Why have 'joints' connecting the rings?

[TallDave]

Shame on Rick. Unless he and the navy get a little more forthcoming, Focus Fusino will crush them in the PR war, and PR equals money.

PR didn't work out so well for Pons and Fleischman.

EMC2 has enough money to do the necessary testing. They need results. If results are good, PR will follow, probably more than they want. The Navy contract implies good WB-8 results may result in a request to build the 100MW reactor that they're asked to supply a design for. After that, it's Katy-bar-the-door if it works.

[ladajo]

I had a great response drafted talking about the gunshy propesnity of current navy and military project funders. Unfortunately my laptop cycled on auto-reboot for an update right when I was hitting submit. Bad words ensued.
Cliff notes version...

If you have read the FY11 Budget reports so far from both the House and Senate Committees as well as FY10, you would see what I am talking about. I see it all the time at work.
Projects that are funded get yanked money pulled left and right based on new priorities or thoughts that something else will work better sooner, or even thoughts that it might not work in a reasonable time.
Everyone is paranoid to have their names attached to a "waste of money".

EMC2 could get upstaged by Focus in the bigger arena. Results are key, and so far the results visble for EMC2 are essentially naught. Focus is perpetuating progress to all, EMC2 is on a VERY short distro list. That is VERY dangerous is these days of mobile money.

[mvanwink5]

If nubs were replaced with 4 stand offs for each coil, where would be the best place to put the coil stand-offs, where the nubs were placed, 45 degrees away, or 90 degrees away? I was thinking 45 degrees away from the original nub location as it would be away from the line cusp, but also away from the corner cusps, and so would have the best chance to be away from electron recirculation paths. Any thoughts?

WB-6 had them (bottom coil) at the nub location, but that may have been because there were nubs there already.

[WizWom]

If nubs were replaced with 4 stand offs for each coil, where would be the best place to put the coil stand-offs, where the nubs were placed, 45 degrees away, or 90 degrees away? I was thinking 45 degrees away from the original nub location as it would be away from the line cusp, but also away from the corner cusps, and so would have the best chance to be away from electron recirculation paths. Any thoughts?

WB-6 had them (bottom coil) at the nub location, but that may have been because there were nubs there already.

You would attach as far away from the corner cusps as possible.

[mvanwink5]

Wizworm, the nubs overheated at the location you are suggesting for the standoffs due to the line cusps (one reason for doing WB-7.1). With recirculation of electrons exiting the line cusps, shouldn't we expect the standoffs in the same radial location to have the same issue? Just a thought.

[D Tibbets]

Wizworm, the nubs overheated at the location you are suggesting for the standoffs due to the line cusps (one reason for doing WB-7.1). With recirculation of electrons exiting the line cusps, shouldn't we expect the standoffs in the same radial location to have the same issue? Just a thought.

The key (I think) is the distance past the mid line of the magrid. The electrons will be traveling in a straight line through the center of the cusp and/ or running along a field line that is nearly parallel in this area. They will mostly do so until they are reversed by the positive potential on the magrid that they would see once thy were past the mid line of the magrid (effectively outside of the magrid). This reversal would occur quickly in a short but important distance past the mid line of the magrids. Apparently this distance was enough for the electrons to reach the nubs. If the nubs were arched more it might help, but this introduces more stresses of the magrid structure. I don't know how hard 10 Tesla fields push against each other, but I suspect it would require a strong structure to prevent warping or breaking.
A stand off behind the magnet casing avoids the electrons in the center of the cusp entirely as those electrons are traveling almost radially outward (and inward once reversed) Electrons traveling off center in the cusp would be on more curved field lines and might reach the standoff before reversing, but because it is traveling along a curved line the distance it needs to travel is proportionatly greater than the liniar distance it would travel if it was not trapped on a field line.

I suspect that the best position for these standoffs may be where the magnets are closet together, because the opposing magnetic fields are closest together and so will be stronger and squished into more linear field lines. The distance from the center of the corner cusps to a standoff placed there is greater, but the magnetic field lines are also weaker there, and they presumably have a smaller radius of curvature, so the distance an electron has to travel along the different curvatures may actually be ~ the same(?). But, consider that the maximum magnetic field strength is less in the corners because they are further away from the magnetic field generating windings. Field strength drops with the inverse square law. So there would be more (much more?) electrons escaping in this area compared to the edge/ funny cusps.
The center cusps would be weakest of all, but I suspect they would be of least concern due to their distance from the magrid surfaces/ standoffs, and because the electron leakage/ escape is least through these cusps.

Dan Tibbets

[mvanwink5]

Dan, I suppose you could be right, that the electrons just reverse themselves and return, but by the pictures it seemed that something (I supposed electrons) were making it past the magrid and returning through the coil centers. Could be just my imagination. However, if that path is taken by enough electrons, then line cusps would be an issue for standoffs. Perhaps I am wrong, but the point of closest approach for two coils would have canceling magnetic fields (hence source of the line cusp) and would have the greatest escape for electrons in that area. Just trying to get my head around this thing, thanks.

[D Tibbets]

Dan, I suppose you could be right, that the electrons just reverse themselves and return, but by the pictures it seemed that something (I supposed electrons) were making it past the magrid and returning through the coil centers. Could be just my imagination. However, if that path is taken by enough electrons, then line cusps would be an issue for standoffs. Perhaps I am wrong, but the point of closest approach for two coils would have canceling magnetic fields (hence source of the line cusp) and would have the greatest escape for electrons in that area. Just trying to get my head around this thing, thanks.

There have been threads argueing cusp recirculation. The concensus seems to be that recirculation is dominated by exit and reentry through the same cusp. If this is not entirely the case, something like what M. Simon mentioned- placing a modest negative potential on the outside of the standoffs might significantly help.
Cusp losses are dependent largely on the area of the cusp. As the funny or semi- linear cusps are squished together the length of the cusp may not be changed, but the effective width gradient) is. This is my understanding of why the Polywell geometry is so much better than a mirror machine in which two opposite polarized ring magnets facing each other. You can push the magnets close to each other to compress the effective width of the linear or equatorial cusp, but to do so you are greatly decreasing the internal volume, while the Polywell avoids this.

But, what I am visualizing is that because the magnetic field lines are so compressed between the closest approaches of the magnets, the field lines stay more nearly parallel to the cusp for a longer distance. so the electrons are confined to a narrower and longer tract and would have more difficulty reaching anything to the side of the cusp (like a standoff) before their direction is reversed and they are sucked back into the machine.

Dan Tibbets

[mvanwink5]

Thanks Dan, if the WB-7.1 chamber (labeled WB-8 ) is anything to go by, the standoffs are where you and Wizwom are suggesting, in line with the old nub location. I suppose standoff location would have already been optimized with WB-7.1 (my imagining).

ps waiting for the upcoming July non-informative government project status report "on budget, on schedule."

[WizWom]

That's just the best you can do without a high current through the standoff - the furthest from focused magnetic field lines, and uncharged.

The field lines outside the core will spread (technically to infinity, practically much less). Electrons exiting the core will follow these field lines, hopefully to arc around and go back in the center of the face; only a portion will do that, the larger the vacuum chamber the greater the percentage of escaped electrons that will. The nubs or standoffs will absorb some, the vacuum chamber walls the rest of the escaped electrons.

The nubs were preferential because they were a conduction path for the charged surface of the grid; standoffs would not be. That would mean that the only interception force is when the magnetic field lines permeate the standoff.

Now, if you have high current superconducting tape, then your single width of tape should make a significant magnetic field, which would shield a nub or standoff. But the engineering of the loops means you don't WANT a single strip current that high.

[TallDave]

I had a great response drafted talking about the gunshy propesnity of current navy and military project funders. Unfortunately my laptop cycled on auto-reboot for an update right when I was hitting submit. Bad words ensued.
Cliff notes version...

If you have read the FY11 Budget reports so far from both the House and Senate Committees as well as FY10, you would see what I am talking about. I see it all the time at work.
Projects that are funded get yanked money pulled left and right based on new priorities or thoughts that something else will work better sooner, or even thoughts that it might not work in a reasonable time.
Everyone is paranoid to have their names attached to a "waste of money".

EMC2 could get upstaged by Focus in the bigger arena. Results are key, and so far the results visble for EMC2 are essentially naught. Focus is perpetuating progress to all, EMC2 is on a VERY short distro list. That is VERY dangerous is these days of mobile money.

I agree budget-cutting could have an impact in the medium term, but WB-8 should already be running so EMC2 will have some data. Being upstaged doesn't worry me a lot -- if anyone gets anything workable off the ground that $2 trillion sitting out there piling up on corporate balance sheets is going to fly into fusion research as everyone tries to do it better. Bubbles are fun on the way up (I once owned stock in Corvis, a company that was the shiny film of the tech bubble. They IPOed at $2B with no customers, just a fancy all-optical switch -- and they made ten times more from that IPO than they ever produced in revenue.) Honestly, I think PW is more likely to be hurt by association with Focus' implosion when it becomes clear Lerner has overpromised.

At the end of the day the battle is going to be won by whoever has the workable concept -- if anyone does. I doubt there is really more than one out there, in the still-unlikely event there is even one out there. And to be fair, if somehow FF does actually have the right idea, then they should win.

EMC2 is approaching this as a science, with proper skepticism. It's pretty unlikely the WB-8 contract will be pulled out from under them before they have some real data. If they can get anything like n*kBolt*Te = B**2/(2*mu0) density and b^.25 loss scaling at .8T, the world will beat a path to their door.

[ladajo]

I agree with your logic, but also temper it with the reality of having seen money yanked mid-stride from promising/productive projects.

There seems to be an urgency these days to try as much stuff as possible quickly and then run with what seems like it is working. The other thought being that you can always go back and dust off some later and try it again later if you want.

There is no rhyme or reason thease days, it is all about the "drive through" mentality, what can I get the quickest. The waste and inefficiencies are insane in this environment. The crazy part is there are so many folks in the upper echelons that really believe they are saving money. Really all they are doing is hiding the waste better, and finding more creative less obvious ways of spending other budget line item funds under themselves. It is very much a micro(macro) socialist approach. And as Maggie so well noted, you eventually run out of other folks money.

If Nebel can demonstrate <again> the threoy is functional, then at I minimium it means that someone else will run with it to see where it goes. For the government, it means that it becomes something to look at again later if it doesn't get finished now. Hopefully, the backers get enough oopmf from WB8/8.1 that they can pursue Demo funding. And again, you are right, if they get the numbers, they have the ammo. But unfortunately, if someone else gets "the numbers" in some other project first...

[TallDave]

I agree with your logic, but also temper it with the reality of having seen money yanked mid-stride from promising/productive projects.

True enough. That Livermore mirror shutdown was a travesty. Tax revenues are falling like a rock, and the GOP isn't going to be as friendly to stimulus. Guess we should hope oil prices stay over $70/bbl!