What vacuum chamber do I use?

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Anton Kristensen
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Re: What vacuum chamber do I use?

Post by Anton Kristensen » Tue Oct 16, 2018 10:09 pm

Jonathan, me and my advisor are currently looking here https://mdcvacuum.com/DisplayProductCon ... atid=m.1.6.
By pressing the button with "lead time" you can see specific chambers.

Chris Giles
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Re: What vacuum chamber do I use?

Post by Chris Giles » Sat Dec 01, 2018 12:57 am

Apart from the cost to buy and run, has anyone got any views on the pros & cons of the different sized crosses, i.e. 2.75", 4.5", 6"? I have a Turbo with 6" CF flange and am yet to collect the high vacuum fittings and valve. I am intending to get a 4-way cross in one of these sizes for ease of construction. I appreciate I could use KF fittings instead which seem to be more common at least in smaller sizes.

Do I gather it is easier to control the behaviour of the plasma in a larger vessel? Perhaps easier to view it as well? I'm wondering if i'm best to spend the extra on 4.5 or 6"...

Best regards
Chris.

p.s. I don't have welding equipment. I only solder small stuff :)

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Richard Hull
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Re: What vacuum chamber do I use?

Post by Richard Hull » Sat Dec 01, 2018 4:59 am

Much depends on what you want to do...........

1. I just want to do fusion to show I can do it, then be inducted into the neutron club, and then have a keg party and go on to the next "thing".
2. I want to do fusion to a really respectable level, (mega mark) to rival the best ever, and then have a keg party and go on to the next "thing".
3.I want to do fusion to a level where I can use the device for experiments in activation and perhaps try different forms of the fusor to possibly improve it or show a better way of doing fusion at the amateur level. Once I feel I have exhausted its possibilities, I will then have a keg party and go on to the next "thing" based on all I have learned and apply them as needed in later life.

#3 is the most laudable.....I suggest a formal, decent investment with a 6-inch minimum system, be it a Cross, Tee, Sphere or Cylinder. 35kv supply minimum with a 40kv + being better, long term.
#2 at least has a specific goal in a higher achievement......I suggest a minimum 4.5 inch Cross, Sphere or Cylinder. 25kv or better supply as a minimum, 30kv or more would make it easier to accomplish.
#1 is just doin' it and nothing more than ego. Most any suitable vessel and gear needed to "git 'er done"......It has been done with 2.75-inch Cross.

What's your idea of a stopping point in this effort? Where do you wish to position yourself in the effort?

99.4% of those arriving here claim they want to do #1............Of those, only 5% make it to #1......Maybe 5% of those who make #1, ever get to #2.... and about 1% of those who make it to #2 tend to go on to make a stab at #3.

Of those making #1, #2 or #3, 99.99% will just go away and are never be heard from again. The best of them, however, do leave with a real idea of just how tough it is to do the "easy fusion" to critical review and will not be fooled by future hype on power ready fusion.

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.

Chris Giles
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Re: What vacuum chamber do I use?

Post by Chris Giles » Sat Dec 01, 2018 5:17 pm

Hi Richard,

thanks very much for the advice which I'm sure others will find useful too. You have made it very clear what we can achieve with the different sized vessels. I'd like my system to be at least capable of level 2 and I will remain ambitious. However, which stage I actually reach is hard to predict there are many challenges ahead! I just have one further question if I may:

I now have a good 30kv 20mA 600W-rated PSU. Is the 30kV PSU inadequate to comfortably achieve fusion in a 6" vessel regardless of whether I try to reach stage 1, 2, 3 or rather is the 30kV PSU inadequate for level 3 regardless of the vessel?

If the latter, i will select 4.5" or 6" depending upon the availability and cost but preferring the 6" if possible.

Best regards
Chris

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Richard Hull
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Re: What vacuum chamber do I use?

Post by Richard Hull » Sat Dec 01, 2018 5:53 pm

30kv is the turnaround point in amateur fusion. If the supply can give the current, easily measured fusion in the 500K + N/s range is possible once a good system is operated by an experienced hand. At 40kv the mega mark is easily attained.

So many things must come together well, from construction to operational skill to hit the mega mark. This goal tends to lie between 30-40kv.

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.

Chris Giles
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Re: What vacuum chamber do I use?

Post by Chris Giles » Sat Dec 01, 2018 6:20 pm

Thanks Richard.

I will consider the 30kV, 20mA supply that I have as good for the foreseeable future and I'll look for 4.5" or larger vessel. I have a long way to go...

Regards
Chris

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Dennis P Brown
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Re: What vacuum chamber do I use?

Post by Dennis P Brown » Sun Dec 02, 2018 11:24 am

I would suggest that you consider a smaller chamber with that power supply. A few people have gotten high neutron fluxes with 2.75 inch "cross" chambers. I had a 30 kV and 40 ma supply, and I did manage around 100 k neutrons/sec in a 20 inch semi-hemisphere chamber.

However, in one successful effort they had achieved a few hundred thousand neutrons using 20 kV, at 10 ma supply in a small cross. Just a thought to consider.

I created a smaller equivalent chamber (using an insert) and significantly increased my neutron count. Smaller is better relative to a fusor. The higher operating pressure required for the same current/voltage matters a great deal. The chamber has more (in my case, twice) the deuterium. It has been suggest that the corners in a "T" or 4-way cross also improve the performance.

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Richard Hull
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Re: What vacuum chamber do I use?

Post by Richard Hull » Sun Dec 02, 2018 8:41 pm

One thing we have not seen, nor has any reporting come forth on the 2.75 cross work, is a "stress limit" test situation. So very much depends on the insulation to get the HV in without arcing in such a confined space. Construction limits and issues are unknown. Heating and survival of the grid at fusion currents and voltages, (energy), needed to approach fusion levels common to fusor larger than 4 inches have not been reported.

While great work and a whole new avenue has opened for fusion on the "cheapish", a number of unknowns abound, especially in how far can these small systems be pushed compared to a 6" or larger system of good design.

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.

Chris Giles
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Re: What vacuum chamber do I use?

Post by Chris Giles » Mon Dec 03, 2018 9:54 pm

Thank you Dennis and Richard.

In the small vessel, the electric field must be a lot higher for the same cathode voltage, perhaps making fusion easier to achieve but harder to control?

I think I get the tradeoffs:

Pros for Smaller ( < 4.5"):
- easier to achieve high neutron count in small vessel (perhaps due to higher potential gradient?)
- less D2 needed in small vessel / easier to achieve higher gas pressure
- smaller components are typically cheaper and more common

Cons for Smaller:
- at 2.75" it is very constrained, plasma is more likely to breakdown & arc

Maybe 4.5" is a good compromise for my setup. I can see a nice 6" Lesker and 2.75" MDC cross on eBay at present. Prices not too different. I'll let them pass for now and see if 4.5" appears, or if we see more experimental results from other fusioneers. I have plenty to do in the meantime...

Best regards
Chris

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