Beam on Target Project (BOT 2021)

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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Mark Rowley
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Beam on Target Project (BOT 2021)

Post by Mark Rowley »

This evening I finally had time to start work on the beam-on-target project. Boring out the 4x4” cube (target chamber) was the first order of business which took several hours to complete. Shown below is the initial rough cut. Polishing the outer and inner surfaces as well as drilling and threading screw holes for the CF flanges will take place in the next day or two. I’m shooting for a vacuum test by the end of the week.

Mark Rowley

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Richard Hull
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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Wow! Mark, you are on a roll here. I look forward to your results, as I am sure, others do too. You are a real buzz saw here, ripping into fusion with a vengeance. You and a couple of others are breathing new energy into the forums by the doing in advanced work.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Maciek Szymanski
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Re: Beam on Target Project (BOT 2021)

Post by Maciek Szymanski »

That’s substantial amount of chip making! Well done! What kind of ion source are you planning to use?
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Maciek, I plan to use a similar version to the RF source shown in this document:

https://hal.archives-ouvertes.fr/file/i ... 1481_0.pdf

It's almost identical to the one Carl Willis and others have experimented with years ago. Expectedly, there will be quite a few iterations as I get up to speed with the tech.

Regarding the chips, almost half a trash bags worth! But fwiw, making the cube was remarkably easier than boring out the 4" round for Fusor2020. Being almost half the distance I didn't incur the boring bar oscillation issue as I did with the fusor. It made for a much more enjoyable time at the lathe and only took 2-3hrs.

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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Yeah but working with a 4 jaw independent chuck is all about setup time for the first machining. Subsequent removals and rotations can involve little or no trouble seen at first set up. Still, if you have and odd piece, it has to be done. I always hated 3 jaw chucks and adapted a nice 6-inch, 6 jaw chuck to my chi-com lathe and spent a couple of hours getting the mounted eccentricity under 1 mil. I also bought a brand new 3 jaw for my Southbend K9. Its original old three jaw had seen a lot of wear since it was built in 1948.

For those curious about lathes used in construction of fusors my FAQ talks about and pictures them at..

viewtopic.php?f=24&t=11534

What Mark has done here, he notes as simple, but it is just a hair advanced for the novice. His noting his difficulty with the 4" cylinder fusor related to the depth his boring bar had to go into the piece unsupported at the cutting bit. This type of thing can create chatter or less that smooth results at the far end and may require flipping the work piece when done to clean up some roughness. Long boring on a lathe can be a test of skill and setup technique with many possible solutions. Those doing work with lathes like Mark, Jon Rosenstiel, Joe Gayo, Joe Zambelli, Maciek, myself and a couple of others over the years are rather rare here.

Special projects outside the norm, like Mark's BOT 2021 project, demand skills like this or big bucks to pay a machinist shop to turn metal into what you see as Mark's finished piece above.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Today’s update
Finished most of the drilling and tapping, polished the chamber walls, and fitted the KF25, feedthru, and viewport. Shipping has been sluggish for the 3.84” dia round stock for the end caps. Hopefully mid next week so I can perform the vacuum test.

While waiting on the those I’ll start work on the ion gun. I’m also thinking about machining my own “quick connect” flange for mounting the test tube. Paying $35 for the Lesker pro versions seems seems a bit excessive so I’ll give homebuilt a try first.

Mark Rowley

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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

A very polished interior. Shades of the famous Zambelli fusor. Getting there, for sure.
Joe Zambelli went on a polishing frenzy in 2001 check out all the images in the entire thread at

viewtopic.php?f=55&t=11184&p=73754&hili ... lli#p73754

The effort makes things look professional and folks appreciate the effort it takes to finish things like that.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Beam on Target Project (BOT 2021)

Post by Rex Allers »

Very nice work, Mark. What metal did you use for your cube?
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

6061 Aluminum, same as the fusor and I believe Jon's cube.

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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Mark, What kind of seals will be used. Viton gaskets? Indium?

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Everything will be Viton unless I need to go to indium for some reason. I still have almost all the indium sealing wire I bought from you in the mid to early 2000’s. Last use was a few months ago when I rolled some out for activation use.

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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

The 4” cube target chamber is complete. Vacuum test is awaiting the arrival of some additional Viton gaskets.

From this point forward I can begin working on the ion source assembly.

As pictured, the orientation is upside down. The insulator is actually the bottom and will be submerged in the oil socket. The ion source will be on the top.
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80DB42F4-D2AB-45D0-AD75-3E74B1A41281.jpeg

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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Fast work indeed. Thanks for the explanation on the physical embodiment.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

The ion source is mostly complete. All that’s needed is the gas inlet port and two small threaded terminals for extractor voltage. A thin ceramic washer will eventually be installed over the stainless extraction anode.

From this point forward I’ll begin building the microwave discharge cavity followed by the Ti target/electron suppression assembly.


The ion source is essentially the same Bayly design used by Carl Willis except that I’m using quartz insulators as opposed to the Ceramaseal insert. Since my custom compression fitting is very low profile the overall length is only slightly longer than Carl’s design.
C8720DBC-96FA-4C54-83D3-1F2AD62A128C.jpeg


This is a closer view of the stainless steel extraction point. Ultimately a thin ceramic washer will cover the anode (also stainless steel).
FEBB2D6A-F97E-4C50-8C90-EC7E44F5CBF6.jpeg


Side view showing HV insulator and viewport.
65021078-8858-48B2-B752-0E32DD11836F.jpeg

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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Keep wowing us Mark. This is great!

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Successful vacuum test of all components. Negligible leak rate and ultimate vacuum levels well below 1 mTorr.

Video of vacuum test
https://youtu.be/O_RsVLQL0io

8EE49DC3-DA21-4EEC-8553-D8BC1164B238.jpeg

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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

I decided to try something unique. Since I don’t have a WR284 waveguide to modify, I'll attempt the hardline coax route Doug Coulter used with his fusors ion source a decade ago. Except for some minor modifications, the NBS design parameters were followed (below pic):

AADF1431-5F1E-4B4E-9C99-5C071A5FF2BF.jpeg

It’s a fairly simple build so if it works then good. If not, well, then I had fun at the lathe so no real loss. At that point it’s just a waiting game till I find a suitable waveguide.

I decided to make mine out of brass and copper. Everything is polished both in and out to reduce the possibility of arcing. It has three tuning points. First is the tuner stub (black knob), second is the adjustable length of the 1/2” outer pipe (hardline outer conductor) and lastly (not shown) is a fine adjustment of the hardline center conductor length(+- 0.25” travel).

81AF0211-5CC9-4B6F-AAEB-04DE6C23C38E.jpeg


Here’s a rough mock-up of how it’ll fit on the discharge tube. The mounting plate for the magnetron has yet to be built so it’s just sitting there for the picture. Additionally, when operational everything will be positioned vertical. If mw leakage is a problem, additional screen shielding will be added around the discharge tube and coupling assembly. Folks who have used these NBS devices report minimal mw leakage however it won’t hurt or cost anything to add some extra protection.
D51D154B-4A0B-4296-8789-BF31969D60B6.jpeg


The power supply to run this will be a bit different than a typical oven configuration. I believe it’s been outlined on the site in years past but I’ll detail it a bit as I get to that stage.

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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

RF ionization is a great idea. I think most folks in the past just link coupled from a ham xmitter. This is really quite novel. I look forward to details and reports on how the slug tuning works. I had a forced 3 credit hours microwave course in college, just as the folks in RF specialization were forced to take one course in the digital realm. I hated it and all of us in the electronic computer focused engineering couldn't wait to toss those circular smith chart computer disks in the trash. We had a saying such that there was little separating any prowess in microwaves from the practice of black magic.

Much later, 25 years later at a hamfest, I purchased one of those monster microwave training kits in two huge black storage cases with every thing that a classroom dedicated to microwave instruction would need......Slotted lines, slug tuner, Klystron, wave guides with hardware, cross polarizer, small dish, three electronic boxes to drive and detect everything to read VSWR, etc. Was there a secret inner need to revisit that which I hated at one time?? Only the shadow knows. I had fun for a few weeks with it and now its two huge cases reside in the attic of the lab. I should have let Bob Reite see it at HEAS. He is a radio specialist.

When wavelengths of RF get extremely short backed by kilowatts of energy, you can get zapped by an unfortunate standing wave and wind up as a mismatched RF load.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Beam on Target Project (BOT 2021)

Post by Bob Reite »

Yes, I work with the stuff and consider the world above 900 MHz to be black magic.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

A testimonial from a man who makes his daily bread in the RF world. A long time lady friend who worked all her life at NRL, now retired, noted they worked at frequencies where they used an opaque phenolic fresnel lens to focus their near IR work! Black magic microwave optics.

Stay safe with your microwave exciter Mark! I know, you know, when you mentioned leaks and proper screening. Probably singing to the choir on safety issues in your case.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Being such an odd and potentially hazardous little device, the safety issues (if any) will be the first thing I’ll report on.

Progress wise, I finished the coupler this evening and am now moving onto the target / electron suppression assembly.

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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Spent about 4hrs last night trying to get the MW exciter to work. Nothing but arcs, hissing, and a very hot maggie. I know the Q is astronomically high so finding the sweet spot between all three adjustments might be the issue. The problem with this is reflected power. It’s so intense that one can’t just switch on the system and tweak the controls for a few minutes until the plasma ignites. Doing so would spell certain death to the magnetron.

I did get brief plasma ignition one time following an occurrence of arcing. Lasted for about 2 seconds until arcing occurred again.

The two places it’s arcing:
1) at the point where the hardline connects to the magnetron antenna.

2) between the tips of hardline and the tuning stub (if they’re close enough).

I fixed #1 by abandoning the machined copper conical antenna cap and instead directly attaching the 1/8” brass hardline directly to the mag antenna.

#2 only arcs when the tuning stub gets within 3mm of the hardline tip. And that’s only with a non-polished stub. The polished stub is a much smaller diameter and does not arc, however, it’s reduced size may is about 30% less than what the design calls for.

So today I’ll try a few more things. Larger polished tuning stub. I’ll separate the filament and HV between two xfmrs so I can throttle the hv. And lastly I’ll try to pre-ignite plasma so the mag can have an easier time latching on to a load.

I was able to land a W284 waveguide on eBay so if this utterly fails I can resort to that. But I won’t until I throw the kitchen sink at this one.

Last two points...
Negligible microwave leakage. Nothing detected beyond a foot from the device. And what is detected at closer ranges isn’t in the danger zone.

Pyrex or quartz discharge tubes have no effect on the above conditions. It’s 100% a reflected energy problem.

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Re: Beam on Target Project (BOT 2021)

Post by Joe Gayo »

Mark,

Have you considered hacking an existing microwave oven's waveguide setup?

I remember reading a BellJar article that discusses this and searched for it after reading your post - http://www.belljar.net/plasma.htm

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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

I'm familiar with the belljar article. After parting out a multitude of ovens over the years I've yet to see one with a waveguide as shown in Fig 2 and 4. In reality they only have a very small launcher ( a couple inches) which is incorporated within the oven cavity. Fig 3 could possibly work but I have yet to consider it. And lastly, due to being too bulky and kludgeworthy, Fig 5 is just plain unreasonable for this application.

It's highly likely the W284 will be the answer:

viewtopic.php?f=12&t=5047#p32355

https://www.youtube.com/watch?v=Zbsnf7XaFKs

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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Carl's three slug tuner sounds like a great idea. One slug might be too critical of adjustment. But what the heck do I know.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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