[TCML] Solid state efficiency, was: mini Tesla coil specs

[Bert Hickman]

Hi Ken,

If I recall, your system had a much longer ring-up time than most 
DRSSTC's and SGTC's. That may account for the different behavior you 
observed. This effect is normally quite easy to observe with coils that 
have quicker ring-up.

For example, see the following clip that was captured last year by Tom 
Warner using high speed video equipment that he usually uses to study 
lightning. In this clip, the camera was operating at 7200 frames/second. 
It shows one of Greg Leyh's coils operating at about 200 BPS, and 
clearly shows incremental leader growth from bang to bang as well as the 
dense glow of countless streamers reaching for the grounded ceiling 
support beam as the leaders draw closer. The "afterglow" after each 
current peak is also quite evident. See:

http://www.youtube.com/user/ztresearch#p/u/10/HD46YWM73n0

Bert

Ken or Doris Herrick wrote:
> Bert (& all)-
> 
> Glad to hear that my hunch is correct.  Regarding band-to-bang 
> spark-growth, I recall this from when my coil was working:  I could 
> produce sparks at rep-rates from 1 at a time to upwards of 20-30/s or 
> so, and burst-widths from about 8 cycles (I controlled it with a 
> cycle-counting IC) up to 5 ms-worth or thereabouts, at ~120 KHz and from 
> a 6"x24" Landergren toroid.  I didn't closely look for it, but I don't 
> recall seeing much difference in the overall spark length, for any of 
> those settings.
> 
> KCH
> 
> Bert Hickman wrote:
>> <div class="moz-text-flowed" style="font-family: -moz-fixed">Dex and Ken,
>>
>> The physics of spark propagation is markedly different for positive 
>> versus negative sparks (in a divergent E-field, such as around a TC 
>> topload). All other things being the same, positive sparks propagate 
>> more "efficiently" in air. Once initial breakout occurs, a 
>> positive-going high voltage pulse will travel further than a similar 
>> negative-going pulse. In a diverging E-field, a positive spark will 
>> bridge a gap at a lower voltage than a negative spark. This is still 
>> true, even though negative corona will "break out" at a lower voltage 
>> than positive corona. These "polarity effects" are well known by 
>> professional high voltage workers and engineers.
>>
>> Ken is indeed correct - there is an "optimal" voltage risetime that 
>> leads to maximum propagation "efficiency". One noted researcher, Yuri 
>> P. Raizer, has developed a relationship for the optimal voltage 
>> risetime for a positive spark to travel a distance of L meters ("Gas 
>> Discharge Physics", page 362):
>>
>> T(optimal risetime) = 50*L (in microseconds)
>>
>> Unfortunately, although the above relationship appears to work quite 
>> well for monopolar impulses from Marx Generators, it's not at all 
>> clear how (or even if) the above relationship can be adopted to the 
>> complex waveforms of Tesla Coils. Using either the RF waveform or 
>> envelope leads to relatively low operating frequencies for typical 
>> coupling coefficients.
>>
>> We also know that the longest TC sparks are not obtained during single
>> single events (bangs), but instead via bang-to-bang growth. Newer 
>> sparks build on the heated channels of their predecessors when the 
>> break rate is sufficiently high (>70-80 BPS). This suggests that we 
>> might try combining polarity effect and bang-to-bang growth by 
>> polarizing the system so that the highest voltage peak after ring-up 
>> is always of positive polarity. The positive peaks will provide the 
>> longest "reach" during propagation. This should be simple to implement 
>> through suitable coupling coefficient and phasing for SSTC, DRSSTC, or 
>> DC-resonant SGTC systems, and should cause optimal spark propagation 
>> for a given input power, frequency, and break rate.
>>
>> BTW, an excellent book (also by Raizer), "Spark Discharge", 1991, CRC 
>> Press, ISBN 0849328683 can currently be obtained for around $38 or so 
>> on Amazon and other large book sellers. This book was originally in 
>> the $130 range. It is technical, but quite readable considering the 
>> complexity of the subject. Any serious spark researcher should have 
>> this title in their library.
>>
>> Bert
> 
> 
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