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Fall 2013 Lichtenberg Run

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Bert

Sun Nov 24 2013, 06:20PM

Registered Member #118 Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72

Hi All,

On November 15th, a dozen physicists, engineers, teachers, and artists from seven states convened at a 5 million volt, 150 kW electron beam facility located in Ohio. This skilled band of "Spark Whisperers" was there to help wrangle electrons during the Fall 2013 Lichtenberg Run. During this marathon run, which used 11.5 hours of "beam time", we irradiated over 1,100 specimens and conducted a large variety of experiments. Some of the more interesting specimens included three huge 15" x 20" x 2" slabs, three machined acrylic guitars, a batch of 14-sided "cubeoctahedrons", and a number of 12" x 12" x 1" 3D masked slabs with two interactive charge layers. We also captured HD videos of some of the larger specimens as they were manually discharged. And, we set up a small HD video camera (RadCam II) to capture HD video of specimens while they were being irradiated by the beam. Following are links to some of the images and videos from the run.

The first image is of physics student Heidi Baumgartner (from oneTesla) basking in the thermoluminescent glow of a large calcite rhomb. The crystal continued to glow brightly for many hours afterwards. The specific color is thought to be from traces of manganese impurities in the crystal structure. Purer calcite (such as Iceland Spar) hardy glows at all.

Following is an experimental 6 x 6 x 1/2" specimen of Lexan polycarbonate (PC). Most of the Lichtenberg figures we produce are made from polymethylmethacrylate (PMMA, or acrylic), and figures in acrylic consist of chains of whitish or mirror-like tubes and fractures. However, PC specimens develop a very finely-branched black Lichtenberg figure inside. Polycarbonate is considerably tougher and more difficult to fracture than acrylic. As the spark channels succeed in blasting their way through the PC, they're constrained to be smaller in diameter than those in PMMA. This causes the energy density within the spark channels to be considerably higher than in PMMA. The walls surrounding the channels become carbonized, creating the black Lichtenberg figure. Because PC is a bit leakier than PMMA, the PC specimens were chilled using dry ice before irradiating them. Note the color change (solarization).

The next specimens used pairs of lead masks and multiple passes through the beam to create two interdigitated charge layers within 12" x 12" specimens. The two charge layers then spark to each other during the discharge process, creating very complex linked interactions between the larger regions defined by the masks.

Following are a couple of different views of an experimental "cubeoctahedron". This is actually the same specimen being viewed from two different angles. The specimen was physically rotated while it was being irradiated using a shielded, battery-powered "hotdog turner".

Following is one of the acrylic guitars we irradiated. Since they were all pre-machined, they all self-discharged as they passed through the beam.

We also captured some HD video clips, a couple of which have been uploaded to YouTube. The first shows a 15" x 20" x 2" specimen being discharged, and the numerous secondary discharges that follow as stranded pockets of residual charge dump into the main spark channels. These small discharges continued, with decreasing frequency, for over 30 minutes afterwards:

Following is a frame grab of one of these huge specimen at the instant it was discharged, showing the brilliance of the discharges. The stored energy in this specimen was estimated to be ~4 kilojoules at charge plane potentials of ~2.5 million volts. The estimated peak discharge current was ~6,300 A. And yes, it does make a very satisfying BANG! Charged specimens of this size are treated with the utmost respect. During the charging process, the partially-charged (2 kj) specimen had to be manually flipped 180 degrees so that the other side could be irradiated. The e-field from these makes the hairs stand up on your arms very nicely... :)

1385314831 118 FT0 Large Discharge Capture6566a

Finally, the last video clip was captured using a shielded HD video camera (RadCam II) looking down on an acrylic guitar as it was transported into, and through, the electron beam. The camera setup was built by one of our team members, Todd Johnson, from FermilLab. Although quite noisy, the image of the guitar self-discharging as it is hit by the electron beam can easily be seen (and heard). However, it looks like our camera need a wee bit more shielding. :^)

Finally, here is another 3D sculpture in a 12" x 12" x 1.5" slab using interdigitated lead masks and two passes through the beam. These are incredibly beautiful when seen in real life. A 2D picture simply does not do it justice...

Physics is Fun!!

Bert

Shrad

Sun Nov 24 2013, 06:47PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

yay! put an RGB LED in each cavity with a sandblasted cover to diffuse light a bit, and you've got a killer stage display!

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