I trust some reading was done.......

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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Richard Hull
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I trust some reading was done.......

Post by Richard Hull »

In all these gun attempts, I trust a good bit of reading was done.

I have looked at maybe making a duoplasmatron gun system (pair). My good friend Tim Raney and I are talking and flapping our wings like we might attempt a first pass.

The key thing is that if using electromagnetic plasma concentration and the normal ion/plasma arc into the gun, one is looking at an energy expenditure of about one kilowatt or so per gun to get about 1-5ma of ions! I am more than willing to supply the 2kw because I don't give a hoot in hell about efficiency, just results. Very little of the energy goes to the filament. Most is spent in the plasma arc at or near the extractor cone. Thus, the need for a tungsten plasma cup. Finally, I note that the filaments and guns are only good for about 10 hours of operation before disassembly of the gun and replacement of the filaments. This due to the filament having to work in a 100mtorr gas. Naturally, one could scale back a bit in the ion current but then one also scales back in the fusion level.

The much simpler right angle ion gun extractor system is not generally capable of more than 50 ua of ion current.

I knew from my discussions with Meeks that the ion guns were a bear to get right and used up the vast majority of all the fusor input energy, especially in the 6 gun systems. (Meeks was the ion gun expert on the Farnsworth team.)

I have been reading and studying. Ion guns of genuine "brighness" (>1ma) are not trivial components.

I would want to isolate anything I build and fiddle with it for some time before commiting to any design. Even then little might come from it. We will see. I would want to shoot for a pinpoint focus at beam collision in any finished device (not spherical, most likely).

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
hellblazer
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Re: I trust some reading was done.......

Post by hellblazer »

Check out

http://accelconf.web.cern.ch/accelconf/ ... /6W014.PDF

From the conclusion:

The carried out experiments shows that duoplasmatron with cold cathode can be used for generation of intense proton beam at CW operation. The developed design of the source produced in experiments proton beam with current about 10 mA during period several tenth of hours without any damages of the source parts. Power consumption did not exceed 500 W. The results of experimental study of cold cathode duoplasmatron on CW operation allow to conclude that this type of duoplasmatron is suitable for using in CW high power linac. The advantages of this ion source are very simple and cheep mechanical design as well as power supply, stability of proton beam parameters and long life time. The main drawback of the ion source is high pressure of gas in discharge chamber and, therefore, high load on vacuum system of the preinjector.

Also note

http://www.pelletron.com/plusion.htm

Beams of He+, O+ and Ar+ are routinely produced with currents on the order of 2 to 2.5 milliamps with arc and extractor voltages of about 100 V and 30 kV DC, respectively. Beams of H+ up to 10 mA can be expected. This source is directly usable for most gases which form stable positive ions.

and

http://www.channel1.com/peabodyscientific/page9.html

With a 1 mA beam
3l
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Re: I trust some reading was done.......

Post by 3l »

That is why I'm hanging back on the gun a little.
50 ma duoplasmatron is a pretty ambitious project.
Good luck to you guys.
I had trouble figuring what to do with the higher operation pressure.
One of the reasons Ive been researching the inductive and microwave ion gun, is the limited filament life that a duoplasmatron has when it runs well... much shorter if a goof occurs....owie!.

Fusion is fun!
Larry Leins
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Richard Hull
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Re: I trust some reading was done.......

Post by Richard Hull »

Again, I was thinking 1ma MAX brightness. Air cooled. No more than 100mtorr gas pressure in the ionizer chamber. I will probably go for straight tungsten filament.

The Russian design and PS-100 are nice but a bit much.

I called Peabody Scientific and the raw PS-100 with its matched extractor gap and no supplies, no gas handling, and no ion optics external to it is $13,900 This will give you folks an idea of what even a moderately bright (~1ma ion scource) is worth without any of the goodies needed to make it work.

I have talked with several people in th' biz and they consider an amateur effort extracting 500ua of deuterons as major undertaking. They universally felt that the effort would result in as many neutrals and scattered electrons in the beam as actual deuterons. They also noted that only the duoplasmatron type design could produce anything like the currents we would need.

Also, the gas wastage would be rather extreme in any bright gun design and some form of reclaimation system would be highly desireable, but probably not really feasible.

Working at a slightly lower gas pressure (conserving D2 gas) and pouring in a bit more ionization energy might just make a super inefficient but still suitable 1ma source........just maybe. Hopefully, without the need for multigallon per minute water lines.

I would go to 500ua energies before I would water cool.

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
hellblazer
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Re: I trust some reading was done.......

Post by hellblazer »

Heck, I'd be happy with 50 ua.

Definitely know this is arcane and expensive stuff.

But what fun would it be if it were all so simple and trivial to do?

Getting a book on ion sources from Alibra. That should be entertaining...
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Carl Willis
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Re: I trust some reading was done.......

Post by Carl Willis »

Would a simple RF ion source be a viable alternative to the duoplasmatron under discussion? As I recall reading in an older text, the glass RF ion source was supposed to be superior at sourcing high fractions of H+ (as opposed to H2+), with low pressures and low gas flow rates as well.
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hellblazer
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Re: I trust some reading was done.......

Post by hellblazer »

Just got some interesting duoplasmatron patents from Delphi. One is for a honking big duopigatron (love that name). Way outta our league. The other two are interesting - especially the one for the air cooled plasmatron. Anyways, hope these are useful to somebody other than me.

Multi-ampere duopigatron ion source

Apparatus and Particularly Duoplasmatron Usable for Ionizing a Gas and Process for Using Said Apparatus

Vacuum-Compatible Air-Cooled Plasma Device
3l
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Re: I trust some reading was done.......

Post by 3l »

HI Richard:

How far into the duoplasmatron project are you?

There is a really neat way to get the high currents you need for fusion with out the crazyness of duoplasmatron. At LBL they have a really neat device that was first used on the Ormak test setup. The device runs on ECR but is basically a box with electrodes. The gadget is scalable to kw pulses fairly easily due to it's modular construction. Their first device will fit on a small desk (100kw). The key to it's high efficiency is the way it is operated, in pulses with a large number of full energy electrons in circulation before a puff of deuterium gas is admitted. This way the electrons can reach their full potential energy before the ionization starts leading to more effecient use of the ionizing electrons. The basic device uses a bank of tungsten filaments to make the electrons. The electrons are collected in the unit untill the proper number and energy is reached. A calibrated puff of deuterium gas. An interval to allow the deuterium gas to ionize. Then the accelerating pulse the deutrons are repelled out of the ionizing chamber at a potential of 120 kv.
The really neat part is the extractor electrodes are a molybendium sheet with slots cut in it.
I think like a router with a fine bit eh?

The only water cooling is on the filament feed lines.
The magnets are the neodynium iron type.
You can see a picture of this device in the Fusion Quest.
It makes the ions that are then neutralized for the heating of the Tokamak Reactor system.

Fusion is fun!
Larry Leins
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Re: I trust some reading was done.......

Post by DaveC »

Maybe I am missing something here, but since ionization potentials are below 20 volts, why do you need electrons in the KeV energy level before they interact with the Deuterium?

I have worked with Mass Spectrometers for years, and it is quite clear in those low current, low pressure, applications, that hardly any increase in ion current occurs above 30 volts!

Now, at higher pressures, like in the torr range and above, you might need KeV electrons to get all the way through the gas volume. But in the micron pressure ranges, you don't need much voltage to expose the entire ionizer chamber to electrons. What you DO need is electron current.

I have had in my mind to look at low current ion guns, to understand what improvements a high beam current density makes to the fusion rate. It should be more or less scalable.

An inefficient system in the nanowatt range, only becomes more inefficient in the watt to kW range. So one shouldn't have to make ion cannons here to get the flavor.


Dave Cooper
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