This project came about to satisfy several needs, i.e., an indoor arcs & sparks project (won’t frighten the neighbors that way), a desire to study & photograph plasma and I needed a half wave coil for my collection. It began in a research phase last summer when I ran across this quote,” the tip of a plasma tendril will lengthen itself continuously while in the presence of a strong electrostatic field,” and another quote saying similar things about argon. I had wanted to build a half wave coil with a primary wound to the needed inductance, tuning to be done by carefully winding the secondary. It seemed like an elegant design and there’s no ground needed with a bi-polar coil. With that info I pictured an acrylic box of decent size, filled with argon, being blasted on either side with the tc and filled with discharges. I finally turned it on and saw that picture 2-27-01.
This coil was constructed with looks in mind and material selection was the hardest bit. I wanted an antique, carved, wooden chest of medium size and couldn’t find one (I went shopping with $500.00 in hand and struck out). I went to about 50 antique stores and finally was relegated to furniture stores and in a small store full of imported Chinese furniture I found the heavily carved, camphor wood box. It’s 27” long, 13” wide and 11” high with carved feet 3.5” tall supporting the box. I knew that I wouldn’t need much power, so I bought a 9000v 60ma Franceformer with 3-year warranty. That has an impedance of 150,000 ohms, plugging that into the capacitive reactance formula gives 0.01768uF for the tank. I targeted 390kHz for this coil and with the inductive reactance formula saying I needed 9.27uH for the primary, I began to build. The Primary is 3/8” k type cu tubing, six turns at 9.75” diam. The secondary is 4.75” OD phenolic, 33.75” wound with 22-awg mag wire for 34.65mH of inductance. I used a ball type safety gap (purchased from Bill Wysock) over the transformer and no chokes. The gap is between the secondary outputs and is made up of six pieces of two inch long .875” diam. cu tube gapped to 20mils with each being quenched with nitrogen or compressed air. The cap is the most interesting component. I used 0.0043uf, 2500vdc Panasonic metallized polypropylene caps, 105 pieces in 21 series chains (an mmc or multi mini cap design). When completed, it measured 0.01771uF (I’ve an extra 1000 pieces of this cap in factory sealed bags of 100 if anyone’s interested). As long as I set the gaps under 26mils they take the full 9000v with no problem and with sustained operation. Eight minutes is the longest continuous run with several being done back to back. The primary did heat up 3 degrees F over ambient after 15 minutes and I’ll measure the before and after temp of the chamber on my next run. The box is four feet long, three feet tall, and six inches deep, like a big ant farm. The bottom piece is 4’ x 1” x 6” acrylic and is fairly heavy, the sides and faces are 3/8 extruded acrylic although the next one will be cast acrylic. There is a 3/8” hole on one end panel at the bottom for filling, and on the same side on the top panel is a similar hole for exhaust. In the middle of each side panel is a 6” x ½” slot for introducing electrodes and a panel to seal the area. A 50 cu ft bottle at @2500 psi is good for 3 runs. The coil is centered four inches from the face of the cabinet and does not attract the discharge.
The noise level is about 70 decibels and is easily tolerated. It’s a fairly awesome thing to stand in front of this, maybe 3 or 4 feet away. Normal people will cut and run, as this is straight out of Frankenstein’s lab and looks much more dangerous than it actually is. A strong electric field is set up on the outside faces of the box, which limits your proximity to about 1.5 feet. In any closer and you start getting zapped, but it’s only 540 watts and 390kHZ for a reason; you CAN take the discharges. Come on over, I’ll let you prove it. One of my next experiments is to put two 35mm cameras side by side on tripods, one with 100 iso color and the other with black & white infrared film and a red 29 filter. I’ll take simultaneous 4 second exposures and will compare the results, then repeat with color infrared and appropriate filter. Then I’ll do the same with my 6x7cm Mamiya’s and delve into the ultraviolet with color film and a 47b filter on one camera and no filter on the other one. I can’t find infrared film in 120 or 220, hence the 35mm cameras for that one. I’m trying to get a handle on what’s happening that we don’t normally see. Electrode design for different effects is an area I’m playing with. Argon is definitely a good thing and there’s also xenon, krypton and several types of neon that have potential, but argon has the lowest breakdown voltage. I also want to reduce the inside pressure by increments of around 50 torr from atmospheric to see and film the changes in appearance, spectrum and operation and perhaps the tortuosity.
The problem is, this does get a bit monotonous although it is a great way to get your volts. To use this as a special effect means to use it for emphasis, in brief runs. Imagine a still, video or movie camera shooting a scene on the other side of and through the acrylic cabinet and at some point the empty cabinet springs to life, inserting this effect between the lens and what is going on beyond it. Maybe as a ‘window’ in a wall at home. Here’s a good one, fill up a video tape of this in action, hit the mute button and use it as a screen saver for your tv. If you have a huge tv, hot damn! (I’m making that tape right now). I like it for observing plasma, it makes lots of it and I can closely and ‘safely’ observe 42 to 48 inch discharges. All in all, a neat little project that does everything I wanted it to do and is a guaranteed jaw-dropper. Look out Halloween! The door opens to total darkness, a slight pause......