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STTR Phase 1 Project

Free Surface Flowing Liquid - Plasma Interaction Facility

Principal Investigator: Jean Paul Allain

Subcontractor: University of Illinois, Department of Nuclear, Plasma and Radiological Engineering, Subcontractor Principal Investigator: David N. Ruzic

Project Summary:

One of the critical technological challenges of future fusion devices is the ability for plasma-facing components to withstand power densities of the order 5-10 MW/m2, for advanced tokamak machines, and up to 50 MW/m2 for off-normal events such as edge-localized modes or disruptions.  One alternative addressing this challenge is the use of free surface flowing liquids as plasma-facing components (PFC’s).  Some examples of these free surface liquids include: liquid-metals such as liquid lithium and molten salts, such as flibe (LiF-BeF2).  Some of the challenges facing this application include: effective hydrogen/helium particle retention, plasma-liquid interaction issues (evaporation, sputtering, spattering), chemical safety issues (i.e. liquid lithium, flibe (molten salt)), tritium inventory, neutron irradiation, power extraction, vapor shielding, and macroscopic liquid-metal removal. 

Understanding of free surface flowing liquid-plasma interactions and associated boundary plasma physics, boundary particle fluxes, bulk liquid-metal diffusion, and surface properties is indispensable in the development of advanced plasma-facing components for future generation fusion machines.  In addition to this understanding, techniques for the removal of significant heat loads (at least 1 MW/m2) by free-surface flowing liquids including turbulence promoters, alloying of key liquid-metals for vapor pressure reduction and diagnostic capabilities to understand key free surface flowing liquid-plasma interactions such as: mean flow liquid-metal velocity, He/H particle retention, particle surface segregation, turbulence intensity, liquid-metal erosion transport; are all crucial in addressing the needs under topic 3 “Advanced Technologies and Materials for Fusion Systems”, subtopic b “Free Surface Liquids for Heat Removal” proposed by the Office of Fusion Energy Sciences.

NPL (Nuclear Plasma Laboratory) Associates, Inc., and the University of Illinois at Urbana-Champaign (UIUC) have partnered to address these challenges and are currently working on developing a national facility that will become the niche for the design and development of advanced free surface flowing liquid modules for future fusion systems.

Figure 1.  FLIRE major vacuum components consist of two chambers each with a turbomolecular pump and CTI cryogenic pump.  A liquid-metal injection system (LMIS) is designed to inject liquid lithium at about 1-10 m/sec flow velocities.

Currently the Flowing Liquid-surface Illinois Retention Experiment (FLIRE) at the UIUC is investigating some of the issues outlined above using an ion source.  A picture of the current design is shown in figure 1.  The experiment, which is already funded, is investigating fundamental processes of the retention and pumping of He, H and other gases in flowing liquid surfaces.  Phase I of this proposal will therefore extend the capability of FLIRE by replacing the ion source with a dc plasma source and adding magnetic field coils to simulate conditions in a future fusion device.  The new facility, under the direction of NPL Associates, Inc. and in conjunction with the University of Illinois, would then test, evaluate and qualify potential free surface liquid designs as PFC’s of future fusion devices in addition to deepening a physical understanding of the interaction of plasma and free surface flowing liquids.

Following the success of Phase I, NPL will progress towards the development of a free surface flowing liquid module that will be commercially available to modern experimental fusion devices.  The experimental efforts in both Phase I and Phase II carried out by NPL and the University of Illinois personnel will be complemented by the close relationship with modelers and theoreticians at the Argonne National Laboratory (ANL) and Princeton Plasma Physics Laboratory (PPPL).

Related Links:

Advanced Limiter/Divertor Plasma-Facing Systems group website

The Virtual Laboratory for Technology

ALIST: Applications of Liquid-Plasma Interactions Science and Technology

Advanced Power Extraction website

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