Testing a Machined Titanium Target
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Testing a Machined Titanium Target
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
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
- Richard Hull
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Re: Testing a Machined Titanium Target
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
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
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
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
- Liam David
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Re: Testing a Machined Titanium Target
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.
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Re: Testing a Machined Titanium Target
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
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
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Re: Testing a Machined Titanium Target
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!
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!
- Richard Hull
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Re: Testing a Machined Titanium Target
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
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
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
- Liam David
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Re: Testing a Machined Titanium Target
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.
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.
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Re: Testing a Machined Titanium Target
Titanium target in both endcaps results in lots of neutrons and makes for one happy fusioneer.
Jon Rosenstiel
Jon Rosenstiel
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Re: Testing a Machined Titanium Target
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
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
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: Testing a Machined Titanium Target
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
-Matt
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Re: Testing a Machined Titanium Target
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
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
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: Testing a Machined Titanium Target
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
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
- Emma Black
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Re: Testing a Machined Titanium Target
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?
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Re: Testing a Machined Titanium Target
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.
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?
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?
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Re: Testing a Machined Titanium Target
I do think a vent hole would be a good idea.
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Re: Testing a Machined Titanium Target
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
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
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Re: Testing a Machined Titanium Target
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.
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.