Calcium and lithium ion production for laser ion source

Area of Science:

• Materials Science
• Plasma Physics
• Space Science

Background:

• NASA Space Radiation Laboratory requires calcium and lithium ion beams for cosmic radiation simulation.
• Highly reactive materials like calcium and lithium present challenges as laser targets due to oxidation.

Purpose of the Study:

• To investigate difficulties in providing reactive calcium and lithium targets for laser-induced plasma generation.
• To assess oxygen contamination in ion beams resulting from target oxidation.

Main Methods:

• Fabricated plate-shaped lithium and calcium targets.
• Used a 6 ns, 1064 nm neodymium-doped yttrium aluminum garnet laser to create ablation plasmas.
• Employed a large spot size, low power density laser to generate low charge state beams and study oxidation rates.

Main Results:

• Significant oxygen contamination was observed in high charge state calcium and lithium beams due to rapid surface oxidation.
• Low power laser treatment of calcium targets resulted in beams without apparent oxygen contamination, suggesting effective oxide removal.
• Lithium targets continued to oxidize even after low power laser exposure, with oxidation rate linearly related to interval time between laser shots.

Conclusions:

• Rapid oxidation of lithium and calcium targets is a significant challenge for generating pure ion beams.
• Low power laser cleaning shows potential for calcium targets but is insufficient for lithium targets, indicating a need for improved oxidation mitigation strategies.
• Understanding and controlling oxidation is crucial for reliable space radiation simulation using laser-produced plasmas.