under extreme temperatures. The Spinning Lithium Attacking Potential Substrates (SLAPS) device at the Center for Plasma-Material Interactions investigates the effect of rotating lithium at relevant temperatures on the corrosion behavior of potential materials. SLAPS consists of a spindle with a variety of mounted samples which rotate in a bucket of molten lithium at operating temperatures (~300C) for multiple days (~100 hrs).Rotation allows the investigation of fluid shear on the corrosion dynamics. Mechanical properties of the materials are of prime concern for this project, so each material undergoes tensile testing before and after lithium exposure to determine how lithium has changed material performance. Additionally, 3D optical profilometry is employed to determine if microscopic surface changes have occurred. SLAPS will allow us to provide candidate materials for use in a variety of components in fusion devices.

High Temperature Corrosion Test Chamber (HiTeC²)

High Temperature Corrosion Test Chamber (HiTeC²) is a vacuum chamber for exposing materials to high temperature static liquid metal, particularly lithium, for extended periods of time to investigate their corrosion behavior. This chamber is based on the former Lava chamber and is located in room 103, NRL. Samples up to 35 mm in diameter and 10 mm in thickness, along with up to 10 grams of lithium, in a molybdenum crucible, can be loaded into the chamber and heated to above 923 K (650 ºC) using the equipped induction heater. The automated system ensures safe and repeatable temperature and pressure control for more than a week without human input. Characterizing the high temperature liquid metal corrosion of relevant materials using this chamber enables improving the durability and performance of next-generation liquid metal plasma facing component and blanket systems.