Re: Parallel and Series LCR Circuit Qs

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi Jim,

	I played with this a little today.  I would think a low value (~100 ohm)
resistor but the 220k ohm of the streamer really is dominant.  

I have trouble with the arc speed.  The "per length" values are easy but
MicroSim like to calculate the propagation speed down the line as:

TD = LEN x SQRT(L x C)

Given real numbers, a 2 meter arc is 6.2nS which is correct for a T-line
but far faster than a slowly reaching arc.  Not sure how to trick it,
yet...  If you go to a longer length line, it just compensates and gives
the same net speed...  Working on it...  It is also very slow calculating
but that is not a big deal...

Cheers,

	Terry


At 12:30 PM 8/10/00 -0700, you wrote:
>and, as I think about it.. what sort of load would you put at the far end of
>the transmission line?
>A short?  An open? A resistive termination (representing the thermal heating
>of the air at the end of the leader)..
>
>There is some discussion in the literature of what happens when a leader and
>spark channel grows, then shrinks back (say, driven from a bipolar pulse
>source).
>
>Probably a resistive termination.  You wouldn't want a reflection back down
>the line,even though, because the line has a significant resistive component
>(representing the heating of the air along the spark channel), the
>reflection would be rapidly attenuated.
>
>-----Original Message-----
>From: Tesla list <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
>Date: Thursday, August 10, 2000 12:20 PM
>Subject: Re: Parallel and Series LCR Circuit Qs
>
>
>>Original poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
>>
>>Hmmm.. what about modelling the spark as a transmission line.  Scaled to a
>>length so that the propagation takes the right amount of time.  Just as in
>a
>>transmission line with an impulse, the source driving it doesn't "see"
>past
>>where the propagation has gotten to.  So, it would appear to have a
>steadily
>>increasing C, as the step function propagates down the line....
>>
>>The series L per unit length would be 1 uH/meter (roughly) and the C per
>>unit length is 5-6 pF/meter (roughly), so the characteristic impedance
>would
>>be sqrt(L/C) or 500 ohms...
>>
>>The propagation velocity of a spark is around 1E7 m/sec, so your
>>transmission line would need to be scaled to 30 times the real length
>>(3e8/1E7), for a scaled L of 10 nH/meter and scaled C of .05 pF/meter
>>(keeping the impedance the same...).  I'll bet you could work the
>>series/parallel R in as well....
>>
>>you could even get fancy and hook up a bunch of transmission lines in a
>>forked pattern, more representative of real sparks.
>>
>>This might start to have time domain properties that are realistic in a
>>simple SPICE type model.
>>
>>-----Original Message-----
>>From: Terry Fritz <twftesla-at-uswest-dot-net>
>>To: jimlux-at-jpl.nasa.gov <jimlux-at-jpl.nasa.gov>
>>Date: Wednesday, August 09, 2000 11:33 AM
>>Subject: Re: Parallel and Series LCR Circuit Qs
>>
>>
>>>Hi Jim,
>>>
>>>At 06:24 AM 8/9/00 -0700, you wrote:
>>>
>>>>> So the Tesla coil "source" basically needs to be impedance matched to
>>>>> supply this "load", optimally.
>>>>
>>>>Of course, the impedance is time varying too, with the C growing as the
>>>>streamer grows....
>>>>
>>>
>>>Yes!  I assume the coil should be optimally matched when the streamer is
>>>longest since that is were every bit of energy needs to be to push the
>>>streamer that little bit further.  If a coil is matched for a 10 foot
>>>streamer, it will not mater if the matching is poor at 1 foot.  It will
>>>have no trouble getting past one foot and on to were every little bit
>>>counts out at 10 feet or the edge of it's available power where fine
>tuning
>>>really counts.
>>>
>>>Of course that "may" not be theoretically the 'best' point considering the
>>>other dynamics going on.  But it is my best guess...
>>>
>>>Cheers,
>>>
>>> Terry
>>>
>>
>>
>>
>>
>