# How to create pulses which are 10ns long and 15kV/ 80A amplitude?

I'm looking for an easy way to create short high voltage pulses. These would be 10-100 ns in duration, 10-30 kV in amplitude (the load is complex but roughly similar to a 200 ohm resistive load). The source can look like either a current source or voltage source during the pulse. The load should (ideally) be shorted outside of the pulse.

It is easy to find adjustable high voltage generators to (for example) 30-50 kV DC, so the high voltage side of that is relatively easy. But I have no idea how to switch 30 kV on (and especially off) in nanoseconds. Triggered spark gap?

EDIT I'm surprised nobody has mentioned stacked MOSFETs (or IGBTs?) as a possible solution. After doing a search I found a few references like this: Stacking power MOSFETs for use in high speed instrumentation. I don't have any experience with this approach but solid state seems way more controllable.

• Megawatt pulses of short duration - try looking at radar circuits. I also note that you've not accepted any recent answers such as this one: electronics.stackexchange.com/questions/195616/… (I remember it because I answered it) but there are quite a few others. Commented Jan 29, 2016 at 10:34
• One of these things that you should tackle only when you really know well what you are doing, and not ask random stranges how to blow yourself up Commented Jan 29, 2016 at 10:43
• Look up Marx generators built with transmission line for capacitors, they produce well-defined pulse lengths automatically (the length of the line/c) and use sparks as switches. Doesn't short the load outside the pulse though. Marx generators don't like to operate at too low a voltage, so 10kV may be challenging for triggering stability. Commented Jan 29, 2016 at 10:54
• @AlexI: the point is, at these energies it is not only easy to blow yourself up (which I do not care about, another darwin award entry) but to blow up other people in the vicinity too (thats something I care about, not only because I could be one of them). The format of this site is too small to mention everything that you need to take care about, so you need to really know what is missing, but then again if you really know about this you would not have to ask here in the first place, so we must assume that there is something missing from an answer here that will make you blow up yourself Commented Jan 29, 2016 at 10:55
• Total energy is about 0.12J, so not much of a bang. That's the same energy as in 1Volt at 1Amp for 120milliSeconds. The instantaneous power is scary (1.2MW) but the short on period (10nS) keeps the total energy down.
– JRE
Commented Jan 29, 2016 at 15:28

Your requirements of short, variable length pulses, high voltage, and high current are hard to achieve simultaneously. Needless to say, for high speed, high voltage, high current pulses, it is imperative to absolutely minimize any parasitic inductance or capacitance in the switching circuit, connections, or load.

The MOSFET cascode will get you to, I guess, 50ns pulses and 5kV into 200 ohms without too much difficulty. There is a limit to how many MOSFETs one can reasonably stack and still have good voltage-sharing and switching performance, so the MOSFETs will need to be overspecified and rise times will not be much better than 10ns. The cascode also cannot turn off rapidly, so if you want square pulses with well-controlled fall times you will probably have to use a push-pull design, although P-MOSFETs are slower to switch and hard to find with high breakdown voltages. Transformer-coupled gate drive is also possible, which could reduce the turn-off times for N-MOSFETs or enable half-H-bridge designs, but the design and construction of the transformers is not easy. See here for an example that achieves somewhat worse performance than you are interested in, or here for some discussion regarding the approach proposed in the article you link and why it is difficult to apply in practice.

Behlke makes many products of this general type, and although some of them can meet your other requirements, none can achieve pulses shorter than about 50-100ns. The on-state resistance is also a significant fraction of your load impedance, and obviously it becomes worse the more MOSFETs one places in series or the higher-voltage devices one chooses.

A Marx generator is good for high voltage, high current, fast-rising pulses, but the pulse length is not easily controllable, and as with all spark-gap-based devices, jitter could be rather large unless special effort is taken to minimize it.

Your only serious option may be something like a Blumlein transmission line or other transmission-line-based pulse multiplier. Here is a page describing it, and here and here are two papers describing voltage-multiplying Blumlein generators. The disadvantages are that varying the pulse duration requires changing the physical length of the transmission line, and the transmission line impedance has to be matched to the load. Triggering it is a problem in itself, although one possibility is a laser-triggered spark gap. These devices are large anyway, but especially a 200 ohm transmission line capable of carrying large currents and yielding pulse widths of up to 100ns will be rather bulky. Possibly you could use 50 ohm transmission lines and a 4:1 transmission line transformer, but achieving good wideband coupling while keeping leakage inductance and inter-winding capacitance small is not easy. One company that makes devices like this is Barth Electronics.

If you can relax the requirement for variable pulse widths, you could investigate commercial Pockels cell drivers or other electronically similar devices, which are based on solid-state Marx generators. These are often limited to providing 5-6kV negative pulses, because this is what Pockels cells require, and do not usually have fast fall times; however, there are exceptions.

One such exception that deserves special mention are those made by FID GmbH. This company makes several products similar to what you require, such as the FDS 20-10NKN5. They are based on a special avalanche-mode device, the fast ionization dynistor, that seems to be almost unique to this company, but which has some very impressive capabilities. It can produce a 10kV pulse with 20ps rise time, or a 1MV(!) pulse with 1ns rise time. I'm not aware of any other technology that comes anywhere close to this level of performance.

You can look for Marx generator. But this is a huge thing, I had the possibilty to see it in work at the transformer testing. It's a device with spark gaps and RC circuits, similar like voltage doubler circuit with RC and diodes. The spark gaps have a function of switching the capacitors parallely charged to series RC circuit. The 1st sparg gap has a needle that is remotely triggered, then the voltages are summing and making a domino effect on other spark gaps. I have seen RC circuits tuned to make 8/50us pulse.

Such pulse is really similar to a spark, although in spark gap the duration is more like microseconds. I would recommend looking for capacitor discharge ignition circuit.

I also think that "blowing up" is a bit panic in that case. The total energy mentioned here is really nothing for a single pulse.

By the way, there must be a piezo element with similar voltage per pulse. I see it all the time in lighters :)

A quarter wave helical resonator AKA Tesla Coil with a spark gap could produce results like this fairly cheaply. Just build a class D amplifier to drive a square wave at 50% duty cycle into the base of a resonant coil and when enough charge is built up on the coil it arcs, this arc is typically 20-100kV at 100's of amps for small coils (6in x 24 in long). The period of the arc is typically in the us or ms range depending on design and capacitive loading on the coil...

• A tesla coil produces streamers, not arcs (they are driven by avalanche breakdown, not thermal ionization), so I have my doubts about the currents you claim here. Plus, this is not a d.c. pulse and there is no easy way to control the spark duration or guarantee anything about rise and fall times. A Van de Graaff generator could potentially be a more useful option, but still difficult to control. Commented Feb 13, 2016 at 19:58

You might find some inspiration in HV cable burn down units.

They safely make use of high voltage pulses to burn away conductive bridging in HV cables with self healing insulation.