some questions

[MSimon]

rcain,

Could you give a link to the Dolan Paper you refer to? Or its title?

[TallDave]

One of the questions I've pondered: is the wiffle-ball effect partly the result of long, very narrow pipe-like cusps that fill with electrons, blocking other electrons from leaving?

My thought here was that in addition to the WB cusps being difficult to get into due to local B field geometry, there might be a repulsive effect from the stack of electrons (this would also attract ions, but if the pipe is narrow enough the effect might be too small to pull in ions unless they get very close, like the lucky-bounce electrons trying to get out). The electrons in the pipe would oscillate back and forth, some escaping on each oscillation but lots more getting stuck, so you end up with an interior density 1,000 or so times greater than outside the B field.

I like this cusp-plugging explanation because it both explains why Bussard's closed-box machines didn't confine well and doesn't require electrons to "recirculate" all the way around the field lines on the outside, which others have pointed out is problematic.

[rcain]

rcain,

Could you give a link to the Dolan Paper you refer to? Or its title?

hi MSimon

Sure, its:

"Magnetic electrostatic plasma codinementi" Plasma Phys. Control. Fusion 36 (1994) 1539-1593 - T J Dolan
Idaho National Engineering Laboratory, EG&G Idaho, PO Box 1625, Idaho Falls,
ID 83415-3880, USA


here:

http://www.askmar.com/Fusion_files/Magn ... nement.pdf

and here is the original 1994 published version

http://www.iop.org/EJ/abstract/0741-3335/36/10/001

i'm sure you know it already. more of an overview of state of the art, circa 1994, but comprehensive, accessible and thought provoking.

[MSimon]

rcain,

Thanks for that. I don't recall reading the paper before, but I may have.

I especially liked the observation of 100 MHz oscillations by Farnsworth.

[rcain]

One of the questions I've pondered: is the wiffle-ball effect partly the result of long, very narrow pipe-like cusps that fill with electrons, blocking other electrons from leaving?

My thought here was that in addition to the WB cusps being difficult to get into due to local B field geometry, there might be a repulsive effect from the stack of electrons (this would also attract ions, but if the pipe is narrow enough the effect might be too small to pull in ions unless they get very close, like the lucky-bounce electrons trying to get out). The electrons in the pipe would oscillate back and forth, some escaping on each oscillation but lots more getting stuck, so you end up with an interior density 1,000 or so times greater than outside the B field.

I like this cusp-plugging explanation because it both explains why Bussard's closed-box machines didn't confine well and doesn't require electrons to "recirculate" all the way around the field lines on the outside, which others have pointed out is problematic.

hi TallDave

cusps difficult to get to - yes this is key, imo.

coulomb blocking - by both ions and electrons - yes - but these are a necessary evil only. Dolan gives some formulae and some numbers in his paper. I'm sure there are more recent/varigated studies.

pipes - are an analytical approximation 'we' have introduced, only. none of the particles have much of a concept of them - they see only spherical-eliptical/conic space.

oscilating back and forth - most definetely, else our machine would have collapsed. (along with most other things in the universe). yes, we do need to consider this as a statistical phenomena. except for those lucky few 'individual' particles who undergo perfect mirror reflections/collisions/intercepts. (or more precisley perhaps, computable ballistics/filtering) these are our babies.

variation of interior density ratio - dunno what inside to outside is - something of order of r^2/r^3 - so coupled with scaling at a 'magic number' of around 6. (...i have a further idea using Stirling Numbers of 2nd Kind to drive regime, more on this later). relative to other radial cords through the machine, cone-blocking acocunts for a scalar magnitude variaton of around 3-6, so far as i can rcall. again, its noted in Dolan, for electrons at least.

re-circulation (recycling) probematic - nah!

just your everyday plasma conduit engineering. i should imagine.

[KitemanSA]

I like this cusp-plugging explanation because it both explains why Bussard's closed-box machines didn't confine well and doesn't require electrons to "recirculate" all the way around the field lines on the outside, which others have pointed out is problematic.

I was under the impression that it had been agreed that "recirculation" has little to do with going around the field lines but only means that the electrons head out the lines and are slowed and returned by the high positive charge on the MaGrid. This exlpanation doesn't seem that problematical to me.

[rcain]

I like this cusp-plugging explanation because it both explains why Bussard's closed-box machines didn't confine well and doesn't require electrons to "recirculate" all the way around the field lines on the outside, which others have pointed out is problematic.

I was under the impression that it had been agreed that "recirculation" has little to do with going around the field lines but only means that the electrons head out the lines and are slowed and returned by the high positive charge on the MaGrid. This exlpanation doesn't seem that problematical to me.

i think it can be used to our advantage, since we can 'locate' the particles at these intercepts. we can also relocate them and condition/transform them if required.

[Art Carlson]

I like this cusp-plugging explanation because it both explains why Bussard's closed-box machines didn't confine well and doesn't require electrons to "recirculate" all the way around the field lines on the outside, which others have pointed out is problematic.

I was under the impression that it had been agreed that "recirculation" has little to do with going around the field lines but only means that the electrons head out the lines and are slowed and returned by the high positive charge on the MaGrid. This explanation doesn't seem that problematical to me.

In simple terms, the problem is that an electric field that causes electrons to return will cause ions to be lost with high energy. If you want to fill out the argument, you need to consider quasi-neutrality.

[rcain]

I like this cusp-plugging explanation because it both explains why Bussard's closed-box machines didn't confine well and doesn't require electrons to "recirculate" all the way around the field lines on the outside, which others have pointed out is problematic.

I was under the impression that it had been agreed that "recirculation" has little to do with going around the field lines but only means that the electrons head out the lines and are slowed and returned by the high positive charge on the MaGrid. This explanation doesn't seem that problematical to me.

In simple terms, the problem is that an electric field that causes electrons to return will cause ions to be lost with high energy. If you want to fill out the argument, you need to consider quasi-neutrality.

or perhaps puncture the cone with another? i dont like the word quasi very much, it reminds me of quango - which as all brits know are formless useless assemblies. how about 'discontinuous'/'alternating'?

we agree though that our greatest concern is with the meeting of slow moving particles with faster ones? brem and thermalisation?

[Roger]

I like this cusp-plugging explanation

cusps difficult to get to - yes this is key, imo.

It may end up being electrons don't want to find them, at least in numbers. They like to be doing something else, no?

Isn't there a flow.... magnetic fields around the coils.... that helical flow, can it sweep electrons to the side?

I like this cusp-plugging explanation

Something has to be occupying them.
Dave, if a few/group of electrons are surfing around the field lines like on that U TUbe video, (wasnt it Indreks?) and they are locally near the cusp, does that inhibit other electrons from getting too close... ?

[Art Carlson]

... If you want to fill out the argument, you need to consider quasi-neutrality.

... i dont like the word quasi very much...

Maybe you don't, but "quasi-neutral" is a well-defined and universally used technical term, so I suggest you use it anyway. It means | n_e - Z*n_i | / n_e << 1.

On the other hand, "quasi-spherical", which is tossed around quite a bit on this forum, is not well-defined.

[rcain]

I like this cusp-plugging explanation

cusps difficult to get to - yes this is key, imo.

It may end up being electrons don't want to find them, at least in numbers. They like to be doing something else, no?

Isn't there a flow.... magnetic fields around the coils.... that helical flow, can it sweep electrons to the side?

I like this cusp-plugging explanation

Something has to be occupying them.
Dave, if a few/group of electrons are surfing around the field lines like on that U TUbe video, (wasnt it Indreks?) and they are locally near the cusp, does that inhibit other electrons from getting too close... ?

links to the mighty works of indreck can be found here:

http://www.mare.ee/indrek/ephi/pw3d_flash.html
http://www.mare.ee/indrek/ephi/pw2d_flash.html

re: electrons prefer something else - yes - any lower ground state, including orbits, gyro-orbits or otherwise..

helical: always to some degree. a straight line is but a geometers crude approximation to this beautiful curve. lines are forced upon nature by our machines.

sweeping aside: yeas, we we have already successfuly partitioned the space. we have basic pump. how it is capable of sustaining fusion-friendly pressures/distances, we fill figure out.

ps: it would be wonderful to see, on indreks animations, the fateful times of 4 identifyable particles in the narrative. say 2 electrons and 2 ions - fred, freida, ronald and jemima. i shall name them. what do you think?

[rcain]

... If you want to fill out the argument, you need to consider quasi-neutrality.

... i dont like the word quasi very much...

Maybe you don't, but "quasi-neutral" is a well-defined and universally used technical term, so I suggest you use it anyway. It means | n_e - Z*n_i | / n_e << 1.

On the other hand, "quasi-spherical", which is tossed around quite a bit on this forum, is not well-defined.

bless. thanks for that Art. please can you tell me what the symbols represent? for the record...

n_e = number electrons
n_i = number ions

in 'defined' space - yes?

what is Z please?

[Art Carlson]

| n_e - Z*n_i | / n_e << 1.

bless. thanks for that Art. please can you tell me what the symbols represent? for the record...

n_e = number electrons
n_i = number ions

in 'defined' space - yes?

what is Z please?

Z is the charge state of the ions, or the atomic number of the element, under the assumption that the ions are fully ionized. Therefore Z*n_i is the number of protons (positive elementary charges) per unit volume. Another way to put is is that the net charge density is small compared to the charge density of the electrons alone.

[KitemanSA]

I like this cusp-plugging explanation because it both explains why Bussard's closed-box machines didn't confine well and doesn't require electrons to "recirculate" all the way around the field lines on the outside, which others have pointed out is problematic.

I was under the impression that it had been agreed that "recirculation" has little to do with going around the field lines but only means that the electrons head out the lines and are slowed and returned by the high positive charge on the MaGrid. This explanation doesn't seem that problematical to me.

In simple terms, the problem is that an electric field that causes electrons to return will cause ions to be lost with high energy. If you want to fill out the argument, you need to consider quasi-neutrality.

Yup, and remember that the hypothesis is that the ions don't reach the outside of the MaGrid because of the deep negative potential well. Only those (hopefully few) upscattered ions will leave, and then yes, take off like a bat...