Invited Paper VT-TuA9
Plasma Window as Vacuum Atmosphere Interface for Various Applications

Tuesday, October 23, 2018, 5:00 pm, Room 203B

The Plasma Window is a novel apparatus that utilizes a stabilized plasma arc as an interface between vacuum and atmosphere or pressurized targets without solid material. In addition to sustaining a vacuum atmosphere interface, the plasma has a lensing effect on charged particles. The plasma current generates an azimuthal magnetic field, which exerts a radial Lorentz force on charged particles moving parallel to the current channel. With proper orientation of the current direction, the Lorentz force is radially inward. This feature can be used to focus in beams to a very small spot size, and to overcome beam dispersion due to scattering by atmospheric atoms and molecules

The best results to date have been the following:

1. Vacuum (pressure of ~ 10^-6 Torr) was successfully separated from atmosphere and from a gas target pressurized up to 9 bar.

2. A 2 MeV proton beam was propagated from vacuum through the plasma window into atmospheric pressure with no measurable energy loss or beam degradation.

3. A 175 KeV electron beam was transmitted from vacuum through the plasma window to atmospheric pressure.

4. Successful transmission of X-rays from a light source to atmosphere.

5. Compatibility tests for transmission of electromagnetic radiation indicated that the plasma window does not generate electromagnetic interference, and that X-rays (away from resonance) are transmitted with negligible attenuation.

6. Electron beam welding in atmosphere (by an electron beam passing from vacuum through a plasma window) was accomplished with electron beams of unprecedented low power. Weld quality for the non-vacuum plasma window electron beam welding matched the quality of in-vacuum electron beam welding.

7. Internal gas stripper of ½ atmosphere helium confined by 2 plasma windows in accelerator vacuum.

Many industrial processes like electron beam welding and melting, as well as, ion material modification have low production rates due to required pumping time, and limits on the size of target objects. Utilization of the plasma arc as a window for targets removes these limitations and increases production rates. Other applications that can greatly benefit from plasma windows are those involving transmission of intense radiation or particle beams like high power lasers or deep ultraviolet photolithography sources, internal gas targets and beam dumpds. Plasma windows are practically completely transparent to high-energy particles and radiation, and unlike conventional windows, plasma windows are completely impervious to thermal damage.