getting your plasma up to 40 million K

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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getting your plasma up to 40 million K

Post by guest » Fri Nov 09, 2001 8:34 am

Page 11 of New scientist magazine has an article about a scientist at the Princeton Plasma Physics Lab, Masayuki Ono who has been studying why the outer atmosphere of the sun is far hotter than the surface. Using the National Spherical Torus Experiment, He managed to generate a plasma temperature of 40 million K (up from 2 million K ) by using distortions in the magnetic containment fields to create "Alfven waves" which transfer their energy to the plasma electrons "Particles get kicked from one wave to the next, gaining energy from each collision" says Ono.

I thought you guys at the Fusor group would be interested in hearing about this as it is after all, an effect concerning the only continuous self sustaining fusion reaction we know of, so it may apply to what we are aiming for. I personally don't have a clue how to generate Alfven waves or their suitability to a fusor but they seem like a better way to heat the plasma. If anyone is interested I'll email the magazine and see if they'll let me post a scan of the article which is only about three or four paragraphs.

regards
Mark Harriss

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Re: getting your plasma up to 40 million K

Post by Richard Hull » Fri Nov 09, 2001 3:40 pm

Plasma heating is often viewed in a couple of different ways depending on who is doing the viewing. A true physicist realizes what is talked about. The public is a vastly different, and for the most part, ignorant audience.

This has been talked about before.

Thermodynamically, heat as relates to plasma or particles of matter is a function strictly of their velocity and that alone. An ice cube could easily exist in a 400 million degree plasma for 200 million years and never melt! Any good physicist or even partly adroit and well read science buff knows this. To the public it is a baffling mystery.

The secret is density. The Solar corona has a highly variable density based on a number of extremely complex conditions. For the most part, the density approachs our best earthly vacuums 10e-10 torr. The particle velocities in the corona are related to complex electromagnetic accelerations received from a broad range of places from sun spots to flares, to the complex solar magnetosphere. The temperature of the corona is usually taken with a telescope or satellite imaging system looking at the doppler broadening of the hydrogen spectrum of the ions within it.

Thus, we see a super heated but ultra tenuous plasma THAT IS NOT TRULY CONTAINED AT ALL. It is most likely that the ions are moving along current streamlines. (in unison for the most part and are not highly collisional - LOCALLY.)

That there are collision here and that there is fusion here is obvious, but at efficiencies that are abysmal.

On earth several schemes involve making the plasma in an ionizer system and then accelerating it only mildly to maybe 5kev and forcing it to densities great enough to fuse via electromagnetic bottling, etc. This is the classic neutral plasma method where fusion relies on maxwellian heating of the tenuous plasma. It is collisional by probability only and therefore has a well understood maxwellian curve of ion energy distribution.

The fusor is a collider. The plasma is formed and a methodogly is used, not to confine the plasma and heat it thermally via a classic maxwellian, but to accelerate the ions and collide them in velocity space. Our ions fall through a gradient and this gradient gives a fixed final and hopefully directed velocity. Ideally, all ions are collisional and are at fusion energy. Containment, if you wish to call it that is through ion recirculation and electrostatic focusing. Consequently, a 20kev fusor device has a portion of its ions heated (accelerated) to 220 million degrees to hopefully hit near head on with other 220 million degree ions warranting a 500 million degree ++ reaction zone in an amateur fusor! In reality, the vast majority of the ions hit at odd angles, become neutralized, go through various non fusion elastic collisions, etc. The important point is that in a 20kev fusor where fusion is just beginning to do good, the fusion is occuring in a reaction zone where one half billion degree ION temperatures are found. This area is velocity space and not a uniformly heated or maxwellian plasma except by waste product.

Good Physicists don't talk temperature except to the press or funding committees...They speak in those terms which have been used and accepted since the 1930s for accelerator work and that is the electron volt.

The plasma in a standard neon sign is heated during operation to about 600ev or 6.6 million degrees kelvin in the current streamline or sheath which is incredibly thin. The light emitted from the signage is due to ION COOLING (recombination). By the time the reduced speed and now neutral gas gets to the super dense glass walls, (100 million times more dense), little actual heating occurs TO THE TOUCH on the outside. The glass is a virtual infinite heat sink to the tenuous heated gas in the tube

(Note* a 20kv neon sign transformer is used only to start the plasma.) During operation the plasma tries to draw millions of amps, but the specially designed, magnetically shunted, neon transformer drops the flux through the secondary to near zero and the secondary voltage falls from 20kev to only about 600 running volts across the electrodes.)

Understanding temperatures in plasmas at the common sense level is more a matter of looking at the density of that plasma to determine if things are hot to the touch........ The only heat sensor we possess. Our brains are better equipped to put things in perspective provided they are informed.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: getting your plasma up to 40 million K

Post by guest » Sat Nov 10, 2001 5:44 am

Hi Richard, I am aware of those issues you mention about plasma density and velocity, I just happen to think that Alfven waves are possibly a relevant method of transferring energy to the gas ions hopefully enough to increase fusion yields. These guys were able to get a 20 fold increase in their plasma temp, which is admittedly very thin as you would expect from a solar corona simulation. How they actually do this and whether it could be generated inside an electrostatic containment system would be interesting to speculate on.

regards
Mark Harriss

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Re: getting your plasma up to 40 million K

Post by guest » Sun Nov 11, 2001 4:26 am

Mark, I knew you were aware of those issues, but others, especially newcomers, need to have the issues explained from time to time.

The waves of which you speak sound interesting. Now it is a matter of figuring out how to generate them and figure out if they have any value in the electrostatic environment of the fusor.

Richard Hull

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Re: getting your plasma up to 40 million K

Post by guest » Tue Nov 13, 2001 5:29 pm

Alfein waves are an aspect of Magnetohydrodynamics.
When a bunch of ions are pushed in a coherent fashion
ie in unison they self organise in order to reduce the induced magnetic fields at right angles to the direction of
travel that would disperse these collected ions. As long as
a critial value of momentum is maintained the wave will hang together. But try to contain that wave by magnetic compression , a bunch of small waves will merge to form one really big one and whoops your tokamack plasma just hit the
wall. This is why I doubt magnetic containment so much.
But Alfein waves could play a good role in 123 Bang.
IEC fusion containment only goes one direction .. to the center,hense the momentum of the ions would form a spherical
Alfein wave that would increase the Paschen curve into the
fourth power of neurtron production instead of just third power scaling usally seen.
Or so theory would have it

Larry Leins
Physics teacher

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Re: getting your plasma up to 40 million K

Post by guest » Wed Nov 14, 2001 9:16 am

Hi Larry, I can relate to the concept a bit more now that you mention they are MHD related. The idea of a beam of coherent ions is starting to sound like some form of ion laser!!!. I've done a bit more poking around and a few sites mention that Alfen waves are a being investigated for fusion use. From what you say about a theoretical fourth order increase in neutron production it would make a small fusor capable of actually frying things, assuming of course you could work out how to set it up in the first place. Thanks for the explanation.

regards
Mark Harriss

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