Six Inch Cross Fusor

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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

I have not been satisfied with progression of my neutron numbers. In fact, they have gone down. I replaced my grid with a beefy 304 stainless tube that proportionally better matches Jon Rosenstiel's to see what would result.

Neutron numbers stay low with the new grid until the grid gets red. For the same voltage and current, there is almost a ten fold increase in numbers once the grid is glowing hot. I assume this change is from thermionic electrons making plasma more efficiently. I get 30,000 cpm on my Russian tube, but it lasts for only about a minute, because by the time my hefty stainless grid is hot, so are the chamber walls. I think I may experiment with grids that make better use of the work function earlier.
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Richard Hull
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Re: Six Inch Cross Fusor

Post by Richard Hull »

I think active cooling is a must, but try going back to a spherical tungsten grid before cooling the cross. Lots of ideas rolling around in my head now with 6 different ways to go from here, (long term).

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

Richard,
I started planning to go back to a tungsten wire grid even before I posted yesterday. I have also been pondering using an unconventional wire spacing. The last time I used a wire grid in the cross, the beams seemed to be influenced by the chamber wall shape, and the beams did not appear focused.

As far as cooling, I have some ideas that will take some time to implement, but in the mean time I have added a second muffin fan.
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Richard Hull
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Re: Six Inch Cross Fusor

Post by Richard Hull »

Jim you are correct the cross is not a great beaming device save for along its axis. a spherical grid will tend to field line along the sharp edges in the cross arms as they are all quite close to the grid compared to the flat ends. Those edges, even if carefully rounded or smoothed/polished are still high field regions and tend to force any beaming solely due to proximity. Naturally it all works to do fusion, the cube is nice solely due to target, (flat end), proximity to the cathode grid, especially due to any target added to and protruding from the near zero distant cathode. (no need to travel down a metal tunnel to get to the more distant target, as in a cross)

The original Farnsworth all spherical system allows for tight field control better than any other form. A short cylinder with a tubular hollow grid is good as is the cube with short cathode to target distances. These latter forms are more beam on target.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

Here is a picture of my latest grid. You can see where the secondary beams form.
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Richard Hull
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Re: Six Inch Cross Fusor

Post by Richard Hull »

Yes, the smoth round ends will not beam against the sharp edges of the cross but yield a rather diffuse coronal glow as the field off the ends is rather evenly distributed about the ends and the equally uniform sharp cross edges. (They share the "glow current" rather smoothly, robbing power from the central beaming) . Only the central beam lines are true hard, visible beams.

Question is there a diamond lozenge on the other side of that cathode?? If not, one of the side arms has a metallic protrusion that is beaming to that area. Screen wire in one of the side arms to protect a view port would probably do this.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

Richard,
There are other beam marks on the grid. There is an almost identical one on the other side, a smaller one opposite my connecting wires, and a smaller one yet near my connecting wires.

The secondary beams seem weak. The one that made the mark you see in the picture goes to my view port. The view port has had no visible damage and when operating has a wide blue fluorescence glow.

Jim K
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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

Some updates:

I have installed a tungsten wire grid in replacement for the SS tube grid. I spaced the wires to leave wider openings to the flat sides of my cross. This seems to have forced most of the heat to one of three of the wires. This grid runs at lower pressures and as a result, at the voltage I ran it, the beams can't really be seen over the light of the tungsten incandescence.

As far as relative neutron production, I can't say. Yesterday, my Russian tube decided it had had enough and failed. Today I used a large, old Nancy Wood BF3 tube that I am still tweaking. It is a little sentiment to noise at the low end but while running it seemed to give real data. I really need to do a moderator test just to be sure, but it was too close to my feedthrough to safely fiddle with. I could see fusion rates improve across the run so I don't think that I was watching xrays. For point of new reference, I saw 60,000 cpm at 40 kV and 7 mA.

As far as temperature, I did NOT see any signs of chambet temperature degrading my neutron numbers. I ran for 5 minutes at 60,000 cpm without seeing numbers sag like they did before with my ring grids. I didn't record the numbers this time but my silver activation cell gave counts right after the run that looked as good or better than counts in saw at higher voltage and currents with ring/tube grids.

Interesting data. More tests coming.
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Richard Hull
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Re: Six Inch Cross Fusor

Post by Richard Hull »

Spherical symmetry is the ideal, but cube and correctly constructed cylinders seem to take advantage of beaming. This is especially true with active cooling in the smaller sized cubes. The cubes do so well due to shorter beam distance (MFP?) and the intrinsic non prominence of the sharp edges found in a long throw cross. Cubes are nothing more than a cross with zero arm length. Cylinder fusors would benefit from large diameter, short length. A 6"X6" cylinder with a direct mounted 2.75 CF HV insulator in the center using a cylinder cathode of a length that would have a shorter distance to the two target ends than from the cylinder cathode body to the chamber cylinder walls. This might be a good performer. The cylinder would be a snap to cool with coiled Cu tubing wound around the cylinder.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

Based on my silver activation cell data I seem to be getting much better numbers with the wire grid than my tube and ring grids. I am using less d for the same voltage and current. Even general area xray dose rates are lower. The first plot is from the ring grid. The second is from today using the wire grid.
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Richard Hull
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Re: Six Inch Cross Fusor

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Yes, a good deal better and much better looking decay curve. Glad it is at least working better for you.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

Posting this today just to share a little eye candy. Because I've been testing out my new heavy water conversion, I did several runs today. The wall loading has been fantastic. I fired up an old Eberline PNC and sitting in my lap six feet from the fusor it read 250 cpm. I was running at 45 kV and 11 mA.
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My picture was probably closer to 30 to 35 kV, but I like the colors. Most of the color was courtesy of grid incandescence, but there some plasma pink too.

Jim K
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Richard Hull
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Re: Six Inch Cross Fusor

Post by Richard Hull »

Great result Jim! It looks as if the wire grid is doing the work for you now.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

I have been looking for ways to reduce noise in my system. I know I must be getting some from my feedthrough connection based on hissing and snapping sounds.

This latest feedthrough iteration is my take on oil potting. It's still a prototype, and I'm still working on the seal. I am procuring a nylon pipe clamp that should help cure the tiny weep I'm getting now.

Jim K
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Dan Knapp
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Re: Six Inch Cross Fusor

Post by Dan Knapp »

Jim, a suggestion regarding oil potting. Something I’ve been planning to try is using Vaseline in place of oil. Warm it enough to pour it in then let it solidify. Yes, heat of operation is likely to liquefy it, but a slow leak during periods of inactivity would be less likely to make a mess.
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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

Dan,
I like your idea. That may also save me the trouble of draining the pot when I pull the feedthrough. So far, I have been using a syringe to suck out the oil.

Thanks,

Jim K
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Joe Gayo
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Re: Six Inch Cross Fusor

Post by Joe Gayo »

Jim,

Is that a poster presentation in the background?

Joe
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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

Joe,
The poster in the background is my son's ISEF (2012 or 2013 I think) presentation. His was the first fusor in our home, and I'm proud to hang his old poster in my lab. It may get put away soon though because I have a chart of the nuclides and I need the space to hang.

His fusor work inspires me still because of how hard he worked and how he kludged his way to neutrons while his high school maligned his efforts. He made his vacuum chamber from a kitchenaid mixing bowl he stole from his mom, and got zero help from the school. A substitute teacher went to the school board to get his project stopped and him disciplined. The school board head was the father of a friend of my son so his project was allowed to proceed. He only won his high school science fair because the physics judge was a local college prof who had done research at Oak Ridge and passionately insisted my son's work was real. He won the regional fair but unlike other winners in the past, he was told he could not advance to ISEF until a fair judge who was a scientist at the nearby Aberdeen Proving grounds could come to our basement and watch my son operate the fusor. He left thoroughly impressed with lots of well wishes for a promising future. My son took an honorable mention at ISEF in the toughest category. Of course, of mutual benefit to me, he did receive lots of help and encouragement from Fusor.net folks along the way. Frank Sanns even showed up at ISEF. The fusor crowd has become like family to us both.. Mike, my son, is now a PhD candidate in medical physics. I still consult with him on fusor matters though he now mostly pokes me to move on to other physics projects. He attends HEAS when he can and has mentioned a desire to attend this year as Richard's lab is like a mecca to us both.

Joe, this is probably more than what you wanted to hear in response to a simple question, but you asked about something that represents a nexus to my own involvement. I moved on from being just his safety officer and project financier to my own efforts. I wish for you and others the same satisfaction working with young people on science. It couldn't be more rewarding.

Jim K
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Re: Six Inch Cross Fusor

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I can't speak for Joe, but I enjoyed the story behind the poster and your boy's struggle to get his work in the fair and on to ISEF. I well remember his system. The irony is the father son team concept got somewhat reversed. Your boy, Mike, did fusion first and then you felt so pumped by his effort, you have tried your hand at it in a totally new project and succeeded. It is always good to hear the tale told of process, struggle, and ultimate success. Thanks

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Joe Gayo
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Re: Six Inch Cross Fusor

Post by Joe Gayo »

Jim,

Thank you for the backstory.

It's clear you are immensely proud of your son, and besides being well deserved it no doubt provides him a source of strength. I'm a believer in science fairs and the characteristics they can foster in those dedicated to learning such as perseverance, problem-solving, and presentation skills.

Joe
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Jim Kovalchick
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Re: Six Inch Cross Fusor

Post by Jim Kovalchick »

I've made some improvements to my cross fusor including getting rid of a wicked leak and arranging the fittings for easier accesses for activation. I believe that I am operating in the 2 x 10⁶ TIER realm. Today I operated at 55 kV and 15 mA for an activation time of 15 minutes. My target was a two inch indium foil.

I'm not satisfied with my NaI detector, peak shaping, and calibration, but it had no problem seeing the lower dominant indium gamma in 900 seconds of counting.

This is getting fun.

Jim K
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Re: Six Inch Cross Fusor

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Jim and I follow each others work almost daily via e-mail. Jim now has a nice large fusor that is doing great. I applaud his effort and friendship in working things out a bit, especially in regards to our old PNC-1 and remball data collections. Nice work Jim!

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Six Inch Cross Fusor

Post by russssellcrow »

Jim Kovalchick,

Your Tungsten Carbide electrode is brilliant!

WC (tungsten carbide) is a neutron reflector, is this a bad thing in the fusor star? Would it enhance fusion yield, or be counterproductive?

WC was used in the original initiator feedback experiments
(Demon Core) during the Manhattan Project, to reflect neutrons back into the initiator. Lewis Slotin fried himself in one experiment, and became a casualty of the project.
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