Sheng Wang’s research while affiliated with Aerospace Information Research Institute, Chinese Academy of Sciences and other places

Non-evaporable getter (NEG) films are extensively employed in particle accelerators to attain and sustain ultra-high vacuum (UHV) and extremely high vacuum (XHV) conditions. This study primarily focused on studying the adsorption characteristics of the main residual gas-H 2 molecules in the vacuum system on the Ti-Zr-V-Hf (110) NEG surface. To carry out this analysis, we employed the first-principles Density Functional Theory (DFT). The adsorption energies of 23 distinct adsorption sites, and particularly the electronic structure of the adsorption sites with the highest absolute adsorption energies (Zr, Ti-V, Hf-V, and Ti-Hf-V), were analyzed by partial density of states (PDOS) and Mulliken charge and bond overlap population calculations. The results of our investigation revealed that the order of effectiveness of adsorption sites is as follows: bridge > hollow > top. Based on the adsorption energy results, it can be inferred that there are strong chemical interactions between H atoms and Ti-Zr-V-Hf (110) surface metal atoms at Zr, Ti-V, Hf-V, and Ti-Hf-V adsorption sites. The results of PDOS calculations also indicate that there is strong hybridization between the H 2 molecule and the Ti-Zr-V-Hf (110) surface at each studied adsorption site, demonstrating the formation of strong chemical bonds between them. The Mulliken charge and bond overlap population and electron density difference analyses show significant changes in charge distribution between H atoms and Ti-Zr-V-Hf (110) surface metal atoms before and after H 2 adsorption at each studied adsorption site, suggesting the occurrence of chemisorption. Additionally, covalent bonds are formed between H atoms and Ti-Zr-V-Hf (110) surface metal atoms at these sites. This study uncovered specific adsorption sites where the H 2 molecule interacts most efficiently on the Ti-Zr-V-Hf (110) surface and where high-energy bonds are formed. These findings can provide a potential pathway to improve the adsorption efficiency of quaternary Ti-Zr-V-Hf NEG films.

In order to enhance the performance and lifetime of the lithium target used in accelerator-based neutron sources for Boron Neutron Capture Therapy (BNCT) treatment, an exploration of target design was conducted based on the 2.8 MeV, 20 mA proton beam. A comparison between scanning magnets and octupole magnets was performed for beam uniform, with octupole magnets selected to effectively avoid localized high thermal densities over short durations. Exploration was conducted on the performance of tantalum and vanadium as interlayers within the lithium target, considering aspects such as cooling, hydrogen diffusion, and neutron performances. This study revealed that, as the majority of energy deposition occurs within the interlayer, the presence of an appropriately thick tantalum or vanadium interlayer has minimal impact on cooling effectiveness, ensuring temperatures remain below 144 ° C. The addition of an interlayer effectively reduces the maximum hydrogen concentration in copper, thus preventing copper blistering. Within the investigated thickness range, the interlayer does not affect neutron spectrum in the forward direction of the target, mitigating concerns regarding its impact on beam shaping.

The performance of next-generation particle accelerators has been adversely affected by the occurrence of electron multipacting and vacuum instabilities. Particularly, minimization of secondary electron emission (SEE) and reduction of surface resistance are two critical issues to prevent some of the phenomena such as beam instability, reduction of beam lifetime, and residual gas ionization, all of which occur as a result of these adverse effects in next-generation particle accelerators. For the first time, novel quinary alloy Ti–Zr–V–Hf–Cu non-evaporable getter (NEG) films were prepared on stainless steel substrates by using the direct current magnetron sputtering technique to reduce surface resistance and SEE yield with an efficient pumping performance. Based on the experimental findings, the surface resistance of the quinary Ti–Zr–V–Hf–Cu NEG films was established to be 6.6 × 10⁻⁷ Ω m for sample no. 1, 6.4 × 10⁻⁷ Ω m for sample no. 2, and 6.2 × 10⁻⁷ Ω m for sample no. 3. The δmax measurements recorded for Ti–Zr–V–Hf–Cu NEG films are 1.33 for sample no. 1, 1.34 for sample no. 2, and 1.35 for sample no. 3. Upon heating the Ti–Zr–V–Hf–Cu NEG film to 150 °C, the XPS spectra results indicated that there are significant changes in the chemical states of its constituent metals, Ti, Zr, V, Hf, and Cu, and these chemical state changes continued with heating at 180 °C. This implies that upon heating at 150 °C, the Ti–Zr–V–Hf–Cu NEG film becomes activated, showing that novel quinary NEG films can be effectively employed as getter pumps for generating ultra-high vacuum conditions.