Apparatus for Making a Deuterated Target

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Mark Rowley
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Apparatus for Making a Deuterated Target

Post by Mark Rowley »

Slowly assembling an apparatus to make some deuterated targets. This is somewhat based on Timothy Koeth’s arrangement shown in this link:

http://www.nuclearphysicslab.com/npl/np ... eparation/

Key differences being the use of induction to heat the material, PEM cell deuterium, and a heating vacuum that’s initially not going to get below 10mTorr. It’s highly desirable to get the vacuum deeper than 1mTorr however I’m not quite ready to hook up the diff pump until confidence is established with the quartz tubing. So for now, 10mTorr will be it. Im assuming the less pure result will still be considerably better than a non-deuterated piece. Subsequent testing will definitely answer the question.

Still have a few things to make before this is operational. Custom flange, quartz tube end cap, custom “quick connect” fitting, safety enclosure, and the induction heater arrangement.

Here’s a crude assemblage of parts which loosely represents the arrangement I’ll be using.

BA73DDF7-938B-4ED0-9C73-5EB7A83D364A.jpeg
Vacuum inlet on the right.

As this progresses I’ll periodically update.

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Richard Hull
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Re: Apparatus for Making a Deuterated Target

Post by Richard Hull »

Great work in "leading the way"... I can hardly wait for the 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
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Re: Apparatus for Making a Deuterated Target

Post by Mark Rowley »

Since I’m limited to 100-200mL of deuterium, I may discard the voluminous T fitting (circled) and feed gas through the exposed left end of the quartz tubing.
F606DAB7-9643-4620-A5D9-2009E8A992BB.jpeg
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Re: Apparatus for Making a Deuterated Target

Post by Richard Hull »

I was a bit worried about the volumes involved when I saw the syringe there. Even with tanked Deuterium, keeping the volume limited in the feed system is the thing to do or shoot for.

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: Apparatus for Making a Deuterated Target

Post by Dennis P Brown »

Once you pump down, you close off the system and allow the deuterium to raise the system to its desired pressure, that extra 'T' isn't going to have much an impact; calculate the total volume for "zero torr". Then the volume of gas in the syringe - I bet the amount in the syringe is well above 10 mTorr for the final volume. Likely you will use far less than that syringe volume.
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Re: Apparatus for Making a Deuterated Target

Post by Mark Rowley »

Quite true Dennis. In fact it’s way more than enough to put it well above 1000mTorr. I’m more or less caught up with Tim’s end goal of positive pressure. Not something I’m planning on doing (and cant with a syringe), but establishing 1atm would be a second best.

Lots of room for experimentation.

Machining is going faster than expected. Good possibility of a first run in a couple of days.

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Re: Apparatus for Making a Deuterated Target

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Finally finished with the machining end of things. Custom made parts are the gas inlet fitting with o-ring and the quartz tube “quick connect” flange assembly. Not shown is an interchangeable 0.75” hose barb / KF25 flange for the vacuum. Hose barb fitting is used with the Yellowjacket roughing pump and the KF25 in case its ever hooked up to the diff pump.

The next bit of construction involves building a stable mounting bracket for the assembly, a protective safety shield to cover the quartz tube, and the electrical hook ups for the induction coil.

Note: The quartz tube shown in the picture is for fitting purposes. The tube used during operation will be more than double the length.

A268644F-F6A9-4FF6-9418-33659B860DC9.jpeg

D063092B-DA24-42F3-9AE5-85FD3D57437E.jpeg

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Re: Apparatus for Making a Deuterated Target

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As somewhat expected, the induction heater isn’t sufficiently heating the thin titanium strips. Some improvements were gained with different coil configurations but nothing good enough to hit 1k deg C. No big deal though, constructing an adequate tube furnace is remarkably simple. I’ll be detailing the build in a few days.

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Re: Apparatus for Making a Deuterated Target

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While waiting on parts time was spent fabricating two thermal dissipators for the quartz tube. The hope is that they can cool the tube enough to prevent damage to the o-rings on each side. During operation the dissipators will be cooled with forced air. If they don’t work then it’s just a matter of ordering a longer quartz tube.

A571C82F-9C73-43BA-9500-320AFD5E1009.jpeg

CB4083A5-9DB5-4848-99B5-57026C56171D.jpeg

952749D7-3AFB-4CBF-A24E-FDC53E089B80.jpeg

F1690AEC-E020-4E59-9E0A-EB5927F58C65.jpeg

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Re: Apparatus for Making a Deuterated Target

Post by JoeBallantyne »

Very nice work Mark.

It would be cool to see a video of that tube furnace in operation.

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Re: Apparatus for Making a Deuterated Target

Post by Mark Rowley »

Custom o-ring seals are doing great. Deepest vacuum with the Yellowjacket pump has been 7mTorr which means a secondary diffusion pump would bottom this out to sub-milliTorr levels with ease.

9mTorr is after about a minute of pumping time.
D3EF3112-4179-43A3-9972-2B2164C999A6.jpeg
Later today will be a stress test of the viton o-rings under heated conditions. Fairly sure I’ll be needing a longer quartz tube.

Here’s the tube furnace which will be incorporated with the setup. Operational temps will be roughly 900 Celsius. My concern with this arrangement is it’s considerably slower cool down time. A redesign allowing for an immediate drop-down arrangement may be required.
DCF66817-50BB-413A-9CAD-54644CB32E89.jpeg
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Re: Apparatus for Making a Deuterated Target

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So far a surprising success. The o-ring areas remained very cool with forced air blowing over the heat dissipators. Even at 900 Celsius neither o-ring area exceeded 35 Celsius (95F)… even after several hours.
6800B259-B9AC-479F-A96F-6CC179E4436E.jpeg

Shown here is the back side of the furnace with forced air blowing over the dissipators. The glowing red alumina heating element can easily been seen in this shot.
636999A7-24E2-457C-A8FD-1241C24019D8.jpeg

This is a comparison between a treated and untreated piece of titanium sheet.
64288EE6-12EE-46B2-8DD1-F45E0A30E885.jpeg

Being a first attempt, the system was gently operating at a reduced duty cycle. The titanium was only maintained at 900 Celsius for just under 2hrs. 100mL of deuterium was not enough to bring the chamber up to 1 atm, but it got fairly close. In the future I’ll use a 150mL reservoir and push the heating duration closer to 3 or 4hrs.

As of now the next step is to install the treated titanium in the fusor.

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Re: Apparatus for Making a Deuterated Target

Post by Richard Hull »

This is fabulous stuff! You really lay it out with a great balance of plenty of images and explanatory text. I remain amazed at your doggedly pursuing the issues that interest you and those of us witnessing your many and continued efforts. A shining example of open source sharing.

You note the 7mtorr yellow jacket number. That is what I got at my best with my old yellow jacket pump on fusor II and III. For a well kept refrigeration pump they are rather fantastic. One of the few I ever had that performed on a par with a good welch belt drive, (which I consider the gold standard).

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: Apparatus for Making a Deuterated Target

Post by Mark Rowley »

Thanks Richard. It’s a definitely a fun pastime, and yes.. the Yellowjacket is a great pump. Thanks again for the recommendation! It must’ve been around 2002 or so.

RESULTS
I decided to install the titanium in the fusor by using a slide-in aluminum sleeve.
B2EE93F5-63E9-44D4-A82E-235526838B92.jpeg
Even though the fusor is water cooled, I expected this to heat up rather quickly causing the typical associated issues. There’s just no way to firmly attach the titanium to the cooled fusor wall without extensive machining.

So today’s run provided promising yet inconclusive results.
For a freshly opened chamber and subsequent pump down, the fusor instantly yielded a TIER of about 5.4E+5 n/s at 55kV / 0.3mA!! Never before have I seen those numbers at such low current and within seconds of switching on the power.

So here’s where it became expectedly troublesome. As I ramped up the voltage and subsequent current, it began to plateau just under 2E+6 n/s. Increasing the voltage any further resulted in a diminished neutron yield. This was not the case under normal conditions as any increase of voltage resulted in considerably more neuts. It’s fairly clear target heating was poisoning the conditions within the fusor. It’s somewhat reminiscent of how things behaved before cooling was added to the design.

So where to go from here? Well, I still have some unrelated projects to complete with Fusor2020 so I’ll remove the titanium target and restore it to normal operating conditions. Once done with the other projects (psu modification and Maciek’s track detectors), Ill make some new deuterated target material and install it in the BoT for testing. Afterwards, a cube fusor may be in the works. Seems like it’d be easy to make water cooled endcaps where titanium targets could be firmly secured to their respective chamber sides. A cylindrical grid would be used to create opposing deuteron beams to hit each deuterated target (similar to Jon’s titanium coated endcap design. Definitely no shortage of projects for the foreseeable future!

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Re: Apparatus for Making a Deuterated Target

Post by Dennis P Brown »

Truly a great effort, fantastic equipment builds, and excellent reporting.

I am not sure this would be a good idea but electrically conductive silver epoxy would readily hold the Ti strip to the chamber wall and maintain the strip at wall temperature, of course. But you'd end up with silver on the walls if you removed the Ti strip. But it would readily hold the strip even under vacuum (I've used the stuff to mount targets in a sputtering system.)
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Re: Apparatus for Making a Deuterated Target

Post by Mark Rowley »

Thanks for the kind remarks Dennis
For a multitude of reasons the fusor has been completely disassembled and probably wont be fired back up again for quite some time. However, when some domestic renovation projects are complete the plan is to go 110% into beam on target systems. The aforementioned results at 0.3mA with a deuterated target make it blazingly clear which system will provide a more substantial neutron yield. As with Richard, I've only viewed the fusor as a source of neutrons for activation experiments. As done in the past, it's really fun meshing this hobby with gamma spectroscopy. With the fusor I just started to tickle molybdnum for TC99m before I reached the capacity of the psu. But with the 0.3mA observation, BoT systems with a deuterated target and relatively simplistic PSU hold high promise for activations beyond Molybdenum.

Like a classic 1950's BoT system, the Fusor too is just a different form of neutron generator, not a fusion energy device that holds promise to generate electricity. The deuterated target was impressive enough that retooling and moving forward towards a water cooled BoT is the only way to go, at least from this stage. It's not a project I'd recommend to anyone new in the Fusor hobby as just about everything has to be custom made.

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Re: Apparatus for Making a Deuterated Target

Post by Richard Hull »

Very wise words regarding the complexity and required skills to follow your path, Mark. I liked your admission related to using the fusor as a neutron source for activation. Ever since I was in college I wanted to do activation experiments. In college at 18 I already had 5 years of monkeying with radiation and various isotopes supplied by Abbott labs in Oak ridge. You could get those in chemical form back then. Neutrons are jealously held by all atoms and it takes a bit of doing to get enough to really experiment with activation.

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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