Re: More pipe cap TSG experiments

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

What's the air flow through the hole, and more important, past the gap
surface?  Is it high enough that the ions get cleared in the 2 or 3
milliseconds between bangs?  Say you've got to move an inch in a
millisecond.. that's a foot in 12 milliseconds, or about 80 ft/second which
is moving right along.

Do you think the problem is ion clearance time or hotspots developing on the
electrodes ? If you observe the gap, I think the former would have the
sparks forming at multiple places, and the latter with the sparks always
attaching at the same place.

The blast gaps made by Marx used supersonic air flow (1000 ft/sec) with
fairly small orifices. These were used for very high powers (10s of kW) at
fairly high rep rates. While supersonic sounds impressive, it's actually
fairly easy to get... a standard 90 psi air compressor through a 1/16th hole
probably is supersonic... maybe even 1/8th inch.. Look for a "choked flow"
table to find out. (like http://www.okcc-dot-com/PDF/Choked.pdf).. anytime the
source pressure is more than twice the exhaust pressure across an orifice,
you're looking at choked flow.

For grins, though, assume 60 psig source pressure (i.e. 5 atm, absolute)
through a 0.125 diameter hole (.012 sq inch) at 1000 ft/sec = .085 cu
ft/sec, which multiplied by 5 (for the increased density) and 60 (to make
cfm) = 25 cfm....(better be a pretty burly compressor...)  at half that
diameter hole, the flow would be 1/4, or around 6 SCFM...




----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, September 16, 2003 9:15 PM
Subject: More pipe cap TSG experiments


 > Original poster: "S & J Young" <youngs-at-konnections-dot-net>
 >
 > A few weeks ago, I reported results of Jim Lux's pipe cap triggered spark
 > gap design.  I got good results using a half inch diameter hole for the
 > trigger side of the gap.  But with my DC resonant charging setup, it would
 > fail to quench sufficiently at power levels over 1 KW DC.
 >
 > So I tried it again with a 3/4 inch hole, allowing a longer trigger spark
 > and more air volume through the gap.  I was able to crank another 100
watts
 > through it before it started losing quench, causing my filter caps to dump
 > their joules through the reactor into the gap, causing the power supply
 > variac to thump and protest due to the large pulses of mains power to
 > recharge the power supply filter caps.  Bad scene.
 >
 > A clue is that when I raise the break rate above about 180 BPS, the filter
 > cap discharges happen much more frequently, indicating not enough time has
 > elapsed between trigger pulses to clear out the conducting hot ions.
 >
 > Sadly, I am convinced more and more that TSGs for high power will only be
 > successful with AC power supplies.  This allows enough time to blow out
the
 > hot ions during  the times the voltage is below the gap firing point.
This
 > leaves the old standby - an asynchronous rotary spark gap - as the most
 > reliable solution for higher power DC powered TCs.
 >
 > Comments?
 >
 > --Steve Y.
 >
 >