Finn Hammer, fusor update.

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Finn Hammer
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Finn Hammer, fusor update.

Post by Finn Hammer »

My cube fusor was presented in the construction forum, viewtopic.php?f=6&t=13857 , but from now, I will use this thread to report progresss and setbacks.

At present, this is not a fusor, but rather the pumping station for the fusor to be mounted on. I am trying to see, if the vacuum gauges that I have are in calibration, and also getting my first experience with a system that can potentially go below the ~10 microns that the fore pump appears to can produce.

Both Baratrons that I have (0.05 Torr) produce 13.31 volts at atmospheric pressure, and this worries me, since the manuals all site 0-10V

Is this normal??:


I hooked the Horizontal Baratron with the intension of using it as the standard with which I would judge the other transducers that I have, one 999Quadro and four 901P's.

Without any data collecting soft or hard -ware at hand, I took notes with pen and pencil, transferred it to Excell and got these curves:
transducercurves.JPG
The lack of data on all but blue and orange is due to that was the time I turned the turbo on, and the pressure dropped so fast I was unable to record it.
Blue line is baratron voltage out, the orange line is the pressure assumed by the 5 microns/volt ratio of the Baratron output. The other curves show the 999 and the 901's, and since they are all quite similar, chances are that they are the ones that come closest to calibration.

I have my experience with mechanics and electronics, I am used to micrometers, gaugeblocks, Pearson current monitors and the like. tools that show remarkable accuracy.
So I am not impressed so far, with these gauges.
Another thing: When I assembled the thing, I did wash with acetone, but was otherwise not so carefull, like wearing gloves etc. and this may be the reason for the mediocre ultimate pressure which is around one micron.
Tomorrow, I will take it all apart, clean thoroughly, wear glove,s fit all new Viton o-rings, and bake the parts before assembly, then we will see a better vacuum, I hope.

When I sealed off the valve between the turbo and the gauges, the pressure rose 1torr in 4 minutes. Leak or outgassing? time will tell.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Sounds like out gassing, but might be a leak. Cleaning is important, but the turbo should yank the pressure even with a tiny leak to submicron pressures. You gotta' get the embedded moisture pumped out once the system is sealed. Oh, please label the x & y axis units in future.

All the Baratrons I have read 10v +/-.1 volt at atmosphere.

Richard Hull
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Fusion is the energy of the future....and it always will be
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

I have some better data now.

I dismantled the assembly, washed it, dried it in the oven at 150 degC

Vacuum parts in the oven
Vacuum parts in the oven

I fitted all new Viton 0-rings and put it together again.
Started up the pumps: same thing, stuck at 2 Microns.
This had me biting my nails for some while, after all, I am only pumping a few tubes, a valve and a cross, right?

Just a couple tubes, a valve and a cross..
Just a couple tubes, a valve and a cross..

It is all (mostly) spanking new and shiny:


New and shiny
New and shiny


I would have thought this warranted better results.....
Then It dawned on me: Due to old assumptions, from when I built the 901P readouts, I had set the supply to 9Volts for the 901P's and the 999 Quadro. This was wrong, of course, on the part of the Quadro at least, which requires 24V, otherwise it stops dead at 2Microns, instead of turning on the filaments for the hot cathode sensor, and track the pressure all the way down to system base level.

RTFM! What a blunder.

Anyway, with this insight under the belt, I made a couple of pumpdowns, the first with only the rotary pump, which is an Alcatel 2005 SD, this brought the pipes, valve and cross, down to 5 microns in 27 minutes, and after one hour it levelled off at 4.7 microns. I seem to have read elsewhere, that this is not an unreasonable number, so for now, I will trust the 999 Quadro.
And I will treat that fine instrument to an oil-free pumping regime, a Pfeiffer MVP 015-2 is on the way home to me.

Back to atmospheric, I recorded data for this chart:


Had some problems labelling the axis, Excell has advanced too far for me.
Had some problems labelling the axis, Excell has advanced too far for me.

After 10 minutes the pressure is 13 Microns, so I turn the turbo on. 1 1/2 minute later, the turbo is at half speed and the pressure down to 3.4E-6. At 13 minutes, turbo is at full revs, and pressure is down to 2.1E-6.
At 30 minutes, the pressure crosses a magic line (to me at least) plunging to a low 9.7E-7.
At this point I turn off the turbo and close the throttle valve, only to see this high vacuum vanish in 60 seconds, where the pressure is up to 1 micron again.
At this point, it takes 17 minutes to reach 10 microns.
I have no explanation to the kinks on the curve both down to, and up from sub-micron levels.

While I write this, and struggle with Exells obsessive auto format of cells, the pumps have been evacuating the pipes, and this is what I saw coming out to the workshop:

3 hours of pumping brought the pressure down to 1.7E-7

I will let it be up to you more experienced guys to judge if these numbers seem plausible.

Down to 1.7E-7, and the x-axis label is still screwed, sorry for that
Down to 1.7E-7, and the x-axis label is still screwed, sorry for that


I am feeling good now, and think I am where I should be, and that my investments in gear and time has not been in vain.
The 2 Baratrons: They are shot (and I can't even sell them on EBay, now that I know it). Pull them apart to see how they are stuck together, probably.
So I am still on the market for a reasonably priced, and well calibrated 100 micron Baratron.

Around 3 years ago, there was a guy posting here, I think he had an Italian sounding name. He built his system in CAD, and showed very meticulously how to calculate the expected system performance beforehand, based on conduction, gass load etc. I would like to reread his posts, but can't find them. Any pointers are much appreciated.

Cheers, Finn Hammer

Edit, and now, 2 hours later, 7.9E-8
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

You are there and more!! One might not expect these low pressures with a normal arrangement. They are fabulously low and you have no significant issues with vacuum at this point. Time to throw on the cube.

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Fusion is the energy of the future....and it always will be
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Re: Finn Hammer, fusor update.

Post by Chris Mullins »

That sounds like Michael Bretti (memberlist.php?mode=viewprofile&u=4025), and this thread on his vacuum systems: viewtopic.php?t=12114.

He has more more details on his website: https://appliedionsystems.com/vacuum-systems/
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Thanks to Chris for the heads up regarding Michael Bretti.

I received the Pfeiffer MVP 015-2 diaphragm pump today, it was really as clean as can be on the outside. I will be talking mBar today, since the pumps ratings come in mBar from Pfeiffer

Sweet little pump.
Sweet little pump.

The vacuum fitting on the inlet of this pump was a push-fit connector of the type that comes out of the catalogue for pneumatic components, so I turned right adventurous, and connected this fitting to a KF-16 welding fitting, with (god forbid it!) Glue lined heat shrink. This worked well enough, though, but then this kind of pump does not dive into the deep pressures, it is rated at 3mBar. Here is the fitting I made:
Fast and furious vacuum fitting. Heatshrink with glue, a new trend in foreline plumbing?
Fast and furious vacuum fitting. Heatshrink with glue, a new trend in foreline plumbing?

When I stuck a 901P pirani gauge on to it (and nice, too, not to have to worry about any oil contamination from the pump) it showed a discouraging 14mBar, not good, for a while I regretted to have bought a used unit from the other side of the globe.
A quick call to Pfeiffer, Denmark, revealed that the repair kit would cost the same as the pump had cost me up to now, so I tore it apart and found, as I feared, dirt and corrosion.
However, after a good rubbing off with alcohol, the surfaces showed only a slight trace of the corrosion, so I gave the valves (which are just tiny rubber flaps) and the inside of the housing a thin smear of Apiezon M, which I then wiped off as much as possible, and assembled the pump again.

(Disclaimer: I was in full mental controll, I did not panic, and I _did_ _not_ _slather_ that Apiezon M on the pumps internals ;-) ).

That half hour was a valuable investment, because the ultimate pressure of the pump lowered to 1.8mBar without ballast, 2.2 mBar with Ballast, which is better than rated from a new unit.

So far so good, but I have only run the Pfeiffer THM 071 turbo with amble backing from my large Alcatel 2005 rotary vane pump, at < 1E-2mBar, so how is it going to fare against the much higher pressure of the diaphragm pump?
Throtteling down the Alcatel, I recorded this curve, where I measured the current draw of the turbo pump controller against foreline pressure.

How the current draw of the controller on a Pfeiffer THM 071 turbo relates to foreline pressure.
How the current draw of the controller on a Pfeiffer THM 071 turbo relates to foreline pressure.

As you see, the pump draws a bit under one ampere at 2.2 E-2 mBar, and it raises to 2.65A at 11mB. 10mBar is the maximum allowed foreline pressure (give and take ;-) ) and I can run it at around 2-3mBar with the new pump, so this should work fine, as expected.

Throtteling the Alcatel down for this measurement session revealed an aspect of the valves, which has had me worried for a while: Backlash in the spindle.
Few things can irritate me as backlash in a mechanical system. Backlash in a throttle valve will add an unnecessary complication when fine tuning the pressure in the chamber during fusion runs, and I am in full anticipation of how to solve this valving challenge. Probably something with a dual spindle valve, a fine pitch spindle nested inside the coarse, stock spindle, perhaps I worry too much.... .

But I will have to try controlling the pressure against a plasma, before being able to conclude anything.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

My gratitude goes to Maciek Szymański for posting the diagram of a basic vacuum station
viewtopic.php?f=10&t=13708
I have been reconfiguring my take on it in CAD.

A wonderfull tool.
A wonderfull tool.

This change took time, but was not hard to make, the biggest toll was on the wallet !.

The inline KF16 valve (good for 1 · 10-8 hPa) was a mouthfull, the choice was between that and a ball valve capable of 1 · 10-5 hPa but I don't anticipate regrets over this choice in the long run, since it sees the full vacuum from the turbo. The vent valve is a Swagelok 6LVV-DPHS4-OR which is followed by a 10Micron filter

I am looking forward to have this station at my disposal. Previously, it was a pain to change vacuum gauges in the attempt to get them evaluated against each other, due to the need to spin the turbo down every time. This is the gateway into the real vacuum world with all the other wonderfull things I can start to use the station for.
I believe that the choice of an oilless backing pump saves me two valves from Maciek's diagram, since the pump does not bleed oil backwards, and also does not need to be vented to atmosphere. If the need for these functions should arise, I will use valves out of the pneumatic catalogue, due to the reduced vacuum levels of the pump.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Chris Seyfert »

Hi Finn,

Congrats! Getting down to the 1e-7 range is an accomplishment. Nice looking setup you have there.

I am curious why you say the baratrons are shot. In your first graph, the baratron data seemed to be tracking quite well with the Pirani gauges, yes? I would not give up on the baratrons yet. Now that you have your ion gauge working, I would recommend pumping down to base pressure with a baratron and zero it properly after a good long pumpout (and gauge warmup), and see if that improves its performance. If you can zero both at once, that would be even better since you can compare them to each other.

As to the 13 volt reading, don't worry about it, just don't use any voltage above 10 volts. Different makes/models of baratrons have different over-range voltages.
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Chris,

That first graph is not a good one, with way too low resolution between traces. I am learning how to present data, and with the new and better pump station setup, I can better catch and display the findings.
In a MKS manual for the high end 120AA transducers, I did read that the out of range voltage could typically be around 13Volts, this was a kindle to hope, but.....
The reason that I say the Baratrons are shot is:
1, They start out with too high a voltage
2, They cannot be zeroed with either the coarse , the fine or a combination of both.
3, Taking off the cover of the baratron gives access to the 3rd. calibration potentiometer, the linearity pot. Turning that down to an end stop does produce a zero reading, but then the rest of the readings get way off the chart, big surprice.

I will give them a 3 chance, though, and that is when my newly purchased and calibrated baratron arrives, then we will see which transducer is off and which one is shot.

I frankly cannot see how to navigete in this domain of pressure transducer evaluation without at least one calibrated unit.
I bought these two baratrons 3 years ago, at a time when I had no experience with vacuum, and no way to test them. It would seem to me, thet there is one good reason for a vacuum component to show up on EBay: and that is that it has been deemed broken by a professional user, then afterwards been picked up by a non professional and listed for sale.
There are of course other possibilities, like scheduled replacements from production, and in these cases there are great bargains to be had.

I will report back as soon as I have something more definitive to say about my pressure transducers.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

All,

A couple of steps forward, with the goal of creating a fully functional pumping station.

I got the parts from Pfeiffer, and welded the buffer tank. Instead of the KF16 foreline plumbing, I decided to run it through in 8mm pneumatic line, and this worked out really well. There is a lot more suction (read laminar flow) at 3 torr than at 3 micron, and this is another really great advantage of the molecular drag turbo/diaphragm roughing pump combination.


This is the present appearance of the station:
Pumping station of my dreams!
Pumping station of my dreams!

There is still room for much more stuff within the framework, but then there should be!

With the parts washed, rinsed and dried in the oven once more, the assembly takes 10 minutes, and it was time to test the functionality of those extra valves.

Udklip.JPG

The curve above documents, that the diaphragm pump reaches 2 torr in 1.5 minutes, at that time I turn on the turbo. 6.5 minutes later the pressure has dropped to 6.3E-6Torr. At this point, I isolate the chamber with the gate valve, and vent the chamber to atmosphere. Turbo still running full bore.
I now isolate the turbo by closing the foreline valve, and open the shunt valve to pump the chamber with the diaphragm pump. 22 seconds later, the chamber is at 3torr, so I close the shunt valve, open the foreline valve and the gate valve, to allow the turbo access to the chamber. 3 minutes later, the pressure in the chamber is at 5.9E-6 Torr.

I repeat this exersize two times, and at 27 minutes, the chamber is at 3.1E-6 Torr, so I close all valves and turn off the power.

The pumping station is mechanically complete now, missing readouts and power supplies. I am very satisfied and happy about the way this turned out.

One odd experience recently: The South Korean customs has a Baratron E28F listed as a restricted item, apparently due to the risk of seeing it reexported to North Korea and other nuclearweaponswieldingwannabee states.
So my Baratron got stuck in customs, sigh.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

Great system Finn and a fine sequence of repetitive pump downs, well graphed for all of see. Seems like the system is well sealed and relatively dry for a first pump down....(thanks to the oven work). In use with a bit of ion bombardment with air it should dip a bit lower.

Sorry to hear about the snafu with customs on your baratron. Hopefully, this too shall pass.

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
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

I have been reading the FaQ over at Leskers:
https://www.lesker.com/newweb/faqs/question.cfm?id=491
relating to the leaks and adsorbtions that can spoil the function of a vacuum system.
Since I have no prior experience with a vacuum system, but am trying to do things the right way, I decided to replicate the Rate of Rise test which is described on the page I linked to.
In short, it gives the student an ability to gain insight in the health of the vacuum environment, particularly related to leaks and contaminations, by looking at the shape of the leak up curve, and by comparing the Rate Of Rise number obtained by solving this equation:
Using the formula:

Q = ((P2 – P1)*V)/T where the result is in Torr.Liters/Second Where:

Q = Throughput, or Gas Load, or Rate of Rise
P1 = Pressure at the beginning of the test
P2 = Pressure at the end of the test
V = The volume of the chamber, in Liters
T = The time between readings of P1 and P2 , in Seconds.

The numbers I have as a basis are in this time/pressure sequence which I recorded today, from a low 3.6E-7 torr to, 100sec. later, 3.7E-5 torr
The volume of the chamber is 0.24 liters consisting of 480mm of 25mmØ pipe and 100mm of 16mmØ pipe.

Here is the time/pressure sequence:

00:02 3.60E-07
00:04 3.80E-07
00:06 1.20E-06
00:08 2.30E-06
00:10 3.40E-06
00:12 4.30E-06
00:14 5.10E-06
00:16 5.90E-06
00:18 6.70E-06
00:20 7.50E-06
00:22 8.20E-06
00:24 8.90E-06
00:26 9.70E-06
00:28 1.00E-05
00:30 1.10E-05
00:32 1.20E-05
00:34 1.30E-05
00:36 1.30E-05
00:38 1.40E-05
00:40 1.50E-05
00:42 1.50E-05
00:44 1.60E-05
00:46 1.70E-05
00:48 1.70E-05
00:50 1.80E-05
00:52 1.90E-05
00:54 1.90E-05
00:56 2.00E-05
00:58 2.10E-05
01:00 2.10E-05
01:02 2.20E-05
01:04 2.30E-05
01:06 2.40E-05
01:08 2.40E-05
01:10 2.50E-05
01:12 2.60E-05
01:14 2.60E-05
01:16 2.70E-05
01:18 2.80E-05
01:20 2.90E-05
01:22 2.90E-05
01:24 3.00E-05
01:26 3.10E-05
01:28 3.20E-05
01:30 3.30E-05
01:32 3.40E-05
01:34 3.40E-05
01:36 3.50E-05
01:38 3.60E-05
01:40 3.70E-05
01:42 3.80E-05


Here is the leak up curve:
ROR 22-04-2021.JPG
This curve looks a lot like a pure gas desorption curve, at least this is what I would like to think.

When I plug my numbers into the equation:

((3.80E-05 Torr - 3.60E-07 Torr)*0.24 Liters)/100 Seconds = 9.07E-08 Torr.Liters/Second

Now, I am not complaining, 9.07E-08 is a fantastic ROR number, but on the other hand, I find it improbable that I should have a system which is several orders of magnitude better than the base numbers quoted on Leskers site, where they talk about 1E-5 as the turning point for a good system.

I assume that going through these calculations is something a 1st year student does once or twice, and then forgets about it and relies on them as proof that he is doing things right.

I would like to arrive at that same conclusion particularly if some kind soul would give my calculation a sanity check.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Joe Gayo »

Is your system baked? (Extensive time at 100degC+)
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Re: Finn Hammer, fusor update.

Post by John Futter »

Finn
I see you are using a bellows type connection from your turbo pump to your chamber

Lose it!!!!! and use smooth bore pipe fittings your conductance will be awful due to the surface roughness of the bellows. Your pump speed is only probably a few liters per sec because of this

the bellows pipe is ok for backing /roughing connections but at molecular flow they are a hindrance
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Re: Finn Hammer, fusor update.

Post by Mark Rowley »

John, is that a condition specific to TM pumps? I have a bellows from my diff to the fusor and has no issues dropping the chamber to the sub micron zone. In fact, the diff is throttled back almost 90% because it’s too thirsty.

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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Joe,

Not baked while assembled. Before assembly I washed components in dishwash, then rinsed in water, skipped the alchohol rinse, baked in oven @150degC. And assembled, using gloves. I did my best to avoid fingerprints. Used a very thin smear of Apiezon M on a couple of the viton rings.

John,
My intension with the bellows was to avoid applying force to the pump, but I will look into getting a smooth bore elbow.
Pumpdown does get awfully slow in the low end, but before I shut it down last night (cannot run overnight due to whine from turbo) it reached 2.3E-7, after an 8 hour pump.
I don't have dry nitrogen at my disposal, for purging, but have tried Argon from the tig welder. This opens the question, which atmosphere am I measuring with the hot cathode gauge.... Can of worms in a way.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Joe Gayo »

Bellows have lower conductance regardless of the pump, especially in the molecular flow region. How much lower depends on several factors (length, minor diameter, etc)

Mark, Your system may be in the transitional flow region and the impact may not be severe.
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Re: Finn Hammer, fusor update.

Post by Joe Gayo »

@Finn

I find your numbers surprising. I would be sceptical of the high vacuum gauge accuracy.
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Joe,
I am sceptic to the core, but also reluctant to shell out the big $$$ for a brand new transducer.
However, there is a 100 millitorr calibrated Baratron on the way from overseas. Hopefully it passes under the radar this time.
Not that it measures way low, but at least down to 5.0E-5 that should give at least a pointer in the right direction.

@ bellows and molecular flow: I see the point, a particle heading towards the pump has every opportunity to hit a wall at an angle where it bounces back instead, or is scattered in all directions except towards the pump.
I have ordered proper smooth elbows for that important transition.

Cheers, Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Maciek Szymanski »

Finn!

I've made some calculations, and your numbers are very good, but not unrealistic for such a small outgassing area.

Assuming wall outgas rate Or = 1e-8 mbar*l/(cm2*s) (according to Leybold's "Fundamentals of Vacuum" in the midle of the rate for metals)

The wall area of S = 52 cm2 (KF25 10x10 cm cross and 10 cm tube plus 10% margin)

The PV virtual leak rate rate will be Qo = 5.2e-7 mbar*l/s

The pressure rise can be derived from:

p2*V = p1*V + Qo*t

as:

p2 = (p1*V + Qo*t)/V

Using p1 = 3,6e-7 Tr, t = 100 s and V = 0,24 l

The final pressure is p2 = 2,17e-4 mbar = 1,67e-4 Tr. Your numbers are better, but by less than an order of magnitude, not a huge difference in the high vacuum world.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
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Re: Finn Hammer, fusor update.

Post by Maciek Szymanski »

And one note regarding the corrugated tube. Generally the conductance between the high vacuum pump and the chamber is the key factor for the pumping speed. In fact, if the conductance is smaller than the pump throughput the pimping speed will be limited to the conductance value independent of the pump size (a "hole to ideal vacuum" case). The pump throat diameters are usually matched to the pump throughput. For other hand the fusor chamber pumped by passage matched to the pump throat will be evacuated very efficiently but the deuterium will be consumed and pumped out with the same efficiency...
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
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Re: Finn Hammer, fusor update.

Post by Joe Gayo »

For turbos, there can be a large difference in pumping speed between heavy (N2, O2, CO2, etc) and light gases (He, H). This can be used to great advantage to conserve D2 but reduce background pressure.
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Re: Finn Hammer, fusor update.

Post by Richard Hull »

For the most part, ideal conductance on smallish chambers can rip a chamber down to the basement real fast, in a well sealed system. Likewise, as noted, you then wind up strangling off the wonderful vacuum conductance so often expensive to achieve once D2 is introduced to literally destroy the beautiful vacuum you have created with ideal matched and maximized conductance. The result, in the end, is at least a fabulously pure vacuum into which D2 is introduced. The silly result is that you must ruin the chamber vacuum by filling the reactor with flowing D2 at a pressure equal to what might be expected of a well used mechanical pump!

I have always been amused by this sad fact in fusor operation. The concept of a sealed vessel fusor, properly pressurized, will work for but a moment in time. I learned this in 1999. Such a sealed device will fuse well, but will bury the D2 in the walls in a few minutes decreasing pressure steadily in a well sealed spherical device. This phenomenon is at the very heart of the early X-ray tubes with no filament, operating at high pressures. Ultimately, these early tubes went "hard" and the power supply could not produce the amount of x-rays needed. (Current through the tube at any voltage determines the x-ray flux) Technicians were kept busy in big hospitals delicately regassing those early tubes with side arms meant to accomplish this task. The modern high vacuum "Coolidge tube" put them all out of work, for the most part.

If one is not hung up on the best conductance in molecular flow regime and has the time to pump to an acceptable level using a less than ideal conductance, the purity of D2 during operation will be acceptable and pinching off the D2 flow will have a much broader adjustment range. Also, the D2 purity will increase steadily as you load the walls to boost fusion.

This is not a suggestion for deliberately limiting conductance, but more of a reasoned methodology specific to what we know as "the fusor operational experience". In the end, do as you wish as it all works in the hands of any experienced operator of their specific fusor. Learn as you gain experience in operation.

The Farnsworth system of the mid-sixties in their best mark II prime with hot filament pigatron ion guns often had reports of 1-2 microns of D2 with 140kv applied at a few ma. This produced great numbers mostly due to the focused ion guns. All of the original team members that I interviewed noted that it took a couple of hours fiddling to balance and set up the "guns" to achieve those results. In some cases, during these tedious adjustment sessions, as the voltage was raised, burn-throughs, melted screens, arc-overs, and other issues ended the session that never came to be as shut down, disassembly, and repairs were made. (1-2 day downtimes)

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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Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

Maciek, Joe, Richard,

Thank you for taking the time to do calculation for me, and writing it up in a way that I can understand.

With regard to the corrugated tube, it probably does not matter a whole lot in fusor operation, although it is always nice to hit low pressures quick. And the purity of H2 is determined by the low pressure to start with.
The Turbo can run in standby mode, around 60% or 54KRpm, but even this is probably too fast for comfort, I wish I had a controller with full speed controll, but that will be for another time. I hope to get away with an almost fully closed gate valve, turbo on standby (because without the dual vane pump, I cannot work against the 2 torr of foreline pressure) feed 1ccm of H2 and see.

But frankly, from now I had better stop fantasising, and wait untill I have got hands on experience. You guys all know howto, I have yet to try it.

I have had a good day in the workshop, where great sacrifices were made to the god of swarf:

IMG_20210424_192441.jpg

I finally got the bulkhead clamp for the viewport manufactured, in copper and phenolic, to stay in line with the steampunk theme. The copper ring holds the 6mm lead glass which I schrounged from a Lesker wiewport. The paper phenolic clamps a KFviewport glass against the o-ring.

IMG_20210424_210215.jpg


I know that during the first learning experience, I will be looking at the plasma directly, but by restricting myself to the 30kV supply, and by having lead glass between plasma and myself, I can be safe.


Cheers, Finn Hammer
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Finn Hammer
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Re: Finn Hammer, fusor update.

Post by Finn Hammer »

In the spirit of documenting the build as it progresses stepwise, here are a few additions to the build:

I got the grid manufactured, 1.6mm tig rod and copper.

IMG_20210506_163250.jpg

Nested nicely inside the chamber,

IMG_20210506_164936.jpg

Another thing that was mentioned was to get rid of the ugly corrugated tube from turbo to main control valve: It did help on the pump down time.
.

IMG_20210521_084406.jpg

Then I got the flow controller mounted, and the piping routed:


IMG_20210522_111710.jpg
This was interesting, because I could now start to get an impression of the range of pressure control I will have, and it fits the bill nicely.
with the turbo on full speed and the main controll valve fully open i get from 3 - 15 micron with 1ccm to 5ccm
with the control valve almost shut, I get from 11 to 42 microns with the same flow figures.
I am feeling a lot more confident about the ability to controll pressure with this addition under the belt.


This is the rig at present, notice that the electricals are temporary, shielded controll cable is waiting to be fitted.

IMG_20210522_111800.jpg

The trained eye will notice that I finally received the calibrated Baratron, and it is a marvel to behold, even though it has the penaltry of a 4 hour warmup time.

I think that I have talked about field controll before, this is something I feel strongly about, since I have decided to run this system dry, without any oil to insulate, or cool for that matter.

The feedthrough looks like this:

IMG_20210523_124718.jpg

Look at all the ugly protrusions just begging to present themselves to the first rogue partial discharge, and create a grounded arc. Uff, ugly!

IMG_20210523_124814.jpg

That was more like it, but only half of the story, 1/3, really :-)
field.jpg

Here is the finished article. Perhaps overkill, I don't know, because the feedthrough may well puncture through the porcelain (I think it is allumina, really) but it is a cool addition and if all fails, I can still use it in another episode.

That's all for now, it is the power supply that is being put into a nice box, that awaits attention now, and a couple of Ludlums in the mail too.

Cheers, Finn Hammer
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