First Fusion for Liam David - Neutron Club Application

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.
Post Reply
User avatar
Liam David
Posts: 518
Joined: Sat Jan 25, 2014 5:30 pm
Real name: Liam David
Location: PPPL

Re: First Fusion for Liam David - Neutron Club Application

Post by Liam David »

I have a 2.75" butterfly valve between the turbo and chamber and I always throttle the pump before introducing deuterium. It does wonders for gas usage.
Dennis, what is the Cv for the needle valve you're using?
I use one with a 0.05Cv (I think the rating is for water, but I'm not too sure), which works OK, but relatively small adjustments do make a significant difference and it can be challenging to get the pressure stable. I have run the fusor several times, both with and without deuterium, and thus I don't think contamination is a problem for my system. Additionally, I can get to 2e-6 torr after about an hour of pumping and the chamber rises to less than 100mtorr after two days and then flattens off, indicating that outgassing or virtual leaks are the only leak sources.
I will try your method of setting the voltage and then adjusting the pressure to establish plasma and control the whole thing. Perhaps it will give me better stability and reduce gas consumption.

In response to Rex's questions and comments:

1. The chamber is a 2.75" conflat 6-way cross, which yields a cavity in the center about 1.9" in diameter. Although such small chambers never reach the mega neutron mark, several members of this forum have demonstrated fusion in a similarly sized chamber, notably Scott and Jack just a few months ago with a KF-50 cross.

2. I'll be posting some more pictures soon, presumably with my next claim. The inner grid is about 1cm in diameter and is composed of two tungsten loops with a wire diameter of 0.25mm.

3. Yes, I should have taken updated pictures before adding the lead vest, but I do have some reasonably up-to-date pictures in my other progress posts. I will definitely take more time in describing my system and adding pictures with my next report.

4. The rigid metal tube is a drierite gas dryer and is definitely not large enough for a reservoir. I borrowed the Hydrofill unit from my school, which just happened to have several laying around unused. I didn't break anything, and I can easily reassemble it for full functionality. I have built a small oil displacement reservoir using two test tubes to replace the hydrostik system. It works OK, but the gas is used up a little to quickly for extended operation which would help in stabilizing everything. Of course I flushed the system several times with deuterium to ensure purity.

5. I have done a few runs where I removed the moderator, but since I have problems reaching stable operation, I can't use this as evidence yet, especially since removing the tube from the moderator causes the counter to jump...

Thank you for the feedback everyone. Progress will be a little slower now that school has resumed, but I should be posting more results within the next month or so in accordance with Richard's new conditional acceptance policy.
-Liam David
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: First Fusion for Liam David - Neutron Club Application

Post by Richard Hull »

You are slowly learning that if you think making a fusor is a chore, learning to operate it is an art form. Money can't buy or instill artifice. I have written to this point extensively.

Doing fusion is not about building a fusor, it is all about knowing how to make it work.

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
User avatar
Scott Moroch
Posts: 212
Joined: Wed Apr 25, 2012 8:48 pm
Real name: Scott Moroch
Location: New Jersey

Re: First Fusion for Liam David - Neutron Club Application

Post by Scott Moroch »

Liam,

Having been down this road with a small fusor I think I can provide some advice. I happen to very much agree with Richard when he says that doing fusion is not just building a fusor. In other words, assembling a vacuum chamber, diffusion pump, gas line, Hv, etc with quality gear does not guarantee that the system is going to produce 1e5-1e6 n/s. For example, it seems to me that sometimes that people tend to purchase very large, fancy diffusion pumps for their systems. In reality, I think that you want the smallest diffusion pump possible. Although it will take longer to pump the entire system down initially, you will be thankful when you try to feed D2 in and stabilize the pressure. One method of course is to seriously throttle down the vacuum system, but this is not always too easy with a smaller system.

In terms of your specific fusor, my first bit of advice is to do everything you can to regulate your vacuum and gas flow. This may require adding an additional throttling valve to your vacuum system, which perhaps you are not prepared to add as of yet. In our KF 50 system we had a 285 l/s diffusion pump (complete overkill, hence my point above) with a 3" throat. This was cut down to KF 16 (~.7") with a throttle valve and a butterfly valve.

A less expensive, quicker solution would be to do everything you can to regulate the gas flow. When we ran the KF 50 chamber we only had a fine metering valve. The valve we used was a Swagelok ss-ss4 needle valve (the finest control valve swagelok makes at 0.004 Cv) and this was not sufficient. With our larger system we had a diffusion pump with a much smaller pumping speed + a throttling valve and an MFC for gas control. If I were to go back to the KF 50 system, I would use the ss-ss4 needle valve, 1/16" capillary tubing and potentially look into a needle orifice. Once you are able to stabilize the pressure in the chamber and maintain a state of equilibrium, everything else will be significantly easier.

Our gas control was very poor in our KF 50 cross but we managed to detect fusion by backfilling the chamber to 40-50mTorr of D2 and slowly bringing down the chamber with the vacuum system. On the contrary, in Fusor II we throttled down the vacuum system first and then slowly inserted D2. This allowed us to basically choose any pressure we wanted and maintain equilibrium at that point. Although this is a bit more difficult in a smaller Cf 2.75" chamber, it is certainly possible.

After that has been resolved, the other issues will be minor. Try your best to keep your grid on the smaller size (i think ours was .3") and relatively symmetrical. We tried the double and single loop, with the single loop being easier to make and install.

Although some of these changes may not be simple, easy, and cheap, some of them can be added to the system for a fairly low cost (capillary tubing, finer metering valve, etc) with ebay.

Let me know if you have any questions and certainly feel free to reach out to me. Best of luck.

Scott Moroch
"In the middle of difficulty lies opportunity"
-Albert Einstein
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: First Fusion for Liam David - Neutron Club Application

Post by Dennis P Brown »

Scott offers a lot of good advice; relative to my needle valve flow rate, it too is a Swagelok unit and I need four and a half turns to get into the range where my fusor pressure is effected - then +/- half a turn creates very strong changes in my system pressure.

Relative to my fusor, closing the gate valve (and waiting for my pressure to just start to rise) and then barely opening it is how I start up my system after flushing and plasma cleaning the fusor first. My D2 control valve is a high end unit so I assume it is similar to Scott's but being a surplus, ebay unit, no idea for its parameters. I get my gas from a lecture bottle of highly pure D2. That, I am certain, also helps with stability of my fusor.
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: First Fusion for Liam David - Neutron Club Application

Post by Richard Hull »

I have never felt, nor have I ever seen, absolutely convincing data related to purity effects of Deuterium admitted into a fusor. As long as the impurity admitted with D2 is only H2 I would think there would be little or not detectable difference between 95% D2 and 99.99% D2 in and amateur fusor device. Water, as an impurity, is another matter and all effort directed at reducing this impurity in any electrolysis of heavy water is a positive thing.

Junk 98-99% D2 is just perfect for the fusor. Anything better had better be a free bottle found lying around a lab or come from some very deep money pockets.

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
Post Reply

Return to “Images du Jour”