A grid design idea

For Farnsworth type designs.

A grid design idea

Postby Doug Coulter » Thu Jan 06, 2011 11:45 am

I've been thinking about grid designs as incremental (not revolutionary) ways to improve fusor Q somewhat, as I have found that doing so even in the worst "static" modes, that doing that also helps the higher Q pulsed modes work better anyway, and it's easy to test. I think that electrons released due to fast ion impacts with just about any conductive grid material are most of the losses, along with mis-focus, so improving both grid accuracy and reducing electron emission should help, I believe. Here is what I currently have in mind, and since it's not really hard to try, I'll be trying it fairly soon. Sigh, things never move as quickly as hoped...so the definition of "soon" is a variable here (and everywhere else, it seems).

NewGrid.jpg
New grid parts



First of all, I've found it's not insanely difficult to machine pure graphite, which has one of the lower secondary emission constants of conductive things, at least when hit by electrons at kilovolt levels -- I can't find data on responses to fast ions anywhere, so there's an assumption that is untested so far. The one pictured has a mistake in it, but I'm going to try it in the tank as my second grid anyway -- you never know what you might find out doing things like that. The mistake is an imperfect symmetry of the vane spacings. Sometimes that helps things, so who knows? I will, soon enough.

Shown next to that are some 1/16" pure alumina rods I got from Accuratus (I have ones half that diameter on backorder, they've got to be hard to make!). The idea here would be to align these along the vanes on the outside around the grid, and cover the inactive ends with larger alumina tubing so there's simply less stuff for an ion to hit head on that is carrying a big excess of electrons due to the power supply input. I'd think that the ions will still see plenty of attractive field from the sides and inside ends of the vanes so it should still work. This would make most electrons released be set free inside the grid, where they might actually do some good, instead of instantly flying to the tank walls to make heat and X rays, or so I'd presume. They'll want out of there, of course, or -- if there's enough positive charge in there, maybe not! Seems worth a try, at any rate under the meme of "try the easy stuff first", so that's the plan.

To make this, I first make another graphite grid, presumably this time without the angular spacing errors (but more on that later*), only first I cut a 1/16" deep and wide groove along the length where each vane is, before I machine out the inter-vane stuff. I could then lay the insulating rods in the grooves, and hold the whole mess together with a couple of tight fitting alumina rings at the ends, which would also get rid of the ions that hit those to at least some extent. The thickness of alumina I have won't hold off the full supply voltage, or so I think, but it may still insulate some, and not so readily supply excess electrons when collided with. Or that's the hope.

*
Various endeavors have found that uneven symmetry is a good thing. It could be perfect symmetry is poison for various reasons. For example, my best main grid right now has a bit of twist to it, due to a machining error (I'm good at making mistakes!). Could it be that's an impetus to get whatever minor amount of recirculation we get -- helps organize the flow in some way?
Could be. An example is Eric Lerner's DPF rig. At first, other researchers had great difficulties replicating his results. He found that it only took the earth's stray field to give just enough impetus to things to make it work, and other workers had been much more scrupulous about making the setup field-free (until the big pulse, that is). When he redesigned to put just a slight twist on his apparatus, and others also did, they all started getting the same results...

I know that as a gunsmith, that the very best barrels (which is the determinate in accuracy, or a main one) don't have an even number of lands and grooves, and one pays a high premium for ones that have 5, rather than 4 or 6. The theory there is that the bullet is deformed less when two lands aren't directly opposite. And it works out in practice. I've built several rifles, by the way, that are accurate enough, at scale, that if they fired protons, I could hit one with another very, very reliably -- and frankly, protons ought to be easier, since they are all identical, unlike bullets (and brass and powder charges), and can be made to all go the same speed at the same time (unlike bullets). There's no wind or barrel vibration problems with charged particles, comparatively. For reference, these super accurate bench-rest guns shoot into a quarter inch (all the same hole -- it just gets a little ragged after a lot of shots) at 400-500 yards on a calm day. And this is with "barrel whip" that if the bullets were to come out at opposite peaks of that vibration would be thrown several feet one way or the other at a mere 100 yards, which is easy to prove by simply putting a finger on the barrel during a shot and seeing how much that throws off the shot. If you imagine a garden hose with water pressure suddendly applied and the end whipping around, you'd be close (and I have some cool movies and simulations done by our defense department that show this).

Could it be that having a vane or rod opposite an opening on the other side is a good thing? Seems no one has tried it, or at any rate, reported on it, so it's something else to try. One could build a model where this helps focus at the interaction zone, so it seems worth a go even if it results in no recirculation. In other words, an odd number of holes or vanes might be a good thing, not a bad one, especially assuming there is any good effect from electrons released on the *inside* of the grid volume. I think there is simply no way to be sure without a try, so I will.
I believe that in addition to the math, which is more useful in hindsight than foresight sometimes (think the three body problem in gravitation, as we have the analog going here), getting that "feel" or gut level understanding about how an apparently simple system can produce emergent behavior is key to being good at this game. Or, well, it has been for me, and I've had a few surprises along those lines already.

I bought a better degree-ing setup for my machines, so maybe I won't make those mistakes so badly, we'll see how that works out when I get some more graphite to chew on (very soon, and Jon's will be in the mail to him soonest). At this point, we don't actually know if it's a good move to work with that stuff -- seems reasonable, but it's unproved, I've only used it for end-caps with W rods, so far. One thing that does seem reasonable is that I can at least theoretically, make these much more accurate than grids made of metal I can machine (can't really plan on cutting tungsten, though I might try titanium at some point if I get a better micro-mill for the lathe toolpost put together).

My composite grid suffers from fit and finish issues -- can't make a perfectly aligned interference fit hole for the rod ends at this point, maybe not ever, where when machining out of a solid chunk of it (inaccurately called billet, as Jerry has pointed out) I can get it a whole lot better, to near the accuracy of my machine ways if I don't flub it up, which is more than ten times better than anything I've yet put in the tank and tried, so far. I have to repeat that so far, grid accuracy has been a super big effect once I started getting anywhere close to good. The difference between huge and medium error wasn't much, but things got better fast going from medium to small, and in this case small is still pretty big compared to what I can theoretically do.
So it seems the game might be worth the candle on that one.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: A grid design idea

Postby chrismb » Fri Jan 07, 2011 7:23 pm

Graphite grids are cool!

I like the idea of shadowing the grid structures with something else that, perhaps, won't shoot off electrons like the grid would.

That being said, I think the majority of the electron loss is actually from electrons liberated in the beams, as the ions/electrons do a cascade-ionisation of the background. That's why you see the beams, because that's where most of the ions/electrons/collisions go. But as you plumb down into the depths of vacuum pressures to see what mechanisms lurk there, then, who knows?!

I would take a moment to repeat something I said over on fusor.net. Magnetic shielding (especially compatible with cylindrical arrangements) could be easily done with external coils and a very modest current. You only need relatively tiny amounts of mag field to arrest the motion of the electrons, whilst having barely any influence on the ions.

The fusor.net post is; http://www.fusor.net/board/view.php?bn= ... 1219430899
chrismb
 
Posts: 620
Joined: Thu Aug 05, 2010 6:32 pm

Re: A grid design idea

Postby Doug Coulter » Fri Jan 07, 2011 10:08 pm

I certainly noticed it didn't take much H field to totally mess up my electron beam device at low energies ~ 1kv. Here the situation is more complex, and there are other things to perturb them. Slowing them down is probably the best you can hope for, but who knows? It seems to take more field than is easily generated outside, I've already tried a big fat speaker donut magnet on the feedthrough just outside the tank, probably a few hundred gauss inside near one end of the grid, and it makes no obvious difference there.

Here I'm hoping that the alumina is a good enough insulator to just limit the current that can resupply it from the power supply with more electrons to knock out, and it's the only insulator I've found that isn't pretty quickly ruined by hot D hitting it. I got the graphite rod today of the right size to fit inside the alumina tubing I got from accuratus, so I'm going to try and get going on building that guy. Going to do that other test we thought of on the fusor first though -- for whether I see lines at 5,6 when not having run fusor main power, as it's easy to do and important to know. Hopefully I had all my other emergencies for the week already, it's been crazy here.

The net grid dimensions should be:
Graphite 3/4" OD, 5/8" ID, with I think 6 vanes instead of my usual 8, because that's smaller than my usual 1" OD and I want to keep the hole to vane ratio similar in the smaller size (should have gotten some ceramic tubing 1" ID, but didn't think of it, and that stuff is very expensive from that source -- 100 bucks a foot more or less). When I ordered it I was thinking of using it as the outer for the feedthrough, but really pyrex works fine for that one, and is cheaper and easier to handle too. You only need the alumina where ions are hitting it hard, which I've figured out how to get with just a little bit of ceramic, the rest pyrex (near ground potential) and quartz (for most of the inner insulator) Just the tip of the conductive stalk needs the alumina protecting it, not the parts down inside the feedthrough.



Pure alumina (vs the stuff that's easy and less than half that price) must be a real bear to make. Without a binder, you have to get it over white hot to make it stick together. I assume that's why it's expensive, as is that graphite (which requires pressure while white hot). The binders in even 94% pure stuff reduce to metals under bombardment. I don't know if there are other substances that are immune or not. Super "hot" H is a pretty good reducing element.

I'm not as sure as you that most of the electrons come off ionizing gas myself. At the pressures I'm running, the thing won't even self sustain without an external ion source, it just goes out.
And the electrons in the recently neutralized ions had to originate someplace. Didn't we agree that we are seeing the light from excited neutrals, mainly? Because there's almost no other plausible mechanism to get couple eV photons in this lashup.

In this setup, I'd think that in only a few seconds, all the original electrons have been slammed into the tank walls in these fields. So the new ones have to come from someplace, and I know for a fact that hitting any conductor that has a big negative charge as hard as these ions do will eject multiple electrons -- they are only what, a few thousands of times higher energy than the work function of any known conductor? In the case of tungsten with ~4v work function, over ten thousand times higher energy than required to knock out a single one, if the tungsten is cold (and it isn't). Graphite *should* be better about that, but we don't really know, or at least I've not seen a measurement on it with ion strikes, it does have a higher work function, but still in the single digits, and is used in valves to cut secondary electron emission, so I thought hey, it's worth a try, and a lot easier to machine accurately than almost anything else. Plus, it's rigid as can be and can take any heat we can generate. It's "pre-embrittled" but I don't let my kitty cats play with it. I only even touch these things a couple times during their whole life.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: A grid design idea

Postby Doug Coulter » Sat Jan 08, 2011 6:45 pm

While I was fooling with the mass spec here, there was a lot of waiting involved, so since I'm having a jones for working in the shop after a hard week, I worked on this some. Here's some pictures I took, which I guess could be in eye candy, or machining, but they are about this thing, so here.
Setup.jpg
Lathe setup to change "billet" into a grid. First hole bored to length.

Boring.jpg
Boring the big ID

Pipe.jpg
Pipe, the hard way

MillJig.jpg
Lathe toolpost mill

MillCloseup.jpg
Mill closeup.

TestFit.jpg
Test fit of pure alumina rod

SlotsCut.jpg
Slots cut


Any machinist will know why I did these things in the order I did. The small hole first (new straight drill), then large hole, then the rest. This is to keep the most material there you can while doing the work on it, because this stuff is fragile. Some people would have bored the big hole first, with the idea that the big drill might make a straighter hole, but I liked doing it this way (drilling the 3/16 hole for the mouning screw first) because it was the first use of that drill -- it's straight, and this way I have a pilot for the bigger forstner bit I used to make the big hole flat bottomed. The circumferential mark on the rod is the cutoff point where the small hole reaches. I maybe should have made this shorter, but a first try is just that. One thing I discovered is that the 1/16" mill I used isn't .0625", it's closer to .06", so I had to jigger slightly and make an extra pass to clear the slightly bigger .0635 inch ceramic rod, those tend to be a little oversize. I suppose they thought you'd have more chatter in the mill than I had and pre compensated. I did all the boring at about 200 rpm, not because you can't go faster -- this stuff likes speed, but then you work in a cloud of graphite dust and it cuts easily anyway. The boring was done with a light, constant torque fingertip touch on the drill drive, and proceeded in a bunch of little spurts as hard and soft parts were hit.

The hard and scary part is yet to come. Now I mill out all the places where those slots are not, those will be the beam holes, and that has to be done carefully as this tool doesn't like making that cut full depth, so it will take awhile. It's something to do after a couple beers, slow, steady, careful, not when excited or hit the wrong control and bam, no grid.

This grid is a lot smaller than the smallest one I've had good luck with, so we'll see. As there is a few hundred buck minimum at Accuratus, it might be awhile before I get more ceramic in a bigger ID. Jerry had the idea that maybe I should just try and metallize the insides of the rods, and forgo the graphite. That's an interesting thought, but I wonder how long the metal would last too. I could perhaps sputter something onto them from the inside, but I'd still need a way to hold it all together. The plan here is to cut some short rings of the ceramic tubing to slip over the ends and hold things in place. Which will also keep inactive but highly charged electrode-stuff from being exposed in the tank to ions, which should help, but who knows? That's why we do this!
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: A grid design idea -- more progress

Postby Doug Coulter » Sun Jan 09, 2011 5:32 pm

Almost done. Just have to cut some ceramic. I took my own advice and turned the middle down some so there'd be less to cut out with the mini mill. Even though it was an interrupted cut, no problems, and it made the rest lots easier. I'll do that first next time. No real issues cutting out the holes, either, except near the end the thing started to mechanically resonate with the tool, so I stuck the center into it lightly.
See pics. This is going to be the most accurate grid I've ever made, though also the smallest, and that may affect things. Next time get the right doggone size ceramic tubing!
FirstHoles.jpg

RodFit.jpg
Rod fit test

AllCut.jpg
The "Whew" moment

FiledNSunk.jpg
Final finishing and countersink for bolt

NoErrors.jpg
Side vew showing one vane hiding another perfectly


Sorry about focus on that last one. Anyone tried taping a reading glass lens over a camera lens?

So, I expect to probably make less neutrons due to the smaller size here, but at lots less power input, for net improvement in Q, but of course, a test will tell all.
Gotta get this sucker into the tank before Bill comes over and drops something on it (private joke) ;)
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: A grid design idea -- finished

Postby Doug Coulter » Sun Jan 09, 2011 8:42 pm

Here are some grids, one of the new design, another one I mis-machined, but will use as a second-grid ion source.

GrGrids.jpg
Done! Now, for testing


Now, does anyone know a good way to get graphite off of ceramic? Chemically perhaps, or will I have to sandblast or something?
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: A grid design idea

Postby Joe Jarski » Sun Jan 09, 2011 9:41 pm

How about an oxidizing flame?
User avatar
Joe Jarski
 
Posts: 231
Joined: Thu Sep 16, 2010 8:37 pm
Location: SouthEast Michigan

Re: A grid design idea - in the tank

Postby Doug Coulter » Mon Jan 17, 2011 6:52 pm

Ok, here is a video of part of the breakin run for the new grids. The #2 all graphite one in the foreground is too large for the 12.5 ma power supply I have on it now, so I may go back to a smaller one. The one above and behind it is the new graphite-ceramic composite grid. After cracking the tank I had to go fishing for a new leak, which turned out to be my tank vent valve, on the foreline side. Sure am glad I have that mass spec and some He to find leaks with -- only took about an hour to find and fix (well, put a band-aid over).
http://www.youtube.com/watch?v=xEl-U9WfB4o



I noticed a few new behaviors on this -- some of which may change or go away as the thing breaks in. At first, I got at most two opposed rays from the main grid, though this one is pretty precise compared to anything else I've had in there. Later, and with more gas pressure to reduce the spot-arcs we get during breakin (which are hard on power supplies and ballast resistors, so you take it slow and easy here) all 6 appeared, at lower volts (due to more gas) and they for crying out loud, rotated back and forth about 5-8 degrees! That was pretty weird and I have no explanation at this point, and I'll just watch for it and try to get a movie if I can make it happen often enough to catch it. The third thing was extremely bursty neutron output. With no changes in any parameter, it would sit there, make the 3He tube count some -- maybe 25 hz (this is all at much lower supply volts than normal here, about 30kv for breaking in). But every now and then, it would get into some kind of bursting mode and really count screaming -- 10khz kinds of things, about the tube limit. I was watching on the scope and these counts (in either case) didn't correllate with the power supply/faraday probe EMI noises at all -- they were off doing their own chaotic thing. Of course, the hope is I can get that burst mode to go all the time, in which case we just got another few multiples of previous performance -- and at lower input power!

I made about 2 mrem of neutrons so far during breaking in (which is far from done, it will take a couple hours more runtime if past experience holds in this case). Since I had high noise, I ran a BTI bubble tube on this to verify that one. I didn't run activation, because it took so long to make those neutrons I could predict that the silver was decaying faster than I was activating it, I might have gotten out of the noise on the indium. Now that things have cooled off a little while doing the youtube thing, I'll try and run a couple more hours tonight and get some real running in if I can get it broken in well enough to run normal conditions. One nice thing about the break in conditions is I get a heck of a lot less X ray output during that than normal, so I'm not going to get fried doing this. Geiger counter barely doubles normal lab background in this mode.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: A grid design idea

Postby JonathanH13 » Tue Jan 18, 2011 6:39 pm

Fantastic work Doug - the first ceramic/carbon hybrid grid! Your hand precision there is a real inspiration ;) and this design could answer some long-standing questions.

>Remove graphite from ceramic

How about hydrogen peroxide? Like Joe said, I guess you really want to oxidise it...
User avatar
JonathanH13
 
Posts: 53
Joined: Tue Aug 10, 2010 3:20 pm

Re: A grid design idea

Postby Doug Coulter » Wed Jan 19, 2011 9:56 am

Well, I'm going to get another chance to touch it. My system sprang another leak that is going to take some teardown to fix, so I may as well. I believe I have a hairline crack in the ion source/gas feed tube, so I'll have to pull all that out and make another tube or fix whatever it is -- the place is very inaccessible at the moment, due to my screening around the area (which isn't needed any more so I guess the fact that it's real hard to put back on there won't matter). This would constitute the first actual failure of any part of the uWave ion source other than a wire to the extraction electrode falling out once. That's a darn good record -- hundreds of run hours with no maintenance is really good in this game. Even the big boys would be bragging about that one if I read the papers correctly.

The HV seems to have found a flaw in the little ceramic retaining ring on the near end, so I need to do something about that anyway. Whether the best fix is to replace it with another one like it or just remove it and put a tungsten wire tie wrap around the end isn't yet known. It's taking me about 2 diamond wheels per cut of that ceramic -- this batch, while not terribly uniform, sure is the hard stuff as these things go -- no wimpy binder holding it together, just sintered pure alumina (sapphire!). Hopefully I'll get things fixed today, as I have visitors coming to see it over the next couple weeks (3 sets!).

Meanwhile, some observations I didn't get to above. This grid draws serious power supply current at lower voltages and gas pressures than any other yet tried, which is pretty unexpected, and continues to do so at lower gas pressures than I've ever been able to run at all with. Some of that could be my leak I suppose, as when we did tests with deliberate contamination, we found a little air to be a voltage reducing stabilizer. However, by the time I got anywhere near the customary 50kv, I was running such low pressure it wasn't stable anyway. I was dealing with some nasty spitting off the flaw in the ceramic, quite a little fireworks show in there as white hot bits flew off and around the tank. This in turn is very hard on the ballast resistor as repeated dumping of the full charge on the multiplier stack into the thing doesn't get limited by the current limit of the supply, which goes full bore charging it back up (2.5+ kw!) and only then starts measuring delivered current -- it doesn't "notice" those 1 amp peaks, being out of range of the current sensor, and out of control of the stack charging mechanism.

Secondly, the visual focus on this one is super fantastic. I've yet to get a good picture of a line focus -- the camera always blooms, but to the eye, this is now inside a couple of mils (considerably smaller than a mech pencil lead). It's very pretty and a nice reward for the work that took. Also bodes well for eventual neutron production -- and at lower input voltages, which can't hurt Q at all.

And speaking of neutron production -- I did make a goodly number in between spitting events, but during the quieter times, saw an interesting set of patterns of neutron production and faraday probe behavior that I'm still trying to sort out for meaning. I had a situation where the thing was operating chaotically, going out, and coming back on (lit) which showed up on the faraday probe bigtime -- when this was "out" the measured tank ambient charge was zero. When lit, I still had the large negative charge on the probe. During the transitions I was getting neutron bursts the fastest I've ever seen and didn't quite get the time resolution measured on the scope to see just when during an onset the neutrons came out -- it was definately at the begininng, but whether just before the probe response or just after remains to be determined. Further, when it was running semi-stable, it would drift into and out of extreme neutron production for perhaps a second or two in either state, and when this one was "hot" boy was it ever hot -- I nearly ruined a BTI detector, filling it with bubbles before I shut down to go and look at it.

I have a place to put this and other detectors where shielding is minimal, but that means I don't go there while the thing is running -- I don't like getting fried myself.

I'm unsure about the operation of the second, somewhat malformed graphite grid. I did get some rays, but never saw a good focus kernel in it. This one draws a lot more current too, compared to what it replaced, and I was never able to get to full voltage on it without it going out with the 12.5 ma current limit in the little Spellman supply. I tried momentarily hooking it to the big one, and promptly fried the ballast R stack for that one (just melted the solder on the resistor chain, pushed it back together while hot, and it's still workable). I did notice on that one that the wobble stick end which is all too nearby (plan to move that elsewhere in the next major teardown) affected the rays in fun ways when moved around near them. But not as much as one might think, either. I'd like to try this grid on main power in the back just to see some things about it. It's fault is one misplaced vane, maybe not total failure, but where it is the field is so non uniform I'm not getting a good picture of how good/bad the thing might be -- which would be nice as it's the first all graphite grid in the tank. So, two firsts.

And of course, I need to totally fix all the leaks to really know how much was air impurity in there -- I had it pretty good for awhile during the running -- no need for extra pumping and the pressure was stable in sealed off mode, but...doesn't take much air to mess things up. My major new leak appears to have happened after all this and my current tank base pressure is a lousy 2e-5 mbar with the pumps going full blast, which is about 3 orders magnitude above what's been normal -- that's gotta be a priority to fix up. Else I can't confidently compare this data with other runs. Further, one of my neutron detectors is on the fritz -- I kicked the kludge board it's on by accident and need to build that up properly so that won't happen again. It's nice to have two of these so I can verify things in bursting -- if they both see it I get a lot more confident. Further, both need to be further pre-amped and stuffed into the multigeiger data aq stuff so I get time-synced information taken by that guy and can look for correlations between conditions and output more scientifically.

So my work is cut out for me right now. I have to also note that while the ceramic composite looked good on paper, mentally pretending to be an ion while looking at the built thing didn't look so great, but here it is working nicely anyway (other than the punch through flaw on one bit of ceramic). I now am wondering if the lack of perfect insulation of the ceramic is a reason for that one. Obviously, there's more to be done. I'll say that the alumina lighting up bright orange in the X ray and particle field is quite pretty contrast to the poisser and rays. This isn't thermal -- it's fluorescence of some kind -- very fast response to voltage etc, whereas if you actually get something incandescent in there, it'll stay hot a long time.

A major note is that X ray production was a heck of a lot less on my safety monitor geiger between me and the thing. If that continues to hold during more normal operation (once I fix the flawed ceramic piece) then hey -- that's a major benefit. For reference on that -- normal background here is 40-70 cpm. Nomal fusor runs produced around 1000 cpm (behind the shielding!). This produced no more than about 200 cpm under very similar conditions, even for the moments I managed to have full voltage on the thing.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Next

Return to Fusors, Farnsworth type

Who is online

Users browsing this forum: No registered users and 1 guest

cron