New fusor "Carl's Jr." nearing operability

[Carl Willis]

My 6" fusor nicknamed "Carl's Jr." (since it is smaller than my former 8" fusor) is close to completion.

There's not a lot of innovation to be seen in the assembled parts thus far, but I do have some fairly ambitious plans for this fusor.
-- I am planning to really push the voltage with this unit, maybe as high as 75 kV. Obviously, the BeO feedthrough will not handle this in air, so the fusor will be mounted upside-down such that the insulator screws into a terminal at the base of a plastic, oil-filled pipe section (which will seal against the side of the 2.75" ConFlat with an o-ring). The oil will help remove heat from the insulator while simultaneously preventing flashover and allowing the design to be more compact.
-- This fusor is water-cooled with the copper pipe that can be seen soft-soldered to the outside surface. This is so I don't have to make a sheath for air cooling and listen to a Shop-Vac roar as in the previous design. Because of the poor thermal conductivity of stainless steel, I am not expecting wonders from this arrangement and I'll have to wait and report how effective it actually is at keeping the flanges cool. I do believe I can manage 1.5 kW this way, especially with the BeO feedthrough under its own oil.
-- I'm going to try a simple "keep-alive" ion source of somewhat novel design, since I plan to run this at high voltages and lower currents than the previous fusor. This ion source will consist of a QF-25 half-nipple containing a fine hypodermic-needle anode with the point facing the center of a grounded annular cathode and separated by a small distance from it. The needle will be supported from a small HV feedthrough in the QF-25 blank, biased at around +10 kV, and fed deuterium (via a metal-glass-metal standoff). An external magnet around the anode-cathode gap will help trap electrons, though it's likely that the gas pressure at the needle point will be high enough for a discharge to be self-sustaining without the magnet.

The rest of the support hardware is ready to go, for the most part. My new little vacuum system has been described already, my deuterium from Matheson is here, and I have plenty of fine equipment for neutron and gamma radiation measurement. High voltage is still under development to some degree. I have a 100 kV / ~50 mA open-air multiplier stack of the full-wave Cockroft-Walton type, but I need to finish the H-bridge driver for it that I started long ago (either that or pick up a suitable RF driver from surplus). The first runs will probably be conducted with a 50 kV, 5 mA Spellman supply already on hand. (My formerly-used x-ray transformer and magnetic-amp controller are with another fusioneer in Michigan).

So that about sums it up. Having major neutrons again will be a joy. Activation has become almost routine for some folks here, and though I intend to do some of that, I would really like to do some new things perhaps involving subcritical fission, or experimenting with some neutron detector ideas that have been floating around in my head.


-Carl

[Starfire]

An excellent and exciting effort and some novel features not seen before - I will watch this space with interest - good luck with the project Carl.

[wayne]

Carl-nice job
I would like to use the oil idea. What is the "safe" oil gap to voltage ratio?
What oil type and where is it sold? Do you plan to cool the flanges? We
have used a conductive epoxy, are you using solder?

wayne

[Jon Rosenstiel]

Very nice, Carl. I'm looking forward to your reports.

Jon Rosenstiel

[Richard Hull]

Carl,

Your efforts are most interesting! I like the keep alive idea.

Your fusor looks like the "water boiler"!...... Los Alamos people would know about this along with any historian of the manhattan project.

Actually, if you succeed in forcing 1.5 kw into this effort, it will be a water boiler.

I wish you every success in this effort and hope the neuts boiloff this thing in keeping with the water temp.

Most insulator problems I have encountered are related to internal arc over, though I have, on two occassions, flashed over my BeO insulator at 35kv+. The key to avoiding air flashover is to hand clean the insulator at every run with absolute ethanol.

I include an image of Hirsch's cave fusor with Meeks in attendance. You will notice the large oil filled hat on top for insulation. This little device was operated at up to 100kv! Hinted at, is the large 12" sphere with the milliamp current meter recessed within it. This was read by telescope! The light was reflected off a large observation mirror in the access corridor to the cave! I still don't know why they didn't meter the ground leg and no one alive can tell me why. I suspect it had to do with the inaccessable internals of the universal voltronics supply set in a 55 gallon oil drum. Metering the ground leg is common practice in the X-ray biz. ( Photo courtesy Gene Meeks personal poloroid collection.)

Again, good luck with the effort.

Richard Hull

[Carl Willis]

Hi Wayne,

I'm intending on just a light mineral oil, maybe even vacuum pump oil that I already have around. Oil should be good to a few kV / mil. Care should still be taken to eliminate points or very fine conductors, so that breakdown fields are not produced on the surfaces. I have not analyzed this concept in detail yet and doubt that I will. I'll just get some parts and follow an intuitive construction approach and it'll probably work at the voltages I'm interested in, anyway.

I may add coils to the equatorial flanges. But I am not so much concerned about the temperature there as I am about the "polar" flanges, one of which has the ceramic-metal seal and the other of which has a viewport. Right now I just have coils on the hemispheres to prevent conduction of heat to the polar flanges. The coils are soldered. Conductive epoxy would probably be OK, but its heat transfer coefficient is necessarily limited by a high silica and organics content.

-Carl