Experiment 40: Glowing Xenon Plasma Tubes!

This experiment came about completely by chance.  When playing with my Whimshurst machine from Experiment 30: Miniature Wimshurst Machine and the small xenon flash tubes from the disposable cameras I disassembled in Experiment 39: Electromagnetic Coilgun, I discovered that the static electricity made an extremely brief flash in the tube.  Intrigued, I connected the flash tube to a 10Mohm ballasted high voltage power supply and discovered that the tube lit up!  The xenon stayed excited and hosted weird bouncing blue-white arcs!  I was amazed!  After quite extensive experimentation, I observed some interesting behaviors.  For example, when connected in series with a small arc gap, the xenon tube's jagged, jiggling arcs changed to a single soft, stationary arc.  I also noticed that touching the outside of the glass tube with a bare finger caused the arcs inside to become smaller and more numerous, as well as more active in their bouncing.  After a while, I decided to make a light-up periodic table specimen of xenon.  I had to get another high voltage supply since the one I originally used was for another project, so I used the CCFL inverter from an old LCD monitor.

After removing the cover of the monitor, I turned it on and probed the inverter board with my multimeter (I identified it based on its "WARNING: High Voltage" label).  I gathered enough information from the voltage readings of the input of the board to identify +12V and GND.  A search of the part number online turned up a datasheet which identified the dimming (0-5V) and on/off (+3V/0V) pins.  Using my ATX lab power supply, I was able to make the fluorescent tube of the monitor turn on at my command.  I used a LM317 voltage regulator circuit to provide a variable voltage to the dimming pin, which controls the current flow and thus the lamp brightness.  I then connected my xenon tube between one of the high voltage outputs and the return on the inverter and tested the setup.  It worked!  With more current, the xenon tube's sharp, jagged arcs changed to an odd sine wave shape with smoother corners.  This made the tube run hot, though, so I ended up using a lower current setting.

During this process, I accidentally discovered that holding a neon or xenon bulb (finger touching glass) near the high voltage caused an arc to jump from the high voltage wire to the electrode of the tube and also made a soft, pleasant glow inside the tube.  I loved this effect and, after many frustrating failed attempts to reliably replicate it, found a solution.  After reading up on how camera flashes work, I learned that a high positive voltage applied to the glass outside of the tube ionizes the gas inside, allowing current to flow and make the blinding white arc.  I tried connecting a camera flash's ionization wire to the high voltage, and with an electrode connected to the return, I got the amazing soft glow!  It wasn't very uniform, though, so I experimented more and found that connecting both electrodes to the return helped the uniformity.

To make the periodic table display, I wound a fine wire around one of my smaller xenon tubes and epoxied the ends in place.  This was my ionization electrode.  I cut a small wood base to fit in my periodic table and made some copper frame wires to hold three xenon tubes in place.  Then, I soldered one large xenon tube to be in an arcing configuration and two other tubes to be in an ionized glow configuration.  These I connected to the inverter so that the glowing tubes shared one high voltage output and the arcing tube got an output to itself.  Since my periodic table wasn't near any outlets, I used eight AA batteries in two 4xAA packs to power the inveter and LM317.  After installation, I was extremely happy with the blue-white light emanating from my Xe periodic table cubby.  Though the project took a long time to complete, I am glad I saw it through.  Noble gases are pretty, aren't they?