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On 4/9/15 7:38 AM, Timothy Gilmore wrote:
Thanks for sharing Doug.
One question to the group...as I am building my new toroid, I was under the
impression that a smooth surface like I saw with Doug's machined toroid
would provide only 1-2 sparks but I saw many like I get on my aluminum
ducting toroid. Is this the case also with machined toroids?
The science of spark development and growth is very poorly understood.
There's a book "Spark Discharge" by Bazelyan and Raizer from about 10
years ago that has a lot of theory, but the summary is that "it's
complex and hard to model"
In my experience, smooth surfaces tend to have many sparks, because a
spark can grow from one place as well as another. The whole "breakout
point" thing (a thumbtack stuck to the toroid, or a screwdriver laying
over the edge) is an attempt to create a preferential point from which
sparks develop.
The visible sparks you see are really the combination of many sparks.
The individual sparks grow very quickly (nanoseconds), dissipating and
reforming on every halfcycle of the RF. IN some cases, the sparks tend
to follow the same path, extending the channel a bit more each time. In
others, it doesn't.
It is believed that there's an interaction between the size of the
topload (which sets the energy available for each individual spark
event) and the resonant frequency, and the bang rate.
If you have a very smooth surface and a very uniform surroundings and a
bit of air movement, each time a new little spark starts to form, it can
form in a new place, because one place is as good as another, and the
moving air disperses any residual "partly ionized" channel as well as
cooling the topload.
A narrow point, with no moving air, can
a) provide a preferential spot for the spark to start
b) get hotter, aiding in spark growth because hot things emit electrons
c) leave the hot air from the previous spark in a convenient place.
But there's a tradeoff.. if the spark forms too soon on the topload, it
drains the energy out of the topload (being fed in from the secondary)
before it has time to accumulate. If there's not enough energy to "feed
the spark", it stops growing.
Tim
On Thu, Apr 9, 2015 at 9:04 AM, Doug <doug11642@xxxxxxxxxxx> wrote: