From: Mike Rosing <rosing@neurophys.wisc.edu>
Newsgroups: sci.physics.plasma
Subject: Re: New Hybrid MM ICF Approach.
Date: Mon, 14 Jan 2002 14:10:30 -0600
Organization: Medical Electronics Lab.
Lines: 183
References: <a1hjom$a6hm$1@saturn.cs.uml.edu> <a1k4qr$13p4$1@saturn.cs.uml.edu> <a1slti$ckus$1@saturn.cs.uml.edu>


Steve Ivy wrote:
> OK here go a few more wild ideas.
>
> Stubborn as a mule, yes but hopefully not to
> the point of beating a dead horse. I can only
> hope not as dumb as an OX either. : )

:-) Same here!

> I believe I now get your point about the B field.
>
> Is the following true, energetic ions attempting to
> escape the plasma (in a radial direction) by definition
> have velocity in the radial direction? And thus are trapped.
> (at least in the radial direction anyhow.) ?

Well, kinda. You have to think of each particle as a 6 dimensional
object. It's got 3 dimensions of position, and 3 dimensions of
velocity. The radial dimension takes care of 4 of those.

Particles close to the wall are going to hit the wall and turn
into neutrals, and then escape. So that's the position dimension.
Particles moving fast, radially, near the center, will be well
trapped.

> If so then as they (attempt) to travel in the
> outward radial direction they experience a lorentz
> force across their path forceing them to move instead
> sideways in an endless loop circling the central axis
> of the solonoid.

They move in a circle, yes. I think of "sideways" as axially,
not angularly (around a circle, along an angle dimension).

> OK since it appears that any movement radially
> will be instantly circumvented by a sufficiently strong
> magnetic field. It then appears that fast moving particles
> escaping is not the mechanism by which "diffusion" occurs.

It's not so simple. The circulating currents of the plasma
give rise to magnetic fields that help or hinder the supplied
field, and collisions cause particles to bounce out of their
nice round orbits. "diffusion" happens for lots of reasons,
and finding them all has been a major source of research
funding for a long time!

> Yes?

Yeah, but you haven't hit the "loss cone" problem yet :-)

> Just thinking about it it appears as though it isn't
> the fast moving ion portion of the plasma that is
> the problem but instead that tiny portion of the plasma
> population that is moving very slow. So slow in fact
> that the B field really doesn't present much of an
> impediment to it's motion. Yes?

that's another loss problem, but pretty small one.

> Still talking about an ion's motion (in the radial
> direction) it's kind of like the B field doesn't
> really create a "magnetic bottle" at all but instead
> (my analogy here) creates a thick viscous fluid through
> which the ions must pass.

the picture they teach in school is that the particles
"stick" to the field lines. Since the field lines run
axially, the particles are "trapped" and can't get away.
It kinda sorta works like that, but the details are killers.

> So continuing with the thick fluid analogy. Objects
> attempting to move rapidly through such a fluid experience
> large impeding forces but objects which attempt only to
> move very slowly will only see very small impeding forces.

True, but the slow moving ones are still slow, so you have
a chance to catch them some other way.

> So if I my take on diffusion is correct I think the
> key to eliminating diffusion would be to keep the slowest
> moving plasma ions from slowly creeping outward.

Good luck :-)

> You would only need to be careful of those ions nearest
> to the outer wall because those are the ones in danger
> of touching the wall.

Or build a "divertor" and use them to pump out your
chamber :-)

> Note that since they aren't moving fast to begin with
> they don't really hold much of the plasmas energy but
> if they did get out they will thin the plasma preventing
> it from maintaining the required high density.

But it's the high density plasma that creates the main losses
because it's changing the B fields on you. The harder you
squeeze, the more it fights back. The energy gain from
fusion has to be more than the energy loss in trying to
hold the plasma in. So far, it's been a *really* tough
nut to crack.

> So with that in mind I still think a rotating E field
> cycled around the wall to sweep up the lazy ions might
> be a good idea.

That generates a current, which generates a B field, which
will cause other problems. You should model it and watch
what happens :-)

> But seeing as inspiration has just struck how about this
> idea instead.
>
> Since you want to keep slow moving away from the wall you
> could spray a cylindrically shaped beam of very fast moving
> neutral particles parallel to the solonoid wall. This fast
> moving curtain of particles will interact with the slow
> moving ions encroaching on the wall. That way no ions

Check out the new ion rocket engines NASA is planning for the
mission to Mars. They do exactly that! There are no walls
in space tho, the purpose of the neutrals is to help focus
the plasma beam because they'd melt the walls of the thruster
nozzel otherwise.

Building neutral beams is something I tried to do 20 years ago.
It works, but I'm not sure it'd ever be economical.

> It is late so let me know if any or all of that was dumb.

:-) Nothing like having fun!

> Oh well enough about diffusion for how. How about the lasers.
>
> Well I didn't pull the laser initiated gaseous plasma fusion
> idea out of thin air.
>
> I know that not too long ago some group announced that they
> had generated fusion and had measurable neutron flux coming
> off of it.
>
> They just fired an intense laser beam through an excited plasma.
>
> That was about all there was to it.
>
> So I know the basic idea works at least a little bit.
>
> All I am adding is the additional elements of magnetic
> containment and lasers coming in from both sides.
>
> I hadn't meant to imply that one could try to trap the ions
> with "laser tweezers"
>
> It's the photon energy accelerating the ions at the ends of
> the solonoid's plasma core which would hopefully then be
> able to compress the remainder of the plasma prior to the main
> fusion initiating laser pulse.
>
> I also hadn't intended to imply that the photons would carry
> enough mass to do much compression.
>
> No I only hope the photons would carry enough energy to get
> the job done. No mass involved except the mass of the ions.
>
> OK?

OK, that's totally different than the way I read it. So you'd
have ICF at the ends of the solinoid and use the expanding
gas to help push from both ends into the center, and then
use the B field to hold it all together.

Nice. I think the B field will screw up the ICF part, since it
has to be pretty damn high for any fusion to go anyway. But
it'd be worth a 1 GHZ processor and a few weeks running to
simulate it.

> Thanks for all the intelligent responces so far.

Thanks for the thanks :-)

Patience, persistence, truth,
Dr. mike