Matt Gibson Fusor

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Matt_Gibson
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Matt Gibson Fusor

Post by Matt_Gibson »

Hi everyone, figured I’d start my own build…

Here is my current setup. I am waiting on gaskets and hardware to start sealing everything up…

Pictured is the start of the fusor project. Specs so far:
Foreline pump: Edwards e2m2
Turbo pump: Pfieffer TMH 071p (not shown)
PSU: Glassman 40kV @ 15mA (I converted it to negative)
Chamber: 4 way cross, 6in by 2.75in.

Deuterium: Reversible PEM fuel cell and SGE glass 100mL syringe.

As I test, acquire, I’ll take better pictures and give more details.

Let me know if anything stands out as problematic, please! :-)

-Matt
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

Nice looking rig. All the best in doing fusion in future.

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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Dennis P Brown
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Re: Matt Gibson Fusor

Post by Dennis P Brown »

Curious, why the large metal torus on the high voltage feed=thru?

Also, what is the unit on top of the power supply?

Good start on your build. Are you going to add a manual gate valve for the pump connection to the fusor?
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

The toroid is to cut down on any corona discharge from the -40kV. The feed through is rated for 20kV, so I’m hoping this lets it get to 40kv…

The box on top of the Hv psu is a 100kV, 1mA multiplier from Glassman. It isn’t part of this system (yet) just needed a place to rest (running out of space).

I have three valves total. One will be for the fusor chamber, another for the foreline, and the third for the deuterium feed from the 100mL syringe.

UPS didn’t make it, so I won’t be able to hook up the turbo to the e2m2 until next week sometime. Once I confirm that the turbo spins up under proper vacuum, I’ll begin bolting everything up and then it’s full steam ahead :-)
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

You might try raising that toroid up a bit. A healthy fan blowing horizontally over, across the insulator at about 1 to 1.5 feet will served to whisk away coronal ions which might support an arc rising due to natural heat convection. This summer I used a huge box fan on high at a range of 6 feet to do the job. It worked wonders....Zero arcs.. and in my hot lab keeps me cool as well.

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
Matt_Gibson
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

I’m hopeful that this extra bit of field control works at 40kV. If not, I’ll see about getting it raised up. A fan will probably get mounted on the rig no matter what as I expect this thing to get hot seeing as I have 600w at my disposal :-)
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Dennis P Brown
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Re: Matt Gibson Fusor

Post by Dennis P Brown »

A toroid might help but if it was me, I'd remove that toroid and simply buy a few sheets of window glass (squares are fine, 8" x 8".) Next, cut clearance holes through the plates (excellent and inexpensive diamond hole saws can be obtained on line). Cut the holes so they can just permit the upper part of the ceramic stand-off tower to pass through these holes. The plates can then rest on the first ceramic "fin". These plates will then stand between the fusor and the top most part of the HV metal electrode. Then add a good thick silicon bead around the ceramic/glass plate interface opening to further insulate and hold the plates in place. This will prevent arc over to the fusor from the HV tip. The toroid could still be put back in place if you desired. An idea just in case the toroid does fail.
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Dennis, I’ll keep that in mind.

I am leaning towards going with the 30kV insulator that everyone seems to be having success with. I am worried that my internal clearance may not be enough. Here is the shot of its underside. The alumina tube doesn’t extend very far…

This leads me to another design choice: To ballast or not. My glassman has overcurrent protection built in, but I don’t know just how “fast” it is or how well it works compared to a ballast resistor.
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Liam David
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Re: Matt Gibson Fusor

Post by Liam David »

I don't think you'll have issues with the shorter vacuum-side alumina at 40kV, but that does depend strongly on how you interface the feedthrough with the grid (i.e. alumina stalk vs. not, geometry, how centered your conductor is, cleanliness, etc...).

I'd recommend at least starting with a ballast resistor. You'll lose a little voltage but plasmas can be punishing to power supplies, especially when the discharge first establishes.
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Finally was able to test the turbo.

Turbo went below what my Pirani can measure and rpm went to max of 90,000 (10v is max rpm).

Getting closer!

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Dennis P Brown
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Re: Matt Gibson Fusor

Post by Dennis P Brown »

As for the lack of ceramic extension into the vacuum system, that isn't as bad as you might suspect - the plasma is both very conductive (over a volume) but has limits in any given small volume at low pressure (under 100 microns); so it is partly self limiting in the normal vacuum range that a fusor operates: 5 -20c microns. All bets off if you go a good bit above that pressure. Then the plasma can focus and support a considerable current. and at near torr range, support an arc.

If your worried, adding a glass tube extension that fits inside the ceramic tube and affixed with some furnace grade ceramic adhesive should work to insulate the rod.

Your turbo had better zero out a micron gauge for your system; an ionization or cold cathode will be required to determine the lowest value. Anything in the mid 10^-5 torr is good for a fusor as "clean" and vacuum tight.
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

So I think that I might have a leak…The new bspp to Kf25 flange didn’t come with an o-ring, so I took one off another fitting. This definitely helped things as before (no o-ring) I was pulling in the Torrs. After this improvised o-ring, it pulls into the mTorr, but now only gets down to 45mTorr after 10mins.

I’m guessing that while the o-ring helped, it’s needing something better. What else can I do? Better o-ring? Teflon tape on the bspp threads?

As of now, I’ve added a 8.5in length of steel tubing (Kf25 ends) and the turbo. I know that I shouldn’t expect the same performance as before these additions, but I expected better.

I have yet to hook up the chamber, so I’m expecting worse after that.
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

Every addition to a piecemeal tested vacuum system will suffer a reduction in performance due to any number of factors. Most often it is something stupid, poor sealing, ill suited additions, etc. The number one issue is that you brought you entire system up to air. Even with valves to close off a tested, partially assembled vacuum system, the new part will be loaded with all manner of water vapor and other vaporous materials that will either require many hours of system pumping or a tedious bake out to bring to a suitable vacuum level.

You are wise in following my vacuum system advice to assemble and test a system step by step. In this manner, you are confident in all the work done up to a point. (Seals are good and the system thus far assembled is good.) Each new addition imposes a trial period of sealing and pumping.

If you get a great idea and go back into the already tested system to add something great like a valve or a new fitting, you fight the battle all over again. Without a whole bunch of heat tape to bake out with, you are subject to long pumping periods and a lot of leak testing. Even technical vacuums can be frustrating to achieve. Scientific grade vacuum levels demand a special level of cleanliness. A good scientific level vacuum system, especially a complex one, is just never brought back up to air unless it is absolutely unavoidable. Such systems are loaded with top grade and expensive valving all along the vacuum path and all pumps are left on 24-7.

A good fusor needs a minimum of three vacuum valves, though two bellows seal valves will do in some cases. The fusor is trapped between a technical and scientific vacuum. Technical vacuum levels, (10 microns), just will not cut it and scientific level vacuums, (10e-6 torr), while nice, are just ridiculous over kill.

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
Matt_Gibson
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Richard,

I have a valve meant to isolate the turbo from the foreline pump, just waiting on more Kf25 clamps :-)

I removed the turbo from the system and found that I can quickly (20 seconds or so) hit 12 microns at the end of the 8.5in steel tubing. I gave the bspp to Kf25 fitting a tighter twist and then reconnected the turbo to the system. It’s better (38 microns after 10 mins) but still not great.

Would this point you towards a better bspp to Kf25 seal?

All in all, the turbo is still able to rapidly drop to “zero” microns, I just can’t stand knowing something can be improved :-)
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Dennis P Brown
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Re: Matt Gibson Fusor

Post by Dennis P Brown »

Don't over react to out gassing. What you describe sounds a lot like it. Don't assume a slow leak automatically. Just a minor aside, we tend to use microns here to be consentient.

When you can read below 10^-3 torr (using a vacuum gauge for those lower ranges), you can do real testing for small leaks and certainly determine if it is just out gassing or not.
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Dennis,

Got my units mixed up after looking at the Pirani so much lately…

I looked back at MTI site and see they sell a gasket meant to go with this converter. They didn’t include it, or make any mention of it. Despite it weighing like a gram, they want $23 to ship it. I’ll see what McMaster has.
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Update:

Finally got my system bolted together and did some initial testing.

I am pretty limited in what I can determine right now because I don’t have any high vacuum gauges (any recommendations?). I have the Lesker Pirani and the MKS901 (needs to be installed still).

I am able to get to 0.1 microns (the limit for the Lesker Pirani) in under 10 mins (I need to actually time this). After 10 hours, my pressure creeps up to 252 microns. I tried spraying dust off into each and every connection point to see if it caused any jump in pressure, but it didn’t.

Haven’t done any baking…Would this pressure rise indicate moisture and not leaking?

Edit: Should add that there are a lot of loose ends and work to be done :-) I know I need to add an alumina tube to my feed through and some space on the main valve to the chamber, for example. Not thrilled having my hands so close to the frame, grounded or not.
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Dennis P Brown
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Re: Matt Gibson Fusor

Post by Dennis P Brown »

First off, very professional looking system.

Second, searching for a real leak when your system climbs just 250 microns in 10 hours is an utter waste of time; that isn't a leak at all - that is very little out gassing from a rather clean system. Baking would be of little value.

Your getting 0.1 micron (1 * 10^-4 torr, bottom of the reading) so are more then likely getting to 10^-5 torr and sufficient for a fusor (starting pressure.) Considering how very clean your system is and the gauge reading to 0.1 micron (bottomed out - likely much lower), you really don't need to measure below that value if you don't want to add another gauge/system. Again, you are essentially there.

If your power supply goes above 30 kV, that steel chamber can start to become dangerously transparent to x-rays; that window -depending on thickness/type of glass - could be a significant x-ray source even at 30 kV. Consider shielding if you determine these parts can't stop the x-rays. To be on the safe side, assume they will and just add sufficient extra shielding. Slate tiles would work nicely.

Remember, x-rays will travel 4Pi steradians so coverage below the fusor is important too - i.e. your lower body will be exposed in that setup too without proper shielding. Think of the fusor as a light bulb (ignore the metal) and that is where the x-rays go. That determines your shielding areas - the threat areas are places that you would be exposed by the 'light' (no shielding) when operating or working around a running system.

So, it looks to me that beside shielding, you just need deuterium and a neutron detection system and you could start doing fusion.
Last edited by Dennis P Brown on Fri Dec 10, 2021 1:47 pm, edited 1 time in total.
Matt_Gibson
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Dennis,

Good to know the system is clean! I spent some time wiping down as much as I could (pretty much everything minus the turbo innards) with 99.9% isopropyl alcohol and handled everything with cotton gloves.

I was a tad worried that my chamber was a bit large for my relatively small roughing pump, but it seems like it’s fine actually.

My psu can go to 40kV @ 15mA, so X-rays are definitely a concern. The viewport is a Lesker Kodial glass type, which I don’t know much about…I’ll probably find some leaded glass to put on the outside. I’ll use my Ludlum to sniff out X-rays very early on so that I can avoid them.

-Matt
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Dennis P Brown
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Re: Matt Gibson Fusor

Post by Dennis P Brown »

Your entire fusor could be transparent to x-rays at 40 kV and significant current. You might very well require extra shielding. Just look up penetration depths of x-rays @ 40 kV and you'll know if the steel case can stop that energy. Unlikely the view port glass will but again, look up the values for those energy x-rays.
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

A GM counter will scream at the viewport often before 20kv. It is the real danger for X-rays. A proper calibrated ion chamber will tell all about X-rays. Barring a proper ion chamber instrument. A good group of 3 dosimeters placed next to the fusor and at various ranges from the fusor will tell of total dose. Use only 100mr dosimeters. The yellow CD types are to read max doses of 600R! (Use the yellow dosimeters only after a total, world-wide, nuclear exchange as you venture out in the smoking rubble.)

My 100mr dosimeters read about 10mr when 1/2-inch from the fusor after about 1 hour of fiddling and doing fusion. At 2 feet, just off zero and in my shirt pocket 5 feet away, zero. This readings are taken at 40kv+
I shield only the viewport area very well with 1/8-inch lead. The fusor, I leave naked and unshielded.

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
Matt_Gibson
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Richard,

Thanks for the tips! I’ll admit, physics wasn’t my strongest in college (I did electrical engineering and focused on power), so I’ve been wracking my brain trying to look for x ray penetration formulas!

I’ll grab some lead next time I order from McMaster (I bet they love me by now) to fix around the viewport.

Speaking of deuterium…I plan to use a 100mL syringe made for gases to capture the deuterium production from a fuel cell. I need a way to regulate the gas into the chamber still…Other than a bellows valve that I have installed, do I need to worry myself with needle valves or MFC’s?

Thanks!
Matt
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

When it come to lead sheeting try Rotometals.com. They have a full x-ray penetration chart and shopping page at the URL below. I see 1/16-inch thick should do you, but I would opt for a bit thicker. 1 foot square sheet of 1/16" is $23. (1/8" is $36 is Overkill). The issue with all metals is that sheet and wire are the most expensive forms of any metal and often command prices 5-20X the market price of bulk metal ingot. Lead is currently just over $1.00/lb on the market at 1000lb lots. The 1/8" square foot is 8 lbs. 36/8 = 4.5X. This is because lead is easy to work.

https://www.rotometals.com/lead-sheet-plates/

They are listed in the primary sources for any and all metals. I rarely have to order metals, but I always find them my best buy in small quantities from 8 ounces up to 100 lbs of metal, especially in rare or oddball metallic elements. Use the primary source forum.

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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Dennis P Brown
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Re: Matt Gibson Fusor

Post by Dennis P Brown »

To control deuterium into a fusor a 'leak' valve of some type is absolutely essential - standard vacuum valves (like bellows) simply do not offer enough control. A leak valve can be made or bought. High quality leak control valves are expensive even compared to vacuum valves but are available from vacuum supply companies. Making a valve that can perform in a somewhat similar manner has been done by people here. If I recall correctly they use a type of fairly inexpensive needle valve (AC grade) and add a very small capillary tube; one could also use a special micro-pin hole (companies make these for the medical industry applications.) Search the Fusor construction FAQ for leak valves - I believe that topic is covered there.
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Re: Matt Gibson Fusor

Post by Finn Hammer »

An MFC is the gold standard of flow control.
I use one of the 10CCM variety, and it gives superiour controll of the flow, and thus the fusor pressure, which can easily be regulated to less than a microns presicion.
Get one, you won't regret it if you do.
And if you should ever contemplate to create an autotuning fusor, you will need one anyway.....

Cheers, Finn hammer
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