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Registered Member #118
Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72
I just got around to putting a video clip on You Tube of an 18" x 18" x 1" Plexiglas specimen being discharged to form a large Lichtenberg Figure. This particular specimen was brought and discharged by local coiler Jeff Larson during our 2005 production run. It was charged using a commercial 5 MeV linear accelerator (LINAC). The estimated potential of the internal charge plane was around 2.2 million volts. You can also see a large number of secondary discharges right after the main discharge. On large specimens secondary discharges can sparkle and sizzle for 10-20 seconds afterwards as residual charges are redistributed within the specimen. Larger specimens must be treated with respect - the peak discharge current is estimated to be 2 - 4 kA, and the electrostatic energy stored within the specimen was estimated at about 1800 joules. Later this year I hope to add some videos from our 2006 run, including video clips of specimens actually being irradiated. When the electron beam hits the specimens, the acrylic glows a brilliant blue color from fluorescence (and possibly some Cherenkov radiation?). Terry Blake captured the video and created the following clip.
Registered Member #118
Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72
uzzors wrote ...
Thats awesome Bert, I've always wondered what the discharge looks like when they are made.
Unfortunately, the camera doesn't really capture the brilliance of the flash or the sound. It's similar to a loud capacitor discharge but somewhat muffled by the acrylic.
Steve Ward wrote ...
I remember that one!
Did you have any luck with large figures this past run, Bert?
We had the best results ever. We tweaked the beam parameters and cooled the material (the run was done on 12/1/07) to reduce leakage current. We ended up using almost 8 hours of beam time to do about 1400 specimens. We also were able to capture a discharge current waveform from a 4" x 4" x 3/4" specimen using a Pearson CT and a DSO. The peak current was about 200 amperes, lasting about 600 nsec. We were also able to pick up some current pulses from secondary discharges. We did a few 3 foot by 4 foot specimens, and these also turned out much better than last year, but not perfect (as yet). We rotated spheres and cylinders while they were being irradiated and got excellent results. The 3D cubes turned also turned out great. We did a few 4" cubes and 4" spheres as experiments, and we learned a lot that we can apply to improve our results the NEXT time. I found out (the hard way) that a hickory handled hammer doesn't always provide protection from getting zapped. And, we had a lot of fun!
EastVoltRe wrote ...
Awesome Bert. Was that Jeff Larson's voice I heard?
Hi Dan - yes it was! Jeff sanded and polished the specimen while we were at the facility, and that was also Jeff discharging it. It was one of the best figures done that day.
Registered Member #118
Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72
Conundrum wrote ...
Spheres, interesting. What do those look like?
-A
In a word - Beautiful! We end up creating a spherically charged region inside the sphere so that many of the discharges follow the curvature of the sphere. We also get some discharges that go straight through the center of some spheres. The 2" and 3" spheres can be seen on the following pages:
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Short video clip of an 18" square Lichtenberg Figure being discharged
