[Prev][Next][Index][Thread]

Re: Skin Effect & Primary Current?

>From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
>To: tesla-at-pupman-dot-com
>Subject: Re: Skin Effect & Primary Current?
>

[big snip]
>     The most dramatic realization for me was that changing L/C ratios
>in the primary had no noticeable effect on dynamic Q. The other one 
>was seeing just how much power is being lost in the gap. Looking at 
>these results from several angles suggested that the gap had all the 
>characteristics of a pair of back-to-back zeners with a voltage 
>drop of about 60 which seemed a reasonable conclusion for a gas 
>discharge.
>
Malcolm,
	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)

Quoting from A. Von Engel _Ionized Gases_ AIP Press, New York, 1993
(reprint from Oxford: 1965) page 259:

	"Thus if with a Cu cathode in N2 (or air) at 1 atmosphere a
potential difference of 350V is observed, if the current density at
the cathode is of order 1 A/cm^2, and if the light emitted from the
cathode region is due to N2 bands{blue/purple jf}, then a glow
discharge is present.  But if (with electrode distances of <= 1cm) the
potential difference is of order 30V, the current density at the
cathode spot 10^4 to 10^6 A/cm^2, and the light emitted from the
cathode region shows mainly the green Cu lines (arc and spark
spectrum), then an arc discharge is present."

Given your observed negative resistance characteristics (prior post)
and 60V drop and my observed blue/purple discharge colour, these gaps
are functioning just short of the arc discharge region. If they were
in the arc region the heavy metal ions would make them even harder to
quench then they already are.  The negative resistance phenomenon is
the result of having not ionized all of the molecules of gas in the
glow discharge - as the current increases, more molecules are ionized
and the voltage lowers.

IBID; page 261:

	"Another aspect is provided by the measurement of the energy
distribution.  In short arcs between carbon electrodes with 5 A in air
calorimetric observations show that about 42 per cent of the total
electric energy flows to the cathode and ~37 per cent to the anode;
the rest is lost by convection, radiation, chemical changes, etc.
When the C cathode is replace by Cu, 45 per cent of the energy enters
the cathode (this may be to high because of the radiation from the
anode spot).  thus about 80 per cent of the energy flows into both
electrodes.. The balance is expected to be different when, for
example, N2 instead of air is used because of the absence of oxidation
of the C anode."

The sealed gaps by Telefunkin? of the late '20s. After a few seconds
of operation, the Oxygen was removed and only Nitrogen was left.

On page 274 A. von Engel states: (which goes against "common"
knowledge)

	" The cathode substances also fall into two groups when the
restriking time is investigated: a circuit containing a carbon arc can
be interrupted for up to about 1 sec at applied voltages of several
hundred V and will restrike without change of the electrode
separation, while a Cu arc when interrupted for 10^-3 sec or less will
not restrike. Hg arcs at low pressure have restriking times of less
than 10^-8 sec."

WHAT? Mercury at 10nS. !!!! ?????  Why are Mercury Thyratrons So Slow?
If low pressure mercury arcs quench in 10nS. why use blown Cu/N2
gaps;) I think von Engel is off here (pun intended)

Although, if the 10^-3 sec number is correct for Cu, maybe we should
consider a different electrode material? (or at least determine if we
are close to the arc region of operation instead of just the glow
discharge region).

	as always; thoughts, comments, snide remarks?

	jim