Re: Single Shot

From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Tuesday, August 05, 1997 11:14 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Single Shot

Hello all,
            I feel it is about time some myths were put to bed 
regarding TCs and TC operation. I composed a post several days ago 
and sent it to Robert Stephens and Richard Hull in that order for 
peer review and comments. At that stage I was reluctant to post it 
to the list as I don't like upsetting people. However, as you will 
see at the end of this, I was encouraged to do so and now send it 
complete with the additional comments. I have no disagreement (and 
indeed agree strongly) with what both of these gentlemen have to say. 
With their kind permission, I am posting this to the list. I am sure 
this is going to upset some who hold strong views to the contrary and 
that is fine. But I have to say to those people, "show us your 
*evidence*". I am sure most on the list recognise the expertise in 
the art of coiling of the two gentlemen mentioned.

 ------- Forwarded Message Follows -------

Date sent:      Fri, 1 Aug 1997 01:14:30 -0400 (EDT)
To:             "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
From:           richard hull <rhull-at-richmond.infi-dot-net>
Subject:        Re: Single Shot


>>     I am concerned also that some seem to hold some erroneous views 
>> on what this tool (single shot) is all about:
>>     (a) myth #1 - output voltage is lower with this test.
>>         It is *not*!  The gap sets primary voltage and this does not 
>> increase if the gap setting doesn't change. The only thing that 
>> changes with repetitive operation is pumping and supporting an ion 
>> cloud and ionized streamer path, which leads to....


I can't believe that others would think that the voltage produced by one
pulse of a system with a fixed cap and voltage might be different from
multiple pulses!  As noted effects outside the coil system make the spark
grow with multiple pulses per unit time, not a changing voltage.  RH

>>     (b) myth #2 - you can't measure primary voltage in repetitive 
>> operation.
>>         False! You can if you use a high voltage probe and 
>> oscilloscope. It doesn't change.

RWS>I agree so far.

I have used a capacitive divider for this purpose with the recent H2
Thyratron work.  Worked great!  I now can monitor both current and voltage
in circuit.

MW>> What do you think is going to fire 
>> at a higher voltage, a cold gap or a hot one?? 

RWS> A hot gap will break over at a lower voltage than a cold gap.

MW>> If primary voltage 
>> doesn't change, then secondary voltage doesn't either.

>Agreed, sort of, with caveat.  Secondary voltage will be tied to 
>resonant Q.  Q varies with top loading.  As you mentioned, there is this ion 
>cloud thing happening when you get into fast rep rate continuous 
>operation which drastically effects the load situation that the top 
>terminal experiences.  I would hazard to guess (still haven't had a 
>chance to measure this kinda stuff yet as my probe is only partially 
>completed), that you may actually see a higher instantaneous voltage 
>in a single shot excitation because there is no ion cloud yet putting 
>a clamp on the top terminal.

This is undoubtedly correct!  I agree with Rob here.  It seems
counterintuitive that the longest and hottest ground attached arcs are
actually the resultof, and are being fed by, at that instant, with a reduced
system voltage from the resonator!!!!  Thank goodness for air pressure,
ionization, and complicated electric fields! RH

RWS>  This is analagous to the slightly 
>higher firing voltage as compared to the extinguishing voltage seen 
>on low pressure plasma devices like a gas filled cold cathode voltage
>tube or even a minature NE-2 neon lamp.  As I say I'm just guessing 
>here as I haven't had the opportunity for a lab measurement.
>What I *have seen* with a more modest divider probe and a vac tube 
>T.C, is an output voltage reaching a certain higher potential (around 
>180 kV P) and then as soon as breakout occurs the terminal voltage drops
>perhaps 30%.  This is the ionized atmosphere voltage clamp effect. With true, 
>non-interrupted CW sinusoidal power it will suck as much power as you can 
>feed into it very happily. This flare sits writhing from a stationary 
>origin point like a fiery bouquet.  From its initiation, its length 
>is extended probably by the square law to input power. The net result is 
>non-impressive streamer output length from vac-toob coils.  The disruptive
>discharge T.C. gets around this in at least two ways.  Firstly, the most
>power is 
>concentrated in the first rise of the output pulse.  This *suprises* 
>the surrounding air which is not yet ionized.  The resultant streamer 
>may not be maximum length, but the voltage goes the highest it can 
>ever get under this initial condition.  Once an ion cloud is 
>developed, hopes of developing these extreme voltage peaks are 
>dashed, unless one has unlimited power.

Rob has pointed up another key item I have harped on over the years.  A
large increase in terminal C must be accompanied by increased power.  I
prefer leaving the cap rather smallish and uping the voltage of the tank or
increasing the rep rate.  If the spiral continues, of course, one must bump
the tank capacitance up accordingly, albeit begrudgingly.  RH

MW>> The equation
>> based on conserved energy has been posted a number of times in this 
>> forum. I know it is held to be wrong in some quarters but then the 
>> views held in those quarters have _not_ been supported by direct 
>> measurement. Moreover, no explanation as to how you can overcome a 
>> fundamental limitation in physics has been forthcoming either. 
>> Whichever view is ultimately correct does not alter in the 
>> slightest what I am saying here.

MW (additional comment: there is now every reason to suppose the EOC 
view is the correct one. If anyone doubts that the model I have now 
constructed of the secondary is somehow fake, I remind them that 
*measured* voltage rise under CW drive conditions is by VSWR - a 
distributed line attribute i.e. I have not just constructed and 
measured a lumped circuit).

>>     (c) myth #3 - The secondary is rung up and up with successive 
>> shots in repetitive operation.
>>         Not true for the break rates we are typically using. I 
>> earlier commented on the exacting phasing requirements for this to be 
>> so. I also noted the spark loss prevents this. Time and time again I 
>> have seen this with the help of a storage oscilloscope. To get a 
>> handle on high speed dynamics, you have to use the appropriate tools 
>> for the job. If you doubt this, get a storage scope, hang an aerial 
>> wire off the probe, place the scope a good distance away from the coil 
>> and see what happens when you single shot the coil and move a ground 
>> rod in to the terminal. You really will get a feel for what is 
>> happening then! Compare the time the secondary rings for when loaded 
>> by spark, then compare that with break rate timing at the BPS you 
>> normally use. Then run the coil normally. At low timebase speeds you 
>> see mere blips which correspond to the gap fires. Speed the timebase 
>> up and you see the secondary rings, beat envelope if the secondary 
>> is lightly loaded, the works.
>>     This is not some airy belief. I will be happy to capture dynamic 
>> waveforms and photograph them with a running coil when I get into the 
>> lab in a couple of month's time. I have already sent photos of single
>> shot coil operation taken off the scope to one or two people.

>Correct.  The only way successive shots will contribute to the ringup 
>of the secondary is if they are occuring in phase, and at a 
>submultiple near to, or actually at the RF ringing frequency of the 
>secondary system.  This is not possible with conventional rotaries.  
>It *is* exactly how a CW vacuum tube TC works, and is why vacuum tube 
>TC's give unimpressive output.  When you input power at the same rate 
>as you ouptut it, there is no storage effect to give bigger, but less 
>frequent bangs.  But you and Nickola know all this very well.  : )

This is well put and should be amplified upon. I think the ring up concept
is a natural confusion resulting from the growing of the sparks over time.
Air ionization channeling and effects which support more spark length with
more bps might lead to this opinion. RH
MW>>      (d) myth #4 - AC operation at mains frequency is somehow 
>> different to DC operation.
>>          Again, not so (apart from the fact that the primary cap 
>> charges to opposite polarities for alternate gap fires). I have 
>> noticed no difference whatever in output characteristics for the coil.
>> Of course that is subjective so a measurement or observation would 
>> make me check that out more thoroughly using more heavyweight tools.

>I have no experience with DC coil operation except with vac toob 
>T.C.'s.  I cannot comment meaningfully on this except that one would 
>think that in the AC driven case, since the cap is being charged the 
>other direction every half mains cycle, then since the current in the 
>Tesla primary will start its ring in the opposite sense as well, 
>you'd (I'd) expect to see an opposite polarity appear at the topload 
>in synch with the mains reversal.  This should not occur when the 
>coil is operated from DC. That statement seems logical to me, however 
>we have both read Richard Hull's posts about electrostatic activity 
>detected in the vicinity of operating T.C.'s driven conventionally 
>from AC and his results are not those that I just postulated.  Again, what
a useful 
>device having my own HV probe will be! 

Rob is wise here.  The pulse polarity nor the electrostatic result can be
effectively changed with DC operation over AC operation.  I gave some
insights as to why this might be so back in January following my experiments
with pure DC systems.  Overall, DC stresses the caps a bit less (no charging
reversals) at a fixed break rate, but a static gap will really "run away" in
a DC system with the DC charging potential being omipresent and the
breaks/sec go to the moon (quadrupled in my system over AC usage at a fixed
gap setting. RH
MW>>      The above is open to correction/refutation as long as such 
>> is accompanied by demonstrable, repeatable and quantifiable 
>> measurements. I object to being told I cannot measure what I 
>> already have. I will dot the i's and cross the t's in two 
>> month's time if the lab remains mine to use.
>> Malcolm

A very good post inspite of your reservations Malcolm.  Others should see it.
Thanks for sharing it with me.


    Thankyou again to Robert and Richard. As I mentioned in another 
post, a full set of photos the waveforms produced by a running, 
sparking disruptive coil will be available from TCBOR in the near 
future. List members will be notified when these are available. I 
hope this will assist those without this kind of instrumentation to 
understand how a TC really works.