High Vacuum Engineering Design, Analysis, and Build of a Small-Scale Multipurpose System

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Michael Bretti
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Re: High Vacuum Engineering Design, Analysis, and Build of a Small-Scale Multipurpose System

Post by Michael Bretti » Tue May 08, 2018 6:02 pm

Richard Hull,

Yes, noise shielding is certainly a major issue with high peak-power pulsed systems. Fortunately I have directly worked with active shielding and noise suppression for electronics and instrumentation around these types of pulsers. It is a challenge, but I have dealt with it before very successfully. One of the systems I actually built for work was a 90kv Marx generator to simulate electron gun arcing faults specifically for EMP and noise shielding for sensitive electronics around the fault. My goal is to develop the pulsers to work successfully with my pulsed e-gun setup, then migrate it over towards pulsed neutron work later (the e-gun setup would be less costly due to the fact that no expensive gas or gas handling is needed.)

Activation analysis was actually the main method of detection I was planning on implementing for the high peak power fast-pulsed systems, and I look forward to the design challenges and getting to that stage of testing.

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Richard Hull
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Re: High Vacuum Engineering Design, Analysis, and Build of a Small-Scale Multipurpose System

Post by Richard Hull » Wed May 09, 2018 3:45 am

The one thing about activation; it is the only warranted noiseless, absolute indication that thermal neutrons had been there. As you note, calibration can be tricky, but with good math and the knowledge to apply it, calibration can be very accurate. You will just need a good averaged flux over time. From this, based on the pulse peak voltage and current, the flux per pulse should be easily computed.

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

Michael Bretti
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Re: High Vacuum Engineering Design, Analysis, and Build of a Small-Scale Multipurpose System

Post by Michael Bretti » Wed May 09, 2018 3:06 pm

Richard Hull,

Thank you for your advice. I also just finished reading that new PDF you posted on activation - really fantastic introductory paper on activation, I greatly enjoyed it and it was very helpful, especially the section at the end explaining different target materials for activation. I was planning on starting with silver, and seeing this list of additional elements to explore has given me some new ideas for experimental test stand development that I think would be very exciting to build and share with the fusor community. Although I won't get to activation for a long time, I can certainly start working on gathering the necessary information and designing the various detector systems.

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Re: High Vacuum Engineering Design, Analysis, and Build of a Small-Scale Multipurpose System

Post by Richard Hull » Wed May 09, 2018 6:51 pm

Silver might have been #1 in my list and it certainly is the most common activated material here at fusor.net over the years.

Rhodium was #1 simply due to the raw data related to it, my own experience with it, and the fact that Enrico Fermi used it all through his work that lead to his Nobel Prize. He was forced to use made-up sources for his neutrons,(radium-beryllium), to calibrate and quantify them, he needed a fast activation element to 100%. Rhodium was ideal.

I had a friend who wisely purchased a 1 ounce bar of Rhodium, a short while back, when its price plunged to $700 per ounce. I contemplated it back then, but waited too long and the price soared again. As noted 1/10 ounce bars are available.

In my activation of my friend's bar, I was pleased that it exceeded silver in activation and that it took only 4 minutes to fully activate to 100% of its attainable radioactivity with a given flux!

As an ideal activation element it will forever remain #1 on any and all lists with only its crippling purchase price being its sole impediment.

Again........

100% of its atoms are ready to activate as it is a single isotope element. Its capture cross section is high and the finished radioactive product has a short half life, meaning weak and limited neutron sources can be rapidly checked out and quantified.

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

Michael Bretti
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Re: High Vacuum Engineering Design, Analysis, and Build of a Small-Scale Multipurpose System

Post by Michael Bretti » Wed May 16, 2018 5:29 pm

New update on the V4 System build. After additional planning and design, I have settled on a table I will be using for the system. Below is a CAD model of the proposed design:

System V4 Dual Purpose Table Assembly - V4 Chamber.png

The experimental table consists of a 2'x2'x3' structure made from 80/20 10 series extrusion. The 80/20 was purchased off ebay for half its original price won during surplus lot auctions. I ended up getting both black anodized and silver 80/20 since that was what was available for cheapest in bidding lots, and arranged it to have at least a symmetric and pretty cool look color-wise. I was originally going to go with a 2'x2'x2' table, however after discussing this project and another vacuum system project with one of my friends, he suggested to save money by combining the infrastructure of the two systems to support both. After some careful planning and design, I have been able to come up with a low-cost solution to support both systems simultaneously. Only the 2.75" conflat based system is currently shown in the model. The roughing pump is in the center, laying on the floor to minimize vibrations transferred to the rest of the structure, but still keeping it within the build volume. There will be ample space for the power supplies, diffusion pump chiller, baffle chiller, and other control electronics. An additional 6" KF25 bellows line will be needed to connect the roughing pump to the main roughing line under the foreline trap.

The second system is based around a 6" conflat tee that I obtained for free. This system will be used for ion and plasma engine testing. Last year I had originally bought a very large 6" throat gate valve/butterfly valve combo for the 21 port custom conflat system I posted about a while ago, which after looking at the logistics to get operational, was recently sold. I also obtained an 8" water cooled baffle for the original system as well. Both the baffle and the valve were $100 each, and in excellent condition. Since I already have another Edwards EO4 diffusion pump, as well as the baffle, gate valve, chamber, and basic feedthroughs, all that is really needed are the two aluminum adapter plates to fit everything together. I was going to build a completely separate system for this setup, but since the diffusion pump is the same as the V4 system, it was decided to extend the table to accommodate this test chamber as well. I will end up splitting the roughing line symmetrically to feed into both diffusion pumps, as well as route cooling for both diffusion pumps and baffles to run off the same cooling system. I will only run one system at a time, never both simultaneously, so in my control architecture I will make accommodations to switch between pumping and cooling for both systems. Initially, this second system was planned for operation years down the road, however using this shared setup, I will be able to deploy it and start testing it in a much shorter time-span, since the infrastructure will already be built and shared from the first system. The cost savings implementing this shared topology is on the order of $2k or so. I will post an updated CAD render of both systems mounted with the proposed roughing line upgrade shortly.

In terms of the actual physical build, the 80/20 has already been ordered and arrived. The remaining hardware is coming in today. I have also already started modeling the chiller block subsystem of the diffusion pump cooling system. The main heat exchangers will be arriving within a week. Once this chiller is qualified, then I will proceed in building a second chiller for the baffles. I will also post design specs of the chiller as I progress further, but I have most of the parts already for the chiller block.

Michael Bretti
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Re: High Vacuum Engineering Design, Analysis, and Build of a Small-Scale Multipurpose System

Post by Michael Bretti » Thu May 17, 2018 3:26 am

Bit of a sudden and unforeseen setback to the above plan. Upon completing the 80/20 table, I decided to open up one of the two hermetically sealed boxes that, when I received them along with the open diffusion pump, was told they were new, unopened pumps. The boxes were the same dimensional size and weight as the EO4 diffusion pump. However, it turns out that they were nothing more than very large circuit breaker boxes. They were such old pieces of equipment from decades ago it was forgotten what was in them and assumed to be pumps. Turns out I only have one instead of three diff pumps that I initially thought I had. Rather disappointing considering a large portion of future systems relied on the requirement of having multiple of the same diff pumps. However I am still quite happy that I have even one diff pump in new condition. I could still proceed to mounting the second chamber since I have most of the parts anyway, but running it will have to wait for now, since the small chamber is priority.

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