triggered spark gap

Spark Plug And Plumbing Parts Bring Nitrogen Laser Under Control

When it comes to high-speed, high-voltage switching, there are a wealth of components to choose from — MOSFETS, thyristors, IGBTs, and even vacuum tubes like thyratrons. But who needs all that expensive silicon (or glass) when all you need to build a high-voltage switch is some plumbing fixtures and a lathe?

At least that’s the approach that budget-minded laser experimenter [Les Wright] took with his latest triggered spark gap build. We’ve been watching his work for a while now, especially his transversely excited atmospheric (TEA) lasers. These are conceptually simple lasers that seem easy to build, at least compared to other lasers. But they do require a rapid pulse of high voltage across their long parallel electrodes to lase, and controlling the pulse is where this triggered spark gap shines.

The spark gap is made from brass plumbing fittings on either end of a short PVC coupler. [Les] used his lathe to put a thread into one of the caps to accept a spark plug, the center electrode of which pokes through a small hole in the metal cathode. To trigger the spark gap, [Les] built a trigger generator that outputs about 15,000 volts, which arcs from the spark plug electrode to the spark gap cathode in the low-pressure nitrogen environment. Little spark leads to big spark, big spark discharges a capacitor across the laser electrodes, and you’ve got a controlled single-shot laser. Check it out in the video below.

Honestly, the more we see of [Les]’ videos, the more we want to play with lasers and high voltage. From DIY doorknob caps to blasting Bayer arrays off cheap CCD cameras, there’s always something fun — and slightly dangerous — going on in [Les]’s lab.

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The Basics Of SCRs

Although the silicon controlled rectifier or SCR has been around since 1957, it doesn’t get nearly the love an ordinary transistor does. That’s a shame because they are quite handy when it comes to controlling AC and DC voltages in things such as lamp dimmers, motor speed controllers, and even soldering iron temperature controllers. [Lewis Loflin] has a short video introduction that will help you get started with these devices.

One of the interesting properties of the device is that once you turn it on it will stay on until you do something specific to turn it back off — sort of, [Lewis] explains it in the video.

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Simple Concepts Behind Complex Coilguns

Coil guns use electromagnetic coils to propel a metal projectile. On the surface they may look rather complicated. But when you break down the concepts it’s pretty easy to learn. If you’ve ever thought of dabbling in this field this lengthy coilgun primer will be a great help.

The basic concept of a coilgun comes in three parts: the coil, the voltage source, and the switch that combines the two. In the build above you can see two spools of wire on the clear barrel of the gun. These make up a pair of accelerators which connect to those huge black capacitors supplying the voltage. The switch they used can’t really be seen but from the article we know it’s a Thyristor; a┬áSilicon Controlled Rectifier (2N6504).

In the video after the break you can see these three parts coming together for a test firing. This is the first step in a longer journey. To achieve higher projectile velocities you must add coils, as in the image above. But spacing and timing quickly complicate the simple concept. But if you can work out all the kinks you end up with some pretty great hardware.

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