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1kJ Electrothermal gun (ETG)

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MrFlatox

Tue Jan 15 2013, 03:42PM

Registered Member #9349 Joined: Mon Jan 07 2013, 08:50AM
Location: France
Posts: 102

take it easy, I did not meant to be aggressive nor disrespectful, and if you understood it that way, I apologize.

Yanom

Tue Jan 15 2013, 04:06PM

Registered Member #4659 Joined: Sun Apr 29 2012, 06:14PM
Location:
Posts: 158

Hey, I just got an idea - how bout a combination ETG/Railgun? You would set up your copper contacts as rails, then the foil (which becomes plasma) would experience a forward force as well as a heating force as it goes toward the projectile. Basically a railgun where the heat losses are used for something?

Maxwell

Wed Jan 16 2013, 03:35AM

Registered Member #8497 Joined: Tue Dec 04 2012, 06:24PM
Location:
Posts: 74

MrFlatox wrote ...

take it easy, I did not meant to be aggressive nor disrespectful, and if you understood it that way, I apologize.

Nahh, don't worry about Yandersen. He's just a bit pompous since he holds one of the highest efficiency CG's on 4HV. Also, he thinks monkeys are the only designers of cg's ;)

Jack A

Thu Jan 17 2013, 11:39PM

Registered Member #2975 Joined: Wed Jul 07 2010, 12:19AM
Location:
Posts: 28

That's awesome!
That switch looks crazy!
Have you tried using more/less aluminium?
Also, from those muzzle flash pics, I can't help thinking that increasing the barrel length might do some good.

MrFlatox

Fri Jan 18 2013, 09:43AM

Registered Member #9349 Joined: Mon Jan 07 2013, 08:50AM
Location: France
Posts: 102

Thanks !

Sure, barrel lengh need to be greater than it is actually, it's the first thing I will modify when I will work on the ETG again.

As I understand it, the BB is propelled thanks to a combinaison of two things :

- the vaporization of the Al foil create hot gases and high pressure spike. It also ionises a path between the electrodes.

- the current continues to flow through ionised gases in the chamber, thus heating up more the small volume of gases contained in the chamber, creating more pressure.

But I think that a large proportion of the energy that the BB receives is actually coming from the second statement. Al foil is just there to open a path of ionised gas between the two electrodes.

Next thing I will also try, is to make a new chamber with a triggered spark gap, to prevent the use of Al foil. When this will be done, I will compare kinetic energy produced by both configuration, and know if Al foil participate actively in the BB propulsion or not.

Yandersen

Wed Feb 06 2013, 12:25AM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

MrFlatox, I just got suddenly wondered what will happen in case of empty barrel shot, if you just put two magnets just near the exit creating the magnetic trap at the exit of a barrel - will it separate plasma or *maybe* form it into a ball lighting?..
Just interestied to see the effect of mag field perpendicular to the way plasma runs out of the barrel... Would you try?

MrFlatox

Wed Feb 06 2013, 08:14AM

Registered Member #9349 Joined: Mon Jan 07 2013, 08:50AM
Location: France
Posts: 102

Yeah I could try. You want to "deviate" the plasma by putting a magnet on one side of the barrel at the exit to see the effect it would have on the plasma ? I also have some microwave oven magnets (toroidal) that i could try.

I only have access to the ETG in the week end so I could not try what you suggest until saturday.

In the meantime, i also started to build another chamber made of steel fitting with less dead volume, and I also try to add a "spark gap" feature on this one. so stay tuned :)

Yandersen

Wed Feb 06 2013, 12:07PM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

Thanks, MrFlatox, I will be happy to wait.
I think you can do sparking with just 1 turn on primary and around 5 turns on secondary (2kV) using the toroidal ferrite ring if you make a 1 mm gap between your electrodes. This way you will surely saturate the trans and get very low parasitic inductance during the shot. Howether, make sure electrodes do not melt - I have no idea how to protect them from it - I did not succeed...

MrFlatox

Fri Feb 08 2013, 08:26AM

Registered Member #9349 Joined: Mon Jan 07 2013, 08:50AM
Location: France
Posts: 102

What would be better between those two options to make a spark gap etg :

-12 turns on Etg side and 4 turns on HV side with air core transformer
Or
-4 turn on etg side and 1 turns on HV site with toroidal transformer core ?

I was also wondering if the pulse HV side could be supplied with a 40kv source instead of the 2kv mentioned above ? Would it works too ? I do not have a 2kv power supply, and i am too lazy to build one with a voltage multiplier from mains. But i have a functionning 40kv one ready to spit some volts.

Yandersen

Fri Feb 08 2013, 03:43PM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

For a 40kV source you are good to go with 1:1 turn ratio on an air-core trans, I suppose - just twist an HV wire with an ETG cable. Where did you got a 40kV source?!

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