Simplified Isolation for High- and Low-Vacuum Environments

Simplified Isolation for High- and Low-Vacuum Environments

Using low-power pumps and vapor-barrier technology for open-hole connections

NASA invites companies to license this innovative vapor barrier system (VBS) that provides a simple, low-cost approach for connecting a high-vacuum environment to a low-vacuum (i.e., high-pressure) environment without the need for expensive, high-capacity mechanical pumps. This proven, patent-pending technology uses the principles of supersonic free expansion to create a vapor barrier between the environments. This approach provides a truly “open hole” vacuum-pressure connection. The VBS maintains a pressure barrier so that an electron or ion beam may be generated in a high-vacuum environment and then passed into a partial-pressure environmental chamber for more versatile material processing. Initially developed for NASA’s e-beam freeform fabrication (EBF3) system, this technology is useful in any application where an electron/ion beam or material must pass from one vacuum/pressure environment to another.

Additional technical details are presented below. For more information about this licensing and joint development opportunity, please contact us by e-mail or phone: or (919) 249-0327.

NASA created this technology (as well as other related technologies) as part of its effort to develop an EBF3 system for manufacturing large, complex parts in remote locations. However, this technology is applicable beyond EBF3.

Like other systems that connect two environments with differing vacuum/pressure levels, NASA’s EBF3 system passes an electron beam from a high-vacuum chamber to a low-vacuum chamber, to melt a metal wire in a layer-by-layer deposition-based fabrication process. (Deposition can take place in the high-vacuum chamber—and, indeed, many systems of this type do so—but this requires a larger chamber and, therefore, greater pumping capacity.)

The traditional options for maintaining vacuum levels when passing a particle or material between the environments are: (1) having a small opening and large vacuum pumps, providing extra pumping to compensate for the leaks; or (2) using an electrical field to create a “plasma window/shield” that maintains the vacuum but requires additional energy be applied to the beam to “push” it through the plasma “membrane.”

NASA’s VBS allows for a truly open hole between the two environments, but it does not require extra pumping to maintain the vacuum or impede the beam’s passage through the hole. In short, the technology provides a cost-effective barrier that isolates a high-vacuum environment from a lower one.

How It Works

NASA’s VBS technology isolates the two environments using a vapor-barrier approach. The isolation barrier is created by injecting a condensable vapor into an aerodynamically designed nozzle that is surrounded by a Meissner coil-type cold trap. Free-jet supersonic flow expansion occurs, resulting in an invisible wall that divides the two environments and enables differing vacuum levels to be maintained.

Why It Is Better

The VBS is less expensive than other techniques for isolating differing vacuum/pressure environments because it eliminates the need for expensive, high-capacity mechanical pumps to maintain vacuum levels. It also requires far less power than a plasma window and offers much better beam transmission, with minimal losses compared to an ion/e-beam passing through a plasma window. The supersonic expansion VBS nozzle design allows for a sharp pressure gradient, decreasing the scattering, defocusing, and attenuation problems that can occur in ion/e-beam applications.

The advantages that the VBS has demonstrated in NASA’s EBF3 system are relevant to other ion/e-beam fabrication systems. For example, the VBS allows the part to be fabricated in a separate chamber from the beam. Although formerly a large, high-vacuum chamber was needed to accommodate the entire process, now the high-vacuum environment surrounds only the “head” of the electron gun, allowing the low-vacuum chamber where the part is formed to be essentially unrestricted in size (see graphic below). This dramatic decrease in the size of the high-vacuum chamber yields significant cost savings as well as shortens set-up and teardown time. In addition, because the VBS enables feedstock to be resupplied without having to open the high-vacuum chamber, the EBF3 system can higher throughput with virtually nonstop processing.

With further development, the VBS technology is expected to allow the EBF3 gun head to become sufficiently small enough to place on the end of a robotic arm, enabling very large and significantly complex shapes to be built.

Simplified Isolation for High- and Low-Vacuum Environments

Using low-power pumps and vapor-barrier technology for open-hole connections

How It Works

Why It Is Better

Patents