Some Diffusion pump Questions

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Lukas Bochtler
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Some Diffusion pump Questions

Post by Lukas Bochtler » Sun Jun 25, 2017 9:15 pm

Hello all,

So as the title states i have a few questions about diffusion pumps. I have most of an electron microscope, that i would like to get working again. some of the things missing so far are the roughing pumps, and the diffusion pump chiller (though i do have a manual for a very over the top chiller that original ran the microscope, but seeing as the original one is specked at 25KW cooling power, i suspect it is massive overkill, seeing as the microscope has a peak power consumption of 5.5 KW).

So, the pump is a 4" diffusion pump, with a 500W heater, model should be (i need to check the actual model installed, but based on another copy of the microscope i have, thats the one that should be in there) DPF-4Z by DAIA.

Based on the label, it has a 500W heater, and based on the manual of the microscope, it needs 1.5 L/min at 10 to 20°C for the water supply.

So, the first question, how much cooling power do i need for the chiller, since i dont have the exit temperature, i cant see a way to calculate the power the pump dissipates into the cooling water. I really dont want oil backflow into the column, so id rather go overboard in terms of cooling, as apposed to having to clean the column. (and possibly replacing the gun filament).

So far i intend to use a 790W aquarium / PC cooling chiller to cool the pump, but im not sure if its overkill or not.

The next question is, what size roughing pump do i need for the pump to work normally, and is there a possibility of using too large of a roughing pump. The diffusion pump is specked at 570 L/ sec pump speed.

The original vacuum pumps (which im still trying to track down, but as time marches ever onwards, the hopes of finding them intact dwindles.), where 145 L/sec pumps that go down to 10^(-2) mbar (if i recall correctly).

If i cant find the original pumps, i am out of luck, since the only ones of the same model (based on guesswork mind you), are not up to spec anymore, hence i would not buy them. So, i was thinking of using a pair (yes it needs two pumps), Leybold Trivac D16B pumps, one for the diffusion pump, and one for the sample exchange chamber. There is the problem of higher pump speed, since the trivac pumps about twice as much gas per second as the originals, as well as going down deeper then the originals.

So, my question is basically, will the D16B's work instead of the originals, or will this create problems with the diffusion pump?

Another thing, i am wondering weather or not i need to change the oil in the pump, the microscope has sat unused for a decade (apparently) before i got it. So, i dont really trust the pumps oil anymore. I was thinking of using Leybold's diffusion pump oil, but am unsure weather this is the best idea or not. (heck i don't even know how to change the oil in this pump, but im working on tracking down a service manual for the microscope, which might help).

Also note: I have a Leybold Trivac S4A pump that needs an oil change, but i highly doubt it will be enough to run the microscope. (also i need it for other projects)

Thank you in advance for any help i receive here.

John Futter
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Re: Some Diffusion pump Questions

Post by John Futter » Mon Jun 26, 2017 5:20 am

Lukas
500Watt heater = 500w heat load so all is calculable from there. It also depends on what the electromagnetic lenes in the column require in input power usually these are water cooled as well for stability (mechanically) of the column
There are only a few Diff pump fluids that I would use
Dow corning DC704 or DC705 or Santovac
Santovac is extremely good but eyewateringly expensive while the DC fluids are cheap especially from China

Better mechanical pumps are totally OK the system will pump down faster

ian_krase
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Re: Some Diffusion pump Questions

Post by ian_krase » Mon Jun 26, 2017 5:28 am

You might need more cooling than that. The water flow rate is the immediately important part, and big reserviors can buy time, possibly lots of time. You can see if the temperature rises though at 20C you will need active cooling. (is slightly warmer water OK?)

AFAIK there is no too-big forepump. Just make sure you can develop the good enough vacuum at the gas load - possibly a problem if big tube manifolds are needed to adapt pumps.

I don't see why you couldn't use a single pump with valves and if the loadlock isn't diffpumped you might get away with much smaller pump.


All three popular diffpump oils: Octoil, DC704, and Santovac 5, have lots and lots of equivalents/offbrands/oem versions.

John Futter
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Re: Some Diffusion pump Questions

Post by John Futter » Mon Jun 26, 2017 6:18 am

I do not like Octoil.............

a disaster if you get something wrong

Lukas Bochtler
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Re: Some Diffusion pump Questions

Post by Lukas Bochtler » Mon Jun 26, 2017 10:13 am

Thanks for your replys sofar.

I have taken a look at the manual, and i dont see any mention of water cooling the electromagnetic lenses. Ill have to check the actual unit to be make sure i have not missed something.

As for the oil, the price of the Santovac oil, it is indeed eye wateringly expensive (more then i had expected). Id take the plunge if i can get only 150ml (which the pump needs) but its still expensive in comparison to Dow Corning.

Ill have to see the price for the leybold stuff, though im not sure if it would be better then Dow Corning ECO-705 (which im currently considering).

Also, what are the differences between Santovac 5 (im guessing) and Dow Corning ECO-705? Also dose anyone have experience with Leybonol 5xx oil?

While im on the subject of oil, what oil would you guys recommend for Leybold Trivac pumps (since at this rate ill have 3 in the microscope room, 2 for the microscope and 1 for the sputtering machine). So far i found the Leybonol 300 oil to be the one recommended, are other oils recommended?

As for the chiller, im currently thinking of using the Hailea Ultra Titan 1500 chiller. According to Aquatuning it has 790 Watt cooling power, so it should cool the pump and trap.

for those wanting to research my microscope (good luck with that) i have a Hitachi S800 FEG SEM

Jerry Biehler
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Re: Some Diffusion pump Questions

Post by Jerry Biehler » Tue Jun 27, 2017 2:44 am

Usually you use something around the size of a Edwards RV8 on a SEM.

Dont worry about the oil, it is fine.

Simplest thing if you dont plan on using it all the time is to just use tap water and just dump the water down the drain or something, 1.5lpm is nothing... Do put a regulator on to heel the pressure down if you have high pressure locally.

My SEM only needed water for the DP, one of the reasons I ditched the DP and went with a turbo. Some SEMs use water to cool sections of the column as well as the sweep electronics so that might not be a viable option for everyone.

For the roughing pumps just use generic rough pump oil from duniway or whoever.

BUT! Here is the main thing, you have a field emission unit which means this has ion pumps in the column because field emitters need really high vacuum. You dont want to spend a lot of money on this machine until you get the column pumped down and the ion pumps running. It may take several days for the column to get to pressure before you can find out if you emitter is shot or not. If the emitter is shot you are looking at a few thousand dollars for an emitter. Thats one of the advantages of a thermionic emission SEM.

So, get or borrow one roughing pump for the DP, ignore the load lock. Run a water line to the DP and get it running and pumping down. Now you get to try and get the column down, there are probably bypass valves to open the gun chamber to the diff pump, you cant leave this open too long otherwise you will get oil contamination in the gun section and really mess things up. You basically want to run this just long enough to get the ion pumps running. Once thats going you can let the machine pump down. You may have to bake the gun section too. I am not sure.

Lukas Bochtler
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Re: Some Diffusion pump Questions

Post by Lukas Bochtler » Tue Jun 27, 2017 10:16 pm

Sadly i don't have the luxury of tap water where the SEM is located, hence why im thinking of using a chiller right of the bat.

I do need to bake the machine, the startup (well most of it) is described in the manual. It requires 8 hours of baking (the gun chamber as well), the vacuum system is fully automated as well, though the mentioned bypass valves are fully manual, Annoyingly the exact procedure is not documented in the manual (if i recall) but it might be in the service manual, which i am trying to track down.

As for the emitter, well i don't even know where to get a new one from, other then getting the electron gun off another S-800 or similar microscope. But, according to the previous owner, the microscope worked prior to its removal (and subsequent damage to the cables). I am quite certain the gun chamber is at atmospheric pressure now, since the bypass valves where slightly open, with the load lock also being open.

Spending about a grand on getting this thing even to the point of doing what you states is unavoidable, due to all cables from the control console to the column where severed (something the original owner only found out after the fact, and was furious about). I am currently also looking into building a new ion pump power supply, since i have yet to locate the original, the only expensive part in that, are the half dozen custom transformers needed to make it work.

But, on the bright side, i was going to build one from scratch anyway, so i might as well restore an old one first. (the old one will probably out preform my own design).

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Re: Some Diffusion pump Questions

Post by Jerry Biehler » Tue Jun 27, 2017 10:24 pm

The automatic cycle is for actual use of the machine when everything is up and running. You have to get the ion pump down to about -4 to -5 before it will start. Hopefully it will.

Don't try to build an ion pump supply. There are ion pump supplies all over eBay. There's nothing too special about them, helpfully there was no communication between the supply and console that can't be overridden.

Emitters can be gotten, it's just they are VERY expensive. There is a guy that has been trying to make his own and having so-so luck with it. You're making a tungsten tip with a tip size of about an atom. Real easy to mess that up.

Lukas Bochtler
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Re: Some Diffusion pump Questions

Post by Lukas Bochtler » Tue Jun 27, 2017 10:48 pm

Well there is a small problem with the use of a non S800 ion pump power supply, the power supply also contains the baking power supply, as well as controller / timer. Also the control console seems to send some voltage references to the ion pump power supply controllers (just 9 op amps). (though i need to do a proper trace threw the schematic book to be sure)

So, here is my plan:

- Try and find the original power supply (it vanished together with the roughing pumps and air compressor)
- Fix the cables (ill be going to my microscope tomorrow to get the high voltage connectors and the little bit of cable left between them, and will be sending a inquiry to a German company specialized in fixing such things. (though they usually fix X-Ray equipment) I will also note down the cable specifications and connectors to make new ones.
- Verify the console fires up once cables are fixed (not sure if this is a good idea without the roughing pumps)
- Get a roughing pump (will probably go for a Trivac D16B, as i like Leybold gear)
- Get the above mentioned chiller (or anyone that will dissipate 500W or greater), as well as a small pump and some plumbing to get the flow rate to 1.5L/min (im thinking of a bypass valve on the main line, that will circle the water back to the tank without it running threw the pump.
- If obtaining the original power supply failed, build a new one.
- Pump down the column and bake it .
- Start the microscope and see if the emitter works
- Possibly take a quick image of the stage... (using a DSLR on the high resolution screen)

Though, i have a vacuum pump, (well its in the mail right now), its a Leybold S4A (it should be able to pump pump 120L/min) do you reckon it will be enough for the first pump down test? Since the originals where 145L/min im not sure...

edit:
Oh and one question, do the ion pumps need to be on all the time? Or can they be shut off when the microscope is not going to be used for a week or so? (i have no problem either way, im just curious)

John Futter
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Re: Some Diffusion pump Questions

Post by John Futter » Wed Jun 28, 2017 6:13 am

No
You leave the ion pumps on 24/7
When down to the correct vacuum they only consume a few watts.
I have a detector chamber that sits in the low ten to the minus nine and it consumes less than a watt to keep it there @ 10kV ion pump potential

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