The development of a manufacturing plan for the alu-minum straight section vacuum chambers of the Siam Photon Source-II (SPS-II) was undertaken through a multi-stage prototyping program. This work began with the successful reduction of the internal surface roughness (Ra) of domestically produced aluminum extrusions from approximately 19.9 µm to below 0.42 µm by polishing the extrusion die. A dedicated prototype was then used to validate fundamental Ultra-High Vacuum (UHV) processes, confirming the integrity of in-house Tungsten Inert Gas (TIG) welding and establishing a baseline for the chemical cleaning procedure via Photon Stimulated Desorption (PSD) measurements, which showed the cleaning provided an acceptable baseline but requires further optimization. Subsequent full-scale fabrication trials revealed critical lessons. An initial build without a fixture resulted in both significant deformations, confirming the need for mechanical support, and contaminated welds, highlighting the importance of meticulous in-process cleaning. A second trial with a first-generation fixture solved the deformation but caused weld penetration due to obstructed tool access. This iterative development process successfully identified the key challenges of fabrication and has resulted in a de-risked manufacturing methodology, based on an optimized cleaning protocol and a purpose-built fixture, for the final production chambers.
Phimsen et al. (Thu,) studied this question.