NSTX-U Machine Core Vacuum Seals Upgrade Design

Journal Article · Wed May 11 00:00:00 EDT 2022 · IEEE Transactions on Plasma Science

DOI:https://doi.org/10.1109/tps.2022.3172568· OSTI ID:1869947

Cai, Feng ^[1]; Smith, Mark ^[1]; Blanchard, William ^[1]; Cai, Dang ^[1]; Hennessy, Jamie ^[1]; Zhang, Han ^[1]; Loesser, Douglas ^[1]

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1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

The vacuum in the National Spherical Torus Experiment Upgrade (NSTX-U) is in the range of 2.66x10⁻⁶ Pa (2x 10⁻⁸ torr). To enhance vacuum seals and lower gas permeation in the NSTX-U and therefore ensuring operation safety and quality, the machine core vacuum seal design has been upgraded using double elastomeric seals and pumped interspaces (guard channels). In NSTX-U machine core, there are six major vacuum seals, including upper and lower vacuum vessel main flanges, upper and lower bellows flanges, and two in the ceramic isolation ring assembly that are mounted to the upper vacuum vessel main flange. The elastomeric seals are commercially available and customized fluorocarbon (Viton) O-rings. To ensure appropriate O-ring compression ratios for the vacuum seal, the O-ring grooves are customized with appropriate tolerances considering specific situations for each seal. In this upgrade, the vacuum in each interspace is designed to reach 13.33 Pa (0.1 torr), thus the overall pressure difference crossing each double O-ring seal is expected to be reduced by at least three orders of magnitude, and accordingly the overall rates of leakage and permeation will be lowered by three orders of magnitude. The corresponding pump-down times for each seal, at room temperature, are estimated at about 60 s. Additionally, the vacuum pumped interspaces will be able to function as a real-time leak monitor.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-09CH11466
• OSTI ID: 1869947
• Journal Information: IEEE Transactions on Plasma Science, Journal Name: IEEE Transactions on Plasma Science Journal Issue: 11 Vol. 50; ISSN 0093-3813
• Publisher: IEEE
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
NSTX-U
ceramics
double o-ring
fluid flow
monitoring
permeation
plasma temperature
pump-down time
pumped interspaces
pumps
seals
structural rings
ultimate pressure
vacuum