Diamond Shell Fabrication for Laser Fusion Targets
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Solution Overview
Problem
Producing hollow fuel shells of uniform size, shape, and thickness for laser fusion is challenging due to plasma instabilities caused by high-powered lasers, which create energetic electrons that penetrate fuel pellets prematurely, leading to uneven heating and compression difficulties.
Innovation Solution
A method for fabricating spherical shells with a closed, uniform diamond layer of nanocrystalline diamond film, achieved by depositing diamond films on spherical substrates using a vacuum chamber system with a rotating substrate holder and removing the substrate through micron-sized holes using focused-ion-beam etching or optical irradiation, resulting in shells with surface roughness less than 400 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-powered lasers are used to implode fuel pellets for laser fusion, then fusion reactions can be initiated, but plasma instabilities occur causing energetic electrons to penetrate the core prematurely and create uneven heating
Solution Approach 1:
The fuel pellet is segmented into a hollow shell structure with a cavity interior, allowing the laser ablation pressure to act over a larger area and volume for a longer time, reducing the need for high laser intensity and minimizing plasma instabilities
Solution Approach 2:
A diamond coating layer is applied as an intermediary between the laser plasma and the fuel core, providing a stable ablation surface that reduces plasma instabilities and prevents premature electron penetration into the core
2Use of energy by moving object
If hollow fuel shells are used to increase ablation pressure duration and area, then less laser intensity is needed, but producing uniformly sized and shaped hollow spheres of consistent thickness is difficult
Solution Approach 1:
A substrate structure is created beforehand with the desired hollow spherical geometry and uniform thickness, providing a precise template upon which the diamond coating is deposited, ensuring consistent shell dimensions before the coating process
Solution Approach 2:
The substrate is rotated during the coating deposition process, changing its orientation parameters continuously to ensure uniform coating thickness distribution across the entire hollow shell surface
3Strength
If a diamond coating is applied to resist abrasive degradation and absorb mechanical stresses, then the shell gains hardness and stress resistance, but the coating process adds complexity to the manufacturing
Solution Approach 1:
A composite structure is created by combining the substrate material with a diamond coating layer, leveraging the high hardness and stress resistance of diamond while maintaining the structural integrity of the substrate, achieving enhanced mechanical properties through material composition rather than complex processing
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
The produced diamond shells resist abrasive degradation, absorb mechanical stresses, and can be optically transparent, enabling their use in ball bearings, inertial fusion targets, and other applications while maintaining uniformity and chemical stability.
Implementation Method 1
depositing diamond films on spherical substrates using a vacuum chamber system
Implementation Method 2
removing the substrate through micron-sized holes using focused-ion-beam etching
Implementation Method 3
removing the substrate through micron-sized holes using focused-ion-beam etching or optical irradiation
Data Source
AI summary
A novel method for fabricating diamond shells is introduced. The fabrication of such shells is a multi-step process, which involves diamond chemical vapor deposition on predetermined mandrels followed by polishing, microfabrication of holes, and removal of the mandrel by an etch process. The resultant shells of the present invention can be configured with a surface roughness at the nanometer level (e.g., on the order of down to about 10 nm RMS) on a mm length scale, and exhibit excellent hardness/strength, and good transparency in the both the infra-red and visible. Specifically, a novel process is disclosed herein, which allows coating of spherical substrates with optical-quality diamond films or nanocrystalline diamond films.