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 pressure/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).
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 would 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 method. The cost for small (large) quantities is approximately $1900 ($1100) each window assembly with 10 mil (0.010-inch) thick PS-200 material.
Materion Electrofusion also provides design guidance via online publications. Here are some links:
