Gas permeation through a high density polyethylene microwave window

Journal Article · Thu Jul 01 04:00:00 EDT 1993 · Journal of Vacuum Science and Technology, A (Vacuum, Surfaces and Films); (United States)

DOI:https://doi.org/10.1116/1.578508· OSTI ID:6290179

Nguyen-Tuong, V ^[1]

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1. Continuous Electron Beam Accelerator Facility, Newport News, Virginia 23606 (United States)

Due to its low dielectric constant and low loss tangent, high density polyethylene (HDPE) has been selected for use as a high power microwave vacuum window in the Continuous Electron Beam Accelerator Facility cryounit. This window isolates the cryounit waveguide vacuum from the dry air in the external waveguide system. Gas permeation through the window will lead to cryopumping of the gas onto the cold waveguide walls and the cold ceramic window of the superconducting cavity. The gas load from permeation and outgassing of the window have to be minimized, due to the possibility of arcing when high power is applied through the waveguide. The outgassing and permeation of air through the 3.2 mm thick HDPE window were measured using the throughput method. A typical outgassing rate of 5.0[times]10[sup [minus]10] Torr l/s/cm[sup 2] for samples baked out at 70 [degree]C was observed 20 h after pump down and bakeout. The gas load due to permeation through 34 cm[sup 2] of the window was 1.6[times]10[sup [minus]7] Torr l/s. The gas permeation through the 3.2 mm thick HDPE coated with a 300 nm barrier layer of SiO[sub [ital x]] was also investigated. No improvement was observed. It was presumably due to the presence of defects in the deposited SiO[sub [ital x]] layer.

• DOE Contract Number: AC05-84ER40150
• OSTI ID: 6290179
• Journal Information: Journal of Vacuum Science and Technology, A (Vacuum, Surfaces and Films); (United States), Journal Name: Journal of Vacuum Science and Technology, A (Vacuum, Surfaces and Films); (United States) Vol. 11:4; ISSN 0734-2101; ISSN JVTAD6
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
430100* -- Particle Accelerators-- Design
Development
& Operation
ACCELERATORS
CAVITY RESONATORS
CEBAF ACCELERATOR
CHALCOGENIDES
COATINGS
CRYOPUMPS
DEGASSING
ELECTRONIC EQUIPMENT
EQUIPMENT
LABORATORY EQUIPMENT
LINEAR ACCELERATORS
OPENINGS
ORGANIC COMPOUNDS
ORGANIC POLYMERS
OXIDES
OXYGEN COMPOUNDS
PERMEABILITY
POLYETHYLENES
POLYMERS
POLYOLEFINS
PUMPS
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SILICON COMPOUNDS
SILICON OXIDES
SUPERCONDUCTING CAVITY RESONATORS
SUPERCONDUCTING DEVICES
VACUUM PUMPS
VACUUM SYSTEMS
WAVEGUIDES
WINDOWS