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Registered Member #3282
Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224
cedric wrote ...
Microwatt wrote ...
i am looking to build a nanosecond pulse generator for 25kv. What sot of circuitry would get me 2-5 nanosecond pulse width and 10kps.
2 to 5 ns pulse width is really very short ,gaz filled tube have a typical rise time of 30 ns or more,there is a easy and sheep way to do a ns pulse at up to few khz :by using the so call blumen system from nitrogen tea laser it's possible to get rise-time of 10 nanosecond easily. a sharpening gap (typically a very small gap on the output) can decrease the rise time down to 2 or 3 ns.for the high frequency ,the more easy way to drive a spark-gap in the khz region is to use compress air and to blow the gap,
here is what is left of an early prototype,the resistor or inductor witch was connecting the two plate melted du to missing load to absorb the pulse,this specific pulser can reach about 2khz with 15 kv and feed a 75 ohm coax,the sharpening gap is just at the end of the coax central conductor.it recuire about 5 bar of a small compressor to operate.
this system simple and relatively efficient and I am pretty sure any patent have expire by now but the regularity of the pulse is not as good as solid state.
Can you use a magnet instead of air to push the ions out? what is the jitter for the spark gap. is that board impedence matched? what would the maximum size be for a transmission strip aparatus as above? what are the pcb board paramters for a generator such as above? can you use plexiglass sheet?
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Why would you use a magnet when a good old fan works perfectly well? I believe the plates can be of any size, and the dielectric can be any dielectric. Plexiglas sheet is rather thick, and will probably give you low capacitance. I'm quite curious as to what this is for. It vaguely sounds like a CuBr laser...but my guess is most likely wrong.
Registered Member #3282
Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224
The fan is a mechanical component. i wish to stay away from thus systems. Why would a magnet not be effective? wouldn't lorenze forces create a momentum? certainly a peak pulse of say 10A and 10K Gauss would make a peak force or how many hundreds of kilograms? what about a liquid based spark gap?
see picture below. space between hemispheres is a liquid dielectric.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
cedric wrote ...
...and I am pretty sure any patent have expire by now...
I dont think patents in the US protect against one-time copies for personal or academic purposes. so long as you dont sell it, or mass produce them and give them away.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Microwatt wrote ... ...Why would a magnet not be effective? wouldn't lorenze forces create a momentum? certainly a peak pulse of say 10A and 10K Gauss would make a peak force or how many hundreds of kilograms?
Do the math - it doesn't get much simpler in quantitative electromagnetics. At best (current perpendicular to magnetic field), 10 N per linear meter. In 1 cm gap, 0.1 N or the weight of about 10 grams. If your current pulse lasts 10 ns, the plasma column will acquire a transverse momentum of 1 nanonewton-second. From its mass you can figure the resulting velocity.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Microwatt wrote ...
I have an lifter project. the 5ns pulses will allow me to use higher voltages and currents. the ultrashort pulse stops breakdown streamers.
Lifter, As in DeSeversky? Ive tried high pulse rate of HV to narrow the gap and still resist streamer breakdown, it did not work well.
My experiment similar to your's was completed my senior HS year in 1999. Also, two seniors here at CSU Chico tried the PRR, PPM, PWM, method too, in 2007 and they had the same probs i had.
F = (I x d) / K ... just does'nt average well given the distance (and time) that e-field traverses. I am currently developing a better design. I could PM you.
Registered Member #2941
Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143
Microwatt wrote ...
cedric wrote ...
Microwatt wrote ...
i am looking to build a nanosecond pulse generator for 25kv. What sot of circuitry would get me 2-5 nanosecond pulse width and 10kps.
2 to 5 ns pulse width is really very short ,gaz filled tube have a typical rise time of 30 ns or more,there is a easy and sheep way to do a ns pulse at up to few khz :by using the so call blumen system from nitrogen tea laser it's possible to get rise-time of 10 nanosecond easily. a sharpening gap (typically a very small gap on the output) can decrease the rise time down to 2 or 3 ns.for the high frequency ,the more easy way to drive a spark-gap in the khz region is to use compress air and to blow the gap,
here is what is left of an early prototype,the resistor or inductor witch was connecting the two plate melted du to missing load to absorb the pulse,this specific pulser can reach about 2khz with 15 kv and feed a 75 ohm coax,the sharpening gap is just at the end of the coax central conductor.it recuire about 5 bar of a small compressor to operate.
this system simple and relatively efficient and I am pretty sure any patent have expire by now but the regularity of the pulse is not as good as solid state.
Can you use a magnet instead of air to push the ions out? what is the jitter for the spark gap. is that board impedence matched? what would the maximum size be for a transmission strip aparatus as above? what are the pcb board paramters for a generator such as above? can you use plexiglass sheet?
this pulser have a very small internal resistance so it can match about any load(it does not match the load but you get maximum voltage in each case),this one was build of 0.8 millimeter pcb as dielectric,the square are 8cm by 8cm and have a capacitance of about370 pf each.the maximum size of the assembly depend of different factor such as energy needed per pulse ,impedance and rise time ,having a low impedance help to keep the the rise time low,typically this type of system is build using coax as capacitor but then the pulser is only matched for a load of the same impedance than the coax use ,in this case the pulse length is define by the length of the coax (20 cm for 1 ns) the jitter of the spark gap is pretty low for a spark gap ,this is because blowing air at few bar create very fast wind witch "reset "efficiently the gap whoever jitter still occur and the pulse regularity is not perfect,using magnetic field to cut the arc is may be possible but in my experience it does not work at those frequency,the air blow have an other advantage is that it cool the gap so that it's possible to run it for expended period of time.I say that this system was tested to 2 khz at witch it was taking 400 w from the plug,the gap was not the limiting factor here(but my power supply). finally,any dielectric can be use of course Aldo they don't have the same dielectric property...
Registered Member #2662
Joined: Fri Jan 29 2010, 10:14AM
Location:
Posts: 36
If you want a something fast and highly repetitive then you could try a 'corona stabilised switch', these are like spark-gaps but are capable of switching at rep rates approaching 10kHz. They were developed several years ago at Strathclyde Univ and have received renewed interest recently; pretty much because they are relatively simple to design and use. I've worked with them in the past switching around 30kV 2kA @ 2kHz... they work, but I'm a little sceptical about the proposed mechanism of 'corona stabilisation'.
A reference: J A Harrower et al 1999 J. Phys. D: Appl. Phys. 32 790
Abstract Self-closing corona-stabilized switches have been developed to operate at pulse repetition frequencies (PRFs) which extend well into the kilohertz regime. The performance of these devices illustrates that corona-stabilized plasma closing switches are an effective alternative to conventional uniform or quasi-uniform field switches which utilize gas-flow techniques, high gas pressures or both to achieve high-PRF operation.
Corona stabilization takes place in electronegative gases such as air and and requires the presence of a highly divergent electrical field. Under dc, or slowly rising charging voltage conditions, a space charge develops around the highly stressed electrode which prevents premature breakdown and allows full voltage recovery to take place. This means that PRFs extending into the kilohertz regime can readily be achieved. Self-firing corona-stabilized switches have been demonstrated to provide PRFs of up to 5 kHz and triggered corona switches have been shown to be capable of operation at 10 kHz. The lifetime of corona-stabilized switches has been demonstrated to approach about 10^8 shots.
The paper describes the design of a corona-stabilized switch, including detailed electrostatic field analysis of the electrode geometry. This analysis was undertaken to establish the effect of the electrode geometry on the field distribution within the switch. The switch design was flexible and allowed a study of the effect of certain parameters on the switching performance. These parameters include the gap spacing, the gas pressure and the profile of the electrodes. The switch was operated under single-shot conditions to establish the breakdown voltage against pressure (V-p) characteristics and in a continuous repetitive mode to assess the PRF operation. The results show that the best repetitive performance is produced using electrodes which generate a high field over a region sufficient to generate a stabilizing corona.
There's many more papers availiable if you do a quick google search.
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nanosecond pulses
