Friday, December 24, 2010

Vaporizing some aluminum, taking some pictures

Part of our bachelor project was working with a small scale single turn coil apparatus for creating high magnetic fields. This allowed for some nice plasma pictures!

The principle of single turn coils in a nutshell: you dump a whole lot of energy from a capacitor bank in a (single turn) coil. Once you get a few kiloAmperes flowing, you get a pretty high magnetic field, but the coil also endures intense magnetic stresses and a lot of Joule heating. Ultimatly the coil snaps after the peak field is reached and the vaporized metal turns into a nice plasma. The remains of the coil fly off outwards, keeping the sample intact.

I photographed the plasma and pieces flying off with a long exposure in a dark room. I was slightly worried about frying the sensor, as there is a lot of high energy UV light coming from the plasma. I actually stacked on two UV filters just for some peace of mind. I was still constantly checking the sensor during the first few images.

This is the best picture, it's an aluminium foil completely flying to pieces on our little testing apparatus (Click for deviantArt page where you can see the full resolution version)

This was done as a long exposure in a dark room with a 250mm lens stopped down to f/11 on ISO 100. It was one of the first photos I shot, I did some f/32 shots at first (to protect sensor), but those coil shots were less bright, so I opened up the aperture. Then this one blew up much brighter then before and kind of took me by surprise. The sensor is still OK though!

These pulses can reach about 2T, hence the catchy title 'Two Tesla Plasma' (go ahead, say that out loud. It has a nice ring to it, right?)

I also tried to get a 3D image by using a second camera from a friend of mine. Click the image below to see the effect (WARNING: I can NOT be held responsible for possible epilectic seizures)

The parallax looks a bit odd because both images were shot at 250mm on a cropped sensor. Using a focal lengtch that matches the human eye more closely would probably have made the effect much better, but I'm not too fond of getting the cameras that close to the glowing metal pieces flying everywhere.

So, everyone go and study physics: where you can blow stuff up and get pretty pictures -- for science!

[Edit] For those interested in more info, you can skim through the paper hosted at github (Don't mind the bleek results, we had some problems and serious time constraints).


  1. more turns, higher magnetic field.
    That is why electromagnets have many turns.

  2. get a Casio EXILIM Pro EX-F1 high speed camera (relatively cheap) that would make an awesome shot I think !

  3. Very cool pictures!!! IS nature not a miracle!?!?! thank you. :D

  4. @Anonymous:
    More turns = higher resistance = more Joule heating. Also, using only one turn makes the coil explode outward, not damaging the sample. You do not have this advantage when doing a multiple turn destructive test (you destroy the sample too, in that case).

    The actual peak field is achieved after about 50 microseconds (that's when the coil snaps). The plasma hangs around for a couple milliseconds or so. I'm afraid that's a bit too fast for a consumer high speed camera.

  5. thank you realdfre