Charge that bitch up. (practical plasmas under bad vacuum)

So, here are the videos I recorded while experimentint with the refrigeration vacuum pump:


  • Voltage: 350/500V
  • Current limiter: NO.
  • Plates: Aluminium.
  • Vacuum: Around 300 microns.
  • Plasma trap spacer: 4,5mm.

1.- Just testing the magnetic trap with lower gap. Glowing hot aluminium can be seen at some point.

2.- Wondering what would happen if the magnet was inside the chamber? Magnet is at positive potential, copper foil is isolated.

3.- Same setup, but copper foil at positive potential.

4.- Magnetic effects on the residual plasma bubble

5.- Magnetic effects on the residual plasma bubble, in slow motion.

6.- Trying to start the sputtering plasma without low enough pressure, generating sparks in the ionized gas. Once the vacuum gets further down, the plasma stabilizes.

And that’s all I got with the not-so-good vacuum pump.

See ya!

6 responses to “Charge that bitch up. (practical plasmas under bad vacuum)

  1. Don’t know too much about this aspect but will look into it. I want to make dichro glass. But My Neon setup uses similar tech which may inform you usefully…

    To strike the tube we lower pressure to about 0.6kPa. This higher pressure is so we can heat the air in the tube and warm the whole unit uo to 250C for outgassing. Also the amount of voltage is much higher because we have long lengths in the tubes. so we might use 15kV at 1 Amp which is ridiculously high and very dangerous. Your short length is presumably why you can get away with 500V. The voltage is directly related to teh distance to jump. once set we do not change ot for other parts of the process.

    I see you use a lot of power and its not current limited. A neon transformer (old style with iron core) has an extra iron region which acts as a magnetic shunt so is current limited. in a sign transformer this is usually 20,30 or in some cases 60mA. So a lower voltage unit say 2kV at 20mA is readily available. It is AC however to get even wear on the electrodes. So DC reciticafion is needed for plating. Your diodes look great :)

    So once we have heated the tube we evacuate more air out – down to 0.2kPa which directly bombard the electrodes with electrons until they glow cherry red (we have a getter we need to activate for long tube life). So as the pressure drops you will need to lower the current to avoid sputtering(destroying) the electrodes. but this is perhaps your intention as you are plating. But I assume you do not want the the electrode to wear away but instead have the electrons strike the donor material as they travel from source to destination. I need to read up more on your needs.
    Hope this is helpful

    • Thankyou for the input!, much appreciated, btw. ^^

      Yes, the current limitation is an issue, I’m still waiting for some 100W 100/50 ohm resistors (just going overkill there) to install on the positive side of the circuit, and that should help with current management, and also, now that I think of it, I can’t remember having measured the current in the setup, those 500mA are from other’s peoples measurements. I am also waiting for dedicated current and voltage testers to have a better grasp on the power I’m using.
      As an afterthougt, could it be that what I’m doing is more like making a “neon” sign work by brute force (mantaining the high vacuum with the pump)

      • Very early Neons also used a running vacuum to operate. They were called geissler tubes I think. The main problem is using air which instead of sputtering will use the O2 to create new molecules instead. I.e. highly reactive which is why must use Argon (or Neon) as non-reactive but argon more common and cheap. Neon tubes do try to get under 10 micron and closer to 1-3 for long term stability – 25 years or so so different set of criteria they are trying to meet. Most refrig pumps tend towards 50 microns IIRC. Should be fine for sputtering though. Was watching Applied Science on this topic
        can see now how the sputtering happens by forcing the electrons in a magnetic loop to drag the Argon atoms down to sputter the target and scatter to the destination. His cracked, it got so hot – hot because of the electron energy which is related to current once voltage established. So higher current means the sputtering action is more kinetic and therefore creates heat at the surface.

      • Didn’t know that about neons! what where they used for?(will check wikipedia) I mean, they don’t sound much efficient if they need a running pump all the time. XD
        I bought a decent refrigeration pump, but the best I managed was about 300 microns, barely enough low pressure to prevent arcs and initiate sputtering. As for heat management, yes, absolutely, I am working on that too, I once fused (on purpose) the copper target I had in the chamber. Shame Aplied Science didn’t gave data on current/voltage for the cracked ITO, might have been interesting.

      • single stage electric pumnp is for refrig and 50 is best with new vanes. 300 is fine. For better vacuum look for 2 stage electric pump or motor/belt driven like Welch 1402 second hand. Beware mercury contamination from old Neon plants though. Generally safe. Typically 10microns or lower. The lower the vac the higher the speed of the elecrons and therefore the sputtering. (Nothing in the way).
        Geissler tubes not really used for anything – people stil make them. forerunner of Neon which was first commercially useful mecahnism – Claude patented the Electrodes and sewed up the entire industry for 50 years.

      • Well, then my “new” (there is a rebuild log in the first post about the whole vacuum chamber thingy) two stage pump is underperforming a lot, achieving at much, 33 microns just after rebuilding. Heh…well, I sure don’t have money to look for another pump, so I’ll have to make do. /cries in silence/

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