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Re: Skin Effect & Primary Current?

>From: EDHARRIS-at-MPS.OHIO-STATE.EDU
>To: tesla-at-pupman.COM
>Subject: Re: Skin Effect & Primary Current?
>
>
>
I wrote:
>
>>
>>>     At this current density your gaps are in the glow-discharge
>>> region (don't believe me? look at the light emitted. Is it blue:
>>> indicating a Nitrogen glow discharge? or Green: copper? ?/iron. =>
>>> arc)
>>
>>Bright blue.
>Glow discharge regime, not arc! On my rotary, with iron/steel bolts,
>I'm eroding to gap => arc; maybe this is why I'm having so much
>problem with "power arcs"?
>
>------------------------------------------------------------------
>EH>
>
>While it is true that glow discharges emit the characteristic 
>spectral lines of the gas that constitutes them, this isn't a
>good way to determine if the process is really an arc or a glow.
>I use magnetron sputter guns to deposit metal films here at OSU.
>These guns operate in the glow discharge regime with current
>densities of about 0.1 Amp/cm^2. [dischare current density is the
>total current/discharge (not electrode) area]. Still, these glow
>discharges emit very strongly in BOTH the gas and electrode
>spectral lines. 
You are saying that there is NOT a clear 'cut and dried' dividing line
between a glow and arc discharge.
I should have guessed that, given 6 orders of magnitude difference in
my quoted material.

I'm learning.
>
>Most of the spark gap dischages I've seen for tesla coils and the
>like are not dominated by the spectral lines of the gas or electrode.
>Instead they are rather white/blue - indicating extreme temperatures
>associated with arc phenomena.
Am I confusing blue with purple, given a quick glance v.s. a look with
a #8 (greenish) welding filter? I would guess so.   ? 
>
>Glow discharges tend to envelop the entire electrode surface so
>that the current density is relatively uniform just near the electrode
>surface...>Arcs, being more 1-d on the other hand, tend to form hot spots on the 
>electrode surfaces where the current density can be very high.
Bingo! My experience is NE2's v.s. ARC welding. (I try to keep glow
AND arc discharges out of my electronics engineer profession work;)
>
> This pitting does not happen in the case of
>glow discharges since the electrodes are 'sputtered' much more
>uniformly. 
1 gap segment 'to work', I'll look at it under low magnification.

>Since the temperature of an arc is so high, unlike the glow,
>one should also see a black-body radiation curve superimpodsed on the
>spectral lines of the gas and electrode materials. This black-body
>radiation is responsible for much of the 'whiteness' of arcs.
>
Are these really arcs vaporizing metal as the conducting ions?
>
>Finally, arcs usually have lowwer voltage drops than do
>glows. Typical arcs might have 50-200volts drop depending heavily
>on the current, whereas glow dischage voltage drops are 
>*charateristically* independent of current and are typically 200-
>1000 volts. ( neon gas will 'glow' down to ~70v, however).
[snip]
>If you have 100 amps and the discharge area is typically (~0.5mm)^2 then
>you have a current density of 40,000 amps/cm^2. That's hot! I'm 
>pretty sure you're really in the arc regime. Remember, it's not the
>total electrode area, only the area of the electrode which is actually
>surporting the discharge at any one time ( the bright spots).
>
>
I've got it now! Malcolm, in a previous post mentioned 60 volts as his
spark gap voltage. I was differentiating neon's 60 voltage drop with
mercury's 13 volt arc drop, not a generalized glow with a generalized
arc. Bingo, light on (pun intended;)
>You might want to look at Gaseous Conductors by J. D. Cobine.
>
I will.

Edm thank you very much!

	jim