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Deuteron Accelerator Project

Posted: Mon Jun 15, 2015 9:22 am
by Dennis P Brown
Well, after reading Mr. Wells very interesting post on his progressing accelerator project I decided to return to my long running deuteron accelerator project. I especially liked his approch to testing his system.
Looking at my system I decided to deal with a few older problems.
Addressing one of my long range tasks I finally decided to upgrade the mechanical pump. So I dissembled the entire accelerator system - including removal of all shielding and all the major vacuum components so that I could add the larger and better performing mechanical pump - in hindsight, glad I did for two reasons that I'll address shortly.
This "backup mechanical pump" has well over twice the "gas" handling capacity of my smaller original pump that was used as the fore-line for the turbo pump - this did require some rebuild of the stand but this was minor.
Since the vacuum system was now mostly apart I took the opportunity to remove the turbo pump again and check for the glass fragment. To my surprise the small glass fragment within the unit appeared to be gone (shaking produced no noise at all) - I guess my first attempts at removal (shaking method) must have either removed it (or the fragment moved down through the blades and reached the pump bottom) or the fragment wedged itself into a harmless position (like in a stationary blade.) Regardless of which occurred, I re-assembled the accelerator vacuum system with the turbo and everything tested out fine (less the accelerator tube which has been removed for further planned modifications.) The system (even after being in very humid air for awhile) quickly reached 2.2 x10^-5 torr. I stopped the test after that point since lower ranges would be difficult to achieve without a full bake out and running the turbo puts needless wear on the pump.
During the breakdown of the complete vacuum system I discovered that some vacuum components near the accelerator tube still contained glass fragments from the breakage of the original accelerator tube. While the turbo now has an excellent protection screen, glad that screens performance wasn't tested the hard way by these fragments.
Well, today I cut my accelerator tube shorter - since the number Einzel lens in my system was excessive. As someone here correctly pointed out, nearly all the deuteron acceleration occurs between the first two Einzel lens. This also necessitated that I modify the accelerator's tubes electric field smoothing system (it too needed to be made shorter) and reduce the number of collector plates for the Einzel lens.
I will reinstall the accelerator tube (less the electric field smoothing system) and over the next few days, bake the entire system under high vacuum (just down to the turbo head.) Then do a high vacuum test. Hopefully, the system will again reach the mid to low 10^-6 torr range like it did previously (hopefully, the new ceramic accelerator tube doesn't leak!)
At some point I will revisit the VDG system (the current "show stopper" with its abyssal performance of 1 - 2 micro-amps) and either give up on the unit (after another attempt to upgrade it), build my own, or breakdown and buy a larger unit. This phase of my project will be put on the back burner as I get ready for an oversea's trip to visit my daughter at her internship job at the French National Scientific Research Institute for the summer. Also, I desire to restart two other critical projects related to some home research projects - one even is fusor related.

Re: Deuteron Accelerator Project

Posted: Wed Jul 01, 2015 4:06 pm
by Dennis P Brown
As promised, I am including an update. I removed all shielding on the electro-static linear accelerator (ESLA) and have nearly finished adding a tiny deuterium tank that will be completely enclosed within the VdG hemisphere. Also, I added a far more powerful mechanical pump (gets down to a single micron) and removed un-needed vacuum devices to reduce out gassing. This logic for putting a small D2 tank in the VdG hemisphere (it will be filled to about atmospheric pressure only) is that I'll have no feed line going into the hemisphere; thus eliminating a major shorting line that reduced both the current and voltage from the VdG. I will provide a photo soon of the finished D2 tank connected to the LA in the hemisphere.

A photo of the bare linear electro-static accelerator ceramic tubing with external Einzel lens charge collectors is included. The mini-tank can be seen in the first photo lying on its side. Since then, I have made the D2 tank even shorter. Besides adding this feature, the accelerator tube is ceramic and has fewer Einzel lens. The system, after bake out has reached 4.5 *10 ^-6 torr, which is low enough. Still, the VdG needs work. As such, I may use my +30 kV high current supply to excite the accelerator's main hemisphere to get a good current but very low energy deuteron beam (25 - 30 keV.) This should produce some neutrons, I'd think when striking a deuterated plastic target. I will add a plastic shield around the hemisphere if (rather when) I install the +30 kV cable. That PS will provide 2200 watts continuous and far more in a short ... not something I want out in the open ... .

Of course, I will first have to build my neutron detector if I really want to see interesting results. My target holder (large object wound with copper tubing at the left of the vacuum cluster holding the accelerator tube - it extends into the center of the cluster and is vacuum tight) is electrically isolated from ground (it electrically floats when not being water cooled and when I turn off the electron suppression voltage) so direct current readings from a deuteron beam can be obtained using a micro-amp meters I have wired to it via a switch. Also, I have a small viewing port glass window allowing me to directly look at the target (it is inclined at 45 degree's towards the viewing port. Besides making the deuteron beam impact region fully view-able, it spreads the "beam" out over a larger area thus reducing thermal load on any target material (like my deuterated plastic film ... .))

Re: Deuteron Accelerator Project

Posted: Wed Jul 01, 2015 6:34 pm
by Richard Hull
Nice professional looking system. With a targeted system, the X-ray hazards are important to watchout for. Of course, your beam current will determine that issue.

Richard Hull

Re: Deuteron Accelerator Project

Posted: Mon Jul 06, 2015 10:55 am
by Dennis P Brown
First, thank you Richard. Hope that it (some day!) actually works rather than just being eye candy! (lol)
Added the deuterium fill station and tested the tiny D2 tank; I converted a much longer Al tank into this small tank - cutting and epoxy sealing. This tank held vacuum down to the low 10-^5 torr so it appears ready to go.The tank will only be filled to about atm so it will not ever "see" high vac. A special fill valve will admit D2 to the accelerator tube directly from this small tank. It has to be small so to both fit in the Van de Graaff globe and not be too heavy ... .
The vacuum (was) holding - the turbo was in Standby Mode yet still reached 8 * 10-^6 torr! Then, of course, adjusting the new D2 fill valve to the end of the accelerator tube, the fill port broke off damaging the accelerator tube. The repair isn't too difficult but really have to re-engineer the assembly to be far stronger ... two steps forward, one back ... life in high vac linear electro-static accelerator building. Not that the fusor hasn't had issues now, either.

Re: Deuteron Accelerator Project

Posted: Mon Jul 06, 2015 5:50 pm
by Dennis P Brown
Aside: repaired the accelerator tube. the glass cutting band saws are amazing - cut through glass or ceramic tubing like a metal band saw through aluminum. Installed a very strong end part assembly that allows the leak valve/D2 tank to be de-mounted using a KF-clamp/O-ring on the end of the accelerator tube.

Re: Deuteron Accelerator Project

Posted: Mon Jul 13, 2015 12:19 pm
by Dennis P Brown
A quick progress report on this project: my first iteration on the new gun wasn't working. So I decided to remove this unit and design another. After a few more false starts, finally found a suitable "housing" that was small enough and yet offered a good vacuum fit to my accelerator tube. Have now machined the basic ceramic parts for this new, and smaller but stronger deuterium gun assembly for the accelerator tube. Now waiting for a small diamond drill to arrive so I can finish this part of the accelerator and install it for vacuum testing. As I am learning, some devices are far, far more complex than one thinks until it hits the harsh reality of building and testing ... .

Re: Deuteron Accelerator Project

Posted: Thu Jul 16, 2015 9:00 pm
by Dennis P Brown
A quick update: finished installing the two power supplies and battery and 12 volt rheostat in the Accelerator's main sphere. This unit will be installed on the end of the accelerator tube with the gas leak valve and micro-deuterium tank. This will complete that section of the accelerator. Decided to machine mounting supports for each component within the dome. These mounts were just epoxied with 5 min. A band saw and grinding wheel and drill press was all that was needed. Even with the deuterium tank, the inside will not be as "crowded" as I feared. The weight is 80% battery so the rest of the components don't add much - the deuterium tank is aluminum and very small. The accelerator tube needs high vac testing again and that will take some time. The - 25 KV voltage multiplier is under oil and in a small white plastic bellows. It is fed by the 3 KV PS.

Re: Deuteron Accelerator Project

Posted: Tue Jul 21, 2015 8:59 am
by Dennis P Brown
Here is the main sphere with the aluminum super mini deuterium tank mounted and the entire system installed on the accelerator's tube. The D2 leak rate control valve, tank valve, and tank line tested to high 10^-6 torr with the turbo in stdby mode so the system is leak tight (after an hour pumping with the system having been open to air w/no bake out.) Basically, just trimming until I can either obtain or make an upgrade VdG for the high voltage needed to get this system working. Did test the battery driven neg. 25 kV system for the deuteron gun and it worked well (keep forgetting it has minor caps and these do not discharge quickly - so, shocking when handling ... .) Really the interior is not as crowded as the photo makes it appear. There is enough room so I can still access the D2 leak control valve and even the hardware holding the entire system to the accelerator vacuum tube. All the components in this sphere - D2 tank, leak valve/line, 3 KV DC/AC PS and Voltage Multiplier and battery can easily be removed. Each component has their own support mount.

Re: Deuteron Accelerator Project

Posted: Mon Jul 27, 2015 10:48 am
by Dennis P Brown
Still awaiting a few parts so I continue to upgrade sections to both kill time and improve the future operation of the unit - one such "upgrade" was my designing, then assembling and vacuum testing a beam collector to measure the current that the device may produce. This beam collector will not be "adjustable" - i.e. be able to move into or out of the beam under vacuum; but rather, will be installed/removed as needed. I do have a small glass slide for beam imaging that can be moved into/out of the beam while still under vacuum.) The electron anti-back streaming system has been simplified to make it easier to operate.

Seriously considering building a very large Van de Graaff to up the system's current. The voltage need not be very high - 200 kV to 300 kV, which would be fine but I need at least 20 milli-amps output or if possible, higher would be better still. Most commercial units have issues I now see. I've built every other secondary support system for the accelerator so this is something I'm strongly leaning towards. I only recently realized that the extra large dome required for a new high current system would be absolutely trivial to construct using a very simple hemisphere design developed long ago for VdG's in the 1930's - mystified why this design is no longer used (a long cylindrical metal tube is caped by two "normal sized" half hemispheres on each end. This design allows a very wide belt to be installed, offers more charge collection capacity, and is very easy to assemble.) So, since creating a proper dome was always my previous "show stopper" preventing me from trying to build one - that is, making a standard spherical dome large enough was/is frightfully difficult - that problem has been solved. So, now I have little excuse not to try. Once I do start that project I'll post what I did to solve the construction issues.

As Richard correctly pointed out, all such accelerator projects using electro-static systems require huge belts and domes to be viable. Since I have recently discovered exactly how simple making good belts is (ridiculously simple; it looks difficult but sure isn't. There really is no reason to ever buy a belt) and with the the new dome design (really just a std 1930's design using an existing "split dome" I already have on hand) and having a much larger motor, which I also currently on-hand, the most difficult parts of the job, I think, are done.

So, after the conference at Richard's, I intend to tackle that project ... or at least see if there are other "show stoppers" to building such a device. I can always buy a larger unit and fix its problems if all else fails ... which is becoming my standard by word relative to building a large electro-static accelerator... lol.