From: edwlt12@lims02.lerc.nasa.gov (MIKE JAMISON)
Subject: Fusion Musings
News-Software: VAX/VMS VNEWS 1.41    
Organization: NASA Lewis Research Center
Date: 28 Sep 1992 12:01 EST  

My latest issue of NASA Tech Briefs (September, 1992, Vol 16 No. 9) has an 
article on a Four-sector Cylindrical Radio-Frequency Ion Trap.

According to the article, the device would be able to store a "relatively 
large" quantity of ions.  (I've asked for more info, but won't get it for a 
month or so).

The device pictured is shaped basically like a can, with two ends which can 
be biased w.r.t. the four RF sectors, to move the ions towards the center 
of the trap.

To give you all an idea of where I'm coming from, an idea for using a 
charged, rather than electrically neutral, plasma for fusion has been 
kicking around in my brain for about ten years now.

The idea progressed from something like the Migma machine to its present 
state, which is basically similar to a Tokamak with charged beams injected 
tangentially and in opposite directions.

Problems with the idea include:

1)  Centrifugal force.  The ions will smash into the outer walls of the 
vessel if nothing is there to stop them.  A B field will cause them to 
migrate up or down.  This can be compensated for by use of an electrostatic 
field opposing the centrifugal force.

The problem here is that the electrostatic field exerts a constant pressure 
on the ions, but the centrifugal force is a 1/Radius force.  i.e. not a 
stable situation.

BTW, Tokamaks should have a similar problem.  The centrifugal force should 
cause the positive and negative ions to separate.  A simple model will 
involve two "cylinders" of charge, one positive, the other negative.  As 
the cylinders move apart, the attraction between them increases.  
Eventually the attractive force between the cylinders of charge balances 
the centrifugal/magnetic pressure pulling them apart.

I've been meaning to simulate this, but haven't yet :(

2)  Because the plasma is charged, it will try to dissipate.  Again, the B 
field comes to the rescue.  As the charged particles try to move apart, 
they will experience an opposing force from the B field (the B field is 
concentric with the toroid, like in a Tokamak).  The final result is that 
the particles "swirl" in circles perpendicular to the B field, as well as 
travelling along parallel to it.

3)  Plasma density:  Using only electrostatic forces to counteract combined 
centrifugal force and electrostatic repulsion, I came up with a density of 
about 10^12 ions/cc maximum, given a 1 meter radius toroid and 1 MeV/meter E 
field.  The centrifugal force would keep the ions away from the inner wall, 
and the electrostatic field would keep them away from the outer wall, 
leaving the upper and lower parts of the toroid as the problem...  (That's 
where the B field comes in).

The latest configuration of my "reactor" takes the form of an octagon, for 
two reasons:

1)  It's easier to go to a tubing store and buy a bunch of straight pipe, 
along with eight 45 degree elbows, than it is to buy a toroid  (I think the 
plumbing guys would look at me *very* strangely if I asked for 50 feet of 
curved 6" tubing, as opposed to 8 equal sections of tubing and eight 45 
degree angles.  That would be bad enough :)).

2)  Most of the distance travelled by the ions is straight.  The "new" plan 
would be to have the B field along the straight runs be at a given value (a 
few Tesla).  The B field in the bends would be several times the strength 
of this.  The ions would tend to scrunch together travelling through the 
bends.  The electrostatic field used in the bends, to compensate for the 
centrifugal force, would be more effective, since the delta of 1/Radius for 
the ions would be minimized.

3)  It might be possible to use the ion trap configuration, at least in the 
straight runs of the machine, to help to focus the ions, keeping them away 
from the walls of the machine.  With luck, the ions would stay trapped (i.e
 wouldn't diffuse to the walls) long enough to fuse.

A few notes:

a)  This machine (if it works) could be used to burn D-T, or H-B, or 
whatever two fuels you want, very easily.  Inject one fuel in one direction
, the other in the other direction.

b)  With a density of 10^12 ions/cc, the probability of one ion hitting 
another is something like 1/several million per meter travelled.  
Sufficient trapping time is on the order of 1 second or more for any 
appreciable amount of fusing to occur, given an initial energy of about 20 
keV.

c)  The reaction isn't self-perpetuating.  This means that ions will have 
to be continually injected at ~20 keV (depends on which fuel you're burning
).  I don't see this as a big deal, as long as the output can accomodate 
the additional input requirement.

Uh, sorry to bend your "ears" (eyes, actually) with this long, rambling 
post...


Mike Jamison
Newsgroups: sci.physics.fusion