The color of IEC plasma

[Dan Tibbets]

I agree that the glow discharge seen in a fusor is primarily due to spetroscopically defined colors. The glow is essentially the same as a neon or flourescent light. Depending on the fill gas- neon, argon, helium, etc. the color will be different. The visible light comes dominately from electrons dropping from excited orbits to lower or ground state orbits. Hydeogen alpha and beta wavelength lights are obvous choices with a hydrogen gas. Beta is deep red and alpha is yellow(?) Depending on the aviable energy , dominate state of most of the hydrogen ions, atoms and moleculaes there may be some percieved color gradation in the color as the contribution of these two basic hydrogen spectral lines vary in intensity. Molecular spectral lines tend to be more in the infra red region, and the most energetic atomic spectral lines tend to be more into the ultraviolet. Once fully ionized , I do not thinkyou see spectral lines(?). Just black body radiation based on temperature (and braking radiation which tends to be in the X-ray region). Because the gas/ plasma is rarified, you do not have any significant perceptible black body radiation. I think it would be completly washed out by the spectral emmisions.

This wordy ramble is concentrating mostly on only a pure hydrogen gas. Once other gasses and contaminates are added inthe picture becomes even more complex. As the vacuum drops the gas in the chamber can indeed vary. Mostly from gasses and solids incorperated in the walls and wires. The plasma/electrons and just normal outgassing will introduce copper, iron, nickel, sodium, water, nitrogen, oxygen, carbon,argon, ete., etc. in varing amounts. These all have their spectroscopic emmision lines that can contribute to the mix that gives a final percieved color.

A few years ago, there was a claim that a yellow-green spectral line detected by a contributor was due to a helium spectral line and thus a indicator of fusion. Discussion reviled though that any such helium was way too tine to be detected. The line was probably from sodium line emission derived from sodium sputtered off of the glass by the electron beams/ plasma bombardment. This illistrates that the net perceived color is a complex mixture of various element spectral lines, and this can change as the chamber is pumped down and plasma cleaned. The pressure changes- but so does the gas composition. In chambers that have been conditioned by prolonged pump down and plasma cleaning, the color may most closely approach a pure emmision line color dominance of say hydrogen alpha and beta combined ( I assume dominantly hydrogen beta if a deep red color). It should be noted that the best fusion comes from these conditioned machines which also implies the most pure fill gas conditions.

Dan Tibbets