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Registered Member #2566
Joined: Wed Dec 23 2009, 05:52PM
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Posts: 147
Interesting research on laser guided arc discharges conducted on 350 kV Tesla Coil:
Fig 6 are typical discharge current oscillograms for laser triggered discharges. Note how strongly damped are these wave shapes. Isn't that unusual? Secondly, isn't such strong damping in contradiction with antenna signal shown in Fig.2.(b) (althought peaks are not shown)?
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
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They used delivering 0.3J in a little under a picosecond, which is about a terawatt of peak power, not quite within hobby reach sadly.
It is interesting to see their results, although I really wonder what the people running the laser thought about having a tesla coil next to their multi-million dollar laser and associated electronics.
Note how strongly damped are these wave shapes. Isn't that unusual?
Damping depends on the arc resistance, here in the kohm region and the arc inductance together with the inductances in the grounding wiring. In our case we have a tank made from the tesla top load, the inductances mentioned and the arc resistance. From the oscillating freq, about 10MHz from Fig. 6 and the top load of 30pF, the inductance is about 10uH. Q is 2*pi*f*L/Rarc, or about 0.5 for an Rarc of 1k. So the tank is indeed strongly damped.
Secondly, isn't such strong damping in contradiction with antenna signal shown in Fig.2.(b) (althought peaks are not shown)?
I guess the oscillations in Fig. 2 arise from a tank like behaviour of the antenna plate together with the cable to the scope. The oscillations don't seem to have anything to do with the arc itself, since they also appear, when the laser fires.
I found most interesting the short times necessary between laser firing and voltage maxima, i.e. on the order of us's. It is well known, that at burst rates at e.g. a 100Hz, arcs will almost follow previous arcs, even though the arc to arc time is then 10ms instead of us.
Registered Member #2566
Joined: Wed Dec 23 2009, 05:52PM
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Posts: 147
Uspring wrote ...
Note how strongly damped are these wave shapes. Isn't that unusual?
Damping depends on the arc resistance, here in the kohm region and the arc inductance together with the inductances in the grounding wiring. In our case we have a tank made from the tesla top load, the inductances mentioned and the arc resistance. From the oscillating freq, about 10MHz from Fig. 6 and the top load of 30pF, the inductance is about 10uH. Q is 2*pi*f*L/Rarc, or about 0.5 for an Rarc of 1k. So the tank is indeed strongly damped.
But normal arc discharges to good grounding aren't so damped. That's the point. Usually, it's 5-10 cycles before arc dyes out...
Is that for tesla coil arcs or DC arcs, e.g. from a marx? TC arcs are long for their voltage, which implies higher arc resistances and thus stronger damping.
Registered Member #2566
Joined: Wed Dec 23 2009, 05:52PM
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No, I was referring to flying pigs and the linked article is about sparrows. Classical Tesla Coil grounded arcs foot or two long . If you measure discharge currents, you'll probably see they oscillate much more.
Might be so. In my calculation I found the inductance needed for a 10 MHz oscillation (10uH) to be rather high. It can't be explained by a single piece of short (maybe 1m) of wire, so it is caused either by long ground wiring or some effect in the arc. Lower damping requires even higher inductances, which would also imply lower oscillation frequencies. I don't have any data about this, but I think it is possible that particularly long ground loops might have the required higher inductances with corresponding lower damping.
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Laser-guided Tesla Coil discharges
