Fusor Update - Liam David

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
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Liam David
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Re: Fusor Update - Liam David

Post by Liam David »

I found what was limiting me to 35kV. The centering washer slipped and let the grid become misaligned. Moreover, I think I overtightened the grid stalk, which cracked the ceramic shielding washer when everything got hot. I just got some more washers in and will be back in business soon. The colorful sputtering probably didn't help the arcing either.

Offset cathode
Offset cathode

While everything was apart, I examined the cathode a little closer. There's a clear asymmetry caused by the stalk, certainly outside and probably inside the cylinder. The two bands on the ends thicken near the stalk and converge to it, and there's an interesting "cusp" on the inner wall. The patterns are more pronounced than last time because of the longer runtime and higher powers.


"Cusp" in pattern caused by stalk asymmetry...?
"Cusp" in pattern caused by stalk asymmetry...?

Ring where current flows in?
Ring where current flows in?

Asymmetric bands, caused by stalk.
Asymmetric bands, caused by stalk.


This is how the moderator is positioned for activation:

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Silver from Rio Grande, with two pieces of indium.
Silver from Rio Grande, with two pieces of indium.
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Jim Kovalchick
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Re: Fusor Update - Liam David

Post by Jim Kovalchick »

Liam,
Your grid pictures look like you are getting arcs secondary to the tube axis like I am. See my latest post for picture.

Jim K
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Liam David
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Re: Fusor Update - Liam David

Post by Liam David »

I haven't had any arcing, just the occasional sparking thanks to my grid shifting off-center. The spots on the side are from secondary beams that form once the voltage gets high enough, something like 5kV.

Deliberately off-axis, secondary beam downward
Deliberately off-axis, secondary beam downward
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Richard Hull
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Re: Fusor Update - Liam David

Post by Richard Hull »

I love that "cock-eyed" view of the interior of the cathode. Lots of interesting data in that view related to fields.

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
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Jim Kovalchick
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Re: Fusor Update - Liam David

Post by Jim Kovalchick »

Liam,
I meant to say beams not arcs. I can see them in your latest picture.

Jim K
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Liam David
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Re: Fusor Update - Liam David

Post by Liam David »

Arrived today, will be machined likely next week:


PXL_20210224_221335526.jpg


Both the chamber and endcaps will be fully water-cooled, and I have a few modifications that should help the field symmetry. I'm looking to push past 60kV, and with how I've arranged the water cooling, the angular neutron distribution should be minimally affected. Simulations show a max temperature of ~30C at the beam spots with 1500W input power, which is far above the 600W my supply can do at 70kV.


Getting better symmetry, and can push 45kV with the repaired feedthrough. There's static buildup somewhere and some sparking that's limiting the voltage.


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Mark Rowley
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Re: Fusor Update - Liam David

Post by Mark Rowley »

I always enjoy reading your updates Liam. Top notch work.

Very much looking forward to your cube build. I foresee good things on the horizon!

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Liam David
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Re: Fusor Update - Liam David

Post by Liam David »

Thanks, everyone, for the compliments. Been spending as much time on fusion as I do on school recently...

I found the actual source of the arcing and instabilities, which was only exacerbated by the offset grid. In moving the feedthrough quartz up and down, both for positioning in the chamber and servicing, vacuum grease from the o-ring and dust built up in a small ring. This got baked onto the quartz and limited the voltage to ~35kV. Now with some conditioning I can hit 50kV, limited primarily by x-rays. I have the lead shield top off for air cooling and scattering is an issue. Neutron rates are ~800kn/s @ 45kV, 8.56mA and can be held indefinitely, with brief excursions >1.3e6 (~100kcpm on the tube). Heating prevents me from exceeding the mega mark continuously.
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Re: Fusor Update - Liam David

Post by Richard Hull »

Good work Liam! 1.4 million n/s is about the best I ever did with fusor IV at 45kv. (my current limit on voltage.)

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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Liam David
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Re: Fusor Update - Liam David

Post by Liam David »

Maximum neutron rate is now 2e6 at 50kV, 8.56mA, though excessive sparking prevented me from maintaining the output. When I lower the current, however, I can push the voltage much higher. At 59kV, 0.86mA, it produced 4.1e5n/s, which gives a Q value of 9.2e-9. The theoretical output at 59kV, 8.56mA is 4.1e6n/s, which is a factor of 2 higher than I measured at 50kV, 8.56mA. Seems to check out. There were brief forays into Q>1e-8, but this could just be due to Poisson statistics with the counts. The field at the feedthrough is starting to get pretty high--high enough that it likes to charge up ungrounded metal bits in the vicinity. I will need to add some field control to the top, probably a small toroid.

Plasma.jpg
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Liam David
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Re: Fusor Update - Liam David

Post by Liam David »

A quick update while I'm working on upgrading my new system, which will hopefully come online in the next month or so.

I have a bubble detector and can thus finally calibrate my detection gear, but I've found a discrepancy in the results.

Over 988 seconds at ~33kV, 8.5mA:
3He detector at 48cm registered 156546 counts
Bubble detector (24/mrem) at 22.5cm gave 70 bubbles
Ludlum 2363 with Priscilla probe at 39cm (to the face) accumulated 0.44mrem

OpenMC simulations and 3He tube give 1.09e6 TIER
The bubble detector gives 5.27e5 TIER
The Ludlum 2363 gives 2.40e5 TIER

I'm not surprised that the simulations are off by a factor of ~2 as they cannot account for everything and material composition/distribution assumptions create errors. I'll look into why but it's certainly good that it's the right order of magnitude. What surprises me the most is the bubble detector/Ludlum discrepancy... It's possible that the Ludlum calibration has drifted since 2013, but a factor of ~2 seems unreasonable. Finn noted in a recent post that the same detector indicated a dose rate lower than expected based on the voltage/current input. Perhaps it has the same cause? My first guess, assuming I'm not missing something obvious, is that the detector distances are not in the far field relative to the source distribution. Unfortunately, my lab space and relatively low output make far-field measurements practically impossible. Also, it's certainly not thermal scattering as the Ludlum reads lower and it's sensitive from thermal to many MeV.
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Re: Fusor Update - Liam David

Post by Matt_Gibson »

Nice to see some more results with the Ludlum and Prescila probe.

I’m trying to judge how good/bad my recent success is…I hit just over 8mR/hr with mine running 39kV and 7.5mA, 2.5cm from the face of the chamber.

Can you get your “hammer” within 2.5cm of your fusor to see what you get?
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Liam David
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Re: Fusor Update - Liam David

Post by Liam David »

What's your total distance from the chamber center to the probe face? With your chamber size you have all the info you need to approximate TIER.
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Re: Fusor Update - Liam David

Post by Richard Hull »

Neither Matt nor Liam in the above posts gave a critical value!!! How much fuel did you have? Let's get it into our heads. Three that is (3) values are important

1. Voltage: Where on the cross sectional chart of the fusion "fuel" are you operating?
2. Current: How many possible fusion "fuel" deuterons are you putting into the ongoing reaction?
3. Pressure: How much actual Fusionable "fuel" do you have in the reactor vessel?

I operated at 5 microns and 30kv! Tells us nothing
I operated at 30kv and 5ma! Tells us nothing
I operated at 10 microns and ran at 20ma! Tells us nothing

Give three full operational parameters. Then we will know the full story about where you were operating. It is certainly assumed both Matt and Liam knew their running pressures. Sadly, we do not.

I really hate to keep reiterating this. I would love to attempt to weight in on the conundrums above, but have no idea where you guys were so far as operational points.

Even with different reactor geometries and sizes and now three methods of measuring, It would be nice to know one full indisputable operating point before attempting to help in comparing apples and oranges.
With all these variables in the mix, it would be nice to have one given constant starting point.
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: Fusor Update - Liam David

Post by Matt_Gibson »

I’m running at 18.1 microns with a deuterium flow rate of 1.5sccm. Hammer face is about 3in from center of chamber.
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Re: Fusor Update - Liam David

Post by Finn Hammer »

Liam,

I am interested in knowing how you arrive at, or where you read, an accumulated mRem number from the Ludlum.

Cheers, Finn Hammer
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Richard Hull
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Re: Fusor Update - Liam David

Post by Richard Hull »

Matt, your readings seem spot on to my readings or within reason. I did fusion and posted it 1 day ago. You might have read it. I put in about 41kv, 2kv higher than yours. I ran a current of 10.5 ma, ~3 ma higher than yours but about 10.5 microns of D2, about 7.5 microns less pressure and read about 8 mrem with two BF3 systems about 2-3cm from my fusor shell. As such, your 8rem reading sounds about right, all things considered. I am waiting to hear Liam's pressure. Without knowing his pressure, I would think that 2-3x10e5 sounds about right. 33kv at such a low current is an awfully low voltage for anything like the mega mark. However, if his pressure is really super high then.....?? I would tend to believe the Ludlum and the BTI are in the ball park and the Ludlum closer, but a lot of runs and averaging are needed between the two.

Liam's 3He system is half a meter distant and getting ~1900cpm (averaged). I do not see how he gets the mega mark and assume there is some issue with his calcs relative to his mega figure. To believe the dosimeter and use it for calibration of the 3He counter, One needs to make about 30 runs using both the bubble and 3He systems and then do an overall average to arrive at a one minute count multiplier for TIER. This effort took me two months to complete back in 2004-2005 time frame. The Ludlum, as I said, seems closer, but the BTI should not be disregarded........Finally, What was his pressure?????

My recent run.....
viewtopic.php?f=13&t=14084&start=40

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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Liam David
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Re: Fusor Update - Liam David

Post by Liam David »

To be clearer, I'm using the bubble detector as my calibration standard. The mega mark with the 3He was based only on the simulations and the numbers reported here on out will be adjusted to match the bubble detector. I'm fully aware that the uncertainty thus far is sqrt(70) = 8.37 or 12%. I'm working on figuring out why the simulation over-reports, and am making a higher-fidelity model of my setup moving forward. It takes quite some time to transport 1e9 neutrons through a complicated model.

My 3He tube gave (156546/988)*60 = 9507 CPM, not 1900 CPM. It's also not in a very large moderator, having only 3cm of paraffin. The pressure was 13-15 mtorr corrected for deuterium and flow rate was ~1.4 sccm. To give a sense of scale, a simple CAD model:

Capture.PNG

Finn, I wrote a Matlab script to query and log the Ludlum at 1/2 second intervals, like the manufacturer software does, and then just summed the dose rate x 1/2 s. I posted the code in the main Ludlum thread if you have access to Matlab. You could also use the integrated dose function in the counter: reset it by holding the ID switch while powering on the meter. It seems to work well, and with the neutron rates you're likely hitting, I think you'll have 2-3 sig figs to work with.

Matt, based on your numbers you are getting about (8 mrem/hr) x (28080 n/cm2/mrem) x 4pi x (7.62 cm)^2 x (1 hr/3600 s) = 45,500 n/s.

For the bubble detector, I used both hand calcs and the standard Bee Research calculator we all use. With the Ludlum at 13 cm (closest I can get) and upping the voltage to ~40 kV at 8.56 mA and similar pressures, I can hit 20 mrem/hr.
Last edited by Liam David on Thu Jan 06, 2022 1:37 pm, edited 1 time in total.
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Re: Fusor Update - Liam David

Post by Richard Hull »

Liam thanks for the pressure reading. Your answer of 9500 cpm is correct but you displayed equation is wrong. It should be (156,546/ (988/60)) = 9507.

Your pressure tends to militate to the 2-4X105 range TIER.

Your volume calcs should be a cube = to the long dimension of your moderator with the moderator at the Center of one wall of the cubic volume, assuming they are is the dame plane. Draw your straight line neutron paths to the moderator extremes in two axis and then ignore that small volume. The other ray missed volume represents the lost ray volume. figure from there. What is your full volume of the entire moderator. subtract it from the lost volume of rays and this is the key ratio. I did not do this and now must redo my own reduction!!! silly me. I put my volume calcs with the moderator in one corner of the volume instead of jammed against the center of one wall of the volume! I must redo my FAQ on this effort. We fail, we make corrections. #@%^&!#

Just remember, it is your moderator that goes against the wall center in the volume the source of neutrons is placed relative to it within the volume at whatever range.

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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Liam David
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Re: Fusor Update - Liam David

Post by Liam David »

I recently posted about a reconfigured vacuum system and some repairs/upgrades to various things. All the while, and for much of the last couple of years, I've been quietly working on a new fusor in the background. I'm on iteration 2 of a device that falls somewhat well under the "cube" category, and I think it's high time I share some details. The most recent one came online just today, and the results are very promising. I still have some tweaking and conditioning to do, so I'll start a new thread sometime within the next week or two. In the meantime, a teaser:


PXL_20220803_181215260.jpg


My current record for silver activation is >13,000 CPM on a 2" pancake. Edit: now up to 37600 CPM.
Last edited by Liam David on Thu Aug 04, 2022 4:12 pm, edited 1 time in total.
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Richard Hull
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Re: Fusor Update - Liam David

Post by Richard Hull »

Fabulous silver activation!

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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