Re: Relativistic Runaway Breakdown Model for Lightning

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Greg,

This is an interesting idea indeed!  It would help explain why lightning 
seems to go where ever it wants to, often ignoring the rules of 
electrostatics that we think are in place.  I wonder if the same effects 
could make a difference on even small coils since just a tiny bit of the 
effect could be dramatic in our micro scale situation.

I do not have access to the paper, but maybe we could get it somehow.  The 
local college library should have it...

I was watching a lightning storm in the mountains today.  It never seems to 
follow those E-field charts like it should.  But this accelerated electron 
thing would help explain that!  I one case the lighting traveled down into 
a valley and hit a metal building.  From a pure electrostatic profile point 
of view, that should have been impossible...    I decided it was wise to 
drive on when the strikes got consistently less than 200 yards away 
;-))  But I guess the chances where pretty good it would ignore the antenna 
on my car (a local high point) given this new info ;-)

Maybe there is a chance this might lead to funding for a really big Tesla 
coil like someone we know has proposed :-)))


Cheers,

        Terry


At 01:04 AM 6/2/2005, you wrote:
> Hi All,
>
> An interesting paper by A.V. Gurevich and K.P. Zybin appears in the May 
> issue of Phys Today, titled "Runaway Breakdown and the Mysteries of 
> Lightning."  If you have access to a copy of Physics Today I strongly 
> recommend reading this article.
>
> One of the mysteries they address is how natural lightning can originate 
> and propagate with an average electric field of only [200kV/m] -- an order 
> of magnitude below what is needed to breakdown air at STP [2MV/m].  They 
> provide a compelling argument that a relativistic electron chain reaction, 
> initially triggered by a cosmic ray-induced shower, is the principal 
> mechanism for generating the ionization necessary to trigger the main 
> lightning strike.
>
> The theory for Relativistic Runaway Breakdown states that as an electrons' 
> energy increases, the braking force due to collisions decreases as 
> 1/energy, until the electron starts to become relativistic and reaches a 
> 'critical runaway energy' of 0.1 to 1MeV.  At this point, if the electron 
> is in an electric field greater than about 200kV/m it will actually 
> accelerate; it's frictive forces now being less than the accelerating 
> forces.  The relativistic electron can now ionize other atoms, spawning 
> new relativistic electrons in a chain reaction.  The electric field cannot 
> by itself originate the first relativistic electrons, as there's too much 
> friction on the slow, classical electrons.  However, a cosmic-ray-induced 
> shower can provide the seed electrons.  The authors provide a substantial 
> amount of fascinating data, collected from both terrestrial observation 
> stations and from spacecraft, to support their theory.
>
> One of  the collaborating researchers, G.Milikh, recently gave an 
> interesting powerpoint presentation outlining the Relativistic Runaway 
> Breakdown process, and how runaway electron beams can produce some of the 
> diffuse, high altitude discharges observed between thunderclouds and the 
> ionosphere.  Milikh's presentation can for the present time be downloaded 
> from here:
> http://www.lc.leidenuniv.nl/lc/web/2005/20050509/presentations/Milikh.ppt
>
> This theory has some very interesting implications for large coils.
> Assuming classical electron behavior, there is a critical maximum size for 
> a disruptive coil, beyond which it's ability to produce longer sparks 
> falls to zero.  This is due to the Fo larger coils becoming so low that 
> the minimum possible time between firings starts to exceed the ion 
> recombination times in air, allowing the arc channel to fully extinguish 
> between firings.
>
> However if one allows for relativistic runaway breakdown effects, there is 
> a critical *minimum* coil size that reaches the state where only 200kV/m 
> is needed to generate the arc channel.  Both Gurevich and Milikh calculate 
> that the characteristic length needed in air for the exponential growth of 
> a relativistic runaway breakdown is about 50m.
> Milikh suggests that the electric field needs to be supported over a 
> length several times this, about 150m.  To achieve this scenario, a twin 
> coil system is required with a physical scale of about 240ft high, 50ft 
> diameter each tower, and a tower to tower spacing of  about 450ft.  Each 
> tower would need to generate a peak voltage of about 15MV.  These are 
> back-of-the-envelope calculations of course, but such a coil structure is 
> arguably practical.  Perhaps the most important point, however, is that 
> there might not be a maximum limit on coil size, but rather a 'dead zone' 
> between the maximum classical limit and the minimum relativistic limit 
> described above.
>
> -GL