Just measured the wire with a digital caliper, and it measures 0.08mm.

The pressure was a bit higher in the test chamber, about 30 - 50 mBar, my test chamber is not the best built thing in the world . Anyways, enough pressure to create plasma. Strangely, on one of the tests I did today, the breakers did not pop. They did pop on the rest though.

About the breaker problem, what if I charge another smaller cap, to 320v, say, 100 or 200uF and discharge it through the wire using a relay? Would the relay be damaged? (It's meant to switch 230v AC at max of 10A continuous, and controlled with 12v DC)
I think such a cap would probably suffice to vaporize the wire.

 

testing caps of charge to vaporize wire is ez, just charge them and short wire to cap, see what happens.
voltage doesnt need to be high, its the amps the turns wire into vapor. just use a car batt and just swipe the pos wire across pos of batt to get a fast pulse on the wire, just dont touch the wire.

or, get a rheostat and mod a microwave over x-former so you can get low volts with up to about 1000 amps. you can use a std wall switch as the "relay" to burn the wire, whether using batt or rheostat with x-former.

the thing is, any other continuous electrical source that creates the plasma will want to use the plasma to keep going, hence why i suggested a igniter.

your experiment has some tricky timings to worry about.

 

That is in fact the general idea. You create a plasma with whatever means you use, and that plasma acts as a short circuit for the capacitor, with the high current provided by the cap maintaining a lower voltage arc.

What I could simply do, is short the main cap directly with the wire, this would, as you mentioned, waste some joules, however, in my current setup, that is not really a problem. The problem though, is the kind of switch required to short the cap. I will do some tests, but I don't think the 230v 10A relay will be able to handle the discharge. I could search for a tougher relay. What do you think should the Amp rating on a relay to switch such a pulse? I'm especially worried about sparking inside the relay when the contacts close.

Anyways I'm building a PCB to test different caps for shorting the wire.

 

RE:""
What is a vacuum? It is low pressure. How low?""
From the standpoint of physics, the vacuum is strongly defined as state at which, depending on vessel size, there is no more dominating collisions between molecules, so the dominates the collisions between vessel walls and air molecules. So, in the very small chamber You may get the vacuum already at 0,01 Torr, however in multiple meters large vessel even 10^-6 Torr is still bad vacuum.

Sorry to question author, but aim is pure unrecognizable, so is difficult to make a good advice. But generally: according to Haifa Technion underwater electric blast laboratory publications, the only way to get the good speed is to boost the voltage and decrease the capacitance. Because inductive loss of voltage in cabling, even if they ar soooo short as meter both wires together, are tens of kilovolts or more. They stated that optimal voltage lays between 50 and 100 kV. For ignition of course is used the third electrode, similar as all excimer lasers do, with radiofrequency oscillator. RF ICP is highly ionizating, so it triggers the more stable vacuum. Vacuum systems often caunts that 1 kV/mm is roughly safe distance but 3 kV/mm is sure sewing through. Note, air at STP is ca 3 times stronger, but elegas gives more 6 times strength. The best way to realize the RF ICP is the Clapp circuit. If to use the IXFH42N60 then Clapp capacitors betw S and gnd and G may be eliminated. Their role will be played by parasythics of that mosfet. The freq - moderate power may try up to 100 MHz, but for full power the 35...39 or 40 is the maximum with this transistor. Take it easy with bias resistors, they burns up under the HV RF. It must be fed via choke into contrast with `normal` Clapp circ.

 

I think you are lost in a previous discussion point, we are no longer concerned with the vacuum levels. And the volumes of both of my chambers are very similar.

As for the rest of your message, I stopped reading halfway through. It would help if the info was organised, divided into sections, and had less spelling mistakes.

 

RE:""It would help if the info was organised, divided into sections""
1) The only way to increase the speed is boost of voltage. There are no any other choices. The core of problem is inductance of wires 10 nH per cm.
2) The safe voltage and sure unsafe voltages in vacuum is much smaller than in air. Be guided by figures given.
3) The ignition ought be done by RF plasma. Other methods are unstable.
4) RF source may be connected via small capacitors parallel to main DC source, or better be connected by third electrode.
5) The best way to realize RF oscillator of many kilovolts output is Clapp circuit. If You realize that circuit I described, there are only few details so simple, as the two to source bounded capacitors may be omitted. In the https://en.wikipedia.org/wiki/Clapp_oscillator those for omitting are named C1 and C2.
6) However there is wrong DC pathway in Wikipedia, the source MUST be connected to choke of ca 3 uH (some 10 to 30 turns on 25mm, coreless) what via ca 0,1 Ohm resistor (nichromium wire, few cm long) is connected to gnd pole.
7) Tank capacitor must be designed for high voltage, high frequency and very high reactive power.
8) In the quoted article must be added biasing resistor, ie divider via the RF choke. It ought give about 4 Volts, for example 10k plus 2k2.
9) The optimum Vcc is ca 20-24 Volts. At these the RF otput will be ca 2-3 kV depending on Your coil Q factor. If there is need for larger voltage, use the tapped coil like an coreless transformer.
10) The system is capable to ignite the plasma in vacuum at least one to two inches afar.
9) My last 15 years I am elaborating such circuits every each day, so what I am telling those are well proven things. If You ignore, You shall invent the principle of bicycle by anew.

 

Ok, much clearer now, to be fair, English is not my native language either.

In point 1), you mention speed. Speed of what?


Also as a side problem, regarding the earlier idea of burning a wire, a wall switch did not cut it. It passed the discharge just fine, but the contacts welded together, and the switch stopped working.

 

Using a large SCR would probably solve the relay problem. You can get SCRs that will handle surge currents of over 1000 amps.

Les.

 

RE: ""you mention speed. Speed of what?""

1) Your first mail started with :"I need to discharge as fast as possible". Or other wording, need to get as high as possible the di/dt. Here Your major enemy is parasythic L of just straight wire at so high currents. Just look at Google for Haifa Technion lab publications on this topic!

2) SCR has di/dt in range of kHZ, whilst plasma ignition gives picoseconds. If `fast` means miliseconds, the SCR is OK.

3) RE:""About the breaker problem, what if I charge another smaller cap and discharge it using a relay? Would the relay be damaged?"" Then You shall be made an exact copy of topology of contact welding apparatus

 

Quote: "Using a large SCR would probably solve the relay problem. You can get SCRs that will handle surge currents of over 1000 amps."

Nice idea! I found one that is rated for 300 amps. Since it is a solid state device, and the high current pulse is very short, do you think it will be able to handle it without breaking?

 

RE:""do you think it will be able to handle it without breaking?""
Typical current off the capacitor of 5kV and 100 uF is ca 20-200 kA in pulse. Your case is slightly less weighty, but anyway You must be prepared for kiloamperes. Many cheap 2kA (pulse) thyristors are at Farnell for so small as 20 USD.

 

And do you think that 2kA peak current would work?

 

I would think that the ESR of the capacitor bank will be the main thing that limits the peak current. You may be able to find the ESR value of the capacitors from the data sheets.

Les.

 

did the model rocket igniter work ?

 

Quite the sentence! I didn't exactly use a model rocket igniter, but rather a fine strand of wire shorting both electrodes.

Even though, it worked wonders! Capacitor discharges, plasma generates, it works!

However, it would be more accurate to say it worked, once. Yep, the wall switch didn't withstand the discharge and its contacts welded together. I will upgrade to an SCR, controlled by a separate pcb.

But it worked!! Gotta thank you and the rest of people on this forum for that.

Glass tube arriving next week (ordered two this time, to be safe), testing in the actual device still pending, but I look forward to it.

 

if the wire is shorting cap to create the plasma for cap to discharge, why is a wall switch in the mix? is the switch inline with the cap electrode and thats how you trigger it?

 

Yep, exactly. It is used to connect the cap to the wire, as if it was already connected, it would burn while charging the cap.

 

Doesnt the vaporization of the wire screw up your vacuum and skew whatever results you are trying to measure?

 

Doesnt the vaporization of the wire screw up your vacuum and skew whatever results you are trying to measure?

its gonna affect lots of things. heck, some of that cap charge is used to heat and vaporize the wire, hence some of the cap charge is not even in the plasma.

from what OP said about the study, probably better to build the test apparatus like a flash tube, this way the inside remains constant. or better yet, just use a flash tube of proper size but connect it to the HV cap and trigger it like std flash tube are triggered, then study it knowing what's inside the flash tube (pressure & gas type).

 

A circuit like a tig hf start would
probably work as well, and not introduce additional inductance, but depending on what is actually being measured the oscillations might not be wanted.