Transpirational First Wall Cooling via Lithium Phase Transition
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Solution Overview
Problem
Plasma chambers face structural damage and plasma contamination due to refractory metals like tungsten melting during unstable events, causing energy deposition and atom evaporation, which existing coatings like lithiumization or boronization only partially mitigate.
Innovation Solution
A first wall structure with a refractory metal inner wall and a solid deposit of lithium or tin, where the deposit's boiling point is lower than the metal's melting point, allowing for transpirational cooling by melting and evaporating to absorb heat before the metal melts, and a refilling system for longer-term use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a refractory metal inner wall is used to withstand high temperatures, then structural strength is improved, but the metal melts during unstable events causing structural damage and plasma contamination
Solution Approach 1:
The patent utilizes the phase transition of lithium from solid to liquid to gas. During unstable events, the lithium deposit melts and then evaporates, absorbing large amounts of heat through latent heat of vaporization. This phase transition occurs before the refractory metal melts, protecting the structural integrity of the inner wall while managing the thermal load from plasma contact.
Solution Approach 2:
The lithium deposit acts as an intermediary layer between the plasma and the refractory metal inner wall. During unstable events, the lithium absorbs heat and evaporates, preventing direct heat transfer to the refractory metal structure. This intermediary substance protects the structural wall from thermal damage while the evaporated lithium atoms are less harmful to plasma than refractory metal atoms.
2Quantity of substance
If lithiumization or boronization coating is applied to reduce contamination, then plasma purity is improved, but the coating wears down during unstable events and does not prevent structural damage
Solution Approach 1:
The lithium deposit is designed to undergo phase transitions during unstable events, melting and evaporating to absorb heat. This controlled phase change provides a sacrificial mechanism that protects the underlying refractory metal structure, while the evaporated lithium atoms are lighter and less damaging to plasma than tungsten atoms would be.
Solution Approach 2:
The patent changes the physical state parameters of the lithium deposit dynamically. During normal operation, the lithium remains solid and maintains the first wall structure. During unstable events, the lithium transitions to liquid and then gas phase, absorbing thermal energy and protecting the structure. This parameter change allows the same material to serve multiple protective functions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively keeps the refractory metal cool, reduces structural damage, and minimizes plasma contamination by using lithium's latent heat and low atomic mass to absorb energy during events, with a refilling system ensuring continuous operation.
Implementation Method 1
using lithium's latent heat and low atomic mass to absorb energy during events
Implementation Method 2
the deposit's boiling point is lower than the metal's melting point, allowing for transpirational cooling by melting and evaporating to absorb heat
Implementation Method 3
transpirational cooling by melting and evaporating to absorb heat
Data Source
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AI summary
A first wall structure for a plasma chamber (200). The first wall structure comprises and inner wall (201) and a solid deposit (202). The inner wall is formed from a refractory metal or an alloy or composite thereof and has a plurality of pores. The solid deposit in thermal contact with the inner wall, such that the plurality of pores provide a passage from an exterior of the first wall structure to the deposit. The deposit consists of a material having a boiling point less than a melting point of the refractory metal. The first wall structure is configured such that at a normal operating temperature of the first wall structure, the deposit is solid.