Micro cyclotron

This is a project that I posted on the fusor.net site a while ago and thought it might be of interest here.
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A couple of storms blew in last week and the weather turned brutal. Don't believe everything you hear about San Diego being in perpetual summer. Temperatures plummeted down into the 50's and I huddled around the fireplace for over a week. Got some good reading in, though. Eventually cabin fever crept upon my brow, so the decision to brave the elements was set into motion.

I'll start with some pre-storm info to catch things up. The VDG accelerator column (as previously reported) was a good start in its own direction. However, work on the micro-cyclotron (uC) needed to be accelerated (pun) so that the projects would be back on equal footing. I had ordered a pair of NIB N50 magnets from 'magnets4less.com'. While waiting for them to arrive, the larger transformer was chiseled and filed into shape. (See previous cyclotron post for details).

When the magnet package arrived, I opened it up and saw a pair of shiny 1" thick by 2" diameter N50's separated by plastic spacers. They were nestled in foam peanuts and looked for all the world like the baby Jesus sleeping peacefully in the Nativity scene. I lifted the joined pair gently out of the box and admired them in seraphic wonderment. It didn't take long to realize that I was actually fondling a hand grenade from which someone had already pulled the pin.

Getting the magnets into the yoke was an experience that goes beyond imagination. I thought I knew about NIB's from working with the collection of N42 types that are stuck, somewhat permanently, to various things around the lab. Well, those smaller N42 magnets are barely even the shadows of the large N50's. The closest I can get to a simile is to say that trying to safely intercede between the ferocity of a pair of large N50's is like trying to clean a loaded large caliber hand gun that has a hair trigger and the hammer cocked. Take from this what you will. Somehow I can't see these magnets being available to the general public for long.

Anyway, sparing you guys the clinical details of the magnet nightmare, I'll move onto the effort of the remaining challenge to make the major (and most intimidating) parts of both the VDG and uC accelerator assemblies on the back patio and with only hand tools. Being that the VDG effort became svelte and simple, I had to come up with something comparable to those results for the uC. The answer came to me during an ethanol fired, cannabinoid enhanced, vision. We're not talking Johnnie Walker wisdom here, this was the real thing!

Einstein said that things should be made as simple as possible, but not simpler. Reflecting upon this profound sapience, I was guided to the understanding that cyclotrons were overly complex. It was like when I was a kid rebuilding a carburetor. There were always parts left over. Obviously the manufacturer had designed a device that was also overly complex.

To this end it became clear that, with the right materials for construction, a uC could be fashioned quite simply. The magic trick is to replace the major parts that fit between the pole faces with a material that is both, and at the same time, an excellent conductor and also an excellent insulator. Hey, I'll call it a Hot Fudge Sundae! The magic material is double sided printed circuit board. This material and the supplies needed to make the PCB do it's stuff are readily available at Radio Shack, Fry's, eBay, etc.

With the PCB materials I can etch the dees and any ion source traces on alternate sides of the board. Ancillary circuits for tuning and such can also be etched in place. The core material of the PCB is a good dielectric and easy to work with using only hand tools. As can be seen in the photos, a piece of copper pipe can be cut to form a pair of half circles that will support and separate the two sides of the PCB between the pole pieces. These pieces can be easily soldered into place to form the dees and a self contained vacuum chamber. All electrical connections can be attached from the outside without the need for vacuum penetrations (except for the ion source, of course).

A ceramic post can be placed at the center of the of the dees intersection for support if necessary. I expect the deflection of the PCB to be minimal because of the small area under vacuum. This stuff is really stiff and has the inherent characteristics of a constrained layer damping material. Sealing the space between the dees for the purpose of the electrical and vacuum requirements can be accomplished by using solder paste and a hot plate. The gap between the pipe sections is equally simple. We now have a vacuum chamber, dees, and electrode system that is basically a one-piece throwaway unit. It will be easier to replace than fix.

This handcrafted trick Sundae wouldn't be complete without some 'whipped cream and walnuts', so I'm going to add a specialty pump to the package. The pump will consist of a cryo-sorption pump module that will allow the operation of the uC to run as a quasi-closed system. The singular nature of this type of pump for this application is that it has a huge capacity for pumping everything vaporous and gaseous except for H, He, Ne, and their isotopes. From a normal pump-down of atmospheric gases and vapors, the restriction of best vacuum is limited by the partial pressures of He and Ne. This can be as much as several mTorr. If the system is first back-flushed with argon, the pressure can easily drop to below 1 mTorr. Any of the villainous H2O vapor, in a leak free system, will be permanently trapped in the sieve until the pump is regenerated. This will also make the electrolysis of D2O the method of choice to source the D2.

Assuming that the system is leak tight, a previously regenerated pump module, if properly attached to the uC, will never return to atmospheric pressure when it is thawed out. This is a great advantage over conventional pumping requirements. I'll just mix the Ar with H2 or D2 in the appropriate amounts to get the pressure I need to make everything work. It will also take care of any issues regarding the out-gassing of an unbaked system. The preliminary targets can also be sealed in to keep the system hermetic.

The images include a bonus picture that may be helpful in scaling this project.

Standby for further breakthroughs!