Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

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RobertTubbs
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Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Hello Folks,

It's been some time since my last post and I have some tasty morsels to share.

Over the last 9-months I've been working on a small accelerator system, the principal use of which would be to aid in the instruction of High-School Students at the Northwest Nuclear Consortium in Federal way, 50 miles South of my home in the greater Seattle area. A Fusor has done well for them but the next steps were very much needed to be available for some of the more advanced students. So before I relocate it out of my Kitchen and down South for the kids, I'd like to share it with the community, so that use can be made of what was learned and perhaps facilitate some others who'd like to do similar.

The system is a teaching tool, and for the time being it's limited to about 35kV, X-rays are virtually nonexistent (short perhaps those that exit the windows) and Neutrons are limited to approximately 10,000 TIER.

When the time comes that additional neutrons are needed for their projects or research then a new feedthrough, power supply and additional shielding can be assembled but I think I'd like to have them involved in that process. I feel this gives ample time for folks to get comfortable with that machine as it's initially introduced.

----

Construction:

-The chamber is a 6" Dia cylindrical Chamber, the same one I used for my Fusor and that Jake Hecla later borrowed for his.
-The pumps are a Varian SD-90 and a Turbovac-50 with NT50 Controller.
-Power supply is a reversible polarity Hipotronics Supply that peaks at about 35kV.
-The present Target is a 1-gram 1945 90.5% Gold, 9.5% Copper Dos Peso lovingly hammered into a machined down aluminum cylinder with a 1/4-20 thread in the back where it mates to the HVFT.

-ION SOURCE: ~100W Capacitively Coupled RF Plasma source, with Large Neodymium toroid and differential pumping through a 6mm orifice - no extractor bias is necessary at this time; the target's been doing all the work.
Typical Beam Current: ~50uA.

----

This system and its various components were largely formed through trial and error; there were about 7 attempts at ion sources, mostly to make the matching, differential pumping and materials QC requirements happy. The target has gone through three different iterations, originally 2 micron titanium sputtered copper substrates - they were found too delicate for my taste, primarily due to my flat out refusal to add a defocusing lens which ultimately destroyed the sputtered layer. What's used now is the gold target which I find to perform well enough, to say nothing of its appeal and near indestructible nature.

Other modifications are some tinkering with secondary electron suppression using magnetic fields; you'll note in some of the photos something that looks suspiciously like a worm clamp with two "horns emanating from the target. By having a strong magnetic field going perpendicular to the target, just in front of the targets face I've noticed that I can substantially reduce the overall secondary emission, likewise the occasional discharges that rock the system due to breakdown have been eliminated. I credit Jake Hecla for finding a subtle reference to this technique in an older book on the shelf at his university, he and I have collaborated and shared information throughout our mutual BoT pursuits, and I’ll let him make his own announcements when he's ready but he's surely not too far behind.

Here are some pictures of the setup and an attached link to a 1-minute long YouTube Video of operation, if there's demand for more info I can provide more as it's desired.

Disclaimer: The video was of first neutrons on February 24th, the system is more stable at this time and output has increased substantially. http://youtu.be/DS8Y-53onEE

In conclusion I'd just like to say that this has been one of the most educational projects of my life, the black magic and little odd happenings of these systems intrigue and excite me in ways that I haven't enjoyed since my original Fusor experience some years back. I highly encourage others to attempt BoT work as it opens up a whole new chapter in one's knowledge. I have been very humbled by the experience.

Warmest Regards,
Robert Tubbs
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Richard Hull
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by Richard Hull »

Robert,

Nice effort! I have created a small extra section related to BoT fusion on the fusioneers list. While we are all doing some BoT fusion in fusor's you must be recognized for doing and reporting on the first specific effort ala simple accelerator using an ion source. Check out the neutron club listing.

Yes, not many neutrons, but there are neutrons due to this specific effort.

Keep up the fine work.

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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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by Mark Scott-Nash »

Excellent!
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by KJNW »

We, at the NWNC are proud of you, Robert... Good Job.
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by Bruce Meagher »

Very impressive and thanks for sharing. It appears the pressure in the chamber is pretty high. Can you share a little more on the vacuum setup and the chamber pressure during the run?
RobertTubbs
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Richard, that is really cool, I checked it out. Thank you very much for the mention!

Carl G, thank you, and thank you and David for your continued support.

Bruce, I lack the funds and instrumentation to give you any real analysis on the pressure and of course my Thermocouple gauge is useless below a micron. It's probably somewhere around 10E-4 or 10E-5 Torr with the valve wide open to the Turbovac a few inches away, it's a lot of bear skins and stone knives that got this setup to where it is and I'm still getting it tuned in. I'll endeavor to provide more information as it's available to me.

I did get a hold of an old inverted magnetron gauge, which is still on the shelf, but I've yet to throw together the instrumentation for it to read anything.

Additionally I'm down to about 40PSI in my D2 lecture bottle which was originally provided to me at 500PSI by Carl Willis for my Fusor back in ~2009, so before I do anything else that's likely to be my first battle. That stuff is prohibitively expensive and bureaucratic to acquire around here.

Regards,
Robert Tubbs
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by Richard Hester »

I hate to bring out the horse corpse to inflict another few bruises, but this sort of setup would be a way to easily (relatively speaking) observe p-B11 fusion. A PIPs or surface barrier detector would be needed inside the vacuum, possibly with a lead foil shield and an MCA to discrimnate the alpha signatures from random rubbish. The U. of Wisconsin efforts regarding detection of the high energy protons from D-He reactions are relevant, though a major concern of theirs was screening the detector from stray electrons. In this case, hard X-rays would possibly more of a concern.
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Howdy Folks,

I've been a tad under the gun at the day-job, but nonetheless have been tinkering with the system for a few minutes every night when I get home.

I've brought the beam-current up a smidgen and also have begun testing different target materials - still of course mounted inside my lathed aluminum holders.

Thus far I've tested:
2-micron Ti coated copper substrates - Produced trace neutrons due to Ti ablating off during long/intense runs. (Hydride Based before Ti ablation, Ion Implantation in Cu resulting reactions)
Gold insert in machined aluminum holder - produces neutrons, still in the process of testing. (Ion Implantation based) [Pictures 3 & 4]
Uranium Dioxide insert in machined aluminum holder - produces neutrons, and huge numbers of secondary electrons, still in the process of testing. [Pictures 1 & 2]

Enjoy the pictures,
RT
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Richard Hull
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by Richard Hull »

Fine work robert? keep it up! We are intrigued by your efforts.

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
RobertTubbs
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Update.

The little accelerator system is not so little now, I've attached the beast's head to the body and installed the system down at NWNC.

Some initial lead sheet was thrown on some of the problem areas (i.e. Glass Envelope & Viewport) - It is my hope that we could start doing neutron runs with the kids in a week or two.

Enjoy the eyecandy,
Robert Tubbs
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Dennis P Brown
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by Dennis P Brown »

Impressive! Small can be beautiful but like an iceberg, the underlying support equipment (power supplies,vacuum system,gauges, controls,supports) really explode the size and complexity of even the simplest gun!

Great work and thanks for sharing the apparatus.
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Richard Hull
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by Richard Hull »

Yes, creating a non-earth-friendly environment in order to provide a specialized pure atmosphere in which to move charged particles about in a controlled manner can involve a lot of volume absorbing gear. We are really creating our own little, highly controlled electrical universes in a can. Still, ain't it fun!

Nice work Robert!

Ricahrd 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
RobertTubbs
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Update 8/3/2014:

I've upgraded the machine a bit since my last post.

The machine now sports an inductively coupled ion source and a differentially biased electron suppression shroud. See the brief video of the system here: https://www.youtube.com/watch?v=DdLe6No5he4&app=desktop

I'll keep improving things as I go, it's a forever rough draft.

Thanks for the kind words, all!

Enjoy the pictures and a video of the machine running.
RT

edit: I have no idea why the first picture displays as sideways, click on it and you'll get the correct upright view.
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by George Schmermund »

Robert - I'm enthused by the effort that you've put into your BoT machine. There is a faint, but growing interest here regarding this method of producing nuclear reactions. Certainly a lot more work is involved in getting a BoT machine up and running compared to a fusor and, as you've pointed out, it's a project for the advanced experimenter. Few here will ever accomplish more than a fusor, but you're demonstrating that a more serious approach to doing fusion physics is within the reach of the advanced hacker.

I applaud your dedication to the cause and hope to eventually join the ranks of the BoT heads here. Salute!
Anything obvious in high vacuum is probably wrong.
RobertTubbs
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Thank you for the kind words George.

Doing beam on target to a level that allows one to say "I've done beam on target fusion" is well within amateur reach. However, a BoT that could compare with the typical actively pumped industrial systems from 10-15 years ago is my goal - something I'm slowly stumbling towards.

I'd also say that BoT opens doors beyond fusion research, for example I've been playing with the idea of changing around the system someday for some experimentation in focused ion beam milling. FIB is about as far from my reach now, as the BoT was after the Fusor.

Leveling up let's you see what's possible next, that's the greatest value of the BoT IMHO.
RT
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Dennis P Brown
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by Dennis P Brown »

Rather than lead shielding (toxic and conductive) why not used 12"x12"x3/8" slate tiles? Home Depot sells these in boxes and are very inexpensive. These tiles are square, can be stacked together and glued, and don't conduct. They have 1/4 the density of Pb so it is easy to calculate the required shield thickness. Disposal isn't an issue unlike lead nor safety concerns in handling or dust. They can be both cut (an inexpensive abrasive blade) or drilled (ceramic bit) if a special shape and/or a hole is needed. They actually look rather nice and professional.

That all said, the accelerator looks very nice.

Have you considered adding simple metal rings along the glass tube body to better contain the protons (weakly focus) and make the electric field more uniform along the tube for more constant acceleration?

Wouldn't mind some more details on your electron suppression system.
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

New [more in depth/nicer] video showing all the equipment and smoother operation.
http://youtu.be/OUDxt2Nya50

Enjoy,
RT
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Some additional and hopefully helpful eyecandy.

Peace out,
Robert

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RobertTubbs
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Miss September.
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Update: Still air brushing the system, tweaking things here and there, here some glorious eye candy.

Beam entering the secondary electron suppression shroud.
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Some updated pictures of the system as it stands now.

-Robert
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by Andrew Robinson »

I like the new paint job. Brings it all together.
I can wire anything directly into anything! I'm the professor!
RobertTubbs
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Some more recent photos and video of things, having just boosted the beam output to about a milliamp.

Youtube link: https://youtu.be/mdv4KpYKKJk

RT
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by Werner Engel »

Robert,
I saw you video and some of the pictures of your ion-source. I have a similar design but want to use a RF-source which is almost DIY. I bought a 1,0 kW SSPA. For connecting the HF-coil to this PA I also selected the MFJ-962D. But when browsing through your video, I saw that you opend up the MFJ device and made some internal connections. Is the 6 Ohm impedance enough, you can reach with the MFJ.962-D - or did you use another trick to adjust it down to 1 Ohm?
Can you tell me a little more about your changes? Unfortunatly I don't have enough know how in the HF area!
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Re: Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]

Post by RobertTubbs »

Another update/photo, as of June.

I've got a lot of projects I'm working on right now.

Among them, bringing a refurbished 100kV multiplier tower online for my setup.

I'm also investigated a long term solution to remote operability, seeing as how my equipment is now interface-friendly.

-RT

P.S. @Werner, what I did there was directly connect to the output on one of the variable caps in the network. I was moving upstream from all the switches and connectors that kept catching fire. ICP likes to ring up and produce arcable voltages. Ham radio antenna tuners are really not designed for this sort of abuse, though with care they can be used.
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