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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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.
48F25601-0D9E-4E2D-882F-B32C8D7D0CDC.jpeg
80DB42F4-D2AB-45D0-AD75-3E74B1A41281.jpeg

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

Post by Mark Rowley »

Success!
Typical, just as I was close to shifting gears towards the W284, it worked.

A couple things resulted in it working:

1) As Carl pointed out, running two transformers (one for the filament and one for the HV) is apparently the standard. Being able to throttle back the 600w magnetron was key to striking the plasma. Switching it on at full output caused debilitating feed line issues resulting in no coupling to the plasma. Lesson learned... a variac is the way to go.

2) The original tuning stub was machined at 4mm diameter. This was apparently too small so by increasing it to 6mm it widened the tuning range to a point where it would properly interact.

Specific to safety, the first 50% of the power range results in no detectable microwave leakage. However, going higher it begins to become problematic. Using brass screen totally fixed the issue. Once I get the screen shield cleaned up a bit I’ll post a pic.

One other quick point... the discharge tube is Pyrex. After 2 minutes of run time at about 60% power it only got warm. Eventually I have full intentions of using quartz, I just dont have any at the moment.


Plasma!
3362C766-3229-44AE-B525-F337DF628965.jpeg


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Re: Beam on Target Project (BOT 2021)

Post by Bob Reite »

Might be late to the discussion, it looks like you got it working, but I'd put in a circulator. That way, the magnetron would always see a good load, any mismatch would go to a reject load.
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 Rich Feldman »

Nice work, Mark!
As with motor-powered cutting tools and x-ray generators, the hazards of microwave power can be mitigated with knowledge, care, and instrumentation.


Re: "Bell Jar" figures 2 and 4.
By peculiar coincidence, the last two MWO's I broke down for recycling had sections of conventional rectangular waveguide between magnetron probe and cooker box.
(Conventional dimensions, but made from stamped sheet metal.) I knew that was common in 1980's units.
These are much more recent, I think both configured for "above the range" installation.
wave2.jpg
wave3.jpg
Oh, and there was one which had no turntable; waveguide ran under the cooker box & fed in through a dielectric floor plate.
All models are wrong; some models are useful. -- George Box
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Thanks Rich. I’ll keep looking for one of those ovens. I cringe at the thought of drilling holes in my newly obtained WR284.

Bob, a circulator sounds interesting. Could one be built without much machining?

Finished off the evening with a deuterium test. I was curious if there was any major difference with coupling which there didn’t seem to be.

Here’s a pic of the current mess with brass screening.
4CB8CEF2-C97F-4DD8-8B8B-4A5A5F93AAA6.jpeg


Brilliant Deuterium Plasma
BC15F552-141C-4A30-87B1-0B6E56DF806A.jpeg

All these shots were at 50% power input. No detectable microwave leakage.


And lastly, here’s a video of the system powering up with both air and deuterium.

https://youtu.be/-m--DU1LsYI


From this point forward it’s housecleaning before attempting beam extraction. Too much clutter and mess in the shop before I can safely move forward.

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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Great save Mark! WE are looking forward to reports on the BOT fusion results.

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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 John Futter »

Mark Well done.
You will find that you get a much higher ion current if you put a repeller electrode in the end of your glass tube 1500 - 2500 volts positive with respect to your cube potential.

during lockdown i made some microwave components for an experimental microwave furnace @ work. This is how a professional goes about getting microwaves to do what is required
thumbnail_IMG_20200730_145045.jpg
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Re: Beam on Target Project (BOT 2021)

Post by ian_krase »

This is fascinating work. Makes me ashamed for mostly sitting on my behind as far as the science goes these last several months.

I wish I was the equal of that machining for the ion gun -- do you have a cross section drawing of what you actually built?


I have only ever seen one other beam on target machine (Thomas Rapp's build) so this is very interesting. I've dreamed of one myself but doubt I will ever be working with the requisite voltage.


I'm curious -- why microwave rather than ICP?
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Thanks John. Wow, that’s the “neutron star” of dense workspaces! The sign on the wall is also quite appropriate. But I sure do like the waveguide arrangement and am slowly collecting pieces to get something similar.

Hi Ian
I’m pretty old school on my project designs. At best I have tattered pencil and paper sketches with rough measurements scribbled about. Mostly everything is in my head as I machine the parts.

This is Carl Willis’ drawing but it roughly depicts the extractor geometry. The big difference between mine is that I use quartz insulators instead of the Ceramaseal insert and no CF fittings.
8949087C-8826-413E-BC54-18301F367C01.jpeg
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Re: Beam on Target Project (BOT 2021)

Post by ian_krase »

Ahhh, it's built up out of tubing pieces and machined plugs? That could simplify things...

I'm still a bit dejected over the failure of my own Penning ion source attempt -- Andrew Setzman I am not.
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

“Plugs” Ian? I prefer the term “electrodes” lol!

Quick update
Extractor seems to work fine however the Pyrex tubing isn’t cooperating with the higher excitation power needed to keep the plasma alive below 10mTorr. Or, I could be that I haven’t learned to properly throttle the differential pumping arrangement yet. Either way, a decade ago both Carl and Doug made it clear Quartz is preferred over Pyrex due to arcing / heating issues. Tomorrow I’ll be ordering a couple sticks of 19mm quartz tubing. In the meantime it looks like a cheap diode met it’s maker on the HV psu. Easy fix but typical nonsense from the project gremlins.

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