Re: Spark Gap Sustaining Current (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 28 Sep 2007 08:31:52 +0800
From: Peter Terren <pterren@xxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Spark Gap Sustaining Current (fwd)

If you supply current continuously then the spark will be continuous. 
However, if it has a significant capacitance with an actual capacitor or 
simply large enough electrodes (scch as a TC toroid) then then the spark 
will discharge the capacitor and the voltage will drop. The spark will 
extinguish in sub-microsecond times and will only spark again when the 
capacitance recharges. This type of spark is bright white, noisy and single.
http://tesladownunder.com/HVBrokenSparksRightPos1.jpg
Consider a supply terminated by a resistor or inductor. Then when a spark 
forms, the current will not be drained to near zero as the current is 
limited and voltage remains present. The spark can be continuous if the 
voltage supply is able to supply this current. This type of spark is a soft 
orange glow, quiet and continuous.
http://tesladownunder.com/Flybackbentarc.jpg
The parameters differentiating the two include the current available 
continuously, voltage, capacitance, resistance and inductance.
If you try to have a continuous spark with very little current then even the 
small capacitance of a length of wire may become significant and make the 
sparks intermittent rather than continuous.  Alternatively, corona will draw 
enough current to drain the voltage so no spark forms.
Peter


> ---------- Forwarded message ----------
> Date: Thu, 27 Sep 2007 12:55:46 -0500
> From: Crispy <crispy@xxxxxxxxxxx>
> To: tesla@xxxxxxxxxx
> Subject: Spark Gap Sustaining Current
>
> Hello,
>
> I have a quick question about spark gaps.  How much current is required
> to sustain an established arc in a spark gap in "dead air"?  Let's say
> that there are two tungsten contacts about an inch apart, and an arc is
> ignited by a voltage of a little over 20kV.  Say that the ambient
> temperature is room temperature and that there is not significant
> airflow through the gap other than that which is generate by the gap's
> heat itself.  Is the sustainability of the arc purely a function of
> current through it?  If so, in such a theoretical gap, how much
> sustaining current would normally be required?
>
> Thanks,
> Chris