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 » Tue Jan 05, 2021 7:51 am

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
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Re: Beam on Target Project (BOT 2021)

Post by Jon Rosenstiel » Tue Jan 05, 2021 4:54 pm

Mark,

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

JonR

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

Post by Mark Rowley » Tue Jan 05, 2021 5:30 pm

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.

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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley » Sun Jan 10, 2021 10:19 pm

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

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

Post by Mark Rowley » Sun Jan 17, 2021 4:43 am

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 9:29 am, edited 1 time in total.

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

Post by Richard Hull » Sun Jan 17, 2021 8:58 am

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley » Wed Jan 27, 2021 2:36 am

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
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Re: Beam on Target Project (BOT 2021)

Post by Mark Rowley » Thu Feb 25, 2021 8:16 am

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

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Re: Beam on Target Project (BOT 2021)

Post by Richard Hull » Fri Feb 26, 2021 12:22 am

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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

Post by Mark Rowley » Fri Jun 18, 2021 2:22 am

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



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