Polhe3 Metal Windows
Window & Glass-Metal Seal Pressure Test Setup
- Investigating the possibility of using Larson Electronic Glass brand glass to metal seals as a means to couple metal windows to glass target chamber.
- Pressure test setup was assembled at UVa to test glass to metal seals at typical target cell operating pressures.
- Initial test on a Larson CP-100-T Pyrex glass to Copper metal seal (1-inch O.D.) performed on Nov 16 & 17, 2011. Test piece was pressurized to approximately 10-atm (137 psig) of argon for 24hrs. This pressure was our regulator's limit. The glass to metal seal did not explode. Although, 10-atm is low (typical target operating pressure is 12-atm to 13-atm). No leak tests on the seal have been performed during this initial pressure test. We still need to establish that gas will not leak thru seal at high pressures.
- During Jan 21 thru 25, 2012, the CP-100-T piece was pressure tested again using a higher limit regulator. It survived pressures greater than 21-atm (300 psig).
- In the future, we will investigate whether it is possible to make a GE180 glass to metal seal and if it will stay leak tight at high pressures.
- Ultimately, we would like to place a thin metal window (such as beryllium) on the metal end and then pressure test both the metal window and the glass to metal seal at pressures greater than 13-atm.
GE180 Glass-Metal Seals
We prefer to have GE180 glass as part of our glass to metal seals mainly to cut down on helium permeability thru the glass material. Approximately, the density in a typical 3He target cell will drop 10% every two months for Pyrex but only 10% every 100 years for aluminosilicate (ie. C1720 or GE180). We asked Larson Electronic Glass to experiment with sealing GE180 glass to their metal tubes. They successfully performed the following in house:
- Seal GE180 glass directly to stainless steel.
- Seal GE180 glass to copper via a minimal amount of Corning 7052 transition glass.
Beryllium Foil Material
The company Materion Electrofusion supplies various purity Be foil for the X-ray window industry. They provide the following grades:
- IF-1 Beryllium High Purity Foil - 99.8% Be with surface roughness Ra=40 microinches
- PF-60 Beryllium High Purity Foil - 99.0% Be with surface roughness Ra=63 microinches
- PS-200 Beryllium Standard Purity Foil - 98.5% Be with surface roughness Ra=63 microinches
Initial efforts at UVa to determine Be-window feasibility included providing Materion Electrofusion with a proposed Be-window end cap design in Feb 2012. They could produce a copper frame onto which the beryllium foil material would be fused using a silver based braze. Then the copper frame would be electron beam welded onto the copper-glass seal. This two step process is necessary to avoid melting the glass on the seal if one were to braze the window on directly. Also, since the Be-window aperture is to be smaller than the diameter of the glass-metal seal, a frame is necessary to accommodate the beryllium foil via their proprietary coupling method. The cost for small (large) quantities is approximately $1900 ($1100) each window assembly with 10 mil (0.010-inch) thick PS-200 material. An actual order has not yet been placed (as of April 2012).
Materion Electrofusion also provides design guidance via online publications. Here are some links: