Speaker
Description
Negative helium (He⁻) ion beams combined with tandem accelerators are used in research and industrial processes such as accelerator mass spectrometry and power semiconductor manufacture. The established production method involves double-charge exchange between a positive helium (He⁺) beam and a low-pressure metal vapour, typically an alkali. While this method achieves effective conversion rates of 1% to 5%, it introduces mechanical complexities and contamination issues. Specifically, maintaining the necessary low-pressure environment requires additional pumping capacity, and creation of the metal vapour typically requires an oven and system within the vacuum envelope to vaporize, condense, and recirculate the metal. Additionally, migrating alkali metal vapours can contaminate downstream processes. To address these equipment challenges, our research investigates the use of nanometer-thick solid foils (nano-foils) as an alternative charge-exchange medium.
In our previous studies, we utilized a helium ion microscope (HIM) equipped with a magnetic dipole and a CMOS radiation camera to measure charge uptake efficiencies [P.Jackle et al, 2026, "Production of negative helium ions via transmission through nano-foils", J. Phys. Conf. Ser. 3237 012061]. By transmitting a 30 keV He⁺ beam through various nano-foils, including carbon, gold, palladium, platinum, silicon dioxide, silicon nitride, and titanium oxide, we found that most materials yielded a relatively uniform He⁻ production ratio of approximately 0.02%, whereas we had anticipated substantially different production ratios.
Here we shall describe our experimental campaign aimed at a deeper understanding of the production ratio mechanisms. We discuss measurements of He⁻ production ratios using He⁺ energies of 35, 25, and 20 keV with all previously explored nano-foils. New measurements will also be presented with additional thicknesses of carbon nano-foils, increasing from single-layer graphene. By comparing these new thicknesses and varying beam energies against our established 30 keV baseline, we aim to provide deeper insight into surface versus bulk charge-exchange mechanisms and further evaluate the feasibility of nano-foils for He⁻ ion beam production.
| Email address | pjackle@sfu.ca |
|---|---|
| Funding Agency | NSERC |
| Visitor's Visa | no |
| Classification | Other negative ion sources for fusion, accelerators, and other applications |