Differential Chamber Wall Materials

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Scott Moroch
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Differential Chamber Wall Materials

Post by Scott Moroch » Sat May 23, 2015 12:28 am

Jack and I have been making steady progress on our fusor. Recently we have moved it to a local university, and with school beginning to slow down we hope to make additional progress in the coming weeks.

Recently, we have also been thinking about experiments we could run with the fusor after we achieve neutrons.

After fusion is achieved in the small 5-way cross fusor we will be upgrading to a 9" spherical chamber that is being made for free by a high vacuum company. This chamber will be used for the following experiment....

As we know, beam on target fusion reactions at the wall of the fusor contribute to a high percentage of the total number of fusions in the device. It is frequently seen that as the operation time of the fusor increases, the neutrons per second will also increase due to the deuterium atoms being embedded in the chamber wall. This is often seen by Richard's fusor during his pre-HEAS warm up runs. The goal of our experiment is to determine if there is a positive correlation between the amount of deuterium the chamber wall can hold (depending on the material) and the total isotropic neutron emission rate. Certain metals such as palladium are capable of storing up to 900 times their own weight in hydrogen. In our experiment, we will line one half of the spherical chamber with a metal that is known to store a large amount of hydrogen (such as titanium) and the other half will remain as is (stainless steel) with no metal lining. Two bubble detectors of equal sensitivity will be held equidistant from the chamber on either side. This experiment will control for all other variables in the fusor (voltage, current, pressure, etc.) because both sides of the chamber will be subjected to the same conditions. If the ability of titanium to hold a larger amount of hydrogen does not increase the amount of neutrons detected, we would expect to see the two bubble detectors to show a similar number of bubbles. Because all other variables are controlled for, if we see a statistically significant higher number of neutrons on the side with the titanium lining, there would be suffecient evidence to conclude that the increase in neutrons is due to the larger storage capacity of the titanium metal.

This experiment may also allow us to determine the percentage of fusions occuring at the chamber wall and the percentage of fusions occuring at or near the inner grid. By lining one half of the chamber with a metal that does not absorb hydrogen, and one half that does, we can use the difference in the neutrons detected to determine what percentage of the fusions occured near the inner grid.

Our goal is to conduct this experiment over the summer and then enter our project into ISEF 2016. Does anyone see any flaws in this experiment? Anything we may not have accounted for? Please tell me if you think this is research worth conducting. This experiment is still in the design phase, so I would like all of the opinions I can get.

Thanks!

Scott Moroch

(I do believe that I placed this in the correct forum however, let me know if this discussion belongs elsewhere)
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Bob Reite
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Re: Differential Chamber Wall Materials

Post by Bob Reite » Sat May 23, 2015 6:14 am

I'm pretty sure that the neutron emission will be isotropic and that you will see the same rate on both bubble detectors, even if one wall of the chamber will contribute more ions.

You will have to do the comparison as two separate sets of runs. First, a set of runs with just the stainless steel chamber. You will need to control/monitor voltage, current, pressure and flow rate (get a mass flow controller). Make several runs with that configuration, until you see only minor changes, indicating that the wall is saturated. Then open the system and install the titanium on the whole inside surface of the chamber and run the system again adjusting for the same voltage, current, pressure and flow rate, although you might find that you cannot get all four variables to match again, in that case, try to hold voltage, current and flow rate constant and let the pressure fall where it may. Run the second configuration several times until there is minimal change from run to run and compare the results.
The more reactive the materials, the more spectacular the failures.
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Re: Differential Chamber Wall Materials

Post by Richard Hull » Sat May 23, 2015 7:04 am

Bob is correct in every aspect of his response. He shows he has operated a fusor for a large number of runs and knows that it is tough to get a run-to-run precision return of all conditions. D-D fusion when and wherever it occurs is said to be 100% isotropic. Others, however, have reported "hot spots" about the fusor in neutron measurments due to, what I feel are, totally unexplained anomolies. Given all of the foregoing, Bob's suggestion is about as close as you might come to a clean answer in your experiment.

Yes, this is the ideal forum for your post. It is for folks contimplating real experiments and research that can hopefully advance our knowledge related to the fusion efforts done here. All the very best in whatever tack you might take related to your quest.

Richard Hull
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Retired now...Doing only what I want and not what I should...every day is a saturday.

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Frank Sanns
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Re: Differential Chamber Wall Materials

Post by Frank Sanns » Mon May 25, 2015 2:14 pm

There are some factors that I do not believe have been mentioned yet in this thread. Time of conditioning of chamber does several things with deuterium loading being only one.

Before we get off the deuterium loading, the depth of penetration of both the deuterium and the ions needs to be considered. A very think layer of deuterium sponge will require quite a bit of time and loading. You will need a way to measure that. The literature can help you as there are many studies. Similarly the energy of your ions and the depth of penetration into the sponge layer will be data that you will need to record.

Other factors that need to be considered is the outgassing of grid and walls. Starting up a fusor that has been open to the air is difficult and goes beyond just deuterium loading. Water and air are prolific on the surfaces of the metals and glasses of the fusor. This also is well know and one of the main reasons for "baking out" an UHVC before use. We are to at very demanding vacuum conditions so essentially all of us just use time and glow cleaning to take care of the build of the air and water but even after days there is still appreciable contamination within the chamber. A freshly pumped down chamber will be a ruddy red color for hours. If it is that visible, that implies a great number of other contaminations within the chamber walls, grid, and gas phase.

These contaminates can compete for energy in the chamber and any collisions with deuterium will unproductively bleed off energy and result in zero fusion. This may be more insidious than that as there is ion recycle to consider. The longer the theoretical free path of the ions in the fusor, the more damaging an impurity will be because statistically, there are more chances for unproductive collisions as the paths get longer.

Hot surfaces within the fusor will oxidize and maybe even nitride as the fusor is in operation and it being conditioned. Any ion that comes from the surface in the form of water will ionize into hydrogen and oxygen so high energy oxygen is blasted at all exposed surfaces. Eventually conditioning will replace the nitrogens and oxygens that are being imbedded into the surfaces with deuterium but it is one my step that has to go on before a chamber is fully conditioned.

There is also the sparking of the inner grid on first start up. Some theorize that they are dust particles but I say nay. I have ultrasonically cleaned, not handled the working portion of the grid, immediately installed it in the fusor and pumped down and started running. The grid still sparked. This implies some subsurface impurity, inclusion, or gas is lying in wait for either the temperature to soften the metal enough for it to escape in spectacular style or there is some other early reaction going on with the gasses in the chamber. There have been several studies looking at targets and grids (U of Wisc for one) that shows crater like formations on grids that varies with the fusible gas and energy of impacts. Just one more complication to consider.

These are just some factors that you may want to consider in your fusor design and experimental setup.

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Re: Differential Chamber Wall Materials

Post by Scott Moroch » Mon May 25, 2015 7:52 pm

Thank you all for your insightful responses. I have been spending quite a bit of time reading through older posts regarding beam on target fusion in the fusor. I have read through other experiments done by the University of Wisonsin, Madison such as this one: http://iec.neep.wisc.edu/usjapan/9th-US ... /Rusch.pdf

I have also read through many of the discussions regarding anisotropic neutron emission. One post I was reading through made claims of seeing a slightly higher flux between grid wires: viewtopic.php?f=6&t=3042&hilit=anisotropic

Perhaps the higher neutron flux is due to a higher number of beam on target fusions occurring at the points of the star mode beams. This post also made me think about how we calculate the total isotropic emission rate in a fusor by using the distance between the detector and the poissor. By definition of isotropic emission, this would mean that almost all of the fusions are occurring at or near the inner grid. Yet, there is a good chance that this is not the case, and in fact a good portion of the fusions are actually occurring near the chamber wall. But then again, when we calculate the n/s it is only a rough estimation.

University of wisc. claims to have seen a 30% increase in neutron yield when titanium was applied to the chamber walls. I will take Bob's advice and will line the entire chamber with titanium, rather than only half. Frank, thank you for your advice on contaminants inside of the fusor. For this particular experiment, do you think it is necessary to bake-out my chamber, or would glow cleaning at a higher current be sufficient? I had considered the possibility of baking out my chamber when I change the lining inside because I do know that water will contaminate the chamber. The goal of my experiment is to ultimately attempt to optimize the amount of beam on target fusions that are occurring at the wall of the fusor and any contamination due to water or air will make this process more difficult. From the data I have seen, it appears that a significant amount of fusions occur at the wall and I would not be surprised (if our experiment is conducting correctly), that we will see a significant increase in neutron yield by choosing a metal that absorbs a higher amount of deuterium.

I am also trying design the experiment by taking into consideration the statistical analysis I will do with the data. I would like to test the fusor many times with the titanium lining, many times without the titanium lining, and then take a reading on the bubble detector after the same amount of time has passed since I began the run. If the voltage, current and pressure is roughly the same, this will mean that each chamber wall material will be given the same amount of time to be loaded with deuterium before a reading is taken with the bubble detector. This would allow me to make a distribution of neutron yield with the lining and a without the lining, and then proceed to analyze the data with a significance test. In other words, the "null-hypothesis" would be that the different materials will result in the same yield and the "alternative hypothesis" would be that the titanium will result in a higher yield of neutrons. From there, I would either use a confidence interval or significance test for the difference in two sample means. Let me know if this seems like the correct way to collect and analyze the data from this particular experiment.

Scott Moroch
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Re: Differential Chamber Wall Materials

Post by Frank Sanns » Mon May 25, 2015 9:27 pm

Baking is a nice way to get rid of water but I like time and glow better. Ions can knock off all kinds of contaminates form the chamber and the grid so I favor the long glow approach. I also backfill with deuterium up to 1 torr between runs.

I was thinking about how to best handle the statistics and the answer came to me in an analysis that I did on one of Jon Rosenstiel's runs. He was using a sine wave supply. Neutron output vs voltage was plotted for each cycle and summed at the same place in the cycle. Somewhere on this site is that data. The point being, large statistical data base always trumps single factor at a time done sequentially every time. Too many variables in our system.

So my though was to use a rotating insert near the fusor wall. Maybe 3 or 4 "petals that either eclipse the chamber walls with a deuterium sponge or not. The slow rotation could easily be done with a home made magnetic drive so no special equipment would be needed. I have used magnets to switch experiments within my chamber before while it remains sealed and it works great.

As the petals would rotate slowly, the change in neutron counts as a function of the area of the eclipsed petals moving slowly out and to be hidden again, would give great data on the effect of the target material. This is probably sufficiently novel to gain you a prize in any competition that you might enter. Just remember where you heard it and send me a portion of the prize; oh, they are just medals. Well never mind. lol. No, seriously, I hope this helps you to think things through.

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Re: Differential Chamber Wall Materials

Post by prestonbarrows » Mon May 25, 2015 10:54 pm

Everyone has already given you good advice. As others have mentioned, conditioning the chamber will play an important part in such an experiment and needs to be controlled. The best way to know the state of contaminates in your chamber is a residual gas analyzer (RGA), but these tend to be prohibitively expensive. This will give you an exact partial pressure of water or nitrogen or any other element in real time.

If you can't directly measure the contaminate level, you have an unknown factor in your experiment. In this case, it is best practice to run multiple tests alternating between the configuration-under-test and a control. If the length of these tests is short compared to the time scale that the unknown factor varies, one can make a differential measurement to remove the effect of the unknown factor without directly measuring it. When you take your real measurement, you want the entire system to be as close as possible to the control except for one change.

This is basically what you are doing when you take 'background' readings and subtract them out while making neutron detector measurements. You assume that the background is constant over the timescale of your measurement and independent of what you are actually measuring such that you can subtract it out.

In this case, you want to have a configuration with a titanium wall and a control configuration with a standard vacuum wall. Since you want your unknown to be relatively constant between tests, you will need a way to switch configurations without coming up to atmosphere which would re-contaminate your chamber and make your control measurement not applicable. Vacuum conditioning occurs on the order of hours or days. So, you should have a setup which allows you to switch between configurations on the order of minutes.

A sheet with titanium on one side and stainless on the opposite mounted to a rotating feedthrough is one option. A pinwheel with different materials mounted to it with a shield in front which uncovers one sample at a time is another. A gate valve which blocks line of sight to your target is yet another.

One would then expect to see a high yield with the Ti target active, and a low yield with it hidden. Taking, say, 10 minute counts alternating between the two configurations should result in roughly the same result for each case and a slow drift over time as the chamber conditions and/or the targets load up over a period of hours.

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Re: Differential Chamber Wall Materials

Post by Scott Moroch » Tue May 26, 2015 12:46 am

Frank,

I really love your idea with the rotating plates inside of the fusor. The magnetic drive seems like an easy way to rotate different plates around the chamber wall. Another option that I have been considering since reading your idea is a linear motion feedthrough which would allow me to manually adjust the position of the plates or allow me to add a small servo to rotate the plates. I have been thinking that I could add 3 or 4 plates onto the apparatus. The different metals I am thinking about using are palladium (expensive, but obtainable in small quantities), titanium, molybdenum (or nickel) and possibly a metal that does not absorb hydrogen. I specifically like this idea because it would allow me to keep my chamber under vacuum at all times as well as keep all 4 metals under the same conditions while in the fusor.

When a specific metal covers the detector, I will be detecting the beam on target fusions occurring on that metal, however I will also be detecting the beam on target fusions that are occurring nearby and emitting neutrons isotropically. Perhaps I could use borax to shield the surrounding areas, except for the 3" area that the metal plates will cover. This will allow me to detect only the neutrons from the inner grid and from the BoT from the specific plate. This will also allow me to determine the number of fusion reactions occurring at the wall. If one of the metal plates does not absorb hydrogen well, than when it passes the detector no beam on target fusion will occur and if I am shielding the surrounding area I will only be detecting the fusions occurring at or near the inner grid. I can then take this neutron count and subtract it from the neutron counts I received from when the other plates covered the detector. Let me know your thoughts on this. I may not be considering something important.

Also, the two neutron detectors that we have available are a USA made 3He probe with a gamma spectacular and an eberline PNC-1. I could also purchase two bubble detectors if necessary, however I do not think it is necessary. I am interested in taking measurements when the plate is in line with the star mode beam and when the plate is not to see if there is a significant difference in yield.

Preston,

Thank you for your advice regarding conditioning the chamber and about using a rotating feedthrough or gate valve. Using a gate valve was one of the first designs I had originally thought of, however the design that Frank recently mentioned may potentially allow me to rotate between 3 or 4 different metals. I will look into the possibility of an RGA, however as you said, they are very expensive. My fusor is being tested at a university so I will see if they have any connections on getting an RGA. I would really like to start by getting a mass flow controller to stabilize the pressure inside of the chamber.

Scott Moroch
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Re: Differential Chamber Wall Materials

Post by Jack Rosky » Tue May 26, 2015 2:40 am

Hello All,
Thank you all for your extremely insightful and thought provoking responses to Scott and I's project ideas. I just wanted to jump on in here and bring up the "hot spots" some have noticed with their Fusors. I wanted to see if any of you had any insight to why this may be and if any of you had noticed them in your systems. Most importantly, I want to know whether they coincide where the star mode beams hit your chamber walls. If this is the case, could it be that the hot spots are coming from more BoT fusions at the point the star mode beam is hitting the wall?

Also, another thing that Scott and I wish to see with our experiment is whether there is more deuterium embedding in the places where the beam hits the wall and if so how much more is being embedded there compared to the rest of the chamber. What I am wondering is if there is a way to test the percentage of deuterium embedded in the fusor walls and whether or not these higher areas are responsible for the so called "hot spots".
Jack rosky
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Re: Differential Chamber Wall Materials

Post by Frank Sanns » Tue May 26, 2015 3:09 am

If you recall, the beams are recombination areas. Light is emitted when electrons recouple or drop energy state with a deuterium ion or atom or molecule. Look back in some of the Images Section for many experiments were the star is shown and discussed. Some facts include the moieties in the star exceed the single acceleration potential. The star goes outside of an outer grid that is not the shell like it is not even there. There are a few possibilities including multiple passes allowing it to gain energy greater than the applied voltage and charge movement to the outside of the outer grid. Like I said, look back and there is quite a bit posted on many of these phenomenon.

Localized wall heating is more likely from electron beams than ion beams.

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