Tesla Coil Ionization

[Future JPL Space Engineer]

Could tesla coil's high frequency ionize gases? Such as hydrogen, argon, xenon or so.

Because it is alternative pulsed high frequency, like radio frequency (magnetron)

[swansont]

Considering that you can create discharges with them, the obvious answer in general is yes, though Hydrogen and Xenon would be tougher to do. It's not the high frequency, per se, because even 1 GHz is much too low for a single-photon ionization by several orders of magnitude. The ionization probably comes from creating a very strong electric field

[Sensei]

Hydrogen H₂ requires first to split to two separate H, it's taking approximately 4.52 eV to do so.

Then each H requires 13.6 eV to ionize.

So overall you have to spend 4.52 eV + 2*13.6 eV = 31.72 eV per H₂ molecule.

 

At the same time Helium needs 24.58 eV to ionize to He¹⁺

Argon needs 15.76 eV to ionize to Ar¹⁺

Xenon needs 12.13 eV to ionize to Xe¹⁺

 

Decrease pressure of gases in tube. It should help.

 

Be careful with Hydrogen.

One my tube with Hydrogen that I have made exploded after 3rd ignition by 40+ kV Cockcroft-Walton generator.

It was not hermetic and little Oxygen from air get to inside. Good that it didn't destroy anything in room (50 centimeters from LED monitors).

 

Search eBay for "discharge tube". There is plenty of them.

f.e.

http://www.ebay.com/itm/Spectrum-Analysis-Gas-Spectrum-Tube-set-of-6-Discharge-Tubes-Xenon-Krypton-etc-/301365429384?pt=LH_DefaultDomain_0&hash=item462ac78488

6 tubes with different gases inside, for 80 usd is pretty good price.

Edited October 27, 2014 by Sensei

[John Cuthber]

"Hydrogen H₂ requires first to split to two separate H, it's taking approximately 4.52 eV to do so.

Then each H requires 13.6 eV to ionize.

So overall you have to spend 4.52 eV + 2*13.6 eV = 31.72 eV per H₂ molecule."

No.

you can make H2⁺

http://journals.aps.org/pr/abstract/10.1103/PhysRev.40.496

15.37 Volts

[Enthalpy]

The fields that ionize gases use to be hugely weaker than what would pull an electron away from an atom or a molecule like H₂. The field of a proton at 50pm is 600GV/m while excellent solid insulators break at 50MV/m, gases earlier. Only extreme laser pulses, very short, concentrated and energetic achieve to ionize a gas without having a favourable frequency.

 

If it's not the field ripping an electron from a molecule, it needs a more efficient ionizing process, which is impact ionization. Electrons or ions that pre-exist for any reason (radioactivity, cosmic rays and so on) accelerate in the field over a big distance until they hit a molecule. If they have 70nm mean free path to grasp 20eV, a field of 300MV/m suffices now - not perfectly accurate (because the "avalanche" doesn't need an ionization at each impact), but much better than 600GV/m. Also good: for voltages that clearly exceed one ionization potential, it's indeed observed that the breakdown field multiplied by the mean free path is a constant.

 

The too heavy ions are less efficient than electrons to transfer energy to an electron in a molecule and rip it off. Though, electrons alone can't easily sustain a DC discharge, because they can't replenish themselves at the negative electrode where they originate. Only ions arrive there, and at that location, they must rip electrons from gas molecules or from the electrode. This less efficient process determines much the breakdown.

 

AC voltage can stabilize a discharge better than DC does by relieving this dependence on ionization by ions.

 

Then, frequency does have an effect:

If the half-period is clearly longer than a few electron flight times, nothing special.

At higher frequencies (say GHz), electrons have less time and distance available to accelerate, so they need a stronger field.

For instance light never produces an avalanche ionization.

 

Rare gases tend to be easier to ionize than other atoms. Not quite intuitive, but it results from non-rare atoms regrouping in molecules, where electrons are much deeper in the nuclei's field. Other mechanisms quench an avalanche, especially if some atoms can swallow electrons to make negative ions. This tells why the best insulator gases (SF₆, CF₄) contain electronegative atoms to outperform molecules like N₂ that keep their electrons far better; moreover, these gases also reform spontaneously after a breakdown.

 

[Future JPL Space Engineer]

Thank you all!