It Is A Different Machine

ravingdave · Post by **ravingdave** » Wed May 06, 2009 10:11 pm

I can just about visualize the thinking that's gonna go into this...

David

KitemanSA · Post by **KitemanSA** » Thu May 07, 2009 1:20 am

I think someone needs to be more explicit as to why they think the ion source needs protection from the alphas.

krenshala · Post by **krenshala** » Thu May 07, 2009 4:17 am

I was wondering the same thing. The ion source is going to be positively charged, just like the alphas, so the alphas should (at least for the most part) be directed away from it.

KitemanSA · Post by **KitemanSA** » Thu May 07, 2009 5:42 am

My thought was more that the ion source is probably a very simple, very cheap mechanism and it would take up almost no area, so let the alphas impinge and replace as needed; but yours is good too.

chrismb · Post by **chrismb** » Thu May 07, 2009 6:17 am

Because once bombarded it will sputter and contaminate the reaction core with high z ions.

93143 · Post by **93143** » Thu May 07, 2009 6:22 am

I'm not sure what the plan is with ion guns... I always thought they were going to inject neutrals from the inner side of the magrid and ECR the $#@% out of them as they crossed the boundary into the wiffleball... it seems like that would provide a relatively narrow, very effective killzone for neutrals, particularly with the electrons stripped off previous neutrals still trapped there at the top of the well...

Hang on; that could balance the high edge-region ion density I was worried about on that other thread...

ravingdave · Post by **ravingdave** » Thu May 07, 2009 2:41 pm

KitemanSA

I think someone needs to be more explicit as to why they think the ion source needs protection from the alphas.

krenshala

I was wondering the same thing. The ion source is going to be positively charged, just like the alphas, so the alphas should (at least for the most part) be directed away from it.

KitemanSA

My thought was more that the ion source is probably a very simple, very cheap mechanism and it would take up almost no area, so let the alphas impinge and replace as needed; but yours is good too.

Since RNebel and MSimon have pointed out that with a sufficiently strong magnetic field the alphas will leave confinement through the cusps (retaining most of their energy) it was immediately obvious to me that it would be a very destructive stream of concentrated energy emerging as a sort of beam. Given that the velocity of these alpha particles is between (if I remember correctly) between 1-3 Mev, the only way a positive charge on the ion guns could stop an impact is by being much higher than the (what was it again ? ) 100 kv they are expected to operate at.

Apart from this, the electron sources are also exposed and will likely be bombarded by this same stream of particles.

If this is an erroneous view, please enlighten me.

David

D Tibbets · Post by **D Tibbets** » Thu May 07, 2009 10:15 pm

I would expect the electron guns with high negative potential to be slightly more exposed than the neutral gas puffers or mildly positive ion guns, all of which would be aligned with a cusp. Though it occurs to me that a gas puffer may not need to be at a cusp*. some type of magnetic shielding may be nessisary. Perhaps this could be incorperated into the energy harvesting grid assembly- along with the vacuum port directing flow control. What complications with cusp geometries, efficiencies/ recirculation this would introduce is a another consideration of the 'engeenering'.

* My current understanding is that due to ionization times and sizes the WB 6 type machines would benifit from ion guns, but the larger 'power producing' machines may work better (or at least as well) with neutral fuel injection.

[EDIT- I should have reviewed the first page of this thread. Icarus stated the same thing about shielding at the bottom of the first page]
Dan Tibbets

93143 · Post by **93143** » Fri May 08, 2009 3:07 am

Is there any good reason a neutral injector port couldn't just be integrated into the inward-facing side of the magrid, flush with the casing?

chrismb · Post by **chrismb** » Fri May 08, 2009 6:09 am

93143 wrote:Is there any good reason a neutral injector port couldn't just be integrated into the inward-facing side of the magrid, flush with the casing?

None.

And guaranteed ionisation at the top of the well/edge wiffleball is going to occur by these high density electrons you refer to, presumably.

A few follow up questions;
What *is* the probability of ionisation, then?
What population of neutrals will make it further into the well?
And how will charge exchange with the ions affect all this, seeing as ionisation and charge exchange cross-sections are generally similar (i.e. the probability is much the same that these neutrals become ionised by electrons as dump their electron into an ion coming the other way, thus effectively thermalising the pair if they are at a mid-way point in the potential well)?

icarus · Post by **icarus** » Fri May 08, 2009 8:52 am

Except the mag. field is so strong, in the case being discussed, that the fuel ions may no longer make it into the well before something else happens that changes the physics .... yet to see anyone address the question of what happens when the mag. field force on the fuel ions becomes larger than the electrostatic forces due to the well ... as maybe the case in > 5T field proposed for reactors.

At some level of mag. field strength it transitions from an electrostatic confinement machine, due to electronic charge contained by a "weak" magnetic field, i.e. a mag. field not strong enough to influence ions greatly.

KitemanSA · Post by **KitemanSA** » Fri May 08, 2009 1:36 pm

The MaGrid casing is highly positively charged. Would that voltage be enough to ionize the fuel? If neutral gas were fed to a patch on the casing that was micro-porous enough to weep the gas, would the gas ionize as it wept out?

ravingdave · Post by **ravingdave** » Fri May 08, 2009 2:52 pm

KitemanSA wrote:The MaGrid casing is highly positively charged. Would that voltage be enough to ionize the fuel? If neutral gas were fed to a patch on the casing that was micro-porous enough to weep the gas, would the gas ionize as it wept out?

I am thinking that (using the above idea) an ion would start traveling towards the center of the well, only to be immediately affected by the magnetic field. It would probably look something like this...

I am thinking that starting the ion out with a gyro effect isn't as good as starting it out moving in a nice straight line towards the center. It seems like that would cause too much lateral motion as opposed to radial.

In actuality, I think it would be impossible to get this thing to work at all if you don't get the ions converging on the center.

For this reason I think the ions pretty much have to be released from some area that is sorta neutral magnetically like the bore of the magnet or a corner cusp.

David

ravingdave · Post by **ravingdave** » Fri May 08, 2009 3:28 pm

Here's my quicky drawing of a maybe idea to address the issue of the proton beams coming out of the cusps.

Not shown of course is the alpha collector system which I perceive would operate similarly to a calutron. Now that we have nice beams coming out of the cusps as opposed to a "Radiant" array of alpha particles, the collection scheme (and heat load problems) just got a whole lot easier.

David

chrismb · Post by **chrismb** » Fri May 08, 2009 4:10 pm

ravingdave wrote:I am thinking that (using the above idea) an ion would start traveling towards the center of the well, only to be immediately affected by the magnetic field.

Yes. This is covered by the 'magnetron' condition which sets the minimum E-field for a given B (or max B for a given E) such that charged particles will make it across the electric field in time, as I've mentioned on:

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