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Re: Ions n' arcs
Richard, (all)
Excellent!!!!! This was most interesting and informative. There's really a
lot of information here which I think coilers "coils" can benefit from if
they take note. I've been playing with PSpice simulations lately (thanks to
Terry Fritz enlightenment) and have been having a great time. These
simulations provide a unique look at theoretical coil operation. One can
view voltages AND currents in any part of the system for whatever time
interval favored. However, one cannot say because my voltage and current is
at x potential that my output will be x length. Only real world experience
will define those approximations. But that's ok because, although we know
lengths from experience, the simulations can help define parameters, and if
simulating real world coils, this data along with observational data can be
very useful. What is missing from the simulation is the arc channel
processes you so well defined. I do believe ionic reactions under such
conditions can be simulated, but still, arc length is out of the realm of a
simulation until conditional ionic reactions can be defined (may not happen
any time soon).
>From the vast amount of variables included in the arc channel as well as
what produces it and gives it strength, it should be somewhat satisfying
that in order to obtain growing singular arcs, it is absolutely necessary to
generate an efield with a few kilovolts, with a good deal of current, and a
variable break enabling a cap to release energy at a point when the average
energy causes an arc channel to sustain and grow.
I hate to say it, but coils with static style breaks will probably never be
able to hit this mode of operation. Variable breaks will be needed to tune
the ionization channel which means small neon powered coils will not last
under such conditions. It appears input transformers must be of the pig,
potential, etc.. size and ruggedness to supply such currents, and coils will
need to be relatively large to handle the beat kicked into it among other
reasons. I wonder if coils such as Electrum have considered these
possibilities (probably). It is becoming clearer by the moment that it is
desirable to design to the type of output desired. There was a time when we
would design to cause arcs. Now maybe we can design to the type and length
of arc desired. I doubt that many have designed their coils from the arc
inward. But it does make sense.
Although you have listed the major arc channel components, I have not seen
the specs on a coil that would cause extended ionization and arc growth. Do
you or anyone else have data on such a system including time stamps for
start of channel and end of channel mean times? Would be very helpful and
interesting to simulate and see what type of currents and potentials come
about.
Anyway Richard, thanks for sharing this information,
Bart
Tesla List wrote:
> Original Poster: Richard Hull <rhull-at-richmond.infi-dot-net>
>
> All,
>
> The continued study of arc and gas ion dynamics has had me pouring over
> a number of references. By far the best remains my first love "Ionized
> Gases" by Alfred von Engal. There is a reason for this enthralment by
> myself with this text. I am not alone in this adulation,either! The
> AVS (American Vacuum Society) has thrown this book on its extremely
> short heap of "permenantly-to-be-printed" books known as the AVS
> "classics series". (maybe 20 books total in the history of all printing
> that made their list- I have most).
>
> In short, von Engals was a recognized expert in the field. If this were
> the only criteria he would have been relegated to just an E Pluribus
> Unum amoung countless other "ion/plasma experts" so litering the field,
> not to mention publishing their own "definitive tomes". What makes von
> Engal's work so different, was the mentality and timeless nature of his
> effort. Furthermore the following litany of what makes something
> classic to do'ers in any field of endeavor......... The clear graphs
> and diagrams of emperically derived data........ The relative paucity
> of tedious theoretical equations so locked to rigidly fixed and
> controlled environments......... His open admission through out the
> book that the equations he does offer up are for specific cases and his
> supplying caveats regarding there use in real systems......His treatment
> of a full range of ionization pressures in spite of everyone else in the
> field talking of vacuums and reduced pressure ionization as a
> "given".........open admission of ionic processes that are still
> mysterious in spite of their observational mechanics being well known
> and engineered........ supplying real world, empirically based
> application rules of thumb with the same cautionary caveats he supplied
> for the equations earlier. Writing in a scientific but friendly
> mentor-like advisory tone as opposed to one of complete
> authority................All of these make the book an easy read though
> complete and thoroughly on topic, leaving it in a class by itself and
> thus, a classic!
>
> Regarding my recent discussions on Tesla coil air arcs, I quote this
> following paragraph from page 209 of his work where the discussion
> involves detailing high pressure ionization in intense electric fields
> as relates to emboldened current channels (glows to arcs)...........
>
> "There have been recent attempts to measure the longitudinal spread of
> luminosity in a gap and to relate it finally to the spatial variation of
> the electric field and its change with time. (ref) The transition
> mechanism from avalanches to the more condensed form of discharge remain
> still obscure. An obvious step in the direction of explaining the rapid
> multiplication and rise of current is to include secondary processes in
> the gas such as ionization of excited species which would enable slower
> electrons in the distribution to play an active part besides charge
> transport. (ref.) Once a finite length of path has a high density of
> ionization (which because of time cannot diffuse) the electric field
> along this path length must drop to a very low value. As a result of it
> the field in the remaining gap will rise and the multiplication process
> will speed up. However, there is no satifactory treatment which deals
> with this problem."...................
>
> I am now on my fifth cover to cover re-read of his book in three years.
> I haven't figured out whether I am just slow on the uptake or whether
> his work so complete that it is like a superb Monty Python movie where
> more is picked up after each re-viewing items often missed in the
> shuffle to follow the plot in prior viewings. I fear it is a little of
> both. I have yellow highlight marked so many key passages and thoughts
> that the book is looking more like the Bell System yellow pages than a
> scientific text.
>
> To pick the above salient paragraph apart, we see:
> 1. He starts the thought with the statement of what was attempted by
> recent experimenters to codify and their subsequent failure. Gives
> reference.
> 2. He states that some observation evidence exists whereby the gap is
> filled by successive ionizations, the field drops along the arc channel,
> and provided the ion liftimes are long enough or the energy persists for
> at least that period, a further enhancement of the channel is seen due
> to SECONDARY processes. Gives another key reference.
> 3.Finally closes with the sad admission that no formal mathematical or
> physical treatment of this observed process exists.
>
> He has supplied info on how it appears, from real observations, gaps in
> high pressure gases are crossed by heavy current channels via multiple
> ionizations and re-ionizations in strong electric fields. Then, he
> finally admits that no real theoretical mathametics exists for this
> treatment. It is rather obvious why, to the informed reader, this is
> so. The entire first 209 pages have brough us to this point with a
> myriad of useful but limited equations, numerous qaulitative,
> observational tips with their associated caveats, along with the von
> Engalian truth about numerous little understood processes. A daunting
> task for would-be modelers especially in view to the numerous possible
> secondary processes mentioned. This is often more than the staunch and
> often rabid phyicist can bear. However, folks who actually work in the
> real world (AVS members), elevate this effort full of maybes,
> non-commitals, qualitative tips and addmissions of ignorance to
> "Classic" status. I might be just an old grizzled electronics engineer,
> but I see why they honor von Engals as they do.
>
> We can now understand a lot of why our casual observations of big
> terminal loads, lots of power with lots of arc current and moderate
> voltage make long hot arcs. Also why potential might not be all that
> important beyond supplying an electric field (hopefully intense) around
> the coil.
>
> The key factors for our Tesla coilin' efforts are that air ionization
> can occur with relatively low fields as most atoms only require 10-20 ev
> of energy to lose an electron. While a long reaching, intense electric
> field is strictly a function of terminal potential, ion lifetimes and
> volumetric ion production demands current!! More current makes for more
> ionizationsat any given field intensity and higher levels of excitation
> and ionization also follow current. The mean ion lifetime goes up
> rapidly also as the channel expansion reduces the internal channel
> pressure. Still, for our purposes, the max lifetimes of super excited
> ions are still on the order of maybe, at most, 100milliseconds. Mean
> liftimes of the bulk of the really hot gas jumps from under ten
> milliseconds to around 50 milliseconds. Thus, more energy pulses
> (higher rep rate) of lesser energy (smaller cap) but overall increased
> average energy (plenty of input power from the wall socket and efficient
> conversion) can, to a point, make maximum use of air ionization to make
> arcs go where no real potential difference with low channel current
> could pass. This is concomittent with a moderately high electric
> field (large xl secondary) and high channel current (large terminal
> loadings).
>
> Single chanel arcs which I have stressed, funnel and focus the
> available field (as noted by von Engal above) and allow the ion
> re-enhancement to move out unabated until the ion channel gets too long
> for the repetitive energy to support not only growth, but continued
> existance due to increasing temperatures in the gas dispersing
> mechanically, the ions in the channel.
>
> I hope this helps with the understanding of the object of our "off coil"
> desires.....long hot air arcs! As this is a totally off coil process we
> must reverse engineer for this process alone in the Tesla coil engine.
> This will mean a lot of tradeoffs and a load of multivariable and
> covariant items to juggle. A daunting process which is only hinted at
> and dimmly understood in the best of HANDS and MINDS daily involved with
> Tesla coils. (read- a handful of people on the entire planet)
>
> Richard Hull, TCBOR