Testing a Machined Titanium Target

For posts specifically relating to fusor design, construction, and operation.
Post Reply
Jon Rosenstiel
Posts: 1494
Joined: Thu Jun 28, 2001 1:30 am
Real name: Jon Rosenstiel
Location: Southern California

Testing a Machined Titanium Target

Post by Jon Rosenstiel »

For the past couple of weeks I’ve been testing a titanium target on my cube’s right-hand endcap. The target was machined from a piece of ¾” round-stock grade-2 (commercially pure) titanium. Target thickness is 0.040" (1 mm) Stem diameter is 5/16". So far results have been very encouraging as NPR nearly equals that achieved by the titanium sputter-coated copper endcaps I recently destroyed.

I used a loop of 0.025” indium wire between the backside of the target and the endcap’s machined recess as the vacuum seal. (And heat transfer medium)

Funny story about how I ended up using an indium as a seal. I was Googling heat transfer compounds for vacuum use and indium popped up as a solution. I vaguely recalled that indium’s melting point was kind of low but couldn’t remember exactly how low. I found an online table for melting temperatures of metals and it told me that indium’s melting point was 2450 C. To me that was really good news and I went ahead with the indium seal. About a week went by and the seal was working well but I still had concerns about that 2450 C melting point, just didn’t sound right to me. So, I again looked up indium’s melting temperature and discovered I had been looking at iridium, not indium! Dang failing eyesight! Had I initially known indium’s melting temperature was 156.6 C I most likely would not have used it and gone for an o-ring seal on the target’s stem.

Today I ran a 1-hour test at 600 W input (40 kV, 15 mA). With the chiller holding 5 degrees C endcap temperature leveled off at just over 50 C. Total runtime so far has been 6.5 hours, an hour and half of that at 600 watts input. So far, so good.

Peak TIER from today’s runs.
30 kV, 10 mA, 300 W: 1.2E+06 n/s
40 kV, 10 mA, 400 W: 3.6E+06 n/s
40 kV, 15 mA, 600 W: 4.2E+06 n/s (Runtime = 1-hour)
50 kV, 10 mA, 500 W: 7.6E+06 n/s
58 kV, 7 mA, 406 W: 8.8E+06 n/s (same variac setting as previous run)
60 kV, 10 mA, 600 W: 1.3E+07 n/s

Jon Rosenstiel
Attachments
Titanium target
Titanium target
Assembly
Assembly
Ready for installation
Ready for installation
Air side view
Air side view
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Testing a Machined Titanium Target

Post by Richard Hull »

Jon, I think you found indium's boiling point. However you corrected that. I work with indium seals in my vacuum work all the time and as long as you keep materials at or just above the boiling point of water, you are good to go with indium seals. 50:50 tin indium will still wet glass and porcelain but has a much lower melting point. Indium is a great vacuum seal as its vapor pressure is near zero up to its melting point. The huge boiling point of the metal means vapor pressure doesn't really exist until incredibly far above its melting point.

Unfortunately, being in contact with the hot target Ti, even good cooling would melt the indium.

For those interested in seals that can be keep under 100 deg C, the vapor pressure of molten indium at 157 deg C. is 10e-18 mbar!!! How low can you go!!

Jon, Your machine work is great and I am glad you made a sacrificial Ti target. Now to get a 5/8 rod of Pd. LOL.
Another fabulous report on your cube's ability to turn out the neutrons. You are approaching what a small neutron accelerator tube can do at far reduced voltages. Pulsed sources at 100kev are struggling to hit your continuous levels.


Richard Hull
Attachments
Equilibrium-vapour-pressures-for-In-and-Zn-in-the-200-800-C-temperature-range-data.png
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
Liam David
Posts: 518
Joined: Sat Jan 25, 2014 5:30 pm
Real name: Liam David
Location: PPPL

Re: Testing a Machined Titanium Target

Post by Liam David »

It's interesting that the neutron rates between the coatings and solid targets are essentially the same. The surface temperature of the solid target would have been pretty high, limiting the deuterium target density and growing a thick titanium oxide. The coatings should have performed much better unless something else was going on.
Jon Rosenstiel
Posts: 1494
Joined: Thu Jun 28, 2001 1:30 am
Real name: Jon Rosenstiel
Location: Southern California

Re: Testing a Machined Titanium Target

Post by Jon Rosenstiel »

Richard,

What I initially, and mistakenly, found was iridium’s melting point. (2450 C) I was looking at a table of metals melting points and my old and fuzzy vision eyes played a trick on me, thought I was looking at indium’s melting point when in fact I was looking at iridium’s melting point. Thankfully, it all worked out in the end.

I removed the Ti target (took two or three taps with a small hammer to break it loose) and everything seems ok, but not sure what I would see if the indium had melted. Images below.

Jon Rosenstiel
Attachments
Endcap
Endcap
Target
Target
Jon Rosenstiel
Posts: 1494
Joined: Thu Jun 28, 2001 1:30 am
Real name: Jon Rosenstiel
Location: Southern California

Re: Testing a Machined Titanium Target

Post by Jon Rosenstiel »

Liam,

The something else going on is the smaller cathode I’m now running.
I removed the endcap last night, below find a couple of pix of the target. Width of the beam pattern (at its widest point) is 2.1 mm, length is 5.3 mm.

Jon Rosenstiel

Wow, the target's closeup makes it look like it was drug down a gravel road!
Attachments
IMG_1585.JPG
IMG_1587.JPG
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Testing a Machined Titanium Target

Post by Richard Hull »

Again indium vapor in the fusor could not exist to interfere with D-D fusion as its vapor pressure at 600 deg C. is still under 10e-6 torr. No issues with molten indium in a fusor.

Good seal for your Ti target would be a specially hand annealed, super soft, ring of copper wire.

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
Liam David
Posts: 518
Joined: Sat Jan 25, 2014 5:30 pm
Real name: Liam David
Location: PPPL

Re: Testing a Machined Titanium Target

Post by Liam David »

I'm not convinced that the smaller cathode is making up what should be a much larger difference between the solid target and coating. The 20% is a far cry from the difference I would expect given the titanium deuteride isobar/isotherm curves and the mobility of deuterium in titanium. I think it's oxides and the rapid destruction of the coatings that bring them into the same ballpark... I'll have to expand on what I mean at a later date.

The white stuff in the beam spot is almost certainly titanium oxides, which will significantly reduce the deuterium neutral/ion energy before it hits the titanium deuteride metal surface. This tells me that you have lots of water vapor or other contaminants in the beam, and by lots I mean >>1e-8 torr. Bakeout at 100C at 1e-6 torr can also trash your coatings. The whole situation is just really unforgiving.

The divergent motion of negative ions may also result in a significant proportion of fusions occurring away from the center of the titanium. The cooler temperatures and thinner oxide would help out significantly.
Jon Rosenstiel
Posts: 1494
Joined: Thu Jun 28, 2001 1:30 am
Real name: Jon Rosenstiel
Location: Southern California

Re: Testing a Machined Titanium Target

Post by Jon Rosenstiel »

Titanium target in both endcaps results in lots of neutrons and makes for one happy fusioneer.

Jon Rosenstiel
Attachments
Endcap comparisons
Endcap comparisons
50,000 + cpm Ag activation. 70 kV, 6 mA, 16.1 mTorr, 6-minutes at 1.9e7 n/s
50,000 + cpm Ag activation. 70 kV, 6 mA, 16.1 mTorr, 6-minutes at 1.9e7 n/s
Last edited by Jon Rosenstiel on Tue Dec 06, 2022 2:04 pm, edited 1 time in total.
User avatar
Emma Black
Posts: 198
Joined: Wed May 11, 2022 9:42 am
Real name: Emma Black

Re: Testing a Machined Titanium Target

Post by Emma Black »

wow, what a difference! This is with an aluminium fusor? I wonder if SS would be slightly better than the Std.

Have this waiting to try out via electroplating:
Image
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Testing a Machined Titanium Target

Post by Richard Hull »

Fabulous effort Jon! Great results and shows that in the cube dual targets of Ti result in more fusion. To be significant electrostatic targets, they would need to be elevated slightly above the CF flat holding them. Otherwise, some of the beam energy would go into the SS in the same plane, inspite of the indicated beam spot. Very nice, indeed.

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
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Testing a Machined Titanium Target

Post by Matt_Gibson »

I might have to keep my cube chamber and do some experiments myself after this. I wonder if I could just “stick” some titanium sheeting inside the end caps instead of having to machine something (I have no experience with machining anything)?

-Matt
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Testing a Machined Titanium Target

Post by Richard Hull »

I would imagine heating would be an issue with simple sheeting or foils. Jon's flush mount is in full sinking contact with the cooled target end cap CF flange, and the titanium, itself has some attached mass in the target stud threading post. Any beaming will rather intensely, locally heat any target.

Still, you can always give it a whirl.

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

Re: Testing a Machined Titanium Target

Post by Jon Rosenstiel »

Emma,

If I made an exact copy of my aluminum cube out of stainless steel I suspect it wouldn't work as well because of its very poor thermal conductivity. (The water-cooling channel machined into the cube's base would be pretty-much useless)

Jon Rosenstiel
User avatar
Emma Black
Posts: 198
Joined: Wed May 11, 2022 9:42 am
Real name: Emma Black

Re: Testing a Machined Titanium Target

Post by Emma Black »

That makes sense, the cooling for my little steel cross is pretty rubbish. I suspect electroplating pd will get ruined by the beams before it gets a chance to load up but will report back anyway. Has anybody tried using a Ti sublimation pump?
User avatar
Emma Black
Posts: 198
Joined: Wed May 11, 2022 9:42 am
Real name: Emma Black

Re: Testing a Machined Titanium Target

Post by Emma Black »

Since I've found that I have a bar of titanium, feel like giving this a try. This will be my first time machining titanium at home.

Image

My fusor is stainless however, for now at least, so think I'm just going to try and add some thermal mass by making the target wider and thicker. Rather than go all the way though the endcap and tighten from the other side with a nut, was thinking of a blind tapped hole. Do you think I would need to add a small hole to act as a vent to help with virtual leaks?
Jon Rosenstiel
Posts: 1494
Joined: Thu Jun 28, 2001 1:30 am
Real name: Jon Rosenstiel
Location: Southern California

Re: Testing a Machined Titanium Target

Post by Jon Rosenstiel »

I do think a vent hole would be a good idea.
User avatar
Emma Black
Posts: 198
Joined: Wed May 11, 2022 9:42 am
Real name: Emma Black

Re: Testing a Machined Titanium Target

Post by Emma Black »

Image
Image
Image

An interesting little experiment, after testing for couple of weeks I got a small increase, 10-15% in peak neutron counts. However the cooling was terrible and after a few minutes the current started to creep up and neutron counts would also drop, but this was kinda expected.
Jon Rosenstiel
Posts: 1494
Joined: Thu Jun 28, 2001 1:30 am
Real name: Jon Rosenstiel
Location: Southern California

Re: Testing a Machined Titanium Target

Post by Jon Rosenstiel »

Pretty neat Emma, but I don't understand why your titanium looks like copper.

And FWIW, I recently ran a test comparing commercially pure titanium to 6Al4V alloy. (One of the cube's endcaps had a CP titanium target, the other the 6Al4V target) NPR was down about 15% with the 6Al4V alloy. Had both targets been 6Al4V NPR would have dropped 30%, or maybe more.

JonR
User avatar
Emma Black
Posts: 198
Joined: Wed May 11, 2022 9:42 am
Real name: Emma Black

Re: Testing a Machined Titanium Target

Post by Emma Black »

Your right it does, especially in the photo of the block, ha! Its nothing more exciting than the very warm colour temp of the lighting in the office. Looks normal in daylight or white light.

This is 6Al-4V - I wondered what the difference might be in terms of NPR. I'm going to add two and PD plate it next as soon as some active cooling is sorted.

Image
Post Reply

Return to “Fusor Construction & Operation (& FAQs)”