Fusion Technology

Solid/Liquid Divertor Experiment (SLIDE)

The Solid/Liquid Divertor Experiment (SLIDE) is a high vacuum experiment aimed to test a variety of divertor concepts developed at the Center for Plasma-Material Interactions. An electron beam is used to replicate the heat flux produced in the divertor region of fusion devices. Beam shape and peak intensity can be controlled by changing the magnetic field in the device. SLIDE has tested a variety of divertor concepts and most recently has been used for testing the Liquid Metal Infused Trenches (LIMIT) technology. LIMIT utilizes thermo-electric magnetohydrodynamics to drive the flow when a heat flux (thermal gradient) is applied to the surface. This technology aims to provide a constant, clean liquid lithium surface to the fusion divertor which can handle the massive heat flux in fusion devices and consistently provide the plasma performance benefits of lithium. Recently, work has been done to test the heat flux handling of a variety of different tile geometries, including 3D printed trench designs.

SLIDE has been incorporated in the Actively Pumped Open-surface Lithium Loop (APOLLO) to demonstrate LIMIT’s ability to be used in a full flowing loop system. It has been modified to be able to operate with not only an electron beam but also an ECRH source. The electron beam is able to put up to 15 MWm-2 of heat flux for up to 10 s and lower heat fluxes for longer time periods. With the ECRH source, a Muegge 6 kW, 2.45 GHz source with magnet is able to produce a n_e = 10¹⁸ m^-3 and T_e = 10 eV plasma to interact with the PFC and perform plasma, particle interaction, and absorption experiments.

Flowing Lithium Absorption and Release Experiment for Deuterium (FLARED)

Development of a flowing plasma facing component for plasma operations in a fusion reactor will be critical. Combining all the experience that CPMI has developed with the LiMIT concept, a test component has been developed for mounting in the APOLLO LOOP and interacting with SLIDE. The goal of FLARED is to look at how the plasma and particles interact with a flowing lithium surface and how absorption and desorption is affected. The distributor and collector design uses machine learning to understand how to best distribute and flow lithium to the PFC surface. This is an important aspect of the design of a PFC to make sure that a surface is fully wetted by the lithium/metal. Electromagnetic pumps and flow meters were designed and built in house by the CPMI team and are used on the APOLLO loop for flowing the lithium and measuring the flow speeds. Mass flow rates up to 10 g/s and flow speeds of up to 10 m/s have been measured in the APOLLO loop and have become the basis for a new design of a future HIDRA-LOOP.

HYdrogen Desorption Experiment (HYDE)

The use of lithium as a plasma-facing component in fusion reactors has been shown to increase plasma performance. This is in part due to lithium’s ability to create a low-recycling regime inside the device. These low-recycling regimes are characterized by an absorbing wall that does not allow cold particles to escape back into the hot plasma. Lithium is able to getter any of the fusion fuel or impurity species that make it to the wall. However, the absorption of fusion fuel, specifically tritium poses some concerns for the long-term use of lithium in fusion devices.

At the Center for Plasma-Material Interactions, we are working to develop a variety of flowing lithium systems, along with hydrogen removal systems. The Hydrogen Desorption Experiment (HYDE) is working to develop a distillation column to use thermal desorption as a means to remove hydrogen species from the lithium bulk. This system has previously shown success at hydrogen removal in highly saturated lithium. Ongoing research is focusing on determining the efficiency of the device as a function of hydrogen saturation and developing specifications for its implementation into flowing system under reactor relevant conditions.

An active version of HYDE has now been installed on the APOLLO loop and is currently being used to do active hydrogen extraction studies with a hydrogen plasma interacting with the LiMIT PFC surface. This will demonstrate a way to be able to extract absorbed hydrogenic species, like tritium, out of a loop in real time and show the technology needed for a future fusion power plant.

Actively Pumped Open-surface Lithium Loop (APOLLO)

Long-term use of lithium plasma-facing components (PFCs) cannot rely on the use of static liquid lithium. As lithium is a strong getter of fuel and impurity species, a stagnant surface will readily form an impurity layer which will diminish the benefits of the lithium surface. Therefore, a flowing system must be employed to keep the lithium surface free of impurities. The Actively Pumped Open-surface Lithium LOop (APOLLO) aims to demonstrate the technology for such a system on the lab scale.

APOLLO consists of liquid lithium pumps, flowmeters, safety systems, and PFCs all with real-time response. Lithium is pumped from a reservoir into a vacuum system with an open-surface plate. This plate utilizes the Liquid Metal Infused Trench (LiMIT) concept to drive the liquid lithium flow using thermo-electric magnetohydrodynamics (TEMHD) when a heat flux is applied. APOLLO aims to demonstrate the technology readiness of liquid lithium components for use in larger scale devices.

Test Housing for Advanced Liquid Alloys Surface Studies and Applications (THALASSA)

The Test Housing for Advanced Liquid Alloys Surface Studies and Applications (THALASSA) is a 1.2m x 1.2m x 1.2m vacuum system that is designed to be flexible in the type of experiments that can be put in it. It is the former Mock-up Entry Module for EAST (MEME) which is a replica of the liquid metal module for the EAST tokamak in China and is used for molten lithium experiments and diagnostic development. The volume of THALASSA is double that of HIDRA and has base pressure down to 10^-7 torr that can be achieved.

Currently its main purpose is to test aspects of technology being used for liquid metal loss. It has a lithium loop inside the vacuum system that has an open flowing face that will allow different PFC concepts to be tested with flowing lithium. Some of the aspects of technology being looked at are the wetting of structured surfaces and liquid metal distributor and collector design, for example the “pachinko” design for distributors. A vacuum/argon vacuum suitcase has been built for transport of lithium to the loading dock. Lithium can be loaded in and pumped down and them melted down until it liquifies. Gravity then takes over once the lithium wets the stainless-steel tubing at around 350 C. Then two electromagnetic pumps flow the lithium into the loop system. The flow velocity of the lithium around the loop is about 1 m/s. Velocity through the surface this does change depending on the system.

THALASSA underwent an upgrade through the end of 2025 and early 2026 and with some magnetic coils installed. These are mounted as a Helmholtz set and can produce up to 30 mT of magnetic field.

Lithium/Metal Infused Trenches (LiMIT)

Lithium has one of the highest thermo-electric coefficients. This is also known as the Seebeck Effect. When two dissimilar metals come into contact there is a voltage potential that is set up. This is temperature dependent.

The Solid/Liquid Divertor Experiment (SLiDE) chamber is used to expose divertor concepts to fusion relevant heat fluxes to test their viability.

• Solid/Liquid Divertor Experiment (SLiDE) chamber to test divertor concepts under representative heat fluxes.
• SLiDE generates a E-beam or a ECR plasma.
• Focuses on liquid metal divertor concepts.
• Loop allows liquid metal flow for extended periods without substantial contamination build-up.
• Lithium engineering and de-risking is additional goal for Li loop construction and operation.
• Modular Li loop allows components to be added or removed as needed for testing, cleaning or any planned upgrades/modifications.

Lithium Pellet Production (LPP)

As part of the lab’s capabilities, we can produce small spheres of lithium. Originally designed to manufacture pellets for the PPPL impeller system, it has also been used to produce 6Li pellets for other experiments. The system is very simple with a tube filled with lithium and injecting it into a pool of mineral oil. The advantage of this is that the hot lithium cools very quickly in the mineral oil and gets coated in a non-oxidizing surface keeping the lithium fresh. The back pressure on the lithium will determine the general size of the pellets. There is a distribution of sizes, and a pellet diameter filtering system (meshes of different sizes) is used to sort out the pellets into general sizes.

Capillary Hybrid Porous-flowing System (CHPS)

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Flowing Lithium LiMIT (FLiLi)

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