DC Magnetic Shield for Thomas Jefferson National Accelerator Facility

VitaTech was contracted by the Department of Energy to remove an existing DC shield that was improperly designed in an area where a NASA cyclotron was once located. Over a 20 year period steel rebar and I-beams in the building and adjacent concrete radiation blocks were magnetized. VitaTech designed, installed, tested and certified a 2,500 sq. ft. DC magnetic shield with a 0.5 G (500 mG) shielding performance guarantee similar to the earth's geomagnetic field as required by the researchers.

Inside the existing shield the mean (average) static DC magnetic fields were 1.8 Gauss (G) on the floor with a peak of 4.7 G near the south wall. Levels jumped to 3.1 G (mean) and 6.2 G (peak) when the existing 3/8-inch thick low-carbon steel plate shield was removed. The calculated mean (average) shielding factor (SF) was about 5 dB for the existing shield.

The final performance test after VitaTech's DC shield was installed revealed a substantial attenuation of the DC magnetic fields with a mean of 0.175 G achieving our 0.5 G guarantee, which is a 25 dB shielding factor (increase of 20 dB). VitaTech also designed and installed an automated degaussing system (see wires on the shielded walls) to restore shielding performace every four to eight years as the DC shield naturally magnetizes over time.

VitaTech left the front of the DC shield open providing researchers easy access to the shielded test area. Although elevated levels up to 1.6 G were recorded at the front entrance, emissions rapidly decayed to 0.3 Gauss 1-m inside the shield. Several areas at 1-meter above the floor approach 0 mG: remarkable shielding performance without using highly permeable & expensive mumetal (nickel-iron alloy) materials.

Project Data

Existing Shield Site Survey 3-D Contour Plot Existing DC Magnetic Shield

Previous shield removed 3D contour plot- previous shield removed

New DC Shield Site Survey
3-D Contour Plot After New DC Magnetic Shield Installed By VitaTech

Slideshow

Magnetic Shield Images

Previous DC shield - 2 Gauss average inside shielded area. VitaTech removed this shield and applied a new shield.

Completed DC shield - with degaussing system