From: "Terrell W. Fritz"
Date: Sun, 05 Nov 2000 19:59:12 -0700
Subject: Re: [TSSP] NSVPI - Latter Results
Hi Malcolm and Paul, My paper at: http://63.229.238.62/TeslaCoils/MyPapers/spark1/sparkgap.html has some waveforms in it that may be of use. I also included a bunch of raw data with that paper: http://63.229.238.62/TeslaCoils/MyPapers/MyPapers.htm "Tesla Coil Spark Gap Operation Analyzed at High Frequency Word97 Raw data 1-8 9-16 17-24 25-32 33-40 41-42" The text file explains the 42 scope photos. Cheers, Terry At 10:36 PM 11/5/2000 +0000, you wrote: >Malcolm Wwrote: > >> ...If you buy the notion suggested by a crude analysis of that >> behaviour that gap loss is predominantly V.I rather than I^2.R >> and that Vconducting is approaching constancy, you can see why. > >Yes, I see, it's the small constant Vgap. I suppose by definition >the gap loss must be V.I, so long as V changes sign promptly when >I does, ie we can ignore the self inductance and capacitance of >the gap. Also by definition I^2.R applies, so it's not a case of >one rather than the other - its just that we have to accept that >R is a function R(I). > >A couple more questions, > >Recently Barry posted: > >> ...J.C.Martin in the book "J.C.Martin on Pulsed power" >> ... he gives the formula for spark gap impedance as > >> ((1.7 * L)/ r) + Z >> where L is the inductance of the spark channel, >> r is the length of the resistive phase, and >> Z is the impedance on Ohms of the circuit driving the spark gap. > >> ... he gives his famous formula for the resistive phase of spark >> formation as >> (88/(Z**(1/3) * F**(4/3))) * (rho/rho-zero)**(1/2) >> where the time is in nanoseconds, >> Z is the impedance driving the plasma channel in Ohms, >> F is the field along the chammel in units of 10 KV per centimeter, >> rho is the density of gas used, and >> rho_zero is the density of air at STP. >> Rho will change with bang rate. > >Let me guess that the resistive phase is a short period of constant >resistance during which the arc gets established. It looks to be on >the order of nanoseconds and is presumably relevant to fast >pulse discharges in accelerator and fusion supplies. I take it we >can ignore this resistive phase, since tesla gaps conduct for many >tens of microseconds? > >I guess it ought to be relatively straightforward, given a >digital scope, to capture and store the V/I curves for a >range of gap lengths and widths. I take it they would come out >looking a bit like two diodes back to back in parallel? Are >the V/I curves a function of frequency too, or would one set of >curves do for all? > >If such curves exist, are they 'square' enough so that a gap >can be reliably characterised by a 'forward voltage drop' which >is just a function of the gap dimensions and independent of >current? > >It seems to me that such a set of curves would provide the >essential raw material from which an effective loss resistance >(ie an integrated loss per cycle divided by the mean square >current) could be established for a given gap. > >> My expts also suggest (and appear to be well supported by the >> experiences of others) that as one moves to the high L/C - high V >> regime, quenching type #2 (avoiding power ARCS) becomes more and >> more of a bugbear. John Freau is one excellent experimenter whose >> experiments with high L/C primaries have seen his efficiencies climb >> markedly. > >Thanks, was wondering about that. Is there a primary L/C >record holder I wonder? I've been thinking about rigging up >a high energy single shot primary, using a voltage multiplier >to accumulate about 60kV across the tank. > >Cheers, >-- >Paul Nicholson, >Manchester, UK. >--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.