Re: Marx generator (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Wed, 14 Dec 2005 16:51:51 +0000
From: Mike Harrison <mike@xxxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Marx generator (fwd)

On Wed, 14 Dec 2005 08:56:13 -0700 (MST), you wrote:

>Original poster: Steven Roys <sroys@xxxxxxxxxx>
>
>
>
>---------- Forwarded message ----------
>Date: Tue, 13 Dec 2005 10:27:43 -0700
>From: Gomez Addams <gomez@xxxxxxxxxxxx>
>To: High Voltage list <hvlist@xxxxxxxxxx>
>Subject: Re: Marx generator (fwd)
>
>
>On Dec 13, 2005, at 8:56 AM, High Voltage list wrote:
>
>> Original poster: Steven Roys <sroys@xxxxxxxxxx>
>>
>>
>>
>> ---------- Forwarded message ----------
>> Date: Tue, 22 Nov 2005 20:49:03 +0000
>> From: Mike Harrison <mike@xxxxxxxxxxxxxxx>
>> To: High Voltage list <hvlist@xxxxxxxxxx>
>> Subject: Re: Marx generator (fwd)
>>
>>> Getting all the
>>> gaps to fire together is real important, so you want a good optical 
>>> path
>>> from the first gap (which can be slightly smaller, so it fires first) 
>>> to
>>> all the rest. The strong UV from the spark on the first gap helps 
>>> breakdown
>>> the rest of the gaps.
>>
>> I'm not at all convinced that UV is of any help for the sort of scale 
>> of marxgens we are talking
>> about.
>
>I've read white papers which suggest otherwise.
>

I can see that it is probably an issue for larger marxgens, but thinking about the amount of UV, and
the distance, I have a hard time believing there would be enough energy to have much, if any, effect
on ionisation on a smaller scale device.

Remember that during erection, the current, and hence intensity of the gap spark will be pretty low,
and doesn't go to 'bright white' until the output spark has formed an ionisation channel to 'light
up' with a UV-heavy white flash. 
During erection, the gap is only working against the stray capacitance to ground  of the stages
above it, so current will be pretty low. 
On my marx, if the final output gap is set too wide to strike, the gap sparks are very dim - only
just visible, so the optical energy avaialble a couple of inches away at the next gap won't be much.

On a physically bigger marx, there would be more stray capacitance, and more pre-strike sparkgap
current, and hence more UV.