Tubbs Beam-on-Target Effort [Neuts/Pics/Tips]
Posted: Thu Mar 27, 2014 12:45 am
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
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