Beam on Target Project (BOT 2021)

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

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


Mark Rowley
User avatar
Bob Reite
Posts: 576
Joined: Sun Aug 25, 2013 9:03 pm
Real name: Bob Reite
Location: Wilkes Barre/Scranton area

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.
User avatar
Rich Feldman
Posts: 1470
Joined: Mon Dec 21, 2009 6:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

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
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

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.

Mark Rowley
User avatar
Richard Hull
Moderator
Posts: 14976
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

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.

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
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

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
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

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?
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

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
Mark Rowley
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

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.
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

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.

Mark Rowley
User avatar
Richard Hull
Moderator
Posts: 14976
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Frustration and repairs are the norm when breaking new ground. We are taking notes due to your reporting your successes and failures, which is a good thing for us all. The pioneers always wind up taking the arrows in their backs. Those who follow owe them a great deal for blazing the trail.

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
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Oddly enough the power supply was good. Ended up being a faulty piece of insulation within the HV probe feed line. Being an easy fix I decided to press forward with a deuterium run.

Interestingly, getting a beam with deuterium was quite easy. Not so with regular air. Neutrons became sparsely evident around -15kV and at -27kV it was hitting around 5kcpm. During this short run the beam was unstable as I was trying to keep the microwave exciter at a level where it wouldn’t interact with the Pyrex. Doing so caused a bunch of flickering and very troublesome electron backstreaming. I’ve yet to install the faraday cup as it blocks the viewport. I’d like to get a few pictures before putting it in place.

As the run progressed, I began ramping up the target potential to -30kV. Surprisingly the titanium disc popped out of its holder and fell by the wayside. Almost assuredly it was caused by heat expansion and a set screw arrangement with no indentation (that’ll be fixed).

Instrumentation is extremely crude but will eventually get better. Extraction was at -3.5kV and beam current was well below 1mA.

Once the quartz tubing is in place and some X-ray shielding is arranged I’ll begin some activation experiments.

Neutron producing deuteron beam
BA0BC60C-A7A4-4A98-B34D-6EF8A6E87577.jpeg
BA0BC60C-A7A4-4A98-B34D-6EF8A6E87577.jpeg (25.29 KiB) Viewed 26682 times

Crowded BoT system with HDPE neutron moderator
82562872-6212-424D-8591-0C0B01B74F01.jpeg

Most likely I’m going to replace the lab jack with a simple wooden shelf. Doing so will remove obstruction from the viewport and allow for much easier X-ray shielding.

Mark Rowley
User avatar
Richard Hull
Moderator
Posts: 14976
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Great work, Mark. Once you get this rig really cooking it will be quite a coup, especially if it rivals or nearly equals the your fusor using velocity space volumetric fusion.

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
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Thanks Richard. That would be nice. I’m hoping for a platform that’s a bit more stable than the fusor during sustained high output runs. I’ve got some ideas for an easy to machine water cooled target. If this current iteration pans out and cooling is ultimately required, I’ll probably go in that direction.

This morning I removed the dislodged Ti target. Very little ablation but then again yesterday’s run was only a few minutes and quite intermittent. It’ll be interesting to see how it holds up under sustained / higher powered runs.

AE000D34-E706-4759-BC8C-AB89CF44EEC4.jpeg

Mark Rowley
User avatar
Richard Hull
Moderator
Posts: 14976
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Just curious. Is that a solid machined target or a standard 1 or 2-inch Al sample pan that is ridged? I assume it is solid of you own manufacture, but a pan is fairly flimsy and might move about if charged and not held down.

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
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Solid machined aluminum target holder. Not flimsy at all. Here’s a good shot of it with the Ti target seated in place. Due to the angle of the pic, the set screw is not easily visible (on the right side).

9817BC73-56CC-4A09-A92D-C1F0F6735A10.jpeg

The Ti target is about the size and thickness of a quarter.
The set screw wasn’t centered and it appears to have seated just above the lower edge of the target. So when it heated up, the tension caused it to snap out.

Details on the target:
Titanium (Ti) 24.26mm Metal Disc... https://www.amazon.com/dp/B07V3YL9X8?re ... b_ap_share

Mark Rowley
Jon Rosenstiel
Posts: 1494
Joined: Thu Jun 28, 2001 1:30 am
Real name: Jon Rosenstiel
Location: Southern California

Re: Beam on Target Project (BOT 2021)

Post by Jon Rosenstiel »

Mark,

Very nice indeed. Is your Ti target pure Ti or the usual 6Al-4V alloy?

JonR
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Thanks Jon
The seller claims 99.7% purity and no mention of any alloy content. His ratings are good so that's about all I can put trust in.

Mark Rowley
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Just some eye candy shots today while waiting on the quartz tubing.

This was a very low power run while I was learning how to maximize the differential pumping arrangement. As you can hear in the video I was getting a small smattering of neutrons (louder beeps).

https://youtu.be/sWgvnNpuL7k

Through the viewport
48084695-977B-4EEC-91FB-687594CB9F98.jpeg


The camera was on the inside wall of some lead shielding. Note the X-ray interference.
EA6B6264-C020-4197-A231-9BAB8619CD91.jpeg

Mark Rowley
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

Finished the ECR yoke and adjusted it to ~890 gauss at the center using a Hall effect magnetometer. It’s fairly stable within the 19mm diameter of the quartz tube and begins to change a bit as you get closer to the yoke.

This one part made a substantial difference at maintaining a plasma to 1mTorr and below. Even by opening the Varian HS-2 diff pump to full throttle I couldn’t extinguish it. This effect in concert with the crude capillary type differential pumping should make the ion source quite stable during sustained long term operation. Heating is almost non existent with the quartz and microwave leakage is zero when measuring past 6” from the exciter coupling.

Here’s the deuterium plasma with the TC gauge bottomed out.
D3FCAD19-97F5-4F1E-928A-2004D1B2996C.jpeg


Better shot of the ECR yoke with deuterium plasma at 50mTorr. This was taken before the yoke was properly dialed in.
42F75883-9453-495D-973A-CD0C849F768A.jpeg

Still lots to do. The magnetron supply is still in “oven” pulse mode but throttled back with a ballast resistor and a 0.2uF cap. The entire power supply will be re-arranged in a week or so to provide continuous DC. Just waiting for parts. Electron suppression is also on the immediate to-do list.

Gotta say, so far this project has been (and will continue to be) a phenomenal learning experience. I highly encourage anyone to proceed in this direction after the fusor. And what’s especially cool is the potential of applying this tech back to the fusor after ion source tech is learned. Lots of fun to be had.

Mark Rowley
Last edited by Mark Rowley on Sun Jan 17, 2021 4:29 am, edited 1 time in total.
User avatar
Richard Hull
Moderator
Posts: 14976
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

A learning experience or even a phenomenal learning experience is a great understatement! You will be richer for the effort, regardless. I notice the glass accelerator tube fluorescing due to UV. Now what wavelength? Long UV no problem. Short wave UV with glass again, no problem. Short wave UV with Quartz tube, a real problem. Vacuum UV with Quartz or glass probably not too bad. You know to how to suppress the x-radiation, I would be sure to avoid the UV once a Quartz tube is used.

The images are great and I love the work you are doing here.

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
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

After dealing with power supply issues I had some mild success getting the neutron count up a bit higher. This evenings run netted about 400cpm which translates to ~30k n/s TIER. Target loading in concert with increased gas flow (while keeping pressure at 1mTorr) seemed to play a big part. The initial “5kcpm” several weeks ago ended up being primarily interference from a previously undetected coronal spray that was a few inches from the HDPE moderator. Once mitigated a more sobering number of 50-100cpm was the average. At least now things are beginning to improve.

The bad news is that the 60kV precipitator supply finally gave up the ghost. 1.5 years on the fusor, a brief stint on the Columbus pinch machine, and now this has taken its toll. Unlike the fusor, the BoT requires the supply to run almost full tilt at low current. For whatever reason it doesn’t fare well in this environment so I’ll be transitioning to a decent voltage multiplier supply over the next month or so. I’m hoping to begin activating some foils soon after.

This doesn’t imply the precip supply isn’t good. It just seems more suited for a fusor. And once I resume fusor experiments (gunned?) I’ll be purchasing another 60kV unit. 1.5 years of decent performance was well worth the buck fifty.

1 mTorr deuterium plasma. No microwave detection past 7”. The color is actually more pink however it seems the UV fluorescence is reacting with the color.
C0ABBDB3-8D95-41C8-A7D8-FE4711F9E3E7.jpeg
Mark Rowley
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

After a month of shipping delays things finally began to arrive a few days ago. Latest significant mods were the build and installation of a 10 stage voltage multiplier (150kV max), beefing up the HV feedthru oil socket to withstand over 100kV, adding a 2.5meg HV ballast resistor, and most importantly an electron suppression target assembly.

The target is segmented in two by a quartz insulator. The ring on top shoulders the full potential while the target is about 400 volts less by using a TVS diode. The diode is tucked away under the assembly where there is little to no interaction with plasma. The suppression ring up top is the first iteration for testing. A second version with a smaller aperture and a longer shroud will be tested a bit later. The entire assembly easy disassembles for cleaning or swapping in different Target material.
1853B119-162C-4C81-AB7C-3E74ACD7E935.jpeg

This evening I was finally able to give things a run. Being a ZVS driven flyback/CW multiplier, my starting voltage is about 40kV. I have yet to accurately mark voltage increments on the variac so it actually started at about 50kV. Almost instantly I was registering 650cpm on the neutron detector (17cm from the target / CHM11 / Ludlum 2221). Removing the counter tube from the HDPE moderator dropped the count rate to zero.

By adjusting gas pressure and slightly raising voltage to about 65kV I was able to get 1200cpm on the neutron detector. Beam current was very low which I estimate around 10uA. I’m not totally confident with that measurement as it’s essentially the same arrangement I used for the fusor. I haven’t determined if the old analog meter is registering accurately on the 0.06mA scale.

Before using up of my charge of deuterium I placed the paraffin silver activation counter next to the target chamber. Normal background is 40-45cpm. After 3 minutes exposure the 1st minute of count time netted 70cpm. Minute 2 was almost back to background again. Not too impressive but it is a nice hint of activation. I may eventually switch it over to indium as the gamma spec component is a bit more telling.

Here’s the BoT with the paraffin silver activation counter sitting in front. It contains a LND7311 pancake with a sheet of silver foil over its face.
11350072-5B81-4B0C-A4A4-5E2531A1C28D.jpeg
Over the next few days I’ll work on getting the beam to load up the target as well as address a few limiting hardware issues. I think from this point forward it’s going to be a lesson on how to operate this thing and get all the different parameters dialed in.

I’ll be updating as the numbers increase.

Mark Rowley
User avatar
Richard Hull
Moderator
Posts: 14976
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Beam on Target Project (BOT 2021)

Post by Richard Hull »

Great work on this rather complex and interesting BOT system with a great history of development well documented, Mark. Others just starting out might take this long running thread to heart and give a rather constant update of your work to fusor.net. This is something newbies tend to forget. Instead, they burst onto the scene with a nearly functional demo system or in rare cases a virtual fusing system.
By a posting a good history like Mark has done, we get to see all the mistakes as well as the successes. This way if we wish to follow with a similar project, we would avoid stumbling into the same mistakes.

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
User avatar
Mark Rowley
Posts: 908
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley »

It’s been a few months since I’ve wrenched on this project but it was primarily due to the building of the custom fusor supply.

viewtopic.php?t=13907

Now that it’s complete, work can resume on the BoT project using the new supply as well as incorporating a few other upgrades. Primarily, the first order of business will be to use a deuterated titanium target. If results are promising, a few changes to the ion source and electron suppression assembly are planned. I’ll detail those as the time comes.

Regarding the manufacture of a deuterated target, it require a special yet somewhat simple apparatus which I’ll detail in a separate thread located here:

viewtopic.php?t=14055

Examination of the non-deuterated Ti targets reveal a well collimated beam of slightly less than 1mm. Of note, this particular photo is from an earlier Ti target with no electron suppression and only about 5-10 minutes of run time.

A9BECDF5-5EF7-4CFF-AE22-EDC2E8942FF6.jpeg



Mark Rowley
Post Reply

Return to “Ion Gun Design and Construction (& FAQs)”