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

Posted: Thu Mar 27, 2014 4:45 am
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.



-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.

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

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

Posted: Thu Mar 27, 2014 7:25 pm
by Richard Hull

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

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

Posted: Fri Mar 28, 2014 3:33 am
by Mark Scott-Nash

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

Posted: Fri Mar 28, 2014 2:19 pm
We, at the NWNC are proud of you, Robert... Good Job.

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

Posted: Sun Mar 30, 2014 6:40 am
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?

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

Posted: Sun Mar 30, 2014 8:02 pm
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.

Robert Tubbs

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

Posted: Tue Apr 08, 2014 5:32 pm
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.

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

Posted: Fri Apr 11, 2014 9:33 pm
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,

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

Posted: Sat Apr 12, 2014 4:51 am
by Richard Hull
Fine work robert? keep it up! We are intrigued by your efforts.

Richard Hull

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

Posted: Sat Apr 19, 2014 5:13 pm
by RobertTubbs

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