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Thread: Big Avco Nitrogen Laser High Voltage Cables Type?

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    Default Big Avco Nitrogen Laser High Voltage Cables Type?

    Picked up a giant nitrogen laser head in Ashville about 10 years ago. It's a bigun. I would like to get this working again, but it will be long slow road of frankensteining high voltage parts together. One thing that is stumping me is the HV pulse delivery cables. On the top side of the head, under the faraday cage and beneath each cable port is a male banana style plug sticking up. Then about 2 inches up where the cage is, there is a 3/4" bnc style connector. My guess is that it was some kind of shielded, flexible female banana plug. Any ideas would be helpful as a good starting point for this project. Then comes the fun part in figuring out cable length and capacitor connection arrangement. The laser was made by Avco Everett, this company also did stuff like generating electricity from jet engine ion separation. Not much more info online anywhere.
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    The cables were probably cut to provide an electrical phase delay in sequence to each electrode.
    Your design evolves out of a 1960s group of papers in the journal "Applied Physics Letters".
    That's all the help I can provide. AVco made amazing tech and often had unlimited budget to do it.
    I don't see the spark gap, so you appear to be missing some critical parts.

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    Should the HV discharge be traveling wave, I.e hitting the back electrode first and moving forward. Or should the HV pulse strike all the electrodes simultaneously? The is a grounding screw on the front bottom of the head right under the output slit. I have a 30kv D.C. Power supply from an old molectron. I was thinking of using 2x 40kv caps for peaker/dumpers. Any idea of a good place to find those style caps? I have a custom adjustable spark gap or maybe a rotary SG would work better? Found this diagram online, thought I might go a route similar to it.
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    I'm pretty sure (95%) that is a traveling wave beast using delay cables.

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    That is what I was thinking too, since the tube is so long. So if that's the case then all I will need to do it connect each cable on a common high voltage rail. Just making sure that the discharge cap is forced to hit the last cable to the first, in under 4nS. Does that sound about right? Or do the cables need to have some kind of physical delay mechanism wired in?

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    Quote Originally Posted by MrNIFty923 View Post
    That is what I was thinking too, since the tube is so long. So if that's the case then all I will need to do it connect each cable on a common high voltage rail. Just making sure that the discharge cap is forced to hit the last cable to the first, in under 4nS. Does that sound about right? Or do the cables need to have some kind of physical delay mechanism wired in?

    Google coax cable "velocity factor". You'll find the length of the cable IS the delay. Cables towards the end of the laser where the pulse starts would be shorter, with each succeeding cable being longer so the pulse arrives in phase.

    For most things electronic, one nanosecond is about 12 inches. Actually ~~ 11.85 or so inches for a common wire in air. However, the signal in coax is slow due to increased dielectric constant of the Teflon or HDPE core versus air.

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    It is almost certain that the cables were both delay lines and they may have constituted some or all of the capacitive storage as well. This was often done. Can you provide some images without the screen. The dimensions of the cavity HxWxL will help. If there is no pre-ionization channel then this was probably sub atmospheric and would operate at a few torr with possibly a helium buffer that could be at as much as 10x the nitrogen pressure. This buffer was used in sub-atmospheric nitrogen lasers, not so much for energy transfer, but to stabilize the discharge.

    Is there a gas handling system or is the tube sealed?

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    I hope you don't plan to modify the head to try and get it going, as it's really old (c1967), very rare, and would be a great addition to the Vintage Laser Archive. Please let me know if you'd consider selling it. There are many other nitrogen lasers available to make operational. This one's a museum piece.

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    I would tend to agree here. If this is a sub-atmospheric laser then the head is a very simple construction. You will spend most of your effort on the electrical and gas handling system and will probably find that a shorter tube will be easier to operate.

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    Here's a picture from the 1967 book "Atomic Light: Lasers" by Nehrich, Voran, and Dessel, a great little book full of old laser pictures for anyone interested.

    Click image for larger version. 

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