Re: [TCML] Spark gaps (again)

["Dex Dexter" <dexterlabs@xxxxxxxxxxx>]

Sorry ,neither do I have the books you are referring to.
Conductivity of the ionized plasma increases very fast yes .
But the resistance of the arc in gap depends of the effective
column cross-section,which doesn't change so fast as you desribe.
Expanding shock wave expands radially with velocities in the order of 1 Mach.
How much time it takes to expand from diameter 0.1 mm to diameter
10 mm calculate yourself.

Dex
 


--- jimlux@xxxxxxxxxxxxx wrote:

From: jimlux <jimlux@xxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Cc:
Subject: Re: [TCML] Spark gaps (again)
Date: Sat, 07 Mar 2009 15:56:16 -0800

Dex Dexter wrote:
> Yeah,but the dynamic "resistance" of the gap isn't only the function of current.
> Beside other things,it's the function of time.That was my point.
> 
> DD. 

The arc column heats up very fast (sub-microseconds). I don't have it in 
  front of me, but Edgerton's book or Bazelyan and Raizer probably have 
the data.  The conductivity increases so fast that when you're looking 
at charge moving to the end of a leader; the propagation velocity of the 
electromagnetic field in a leader is significant, more than the time it 
takes to heat the air up.

Looking at the usual tesla coil running at 100kHz or so, a time scale of 
a microsecond is instantaneous.
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