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PostPosted: Nov 21, 2013 9:07 pm 
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alexterrell wrote:
They both use a plasmoid of tritium and deuterium. The power version accelerates two of these into each other, whilst being constrained by a magnetic field.

I don't think that the Helion Energy concept is very different from the one pushed by Lawrenceville Plasma Physics (LPP) -- at least in terms of the problem of concentrating energy in a single, stable plasmoid, long enough to get a decent return on the energy input.

Back in October there was this bit of fusion news from LLNL:

“Coming Through in a Pinch: Z-Pinch Plasma Heralds Novel Accelerator Designs”
https://str.llnl.gov/july-2013/tang

It was also reported on NextBigFuture as “DARPA funds $1 million to design better zpinches and dense plasma focus electrodes”
http://nextbigfuture.com/2013/07/darpa- ... etter.html

I thought this was quite interesting, so I emailed Dr. Victor Tang with a question:

An illustration in the article explains as follows:

Quote:
Deuterium ion density is shown inside this first fully kinetic simulation of a dense plasma focus Z-pinch. The pinch occurs on axis where the density is highest (red). The cross section of a cylindrical hollow anode is shown in gray.


On closer look, it appears that the pinch “on axis where the density is highest (red)” is composed of distinct regions, somewhat like beads on a string.

Specifically, would it be correct to interpret these distinct regions as a series spheromak-type plasmoids ? ….please see illustration picture attached (351 KB).
In this view, the highest density plasma actually occurs slightly AWAY from the axis – much like the plasma torus of a large fusion reactor, except on a tiny scale.
--------------

This was just before the US gov’t shutdown.
A couple of weeks ago I received the following reply:

Quote:
Jaro—Sorry for the lateness of reply to you and thank you for your email. Spheromaks have specific B field and plasma profiles and we would have to take a look at the profiles in the beads to answer your question exactly. In a classic z-pinch configuration these beads would be m=0 instabilities and the field would be predominantly poloidal. A spheromak has both Toroidal and poloidal fields of comparable strengths; we have not put in any seed toroidal (z-axis) B field here so if it is a spheromak config the B_T would have to come from the current. Now you are correct that some of the higher density appears to be slightly off-axis but that will also be dependent on the time-frame you look at in the pinch—i.e. it’s fully dynamic.

In any case, something we need to do more of now that we have these simulations running correctly is to analyze them for greater understanding.

I hope that helps!

V


While not a complete answer to my question, Dr. Tang does seem to confirm that “dense plasma focus” fusion devices like those pushed by companies like Lawrenceville Plasma Physics (LPP), do NOT form nice single well-defined plasmoids.
Rather, they produce very turbulent plasma with energy distributed among a series of tiny erratic plasmoids (“beads”), instead of concentrating energy in a single longer-lasting plasmoid as advertised in LPP publicity graphics – and as would be indispensible for a significant rate of fusion reactions.
In other words, the issue is not just a matter of increasing plasmoid energy, as claimed by LPP, but rather a matter of reducing turbulence and concentrating energy in a single plasmoid.
Unfortunately, fusion experiment generally indicate increasing turbulence with increasing energy, not less.
Anyway, that’s my take on it.

alexterrell wrote:
The space rocket uses a magnetic field to implode a Lithium ring which further compresses the magnetic field, in which a plasmoid is encased, till the plasmoid ignites. This vapourises and ionises the lithium which acts as the rocket thrust.

This scheme is ridiculous, IMO, considering the millions of rings you'd have to transport, in order to run something like a hundred implosions a minute.
Then there is of course the whole issue of Rayleigh instability at high compression ratios during each implosion.
Very unlikely to ever yield useful amounts of energy.


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kinetic simulation of dense plasma focus Z-pinch tang.jpg
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PostPosted: Nov 22, 2013 7:20 am 
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Joined: Jul 14, 2008 3:12 pm
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I don't understand how these guys can claim many times better than breakeven in a much smaller reactor than ITER with a vastly larger plasma-to-reactor interface area per unit power.

Plus the fact that it runs pulsed rather than continuous. That means the peak temperature (and thus radiative losses) must be larger than with a continuous approach like ITER (ok, even the ITER's 10 minutes of operation and then major component breakdown hardly classifies as continuous operation in my book).

Everyone is cheering on these "new" fusion schemes. They all promise the exact same thing: high energy return in a much smaller than ITER package, low cost, simplicity, no issues with plasma instabilities or materials. It's like they just copied that from the marketing textbook on fusion. Completely unbelievable.


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