Update: "Carl's Jr."

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Carl Willis
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Update: "Carl's Jr."

Post by Carl Willis » Sun Sep 17, 2006 5:09 am

My second fusor ("Carl's Jr.") is making some progress, despite my attention having mainly been on other things recently.

-Added cooling loops to 8" CF flanges
-Built acrylic stand and "oil socket" for feedthrough
-Checked for vacuum integrity
-Have most parts (magnets, HV feedthrough, flange) for keep-alive ion source

I'm going to be short on wattage for the first tests: I have a Hipotronics 50 kV / 5 mA supply ready to go (the ion source should allow control over current to get to this operating point), but in the future I will hopefully have a driver for my 100 kV / 50 mA CW stack. The cathode grid will be a 6-loop Rosenstiel-type construction from 20-mil 316 SS wire, and I have plans to check some little SS mesh strainers of various sizes from Target also (mainly speaks to my laziness, but you never know what might work great).

I haven't put oil in the "socket" yet. The socket is just a piece of 3.5" acrylic pipe solvent-fused to a 4" x 4" x 2" block of acrylic, this latter with a hole to accept a piece of de-shielded RG-8 coax (good to at least 75 kV). The feedthrough fits into a copper pipe fitting with a spring in it for contact. A 10-32 screw links this fitting to the cable connector just mentioned.

I will be in neutron production mode as soon as I get the ion source wrapped up. Maybe by next weekend?

-Carl
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Donald McKinley
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Re: Update: "Carl's Jr."

Post by Donald McKinley » Sun Sep 17, 2006 7:15 am

Nice, a work of art.

D.

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Re: Update: "Carl's Jr."

Post by wayne » Sun Sep 17, 2006 11:41 am

Carl,

Nice work. What is a keep-alive ion source? Do you have any drawings?
Where is it in the picture? Will the oil be cooled?

wayne

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Richard Hull
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Re: Update: "Carl's Jr."

Post by Richard Hull » Mon Sep 18, 2006 2:29 pm

I like the external oil bath insulator bit. The Farnsworth team did this a lot. Provided one has internal clearances squared away, this external oil bath idea will let you use an insulator that would be unsatisfactory in air at higher voltages.

Good luck.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Update: "Carl's Jr."

Post by MCL » Mon Sep 18, 2006 6:11 pm

Hello Carl;

Really very nice work! The liquid cooling on the reaction
chamber is an excellent idea, as is the oil-bath for the
high-voltage feedthru. What kind of oil will you use? Can
one use a standard automotive oil, or is there a type of
oil with a high dielectric co-efficient that is best?

I am also interested in your ion-gun. I have been
experimenting with HV DC arcs for ion-generation, and at
first, thought the approach was not working - but a recent
run has led me to revise my thinking on the matter.

My neutron detection is limited to BTI BDR100's
at present, so my neutron rate estimation is a little crude,
but I believe close attention to grid detail, as well as methods
to augment D2 ion production, may yield some useful, and
actionable design improvements for these IEC-type devices.
If you feel you want to share any details on your "keep-alive"
ion source, I (and it looks like several others) would be most
interested in what you are planning, and how you anticipate
it will work.

But bravo on the device construction. It really is impressive,
and I particularly like the way you adapted the berylium oxide
Navy-radio feedthru for high-vac use. I used the same part
for my first grid-version, and did an ugly job with a mig-welder
and some silver-bearing HV epoxy courtesy of K.J. Lesker.
Your resulting device shows the quality of your approach.
I look forward to following your further efforts.
- Mark Langdon

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Carl Willis
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Re: Update: "Carl's Jr."

Post by Carl Willis » Mon Sep 18, 2006 8:10 pm

I'll try to answer Wayne's and Mark's questions about the "keep-alive" ion source. It's not connected to the fusor yet (nor is it even finished, I have to design a holder to keep a bunch of little NdFeB magnets in place, and boy do they want to fly apart worse than anything!).

This concept is very simple and very inexpensive. A narrow, high-velocity gas jet passes into an ionizing region defined by parallel electric and magnetic fields, creating ions that are ejected into the fusor by the electric field or by the momentum of the jet. The E / M field pairing is a feature of Penning cold-cathode sources, in which electrons are forced to take helical paths between anode and cathode by the magnetic field and hence stand a better chance for causing ionization. The narrow gas jet is a feature seen in some modern ion sources designed to produce cold ions and charged molecular species. The high E field in my concept also accomplishes extraction and initial acceleration up to maybe 20 keV (we'll see). I'm not sure if the gas jet and sharp point are necessary or even helpful and I have no idea what behavior to expect. But ideally, the ion source for this application will be able to provide a low-current stream of energetic ions (maybe 50 microamps @ 10-20 keV) that will help maintain an ion population in the Fusor itself when operated in a low-pressure, low-current, high-voltage regime where thermionic emission from the grid is minimal.

A little picture is attached. This is a cross-section of the QF-25 half-nipple the source is built in. Gas enters through the hollow conductor of an HV feedthrough which is connected to a positive potential of several kV (not shown is that there must be an insulating conduit for gas between the gas source and the feedthrough, e.g. a piece of glass tubing). The gas is delivered into a gap by a fine needle, where a discharge forms and ionizes it as mentioned. In the drawing, the E field is in blue, the M field in green, the gas jet in red, and the discharge in magenta.

I've thought of many ways to improve this concept at the expense of some added complexity, but this will be the first trial.

Moving on to the other questions--I am going to put regular vacuum-pump paraffin oil in the socket. I don't foresee more than 150 watts going into the oil even at 2 kW of operation, and I think natural convection will be adequate.

-Carl


-Carl
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Richard Hull
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Re: Update: "Carl's Jr."

Post by Richard Hull » Tue Sep 19, 2006 5:27 pm

Nice idea Carl and while the ion current will be minimalist, it will be WHERE it can do the most good. That is significant in itself.

Nice ideas.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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